1361015_ConcreteinanAMprocess.

1361015_ConcreteinanAMprocess.
This report examines the additive manufacturing (AM) of concrete, its possibilities,
feasibility and advantages over existing techniques. The possibilities for products
made with an additive process are endless, but just replacing existing production
methods with additive ones is still impossible. Although improved freeform production
techniques are the aim of this research, this does not mean that more freedom in
form is by definition the largest improvement that AM can offer at the moment.
From another point of view the implementation of additional functions in traditional
products can be of great value.
A roadmap envisions how the technique has to evolve in order to implement
the characteristic properties of concrete. Product ideas and an evaluation of the
techniques shown in the roadmap are related to the developments to achieve an
to the requirements that have to be set regarding a matching fresh concrete mixture.
Dennis de Witte | Concrete in an AM process Freeform concrete processing
increase in speed, surface quality and strength in the AM production technique, next
Concrete in an AM process
Freeform concrete processing
Dennis de Witte
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Concrete in an AM process
Freeform concrete processing
Master (MSc) thesis
Concrete in an AM process - Freeform concrete processing
Version - 30 January 2015
Author
Dennis de Witte
Studentnr. 1361015
Mentors
Prof. Dr.-Ing. Ulrich Knaack
AE+T - Design of Construction
Ir. Joris Smits
AE+T - Structural Design
Dr.-Ing. Marcel Bilow
AE+T - Product Development
External committee member
Rein Have
AR - Public Building
Delft University of Technology
Faculty of Architecture and the Build Environment
Department of Building Technology
01.West.110
Julianalaan 134
2628BL Delft
The Netherlands
ii
Preface
r (ir.)
This graduation thesis has been written to obtain the title of enginee
and
at the Delft University of Technology at the Faculty of Architecture
d
the Built Environment. The Building Technology master track consiste
courses
of, next to the graduation project, several design and theoretical
about building technology. Because of my technical preferences I decided
e
to broaden my horizon by choosing additive manufacturing of concret
clear
as my graduation subject. While the project progressed it became
The
that material, production technique and products are very related.
be
initial challenge of how and what kind of concrete products should
to how
made to use additive manufacturing in a beneficial way changed
al
AM should be used to be able to process concrete keeping its benefici
in the
characteristics. This interdisciplinary approach created my role
middle of the mechanical experts and the architects.
a half
Comparing one and a half year of aerospace engineering to five and
chance,
year architectural education, where I always tried, if I had the
two
to be on the technical side, I realise that my role is between those
extremes. The idea to work at that place increasingly appeals to me.
Joris
I want to thank my family, friends, colleagues and mentors Ulrich,
and Marcel for the support during my study and graduation.
Dennis
iii
Introduction
Introduction to topic and problem statement
Topic and relevance
Background on concrete
Material composition and properties
Commonly used production techniques
and the resulting products of the last
decades
Research definition
New processing techniques
Introduction to concrete AM
-
problem statement,
hypothesis,
question and subquestion,
research direction,
purpose, and
methodology
Concrete AM techniques
Current concrete printing techniques
- their properties, and
- their resulting products
Potentials of new processes
- optimising material use,
- formability, and
- costs
Printer concepts and design
Future vision
- new printer concepts, and
- new products
Conclusion
Conclusion and recommendations
Figure 1 - Schematic structure of thesis
iv
Abstract
This thesis examines the additive manufacturing (AM) of concrete, its possibilities,
feasibility and advantages over existing techniques. The first part generally focuses
on the characteristic properties of concrete that are important and how they relate
to an AM method, for instance aggregates and reinforcement. After this extensive
introduction in the field of concrete and AM, the current situation regarding additive
manufacturing of concrete is described. On the basis of literature resulting products
are shown and discussed. Their characteristics are compared to detect a match or
mismatch between the AM technique and the produced elements. The outcome of
this evaluation is used to describe improvements which are elaborated in the second
part. This design part consists of a roadmap that shows a future vision. Concrete is
a new material in the field of additive manufacturing. Since it is one of the materials
that hardens by a chemical reaction, considerable attention needs to be paid to the
workability of it in an AM process. Traditional processing techniques are adapted
to these characteristics but concrete does not let itself dictate how to behave. The
roadmap envisions how the technique has to evolve in order to implement the
characteristic properties of concrete. The possibilities for products made with an
additive process are endless, but just replacing existing production methods with
additive ones is impossible. Although improved freeform production techniques are
still the aim of this research, this does not mean that more freedom in form is by
definition the largest improvement that AM can offer at the moment. From another
point of view the implementation of additional functions in traditional products can
be of great value.
Product ideas and an evaluation of the techniques shown in the vision are related to
the developments to achieve an increase in speed, surface quality and strength in
the AM production technique, next to the requirements that have to be set regarding
a matching fresh concrete mixture. These essential aspects of the process lead to
the important conclusion that in the AM of concrete, both material and production
technique have to be matched precisely. Next to matching process and material it is
important to match process and product. Concrete is widely used and not all products
should be made using an AM process. Simply copying standardized elements does
not add the added value layered fabrication methods can achieve if used adequately.
v
vi
Contents
I Literature review
1 AM of concrete
1
1.1
1.2
1.3
1
3
3
Concrete formwork
Freeform concrete in architecture
Topic and relevance of the research
2 Background on concrete
2.1 2.1.1 2.1.2 2.1.3 2.2 2.2.1
2.3
Concrete - the material
Terminology
Cement types
Disposition within the concrete
Concrete processing techniques
Processing in the environment
Conclusions concrete
5
5
9
10
12
18
20
20
3 Additive Manufacturing
21
3.1
Introduction to AM
3.2
AM methods
3.2.1Stereolithography
3.2.2
Laser Sintering
3.2.3
Fused Deposition Modelling
3.2.43D-printing
3.2.5Polyjet
3.2.6
Other AM techniques
3.3
Moving formwork
3.4
Properties of AM
3.5Sustainability
3.6
Conclusions AM
21
23
24
25
26
27
28
29
31
33
34
34
4 Research definition
37
4.1
Problem statement
4.2 Hypothesis
4.3
Research questions
4.4
Research purpose
4.5 Research methodology
4.6Scope
37
39
40
41
41
43
5 Concrete AM techniques
45
5.1 5.2 45
47
Concrete as AM material
Identification of stakeholders
vii
5.3 Techniques
5.3.1 Contour crafting
5.3.2 3D-Concrete printing
5.3.3 D-Shape
5.4 General product properties
5.4.1 Mixtures
5.4.2Reinforcement
5.4.3
Layered characteristics of AM
5.5 AM of concrete
5.5.1 Concrete products that benefit from AM
5.6
Environment: material use, production and sustainability
5.6.1
Material usage
5.7Evaluation
5.8
Points of improvement
5.9
Conclusion AM of concrete
49
51
55
57
59
60
62
64
64
65
67
70
71
72
73
6 Alternatives: other ceramic materials and threats
75
6.1Clay
6.1.1
AM of clay
6.2Threats
6.2.1
Printing of advanced moulds
6.2.2
Changing / adaptable mould systems
6.2.3
Milling of concrete
6.3
Conclusions alternatives
76
80
83
85
87
89
91
II Design
7 Roadmap (printer concepts)
7.1
Design methods
7.1.1
Parametric design method
7.2
Evolved and new techniques for concrete AM
7.3
Vision on AM of concrete
7.4Development
7.4.1
Development in extrusion processes
7.4.2
Development in 3D-Printing techniques
7.4.3
Implementation in traditional concrete processing
7.5
AM techniques: Future vision
7.5.1
Instant curing extrusion
7.5.2
Fibre orientated reinforced concrete
7.5.3
Print mill sand
7.5.4
Elevated support printing
7.5.5
Support net layer spraying
7.6
Advanced extruder
viii
93
93
94
95
101
101
102
104
106
107
110
111
113
114
116
117
CONTENTS
7.7Products
7.7.1
Gradient materialized composite elements
7.8G-code
7.9
Conclusion roadmap
118
119
121
122
III Conclusions
8 Conclusions and recommendations
125
8.1Conclusion
8.2Recommendations
125
127
Appendices
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
130
131
132
132
133
134
134
136
138
1
2
3
4
5
6
7
8
9
-
Experiment with layered concrete
Printed mould
Decomposition of the concrete mixture
Capillary action 3D-printing with water
Extruding on bentonite
Aligned fibre reinforcement
Elevated support printing
Gradient concrete
Technology roadmap by Volkers
Additional information
Literature
Figures
Tables
Glossary
141
143
145
146
Personal information
147
ix
I Literature review
x
1 AM of concrete
There is a considerable amount of labour and material involved in building a
concrete structure. Moulds need to be made, reinforcement placed, concrete
casted and afterwards the mould has to be removed. This process has been
optimised constantly to decrease costs and improve performance. Due to
the optimised processes, an abundance of elements are standardised,
since these standardised elements can be produced in large series, which
helps in recovering the investments. Structural optimisation is in this
production chain inferior to the related costs and profits. This approach
results in repeated and over dimensioned elements. The lack of freedom in
shape is another limitation. Due to the standardised elements the designed
freeform façades are divided in sections, which is done in such a way that
the façade can be build from standardised elements.
In addition to these disadvantages, the rationalisation of the construction
process resulted into very efficient spanning elements with reinforcement
as well. The reinforcement is used, instead or in combination with shapes
that are geometrical optimised, to cope with the applied stresses. In
addition to the primarily function of minimising tension in the concrete,
the reinforcement is used to achieve a kind of structural variations. By
adjusting the amount and location of the reinforcement, the structural
capacity can be changed, so long as it fits between the limits of the
production process.
This chapter explores these challenges of concrete in more detail.
§ 1.1
Concrete formwork
Construction companies face several important challenges concerning the costs of
production. Firstly in situ concrete casting process produces a lot of waste material
that is thrown away afterwards. Especially if not reusable formwork is used (Tam,
Tam, Chan & Ng, 2006, p.1), while in contrast reusable moulds decrease this flow of
waste. Since reusable moulds are rather expensive large series are needed to make
these moulds cost effective, which in turn causes a lot of repetition, for example in
façade elements.
The construction industry has not only to deal with not reusable moulds, but also
with over constructed elements due to limitations in the production processes.
Costs are strongly correlated to production techniques. Hence a lot of elements are
1
standardised, to decrease costs even more. Adjusting a standardised element to
reduce the material use, will not be cost effective, since the dead load in buildings is
not that important as in airplanes. It does not affect the energy use in its service life
significantly and sometimes it is even favourable to have more mass in a building to
temper the fluctuations in temperature (Peck, 2013, p.36).
A lot of freeform elements are casted in situ, although quality of in situ concrete
is harder to control (Elhag et al., 2008, pp.376-377). Therefore, high performance
elements are made in controlled environments. Due to limitations in the size of the
products that have to be transported afterwards, these elements are generally a part
of a standardised building system.
Concerning the Life Cycle Assessment (LCA) of in situ concrete it can be concluded
that this assessment is negatively influenced by in situ casting. Especially over
ordering of concrete (Tam, et al., p.9) and wearing of formwork (Cole, 1998, p.340)
are the main contributors to added CO2 emissions of in situ concrete casting. Since
hardening of concrete produces CO2, it is desirable to have a look at the LCA so that
the evolved production process has not only an economical but a sustainable motive
(1)
1
Figure 2 - Zilverparkkade concrete façade by René van Zuuk Architekten
Rozemeyer, 2013
as well.
2
AM OF CONCRETE
§ 1.2
Freeform concrete in architecture
The use of digital modelling increases in architecture, but to make such freeform
shapes is very hard, since it is either impossible or extremely costly. There are
currently no industrial concrete production techniques that can cope economically
with both these criteria.
Moulds can be made out of different materials, like steel, wood or plastic, and
by different methods like; carpentry, CNC milling of wood, steel or plastic and by
“printing” materials (AM).
Some freeform moulds are made out of CNC milled plastic or plastic that is inflatable.
This is still a relatively expensive way of constructing and will only be feasible if there
are sufficient projects using the same mould. If processing concrete without moulds
becomes possible, more 3D designed structures can actually be built the way they
were designed. In a time period in which everything is designed digitally, the manner
of designing and building is not synchronised anymore, which is shown by the fact
that it is possible to design such material optimised structures that either cannot be
build, or are absolutely not cost effective. In general, the use of automated robotic
construction methods, as already present in automotive industry, are not used in the
construction industry (Buswell, Soar, Gibb, & Thorpe, 2007, p.224).
§ 1.3
Topic and relevance of the research
Moulds and formwork are the limiting factor in today’s concrete processing, either
due to process limitations or due to costs. The relevance of AM increases because of
the fact that architects and engineers design constructions in the 3D environment.
Unfortunately, the benefits of this way of designing have to deal with the limitations
during construction. As mentioned previously, there is no production technique that
can easily handle elements with different properties in a cost effective way. This
can be changed if elements or formwork can be manufactured with a production
process that builds elements by adding layers on top of each other, i.e. Additive
Manufacturing (AM).
Imagine how the Zilverparkkade’s façade pattern (figure 2) would look like if repetition
was unnecessary. The form of the branches could be different all over the façade.
They could differ in thickness in direct relationship to the forces applied to the façade
cladding. Maybe there would be voids inside the elements to decrease the material
3
used and to increase the moment of inertia. Almost everything is possible using an
AM technique.
This thesis will evaluate existing concrete AM processes and show potentials of new
ones in order to minimise the gap between the designing and production of freeform
concrete elements.
4
2 Background on concrete
Concrete has been widely used by the ancient Romans during a 700 year
time span. The Colosseum and the Pantheon, which has different concrete
compositions (figure 3), are prime examples of that usage. Before the
Romans, the Greek used lime and pebbles to make concrete floors in the
royal palace of Tiryns in 1400-1200BC. Other impressive, more recent,
concrete structures are the Hoover Dam, the Panama Canal and the 828
meter tall Burj Khalifa. All these structures share the construction method
that uses some kind of formwork.
Concrete itself is a composite material that consists of granulate and
cement that reacts during curing to become cement stone which binds
the composite together. The consumption of concrete is around 25 billion
tonnes annually and it is by far the most used building material (figure 4)
(Ashby, Shercliff & Cebon, 2007, p.481). The worldwide consumption of
cement was 3004.7 million tonnes in 2009 (Peck, 2013, p.13).
Additive Manufacturing (AM) techniques can become dominant, as the
construction industry starts to shows interest in its potentials, but first
useful knowledge of concrete has to be gathered.
§ 2.1
Concrete - the material
The words cement and concrete are sometimes interchanged. To clarify the
distinction; cement is the binding material in the concrete that holds the aggregates
in position. Cement is the most costly element in concrete. That is why around 80%
of the volume of concrete consists of some kind of granulate. A generally known
ratio of materials used is, one part cement, two parts sand, three parts gravel and
water. In the Netherlands, blast furnace cement is the most used type of cement.
The aggregates have different sizes, where the smaller particles fill the voids between
the bigger ones. Near the surface, in the concrete’s skin, there are relatively more
fine aggregates (figure 5). The cement needs to cover all the surface area of the
aggregates to bind all the materials in the composite. The bounding between the
cement and aggregates is completed by the use of water. Too little water causes
incomplete bounding (figure 6), too much will result in porous concrete (Callister,
2007, pp.582-583). The ratio between the amount water and cement is called
Water Cement Ratio (WCR). To cover more smaller aggregates, extra cement and
fine materials are needed. Cement because the surface/volume ratio increases, fine
5
approx. 9m
1.60m
Roman concrete with lightweight
chuncks of stone and pumice
(density 1.35)
Roman concrete with chuncks
of stone and chips of bricks
(density 1.5)
Roman concrete with chuncks
of stone and chips of bricks
(density 1.6)
43.30m
Roman concrete with chuncks
of stone and chips of bricks
(density 1.60)
Shell from bricks
Approx. 6m
Roman concrete with chucks
of travertine and stone
(density 1.75)
Shell from bricks
4.50m
Roman concrete with chucks
of travetine
7.30m
Figure 3 - Pantheon its different layers of concrete
(1)
1.0E+11
1.0E+10
1.0E+08
1.0E+07
1.0E+06
1.0E+03
6
(2)
Glass
C-fiber
Asphalt
Cement
Wood
Concrete
PP
PET
PE
Figure 4 - Consumption of hydrocarbons and engineering materials
PVC
Gold
Silver
Ti alloys
Ni alloys
Mg alloys
Zn alloys
Pb alloys
Cu alloys
Steel
Al alloys
Oil and coal
1.0E+02
2
1.0E+04
Lambrecht, 1993 in Peck, 2013, p.10
Adapted from Ashby, et al., 2007, p.481
1.0E+05
1
Annual world production [tonnes/year]
1.0E+09
material because the gravel has less voids in comparison to fine sand. In 1 m3 fine
sand is 43% empty space in comparison to only 36% in 1m3 gravel (table 1) (Berg,
Buist, Souwerbren & de Vree, 1995, p.56). The latter can also be found in the density
of the two materials, 1500 kg/m3 versus 1700 kg/m3, that have both their origin in a
rocky material with a density of 2650 kg/m3. Section 2.1.3 contains more information
Formwork
about the deposition within the concrete.
Concrete skin
Concrete core
Figure 5 - Distribution of aggregates in the core and near the formwork
Grain size
Modulus of fineness
Surface/volume
(m2/m3 = m1)
Sand dust
0-0.05
0.5-0.8
135000
Fine sand
0.-0.2
1-1.5
26500
Coarse sand
1-3
2-3
2400
Fine gravel
7-12
4.5-5.5
560
Gravel
12-25
6-7
220
Table 1 - Aggregates surface/volume ratio
(2)
2
1
Adapted from Berg, et al., 1995, p.55
Berg, et al., 1995, p.67
Aggregate
(1)
7
Figure 6 - Porous concrete
Probably one of the most important features of concrete is its price. When compared
to other materials, its Young’s modulus compared to density falls in the expected
range. If the production costs for materials relative to those of steel are compared
to their Young moduli, a shift can been seen for concrete. It has the highest Young
modulus of all materials in that price range (figure 7 and 8).
1000
Technical ceramic
Young's modulus, E (GPa)
Composites
100
Glass
Concrete, stone and brick
Dense
concrete
Dense
concrete
10
Foams, fabrics and fibers
Concrete (structural
lightweight)
Concrete (structural
lightweight)
High performance
concrete concrete
High
performance
Metal, ferrous and non-ferrous
Common brick
brick
Common
1
Polymers
0.1
Elastomers
0.01
Wood, plywood, glulam, bamboo, straw and cork
0.001
0.1
Figure 7 - Young modulus-Density (CES)
8
1
Density, Mg/m3
10
BACKGROUND ON CONCRET
Young's modulus, E (GPa)
1000
Technical ceramic
Dense
concrete
Dense
concrete
100
Concrete, stone and brick
High performance
concrete
High performance concrete
Common brickbrick
Common
10
Metal, ferrous and non-ferrous
Concrete
(structural lightweight)
Concrete
(structural
lightweight)
1
Composites
Foams, fabrics and fibers
Wood, plywood, glulam, bamboo, straw and cork
0.1
Polymers
Elastomers
0.01
0.001
0.01
0.1
1
Relative costs per unit volume, Cv,R
10
100
Figure 8 - Young modulus-Relative cost (CES)
§ 2.1.1
Terminology
Remarkable is that only a cementitious material is called concrete when the composite
contains aggregates that are both, smaller and bigger than 4 mm in diameter. In the
properties of concrete mixtures, plasticity, workability and consistency play a major
role. Important properties of concrete are especially the strength and durability.
Strength is obtained by the kind of mixture, aggregates and reinforcement used. The
combination of these variables in combination with the point of time in the hardening
process determines the strength of the concrete. The strength at a certain point in
time can be very important if an element needs to be de-moulded and transported. If
an element can be de-moulded and transported directly after production this is called
green strength. The fresh concrete used for this is most of the time a fresh concrete
with very little water, called earth dry.
Durability has to do with the resistance against the elements, frost, high temperatures,
the reaction with sulphates, acids, seawater and erosion. All these properties can be
regulated with the type of mixture (Berg, et al., 1995, pp.11-19).
9
Concrete
Aggregate size
UHPC
Self compacting
Mortar
Self compacting
Cement paste
Strength
Lower water/cement ratio
Figure 9 - Concrete labelling
§ 2.1.2
Cement types
Three commonly different cement types used are:
•
Portland cement,
•
Blast furnace cement, and
•
Portland fly ash cement.
The difference between these lies in the chemical bounding that occurs during
hardening. The pore structure of 65%+ scoria blast furnace cement is more closed.
This results in concrete that is extra chemically resistant. The hydration speed of
blast furniture cement is higher as well. It decreases the curing time at higher
temperatures. On the other hand this results in an increased curing time at lower
temperatures. To prevent the blast furnace concrete from drying out, extra treatment
after casting is needed, in contrast to Portland cement. Another characteristic of blast
furniture cement is that it emerges less warmth during the curing, making a thick
construction less vulnerable for cracks. Both have their advantage and disadvantage
properties that need to be considered when choosing a mixture. Besides the type
of cement the type of fresh concrete differs. There are cement pastes and mortars,
10
BACKGROUND ON CONCRET
but concrete itself can be divided in concrete and Ultra High Performance Concrete
(UHPC). The latter does not fulfil the requirements to call it concrete, but that is due
to the old standards. Nowadays they are accepted as concrete since their overall
characteristics are in line with concrete as formulated in literature. In addition to this
division, there is also a difference between self compacting and not self compacting
concrete. The compacting behaviour has to do with the WCR and additives like
plasticizers. Generally it can be said that the WCR increases for self compacting
mixtures and that because of that they are considered weaker (figure 9)
Material
Density (kg / m3)
Portland cement
3150
Portland fly ash cement
2900
Blast furnace cement
2950
Fly ash
2000 - 2200
Rockdust
2650
Trass
2300
Sand and gravel
2650
Sand and gravel (from the ocean)
2650
Basalt
2750 - 3150
Limestone
2200 - 2750
Quartzite
2600 - 2650
Granite
2580 - 2850
Porphyry
2710
Magnetite
3500 - 5100
Baryte
3400 - 4300
Steel
7650
Lytag 4-8 and 4-12 mm
1850
Concrete granulate
2250 - 2450
Masonry granulate
1300 - 1950
(1)
1
Berg, et al., 1995, p.178
Table 2 - Concrete materials with their densities
11
§ 2.1.3
Disposition within the composite
The aggregates contribute considerably in the final volumetric mass of concrete and
they need to be chosen in such a way that they fill the voids between each other.
The remaining voids are filled with the cement which holds the aggregates together
(see table 2 for the ingredients of concrete with their density and table 3 and figure
10 for an example of a distribution of the sizes). This does not necessarily mean that
mixtures with a high fragment of cement are weaker. The cement stone formed out of
Sieve
NEN 2560
1st specimen
2nd
specimen
average
%
cumulative
rounded
C31.5
0
0
0
0
0
0
16
115
119
117
11.7
11.7
12
8
282
282
282
28.2
39.9
40
4
253
247
250
25
64.9
65
2 mm
56
45
50.5
5.0
69.9
70
1 mm
74
63
68.5
6.8
76.7
77
500 μm
89
110
99.5
10
86.7
87
250 μm
69
71
70
7
93.7
94
125 μm
48
52
50
5
98.7
99
remainder
14
11
12.5
1.3
-
-
total
1000
1000
1000
100
-
Fz=5.44
Table 3 - Example of grain distribution
Logaritmic scale NEN 2560
Sieve size [mm]
0
Cumulative rest (%)
10
20
30
40
50
60
70
80
90
100
0.125
0.25
0.5
Figure 10 - Example of grain distribution
12
1
2
4
8
16
31.5
BACKGROUND ON CONCRET
the cement can be considered as very strong. Fracture occurs mostly at the bounding
surface of the aggregates and cement stone. Even in a mixture with a lot of cement
A lot of cement paste
and fine material
like UHPC, the strength relies on both the cement stone and aggregates.
Figure 11
shows respectively a mixture that has a bad composition, a good disposition and one
of an UHPC.
A lot of cement paste
and fine material
Bad disposition
Less cement paste
and fine material
Less cement paste
and fine material
Good disposition
A lot of cement paste
and fine material with
small aggregates
UHPC disposition
Figure 11 - Aggregate disposition
13
The concrete behaviour during curing is influenced by the reaction type itself and the
relation to the deposition of the material.
The deposition of the materials in the concrete determines the product characteristics.
The ratio of large aggregates, small aggregates, sand and ash within the mixture
determines the amount of cement and water needed, since the cement and water
need to ‘glue’ the concrete together. Aggregates that are porous will absorb some
water which has to be taken care of by adding an additional amount of water in
the fresh concrete mixture. After the mixture is calculated, during processing, the
compacting of the mixture is important to obtain the desired strength. Every percent
of air that stays inside above the 1-2 percent will decrease the final strength by 5
percent (Berg, et al., 1995, p.113). If the mixture decomposes the aggregates are not
distributed equally anymore, influencing the concrete’s characteristics in a negative
way. The different materials within the fresh concrete mixture start to float on top of
each other. A mixture with very light aggregates is more vulnerable than a mixture
that contains relatively heavy aggregates. Wet mixtures with a high WCR are also
vulnerable, because the light water will be segregated by too much compacting. It is
highly important to compact the concrete without decomposing the mixture.
The cement paste is in addition to the distribution within the fresh concrete mixture
very important. The cement and water forms cement paste. During curing this
hardens and the space between the formed cement stone is filled with hydrates. Too
much water to process the concrete easily leads to more, so called capillary pores,
in the concrete. These pores are visible by eye. There is simply too much water for
7cm3 air
140 gr cement
paste
ρ 1.94
40 gr water
ρ 3.15
40cm3
140 gr cement
stone
ρ 2.15
65cm3
curing
mixing
7cm3 pores
100 gr cement
ρ 3.15
32cm3
Figure 12 - Curing of Portland cement
14
72cm3
72cm3
BACKGROUND ON CONCRET
the reaction and gel pores. There will always be some pores in the concrete stone
because the chemical reaction binds the water chemically within the cement paste.
100 gram of Portland cement will use 25 gram of water to completely hydrate and an
additional 15 gram will be kept in the gel pores. Theoretically 100 percent hydration
needs 40 gram of water, the WCR should not be lower than 0.4. Internal shrinkage
causes that when 100 gram cement is hardened 7 ml air or water is absorbed (figure
12). This happens because the volume of the element does not decrease (concrete
internal shrinkage), but the reaction creates material that has a higher density. Since
there are no vacuums in the concrete, voids appear. Comparable to the cracking of
clay (figure 13). If the WCR is lower the concrete will, if it is hardened under water,
use some water to hydrate the unhydrated cement.
With a higher WCR the reaction time decreases and the amount of capillary pores will
increase (figure 14). For example if the WCR is 0.33 the relative strength is 1. When
the WCR increases to 0.55 the relative strength will decrease to 0.42 (table 4) (Berg,
et al. 1995, p.135).
During hardening different reactions take place and 100% hydration is hard to reach,
even with higher WCR’s. Figure 15 shows the internal distribution during hydration.
This explains why the relative strength of a mixture with a WCR of 0.33 instead of
0.40 is equated to 1.0.
The fresh concrete consists of the cement, aggregates and water. Since the
aggregates will not shrink or take part in the reaction, the internal shrinkage and
pores only affects the cement paste in between of them. Since the cement paste acts
1
Berg, et al., 1995, p.135
as the glue within the concrete mixture it has to cover all the aggregate material. If
Water cement ratio
Relative strength
0.33
1.00
0.35
0.91
0.40
0.74
0.45
0.60
0.50
0.50
0.55
0.42
0.60
0.35
0.65
0.30
0.70
0.26
Table 4 - WCR and relative strength
(1)
15
the aggregates material is stacked very compact to each other, the internal shrinkage
will be minimised. With a very high cement to aggregate ratio the internal shrinkage
will increase, but not necessarily lead to a weaker concrete. The standard aggregates
are in high strength concrete not strong enough anymore and often their surface
is too smooth for a good binding. For this reason granite stone is used to increase
the performance of in this case the weakest link, the aggregates, in high strength
concrete.
Figure 13 - Cracking of clay
Figure 14 - Cement capilary pores
16
BACKGROUND ON CONCRET
50 % hydrated
internal shrinkage
100
98
95
80
capillary water
volume [%]
67
60
57
ge
lw
ate
r
not hydrated cement
40
35
27
24
20
14
cement gel
0
0
0.2
0.6
0.4
0.8
1.0
1.2
1.4
water cement ratio
100 % hydrated
internal shrinkage
100
98
91
80
capillary water
volume [%]
70
60
not hydrated
cement
ge
lw
ate
r
40
37
28
cement gel
0
00
0.2
0.4
0.6
0.8
1.0
1.2
1.4
water cement ratio
Figure 15 - 50% and 100% hydration of cement
(1)
1
Adapted from Berg, et al., 1995, p.134
20
17
§ 2.2
Concrete processing techniques
A variety of concrete processing techniques have been developed the last decades.
Pierre Luigi (1891-1979) experimented with ferrocement and structural prefabrication
during his career (Iori, 2009, pp.23-27). After the second world war, the shortage
of housing triggered the construction industry to rationalise. New standardised
systemized products followed by tunnel formwork, were used to build multistory
residential buildings out of blocks and beams. Tunnel formwork is a rationalised on
side concrete casting process that is used to make walls and floors of a building at
once (figure 16). Comparable to tunnel formwork is climbing formwork. Instead of
making horizontal compartments it is used to make (stability) cores for high rise
construction (§3.3).
Table 5 shows a comparison of in situ and prefabricated concrete.
In situ
Prefabricated
Material waste
yes
none (failed elements will be
recycled)
Transport
Raw materials
Elements
CO2 emission
Depends on condition
As low as possible
Quality
Depends on condition
As specified
Planning
Costs time at the construction site
Are fabricated before application
Equipment at the construction site
- Moulds
- Preparation of reinforcement
- Concrete processing
equipment like concrete pump
and poker vibrator
- Extra construction workers
- Crane
- Mounting hardware
Material use
Over constructed due
uncertainties in quality
Optimised
Embodied energy
Differs
Differs
Form
Limited by mould
Standardised
Table 5 - In situ and prefabricated concrete processing properties
Related to the different processes, the mixtures have been adapted as well. Concrete
with strengths up to C80/95 are not that uncommon anymore in an era where UHPC
reaches strengths over 150MPa.
C80/95 high strength concrete can, like Ultra High Performance Fibre Reinforced
(UHPFRC) that is reinforced with fibres, cope with greater compression loads, but in
18
BACKGROUND ON CONCRET
Figure 16 - Tunnel formwork
case of increased tension loads extra reinforcement is needed. As showed in figure
9 of both concrete types there is a self compacting mixture which has been adapted
to the newer production processes and allows the fresh concrete to compact itself
between the increased amount and density of reinforcement bars in the formwork.
Formwork
Formwork is used for casting concrete. There are two categories of formwork;
•
Standardized formwork (tunnel formwork, climbing formwork), and
•
Customized formwork (in situ formwork).
The standardized formwork systems are made out of steel. It is reusable strong and
gives a high quality surface finish. The customized formwork can be made using
different techniques;
•
Carpentry,
•
By the use of polystyrene sheets,
•
Additive Manufacturing (e.g. 3D-printing), and
•
Subtractive manufacturing (Milling).
19
Extrusion
Automated processes use a die and no formwork to extrude the concrete. Hollow
core slab floor elements are made this way. The extrusion techniques rely on the
green strength of the concrete.
§ 2.2.1
Processing and the environment
For the durability of concrete it is very important to select the right mixture. If the
environmental impact of concrete is examined, generally it can be remarked that
in situ concrete produces more CO2 than prefabricated concrete elements. This
is caused by the fact that the climate during in situ concrete casting can not be
regulated (Elhag et al., 2008, pp. 376-377). The standardized concrete elements
are generally speaking over dimensioned. To lower the LCA of concrete used in the
building industry, new mixtures have to be composed, or the production processes
have to optimised in order to optimise the material usage. The transport should also
be taken into account, however the transport sector is changing. It can be expected
that in addition to electric cars, electric or hydro lorries will be used in the future. It
depends on the source of the energy whether it is environmental friendly or not. Until
then, CO2 production embedded in the transport should be taken into account. Also,
if concrete is casted in situ, a lorry is needed to deliver the fresh concrete.
§ 2.3
Conclusions concrete
Although concrete is a material that is widely used, the chemical reactions and the
cement hydrates that are formed are very important for the characteristics. During
the last few decades the knowledge about the chemical reaction has increased.
Nevertheless the processing techniques have hardly evolved if compared to the
quality of the mixtures. However the construction industry is also well known for its
conservative behaviour regarding new techniques, which could suggest that evolving
beyond standardized elements is not economically beneficial, or that the best way of
processing is still by using formwork. Nevertheless the expertise on concrete mixtures
of the last decades will be very valuable when introducing new processing techniques
like AM.
20
3 Additive Manufacturing
What is Additive Manufacturing (AM) and why would the building industry
need this process? This chapter introduces the AM technique. AM is a
production method that uses a process of adding layers on top of each
other, to build a component. AM processes also exist in nature. Stalagmites
are an example of uncontrolled AM columns.
Additive Fabrication
Rapid Prototyping (RP)
fabbing
3D-printing
mainly plastics
Rapid Manufacturing (RM)
Production of End-Use-Parts
with AM
plastics
metals
Rapid Tooling (RT)
Direct Tooling
Indirect Tooling
mainly metals
Name by ASTM F42, 2009:
Used for the whole
field of Additive fabrication
Additive Manufacturing (AM)
Figure 17 - The term additive manufacturing
§ 3.1
(1)
Introduction to AM
AM is marketed as a production method that can solve all production problems that
are encountered nowadays. It is like the promotion of every new technique. AM has
potential, but is a relative new technique that requires some improvements before it
reaches the desired potential. It has been improved in the last three decades, but it
took some time before it was picked up by the construction industry (Knaack, Klein,
1
Adapted from Strauβ, (2012) p.19
Bilow, & Auer, 2007, p.126)
AM has been adopted as a general term for multiple fabrication techniques like,
rapid prototyping, layered fabrication, rapid manufacturing, freeform fabrication,
additive fabrication, layered manufacturing, direct digital manufacturing, additive
manufacturing (figure 17) (ASTM, 2009 in Strauβ, 2012, pp.18-19). In this thesis the
terminology AM will be used for multiple fabrication techniques as well.
The AM process can easily be automated, reducing labour costs and additional work
21
Family tree AM techniques
SLS
- for large scale metal
Casting cores
ProMetal casting
- for large scale metal
Voxeljet (3DP) casting;
Chapter 5
e.g. boat-engines
Ceramics and other
materials
FDM techniques
Big Scale AM
3DP techniques
Plastics
Polyjet
Ink Jetting
- fast curing fibre
M3D reinforced concrete
3DP
3DP
Voxeljet
- RapRap
Fabbing - fab@home
FDM
FDM
- fabbaroni
- Makerbot
- large scale SLA;
Mammoth - e.g. prototyping for
dashboards
Stereo Lithography
Apparatus (SLA)
DLP
SLA
SLA
SLS
SLS
High Speed SLS
Metals
DMLS
SLS
Powder bed
processes
LaserCusing
SLM
EBM
- sold for green parts;
ProMetal - intermediate use!
Powder feed
processes
AM processes
from welding
Figure 18 - Family Tree of AM
22
(1)
- developed from Laser
DMD Metal Deposition (LMD)
CLAD
Powder feed
/ wire feed
processes
- sold as DMDS
EBF
In combination with
CNC milling
U.S. Army
“Mobile Parts Hospital”
adapted form Strauβ, 2012, p. 37
LENS
1
3DP
Build-Up Welding
- for jewelery in gold
ADDITIVE MANUFACTURIN
afterwards. Additional work includes removing material but also the handling of the
raw materials itself (Pegna, 1997, pp.429-430).
The construction industry is very conservative. They rely on standardised elements,
even though there is a desire that all buildings should look different. The industry is
innovating, but AM is still not employed on a large scale. In other industries, like the
automobile industry, AM starts to play a significant role.
§ 3.2
AM methods
There are different AM techniques. The scheme (figure 18) from Strauβ (2012)
shows the different categories in the field of AM, based on the type of material.
The most relevant techniques to understand the concept of AM are available for
plastics. These are explained in this chapter and followed by general information
about the characteristics. In this section the information is based on AM Envelope
- The potential of Additive Manufacturing for façade construction by Holger Strauβ,
that contains specific and in depth information on AM.
AM techniques can also be divided in two trends;
•
Fusing materials, and
•
Gluing materials.
The first mechanism uses only the material applied during an AM process, while the
second mechanism uses two types of material to build the element.
23
§ 3.2.1
Stereolithography
Print chamber with
photopolymer curable resin
Laser
Mirror
Selective UV
hardening
Lower building
platform
Fluid material covers
top of model
Remove support material
(Post process)
Figure 19 - SLA method
Stereolithography (SLA) uses an UV light source to cure parts of the light sensitive
resin. The light traces the model in the computer. After one layer is cured by the light
the building platform is lowered and new material is cured on top. Support material
is still needed and has to be removed afterwards. The thickness of the layers can be
reduced to 0.05mm.
Material
Photopolymer curable resin
Resolution
0.05mm
Curing mechanism
Hardening by UV from laser
Moving parts
Focus mirror, print table
Table 6 - Characteristics stereolithography
24
ADDITIVE MANUFACTURIN
Laser Sintering
Sintering
material
Material
§ 3.2.2
Laser
Mirror
Apply layer of
material
Compacting by
a roller
Selective bind
material
Remove support material
(Post process)
Figure 20 - LS method
Laser Sintering (LS) is a method that uses powder instead of a liquid. The powder
is put on top of the existing layer while the platform is lowered. A light source is still
used to selective melt and fuse the material. The melted material forms the final
element. Because the powder is more stable than a liquid, no support material is
needed.
Material
Plastic, ceramic, metal and glass
Resolution
0.1mm
Curing mechanism
Sintering by laser
Moving parts
Focus mirror, material distributor and roller
Table 7 - Characteristics stereolithography
25
§ 3.2.3
Fused Deposition Modelling
(1)
Filament of
material
Extruder
Extrude
Print support
material
Remove support
material
(Post process)
Figure 21 - FDM method
Fused Deposition Modelling (FDM) uses a filament that is heated and extruded by a
nozzle. The extruded molten material sticks directly to the layer underneath. Support
material is needed for overhangs and not well stabilised components. This support
material has to be removed afterwards. The layer thickness is between 0.127 and
0.330mm.
Material
Plastics, rubber
Resolution
0.127
Curing mechanism
Fusing filament
Moving parts
Extruder head
Table 8 - Characteristics stereolithography
26
ADDITIVE MANUFACTURIN
3D-Printing
Granular
material
Material
§ 3.2.4
‘Print head’ and roller
Apply layer of
material
Compacting by
a roller
Selective bind
material with binder
Remove support material
(Post process)
Figure 22 - 3DP method
3D-Printing (3DP) looks like LS, but instead of light, a binder is used to bind the
powder. It is like a printer that puts ink on a sheet of paper. Like LS, after printing
one layer, the platform is lowered and a new layer of powder is applied on top of the
model. Support material is not needed and the layer thickness varies between 0.09
and 0.10mm
Material
Gypsum
Resolution
0.09
Curing mechanism
Liquid binder
Moving parts
Printhead and roller
Table 9 - Characteristics stereolithography
27
§ 3.2.5
Polyjet
Different materials
Photopolymer
curable resin
Print head and roller
Selective
extrusion
UV hardening
Compacting by
a roller
Remove support material
(Post process)
Figure 23 - Polyjet printing
Polyjet printing uses multiple nozzles with a highly liquid material to build / extrude
the element. Those nozzles are fitted in the printhead that moves over the platform.
In this printhead a light and a roller are embedded to cure and smooth the applied
layer of material. The layer thickness is between 0.016 and 0.030mm. Because of its
high resolution, a very smooth element is guaranteed. Support material is needed like
in other methods, that build / extrude only the material that is needed.
The nozzles allow to print with different materials at the same time. Gradient material
is not possible yet, but there are already experiments going on with so called true
seamless gradient materials.
Material
Photopolymer
Resolution
0.016
Curing mechanism
Hardening by UV from laser
Moving parts
Printhead with integrated roller and laser
Table 10 - Characteristics stereolithography
28
ADDITIVE MANUFACTURIN
§ 3.2.6
Other AM techniques
The AM processes described before are based on a printing mechanism that use a
chamber to build in. The extruders move in or at the sides of the chamber. Robotic
arms is a new trend in AM. If desired they can be mounted on a rail system to operate
on a larger work platform. Instead of the fixed position extruders on a rail, these arms
have more degrees of freedom. If an extruder head can move in 6 directions instead
of 3, other processing techniques can be used. The printers in a chamber use only
the three translation degrees of freedom;
•
Along the x-axis
•
Along the y-axis
•
Along the z-axis
The additional three degrees of freedom come from rotation;
•
Rotation around the x-axis
•
Rotation around the y-axis
•
Rotation around the z-azis
These three are available for the robotic arms and Joris Laarman shows such an arm
from ABB that prints in the open air. The project operates under the name MX3D. At
the moment two types of material are processed with MX3D, steel and a polymer. The
steel is a welding machine that builds by welding layers of steel on top of each other
(figure 24) and the polymer can be compared to a two component adhesive. Before
1
MX3D, 2014
extrusion it is mixed in just before the nozzle and after extrusion it reacts very rapidly,
Figure 24 - MX3D Metal
(1)
29
especially because additional heat is added by use of a hot air gun.
Print in support that has the same density as the extruded material is the technique
that lies behind the NSTRMNT 3D printer (figure 25). This printer prints in a gel that
has the same density as the filament. After all the filament is in place an UV light is
used to cure the light sensitive resin. Because the resin is injected in the gel and the
pump can also be used to suck, it is possible to remove material as well. This allows
the user to print and draw in real time. Complex forms will limit the possibilities of
removing material as adjacent filament can hinder access to the place where the
material removal is desired. Scooping out a part of the gel allows the removal of
extruded filament in a more drastic way.
The gel can be reused over and over since it does not react with the resin during
curing. The technique is a two phase production process since a print chamber has
to be filled with support gel before extrusion can take place, but does not negatively
influence the sustainability of the process, since the gel is reusable.
Both processes allow a six axis processing of the filament. The way of curing
determines whether support material is needed or not. If liquid support material is
used the chamber is directly related to the possible element size. Printing without is
more flexible in this perspective.
(1)
1
NTSRMNT, 2015
Figure 25 - NSTRMNT 3D-printer
30
ADDITIVE MANUFACTURIN
Moving formwork
Climbing formwork is actually a slow concrete extruder. It is a technique that uses its
formwork as a moving curing facility. After the concrete has cured, it climbs upwards
to support new concrete (figure 26 and 27). The formwork acts like a nozzle would.
This particular extrusion process is not a continuous process but merely a process
with stages (figure 28). Since the formwork is standardized, but also able to be
changed within the system, it can be considered simultaneously as a changing mould
(§6.2.2).
install additional
formwork for openings
Cement
Aggregates
Additives
Water
Fresh concrete
mixture
Fill
formwork
Cure concrete
Move
fromwork up
Remove additional
support material
Figure 26 - Climbing formwork
Casting and curing
Concrete pumping
Casting and curing
(Post process)
Concrete pumping
§ 3.3
Time
31
Hollow core slab floor elements are made in a similar way. The concrete with very
high green strength is extruded through a horizontal moving die. The die can be seen
as the very temporary formwork. The concrete’s strength is instantly high enough,
allowing the extruder to propel itself against the extruded concrete.
Figure 27 - Climbing formwork
(1)
100
Progress of 3D-printed wall
90
70
Progress of traditionally constructed wall
60
30
20
10
0
0
10
20
30
40
50
60
Time to completion (Hours)
Figure 28 Time of completion
32
(2)
70
80
90
100
2
40
Skyscrapercity, 2009
Adapted from Buswell, et al., 2007, p.230
50
1
Percent complete (%)
80
ADDITIVE MANUFACTURIN
§ 3.4
Properties of AM
AM has next to its advantageous properties also disadvantageous properties. It has
threats and weaknesses. Table 12 shows an SWOT analysis based on Volkers, 2010.
The weaknesses can be eliminated when the AM techniques evolves. For now the
properties that are important are the accuracy, the finishing, material properties in the
produced element and the production time. As long as other production technologies
can produce better and more economical, while these weaknesses of AM are not
solved, they form next to the limited size and mass production large threats for the
AM technique.
In all AM processes the resolution is a dominant factor. An digital model is divided in
surfaces before it is manufactured. During manufacturing the resolution determines
the smoothness of the object. Figure 29 shows the relation between the digital model
and the AM element.
AM is also capable of producing elements that cannot be made elsewise with the
same ease as in an AM process. Complex forms without formwork or moulds are
an example. In most of these processes the production of the mould is the most
expensive stage in the production. For such processes AM has a lot of potential.
Minimised price, minimum waste freeform are promising characteristics. For the
difficult elements AM has a lot to offer, for standardized elements it cannot compete
with the quality and speed of automated processes yet.
Advantageous properties
Disadvantageous properties
Freeform
Resolution can be seen in the surface
Can be used without expensive moulds
Limited production speed
Digital model can be used directly
Can be expensive
Table 11 - Advantage and disadvantage properties of AM
computer model
exported model
AM high resolution
AM low resolution
Figure 29 - From computer model to AM object in relation to the resolution
33
Internal origin
External origin
Strengths
Weaknesses
Geometric freedom
File to factory
No tooling
No inventory/labour costs
Sustainability
Freeform design
Minimum waste
Testing of unique products/certification
Costs per piece
Production time
Properties of materials/anisotropy
Accuracy
Finishing
Opportunities
Threats
Mass customization
Graded materials/Micro structures
Printing composites
Hybrid structures
Limited size/Macro scale
Mass production
Helpful
Harmful
Table 12 - SWOT AM
§ 3.5
(1)
Sustainability
As mentioned in the previous section AM is also more sustainable since no formwork
is needed. To address the exact benefits of AM in relation to the LCA of the resulting
products, intensive research is needed. For each product the LCA has to be calculated.
Generally speaking it can be assumed that AM is environmentally more sustainable
than a multiple phase production technique.
Since the AM technique uses a layered process, the characteristics of the products
differ from the traditional ones. When considering sustainability, durability is also
a parameter. If the lifespan decreases, the sustainability decreases. Evaluation of
produced elements in comparison to known material characteristics is needed and
already an ongoing topic. While the processes evolve, the durability of the products
Conclusions AM
AM is a new and innovative technique that uses certain material characteristics in
combination with a layered application process to build freeform objects. Its full
advantage is when products can be directly produced from the digital model, with
34
1
§ 3.6
Adapted from Volkers, 2010, p.18
will increase and with that the sustainability.
ADDITIVE MANUFACTURIN
minimum use of additional support material that will be wasted after finishing the
object. The field of AM has been improved considerably. With simple desktop printers
costing around a thousand euro’s, a resolution of 0.02mm can be obtained (2015).
Just a few years ago machines cost several thousand euro’s and were not even able
to produce objects with a resolution of 0.02mm.
35
36
4 Research definition
Over the last century the concrete industry has innovated considerably
within their conservative framework (chapter 2). Several examples can be
found in products that emerge from the demand of rational construction
methods. These methods became interesting again and were re-developed
to solve the shortage of houses in Europe during the post war period
(Priemus & van Elk, 1971, p.15). Examples are:
- Lightweight construction systems
Reinforced prefabricated floor elements,
Reinforced prefabricated wall elements, and
Concrete masonry units.
- Tunnel and climbing formwork
The background on AM has shortly been discussed in the previous chapter.
The problem statement and the emerging sub-questions related to
processing concrete will be presented in this chapter. After the research is
delimited, the existing AM techniques are enumerated with their properties
in the next chapter (chapter 5).
§ 4.1
Problem statement
The architects and structural engineers design freeform elements in buildings. The
production techniques for such forms is not synchronised to the ease that they can be
designed (Buswell, et al., 2007, pp.224-225). Rapid manufacturing can be a solution,
but how should a liquid material like concrete, that needs curing, be handled. Studies
related to the field of AM of concrete exist already.
Heads of state already refer to this new state-of-the art processing technique as one
that will revolutionize the way products are made. It has the potential to change how
the production facilities look like next to its capability to produce almost everything.
(Gross, 2013). The challenge is how these new techniques should be implemented in
the construction industry and how they should look like in case of concrete processing.
37
100
90
Existing
Construction
Deposition rate (m3/hr)
80
70
4
Decreasing resolution with
increasing deposition rate
60
3
2
Freeform
Construction
50
1
40
30
‘Desktop’ Rapid
Manufacturing
Micro Rapid
Manufacturing
20
10
0
0
10
20
30
40
50
60
70
80
90
100
Resolution (mm3)
Adapted from Buswell, et al., 2007, p.229
Buswell, et al., 2007, p.230
(2)
1
Figure 31 - Insulating blocks
(1)
38
2
Figure 30 - Resolution/deposition paradox
RESEARCH DEFINITION
§ 4.2
Hypothesis
Buswell, et al. (2007, p.229) show in their article a picture with the resolution /
deposition rate paradox (figure 30). They assume that the desired location of rapid
manufacturing is number 3 instead of where it currently is, number 1. An increase
in speed, without a decrease in resolution, makes the freeform construction process
more beneficial and more competitive. This assumption neglets that other ways of
160
Cost of Construction (Euro/m2)
140
120
Cost of constructing a wall using
3D-printing with a material that
is cost equivalent to raw gypsum
100
80
60
40
20
Traditional build costs
0
Plain wall
Figure 32 - Costs of printed wall
Highly serviced wall
(1)
processing can tackle the resolution problem by direct post processing. Number 4
indicates such a position with an increase in resolution and speed.
Depending on the used AM technique, the speed can be increased with an unchanged
resolution untill certain limits. These limits can logically be found in the speed of an
materials in a polyjet process.
The AM process for the construction industry can be compared to other industries.
The production of a book for example. Using an ink-jet or laser printer several copies
can be printed at home. If an edition involves larger series, like standardised building
elements, a more economical technique at a printing office is preferable. In the
construction industry an in series produced hollow core slab is cheaper than a single
floor that is casted in situ.
1
Adapted from Buswell, et al., 2007, pp.229
extruder’s head, or by the technique used to apply the binder in a 3D-printing or the
39
The hypothesis related to the AM of concrete is:
AM of concrete should only be used for elements that actually benefit
from this production process, either in the characteristics of the emerging
products or by the economical benefits of an AM production technique.
Figure 31 shows a complementary product that an AM process can print. Panels with
different characteristics regarding mass and thermal insulation can be produced like
shown in figure 33.
2.0
Thermal conductivity (W/mK)
1.8
1.6
1.4
1.2
Concrete block work
1.0
Plaster /
Plaster board
0.8
0.6
0.4
Insulation
material
0.2
3D printed panels
0
0
500
1000
1500
2000
2500
Density (kg/m3)
Figure 33 - Thermal conductivity
§ 4.3
(1)
Research questions
current concrete processing techniques and available AM techniques are:
“What are the conditions, regarding production techniques and form,
to benefit optimally of an AM process for producing concrete façade
1
elements?”
Adapted from Buswell, et al., 2007, p.230
The research question and sub-questions that have emerged after investigating the
40
RESEARCH DEFINITION
Sub-questions that emerge can be split in two categories:
Current AM techniques in the concrete industry:
- What are the current concrete AM processes (2014)?
- What kind of products are made with the current concrete AM processes (2014)?
- What are the characteristics of concrete elements made by using an AM process?
- What is the definition of concrete used in such additive manufacturing process?
Evolved processing techniques:
- For what kind of façade elements is concrete AM the best production method?
- How should the concrete AM processes look like and evolve for façade elements?
- Should an AM process of concrete take place at the construction side?
§ 4.4
Research purpose
The purpose of the research is to provide a good impression of the current state of
AM regarding the processing of concrete. This will serve as reference and starting
point to investigate the future possibilities of processing concrete. The hypothesis
has been formulated to delimit the scope, but leaves some space for a search to an
improved or evolved technique. After answering the questions, conclusions will be
drawn on how concrete will be processed in the near future and the next decades.
Recommendations, concept techniques and product ideas are the main goal of the
project.
§ 4.5
Research methodology
To answer the research questions the methodology will consist of a mixture of a
literature review and empirical research.
Before an in depth discussion can take place, it is important that the material
characteristics of concrete are known and kept in mind. In contrast to plastic, the
behaviour and processing techniques of concrete are less well-known outside the
discipline of civil engineering. A chapter on concrete has been included (chapter 2),
to provide some basic information on concrete and as a reference.
41
Identification
In order to arrive at a point from where the possibilities of additional AM techniques
for concrete can be investigated, the identification of the current situation of this
technique is required (2014). Literature will be used to:
•
Identify stakeholders,
•
Present the current technical situation, and to
•
Enumerate the properties and characteristics of the existing AM processes.
Theoretical research
In the theoretical research section, the properties of AM concrete will be examined
in relation to the existing production techniques. The emerging products will be
discussed on the basis of literature. This will show;
•
The characteristics of elements made with the existing AM techniques, and
•
The match or mismatch that may be present between the design and
construction techniques.
The mismatch is interesting because, if a product can be made with a substitute
production method (that already exists), AM has to compete with it. The only manner
to keep a new production technique running, if it is not as cost effective as the
competition, is by using it for complementary products. Matching products and
production techniques need to be well considered to prevent a mismatch.
Research model
After the current techniques are analysed new production techniques, that cope with
a certain absence in an existing concrete AM technique, have to be invented. The
ideas for such machines will be presented. The ideas will be analysed and partly
tested by making a small mock-up. The mock-ups will be used to demonstrate and
analyse their potentials.
The results are evaluated and compared with expected future demands. By using
literature and by investigating the capabilities of the newly introduced production
techniques, an estimation to show the importance of evolving the AM technique for
processing concrete will be made.
The thesis is split into two parts. The research is presented in the first part and shows
the developments in the concrete industry, the match and/or mismatch between the
design resources and a discussion of the production techniques. The second part
introduces new processing concepts, followed by some appendices that show some
experiments in more detail.
42
RESEARCH DEFINITION
§ 4.6
Scope
The goal of the research is draw conclusions related to the AM of concrete with the
help of a design. This will take place in the following framework;
After the literature research, future visions regarding AM and comparisons between
various techniques are illustrated. This evaluation shows the relations between;
•
Consistency
•
Surface quality
•
Strength
•
Usability
•
Added value (integration of parts and services, material use, form)
A roadmap will be used to summarise and show the potential of AM for processing
concrete.
43
44
CONCRETE AM TECHNIQUES
5 Concrete AM techniques
There are several studies regarding the AM of concrete. Before
recommendations can be made it is important that the current situation
is identified. This chapter will introduce, describe and discuss these
studies. The points of improvement discussed in §5.8 will be used for
recommendations, which are used to come to new printer concepts
(chapter 7).
§ 5.1
Concrete as AM material
Concrete AM is a spin off of ‘normal’ AM. The main difference is that the materials that
are used for AM techniques like plastic and steel are homogeneous and can easily be
‘instant dried’. Concrete behaves differently. There are multiple concrete types. For
extrusion processes, like FDM, a dense, rapid curing, mixture is used. In a 3D-printing
process fine powder is used that needs to be bound by a liquid. Figure 34 shows the
basic characteristics of three concrete AM processes.
In addition to the research departments at different universities, companies start
to develop AM techniques for processing concrete themselves. Although they are
based on techniques that are already introduced, they can evolve / change rapidly,
by an investment in the private sector. The scientific research can move to the R&D
departments of multinationals, which can bring momentum in the development. An
example is Winsun new materials, a company in China. They claim to be the first to
be able to print up to ten houses in 24 hours (figure 35), although the technique used
looks like a less advanced copy of Contour Crafting (one of the initiatives in concrete
AM at the University of Southern California).
Challenging is the material processing mechanism for concrete, as can be seen in
table 13. The concrete is not instantly cured like plastic is after application of it.
45
Concrete Printing
extrusion
based
3D
layered
process
D-Shape
Figure 34 - Concrete AM techniques and their properties
(2)
1
Figure 35 - Printed concrete house
(1)
Adapted from S. Lim et al., 2012, p.264
Pei Xin/Xinhua Press/Corbis. (2014)
single
material
46
2
Contour
Crafting
Mechanism
Constituent material
Phase change
Steel
Plastics
Drying
Clay
Chemical bonding
Gypsum
Instant
chemical reaction
Cement
Composite
Concrete
Smart materials
Table 13 - AM material processing mechanisms
§ 5.2
Identification of stakeholders
The stakeholders can be divided in research institutes (like universities), companies
and persons that are involved in fields related to the AM technology.
Research institutes
The stakeholders in the AM of concrete are presented in figure 36. There are evolved
projects shown in literature, like Contour Crafting, 3D-Concrete Printing, Pegna and
D-Shape.
Additionally there are new studies initiated. TU-Delft is not the only institute
researching AM. At the Eindhoven University of Technology a thesis is being written
about parameters that are involved in AM of concrete. With these parameters the
researchers want to predict whether it is possible to produce an element with a
certain fresh concrete mixture or not.
Other useful knowledge can be gathered from people in the disciplines of AM, concrete
processing and concrete technology at the different chairs of the universities, but also
from individuals working in fields related to AM.
Companies
As mentioned in the introduction, companies can start to play a major role. There
is considerable knowledge available at the companies and they can more easily
invest in new techniques by allocating their profits to R&D. One specific company,
Winsun new materials, printed the houses mentioned previously. In France, EZCT,
an architectural office, is experimenting with AM of sand moulds, to cast elements
with UHPFRC (figure 37 and 38). Additionally the first AM machine that uses FDM to
process concrete, the BetAbram, can be bought since a few months.
47
Dr. Dipl.-Ing. Holger Strauss (Hochschule OWL)
Erno Langenberg (printing ceramic)
DUS Architecten (Canel House)
MX3D
NSTRMNT
Sascha Hickert (Hochschule OWL)
Prof. Dipl.Ing. Matthias Michel
AM
ir. Roel Schipper (CiTG TU-Delft)
dr.ir. Karel Vollers (BK TU-Delft)
Adapa (DK) MSc Eng Thomas Henriksen
Rieder Group (AT)
ir. Siebe Bakker
Concrete processing
go
e
f c o n cret
Moulds
Pegna
Ad
d
iti
ve
3D Concrete Printing
ur
Saxion
Concrete
in
D_Shape
Mw. dr. ir. S.A.A.M. Fennis (CiTG TU-Delft)
M a n u fa c
t
TU Eindhoven concrete printing
- prof.dr.ir. T.A.M. (Theo) Salet - support material
- Rob Wolfs - Parameters and concrete properties
Contour Crafting
TU Delft
- Evaluating techniques and searching matching products
- Experiments with new concepts for AM of concrete
Companies
Winsun New Materials - prints 10 concrete houses in 24 hours
EZCT Architecture & Design Research - uses sand moulds for casting UHPFRC
BetAbram - offers a FDM concrete printer
Skanska / Foster + Partners - Licensed by 3D concrete printing
48
(1)
1
Figure 37 - Casted UHPFRC
Schwartz, 2013
Figure 36 - Scheme of stakeholders
CONCRETE AM TECHNIQUES
§ 5.3
Techniques
Concrete printing processes can be used in different fields. Applications can be found
in architecture and construction, arts and design and in the public domain (Lim et
al., 2012, pp.262-263). There are different fields involved as indicated in the scheme
of stakeholders. In the literature there are three interesting and well described AM
techniques that are used for the AM of concrete.
There are also techniques that deform the concrete after it has been casted in a
flexible mould. These kind of processes are performed by Adapa, a company in
Denmark. However, by using the latter method the elements are just curved slaps,
that become a 3D form. Roel Schippers experiments with the same techniques at
the faculty of civil engineering at the Delft University of Technology. In Detmold at
the Hochschule Ostwestfalen-Lippe and now at the faculty of civil engineering at the
Darmstadt University, Sascha Hickert experiments with moulds made out of cloth.
This process looks like the inflatable mould mentioned before.
For now the focus lies on AM methods. Table 14 shows an enumeration of properties
Figure 38 - Casted UHPFRC close up
(1)
1
Schwartz, 2013
of the well described concrete AM techniques.
49
Table 14 - Concrete printer technique properties
50
(1,2)
2
1
-
Removal of unused material
First attempt for freeform
construction
- Massive material placement
- Removal of unused material
Print speed/resolution
Pre/Post processing
Pros
Cons
Adapted from S. Lim et al., 2012, p.264
Added information from Hwang, 2004, p.4
Depending on the type of fresh concrete and used additives
Optimal
Use of materials
i
-
Surface qualty
Tested with zero degrees of layer orientation, which means the force was given from the top of the printed surface
Mechenical properties
>1 m dimension
No
Reinforcement
Print size
unknown
Layer thickness
14.52 MPa
unknown
Nozzle number
Flexural strength
1 mm
Nozzle diameter
28.30 MPa
Portland cement (activated by water)
Binder
Compressive strength
Sand
- Extra process (moulding)
- Weak bonding between batches
due to segmented backfilling batches
by one hour interval
Smooth surface by trowel
- Reinforcement per 125 mm
vertically
- Backfill the mould with a
cementitious material per 125 mm
height
- Smooth surface by trowel
High
optimal
smooth
>1 m dimension
unknown
18.6 MPa2
Yes
13 mm
1
15 mm
None (Wet material extrusion and
backfilling)
- Mortar mixture for mould
- Cementitous material for build
- Limited printing dimensions by the
printing frame, (5.4 m (L) x 4.4 m
(W) x 5.4 m (H)
- Slow process
- Rough surface
- Limited printing dimensions by the
printing frame
- Massive material placement
- Removal of unused material
High strengths
- Compression of the powder for next
layer by a roller with light pressure
prior to the deposition
- Removal of unused material
Reinforcement after printing
- High strengths
- Minimum printing process;
deposition & reinforcement
Low
optimal
layered
>1 m dimension
14-19 MPa
235-242 MPa
No
4-6 mm
6300
0.15 mm
Clorine-based liquid
Granular material
No
3D-Printing
D-Shape
Low
optimal
layered
>1 m dimension
12-13 MPa
72-110 MPai
Yes
6-25 mm
1
9-20 mm
None (Wet material extrusion)
In-house Printable Concrete
No
Build material
Yes (lost mould, becomes part of the
component)
No
Extrusion
Concrete printing
Use of moulds
Extrusion
Contour Crafting
3D-Printing
Pegna
Process
CONCRETE AM TECHNIQUES
§ 5.3.1
Contour crafting
Cement
Aggregates
Additives
Water
Fresh concrete
mixture
Material
between
contours
Extruder with
trowels
Extude two
paths
Use trowels to
smoothen surface
Fill cavity
Figure 39 - Schematic visualisation of Contour crafting
Contour crafting is a process that extrudes a mortar mixture. The mortar is extruded
and a trowel is used to get a smooth surface (figure 39). The process has been
evolved over the years. A second trowel was added to smooth the surface even
better, where after two extrusion heads were used to extrude just the contours of
the designed element. A third extruder to cast concrete between the built walls
was added. Additionally, experiments with different materials, heating and / or
moisturizing the surface were done to improve the surface quality.
Extruding between the trowels is just a part of the contour crafting concept. Next to
the AM of the concrete, other operations can be integrated. As the words Contour
Crafting already says, it is crafting the contours, done by extruding between the
trowels. This is comparable to a potter who forms the contours with his hands
(Khoshnevis, Bukkapatnam, Kwon, & Saito, 2001, p. 39). The main idea is to
print the contours and use the space in between to be filled with other materials.
Insulation is one of them but for structural strength it can be filled with concrete
as well. Experiments with reinforcement elements have been done to gain more
resistance against tension forces (figure 41). Another possibility is to integrate pipes
and wires (figure 42). All these concepts are shown in Khoshnevis’s article Automated
51
Figure 40 - CC in operation and representative 2.5D and 3D shapes and parts filled with concrete
(1)
construction by Contour Crafting related robotics and information technologies. It
discusses complete buildings with the use of Contour Crafting for the walls and precasted beams to support the floor elements. The system becomes an automated
robot that is able to do multiple operations at once that normally have to be done by
multiple machines (figure 43).
Contour crafting is also investigating the feasibility to facilitate the technical knowledge
to build for extraterrestrial applications. The idea is that local materials are used as a
mortar for in situ extruding a lunar base (Khoshnevis, 2004, pp.17-18). In 2013 NASA
funded a study after evaluating the technique in 2010.
The compressive strength of the Contour Crafting elements is around 18.6 N/mm2
(Hwang & Khoshnevis, 2004). This will be considered as one of the weakest concrete
classes (table 17), but is still widely used in the construction industry, because higher
compression strengths are accompanied by increased tension loads. To withstand
1
Khoshnevis, 2004, p.12
these tension forces in the concrete extra reinforcement is required.
52
CONCRETE AM TECHNIQUES
Figure 41 (left) - Reinforcement components and assembly procedures for walls and columns
3
2
1
Khoshnevis, 2004, p.7
Khoshnevis, 2004, p.8
Contour Crafting, 2015
Figure 42 (right) - Plumbing modules and grippers
(1)
(2)
Figure 43 - Construction of conventional buildings using CC
(3)
53
Type II hydraulic Portland cement
4.31 kg
Sand
4.76 kg
Plasticizer
0.36 kg
Water
2.18 kg
Table 15 - Mixture CC
(1)
The mixture used contains a very high content of cement. In fact it is a mortar, but
they sell it as concrete. Table 15 shows that the mixture consists of cement and sand
with a plasticizer to increase its workability.
The WCR is 0.51 which will cause capillary voids within the hardened concrete. The
ratio between sand and binder is 52 : 48. Compared to regular concrete with a ratio
of 17 : 83 this is relatively high. The high amounts of especially Portland cement will
cause a lot of internal shrinkage in concrete. Not just because of the reaction causes
shrinkage, but also due to the expansion and shrinkage caused by the heat of the
1
Hwang, et al. 2004, p.4
exothermic reaction.
54
CONCRETE AM TECHNIQUES
§ 5.3.2
3D-Concrete printing
Cement
Aggregates
Additives
Water
Fresh concrete
mixture
Extruder without
trowels
Extude
(Post process)
2
Domus, 2014
Figure 44 - Schematic visualisation of 3D-Concrete printing
Figure 45 - Bench made with 3D-Concrete printing
(1)
55
3D-Concrete printing is an extrusion process without trowels. The surface of the
extruded concrete is rough (figure 44 & 45). The techniques differs from Contour
Crafting, but exhibit also similarities, as can be seen in table 14.
The compressive strength is between 72-102 MPa, flexural strength between 6-17
MPa and tensile strength between the layers between 0.7 and 2.3 MPa depending
on the speed of extruding and the time to cure in between. There are less voids in
comparison to casted concrete, 1.0% instead of 3.8%. Due to the higher density the
printed concrete has a density of 2350kg/m3 instead of 2250kg/m3 when the same
fresh concrete mixture would be casted. Poor AM concrete gives 4.8% as can be
seen in figure 46 and 47 (Le, Austin, Lim, Buswell, Law, et al., 2012a, pp.561-564).
The voids will, like capillary voids, weaken the concrete’s strength significantly (table
4). Also 3D-Concrete printing uses a mixture that contains a large fraction of binder.
The silica used is also a binder like cement. The sand binder ratio is 60:40 (table 16).
Void between 4 filaments
(1)
90mm
Figure 46 - Voids between printed concrete (concrete printing)
(2)
1
Figure 47 - Mould cast poor and goodprinting structure
Good printing
Le, et al., 2012a, p.559
Le, et al., 2012a, p.562
Poor printing
56
2
Mould casted
CONCRETE AM TECHNIQUES
Material
kg/m3
Sand
1241
Cement
579
Fly ash
165
Silica fume
83
Water
232
12 / ø 0.18 mm polypropylene fibres
1.2
Super plasticiser
1%
Retarder
0.5%
Table 16 - Mixture 3D-Concrete printing
§ 5.3.3
(1)
D-Shape
Material waste
Granulate
‘Print head’ and roller
Apply layer of
granulate
Selective bind
using a binder
Remove lose material
around element
Figure 48 - Schematic visualisation of D-Shape
D-Shape is a process that uses a granular material (sand and stone powder) and a
chorline-based liquid as binder. The granular is used to build the form but also as
1
Le, et al., 2012b, p.1227
support material. This 3D-printing process presents the opportunity to make complex
forms. During the printing process a new layer of granulate has to be applied on the
complete print area. This is relatively time intensive (Lim et al., 2012, p.264). When
the model is finished the powder has to be removed. Internal voids are filled with
powder if no measures are taken (figure 49).
Like NASA that supports Contour Crafting, ESA is interested as well in AM, to build
57
a lunar base. ESA works with Foster+Partners and use Enrico Dini’s D-Shape to
explore the possibilities for a lunar base. The designed dome is supported by a
catenary wall element, which is reminiscent of a bone structure (figure 50) (ESA,
2013).
58
Materia, 2013
ESA, 2013
(2)
2
Figure 50 - Lunar base by Foser+Partners
(1)
1
Figure 49 - D-Shape removing the material that has not been bound
CONCRETE AM TECHNIQUES
§ 5.4
General product properties
The most used technique to make concrete elements is casting and in these processes
different mixtures are used. In AM of concrete this is limited due to the fact that a
mixture with a certain fluidity combined with some firmness is needed. Reinforcement
is also a challenge. For example the way the material is processed with the current
methods causes that reinforcement cannot be placed before printing, but has to be
placed at a different moment and in a different way, during or after the element has
been printed.
(1)
1
Domus, 2014
Figure 51 - Surface 3D-Concrete printing
59
§ 5.4.1
Mixtures
The mixture is crucial and determining factor. A simple experiment performed at
the faculty of civil engineering showed that there is a relation between the strength
and the way the concrete was processed. Three different samples were casted and
tested;
•
An element that was compacted at once after casting,
•
An element that was casted out of five layers, that were applied with 5 minutes
time intervals to simulate a printing process, and
•
An element that was compacted after it had been casted out of five layers, that
were applied with 5 minutes time intervals.
The element that was casted at once and compacted was the strongest, followed by
the layered compacted sample. The strength was respectively 28.58, 28.41 and 23.2
MPa for the not compacted layered sample, after 7 days of curing. Appendix 1 shows
the complete experiment.
If the concrete is additive manufactured with selective binding like 3D-printing, the
capillary action is important. The selective binding relies on the accuracy of the
applied binder. If the binder flows out to the surrounding material, the resolution
decreases and the concrete will not be hydrated completely.
Since the selective binding method uses an additional adhesive instead of cement to
bind the materials together, the concrete mixtures characteristics mostly only apply
for extrusion processes, that use actual concrete.
The composite that is referred to as concrete consists of three different material
categories, the binder, the aggregates and the additives. Each with their function.
The ratio of them in a mixture that is used for AM, can be changed to obtain the
desired mixture.
In casting and spraying concrete (shotcrete) the ratios are used to obtain;
•
A certain strength,
•
The concrete characteristics regarding durability, sustainability and resistance
against environmental influences, and
•
Workability.
The concrete is pumped through pipes and extruded trough a nozzle in case of
an extrusion process. Therefore the processability is, next to the strength and the
characteristics of concrete, very important in an AM process. The shear strength
during processing and the open time of the mixture is of high importance. Those two
60
CONCRETE AM TECHNIQUES
Layer strength (to support additional layers)
High
Fresh concrete with super plasticisers and
retarders as changing parameters within
the mixture
Low
Low
High
Inter layer strength
Figure 52 - Open time, workability and inter layer strength
parameters can be controlled with;
•
The water cement ratio,
•
The aggregates, and
•
Additives like super plasticisers and retarders.
Contour crafting uses a mixture that is shown in table 15. The mixture used by
Loughborough University for the 3D-Concrete printing can be found in table 16.
b
−c
wcf
For CEM II 52.5
33
− 62
f ' cn = 0, 85 ⋅ 61 +
0.4
f ' cn = 72MPa
f ' cn = a ⋅ N n +
When Loughborough’s mixture is calculated with a standard formula the strength
differs to the measured strengths in table 17. This has to do with the high ratio’s of
cement and the processing technique used.
61
Loughborough tested also the workability and the open time of the mixture. To be
able to process the mixture through, in their case, a 9 mm nozzle, the shear strength
of the mixture should be between 0.3-0.9 kPa to have a workable mixture that is not
too wet or too dry. Too wet will lead to filament that it is not able to support layers
above and a mixture that is too dry will cause the the filament to break easily (Le,
Austin, Lim, Buswell, Gibb, et al., 2012b, pp. 1226-1231).
The knowledge about concrete mixtures, inter layer strength and green strength is
available, it only needs to become available for AM processes. 3D-Concrete printing
uses a UHPFRC. The mixture contains a relatively large amount of cement, but maybe
that is not even necessary for all aplications. The sand binder ratio is 60 : 40. This
can also cause a lot of inernal shrinkage and heat in case of Portland cement, with
the possibility of an exceedingly amount of cracking. More information about desired
mixtures for an AM process is enumerated in § 7.1.
§ 5.4.2
Reinforcement
Reinforcement in traditional concrete is embedded to distribute the tension forces. In
additive manufactured concrete it has, if short fibres are used, also the ability to hold
the mixture together during extrusion and curing, because it makes the mixture less
fluid and provides more green strength. The process does not allow fibres between
the layers. The fibres are just in the layers but do not take part to increase the
interlayer strength.
Reinforcement used in the 3D-Concrete printing technique is 12/0.18Ø mm
polypropylene fibres (Le, et al., 2012b, pp. 1231). Because of limitations regarding
the size of the nozzle, the not aligned reinforcement fibres have to be short. Manual
applied reinforcement can be used between all layers, by leaving openings in the
printed concrete. Afterwards the reinforcement can be placed in these openings to
pre-stress the printed concrete. This has been demonstrated in the bench made with
the 3D-Concrete printing technique (Lim et al., pp.266-267). The bars used to prestress the concrete have to be protected and / or covered, because otherwise due to
corrosion the element can be damaged.
62
CONCRETE AM TECHNIQUES
Fck,cyl
[N/mm2]
Fck,cube
[N/mm2]
C8/10
8
10
C12/15
12
15
C16/20
16
20
18.6 - Contour crafting
C20/25
20
25
28.30 - Pegna
C25/30
25
30
C30/37
30
37
C35/45
35
45
C40/50
40
50
C45/55
45
55
C50/60
50
60
C55/67
55
67
C60/75
60
75
C70/85
70
85
C80/95
80
95
C90/105
90
105
C100/115
100
115
higher classes
A lot of cement paste
and fine material
100-110 - 3D-Concrete
printing
235- 242 D-Shape
Table 17 - Concrete class properties
Less caggregates
between the layers
Figure 53 - Layers when aggregates used in AM concrete
63
§ 5.4.3
Layered characteristics of AM
D-Shape uses a process whereby the support of the bounded material is done by the
powder underneath. This is one of the advantages of the 3D-printing process. It has
the advantages of mouldless production and does not suffer under the disadvantage
that AM techniques exhibit due to lack of support. Printing voids is nevertheless a
challenge.
Contour Crafting and 3D-Concrete Printing extrude fresh concrete in layers. The
bounding between the layers, influenced by the open time, is fundamental and
determining the strength of the element (figure 53). D-Shape is the most isotropic
because of the binder that is used.
§ 5.5
AM of concrete
Additive manufacturing can be split in three trends Rapid Prototyping (RP), Rapid
Manufacturing (RM) and Rapid Tooling (RT). RT and especially RM are expected to
become very important in the building industry. The limitations nowadays are the
limited size, accuracy, finishing and the material properties (Volkers, 2010, p.41).
The SWOT analysis indicates the Strengths, Weaknesses, Oppurtunities and Threats.
Bourell et al. (2009) describe two approaches. The approach to make existing
products the same way but better or to produce products we only can produce by
using the AM in a RM process. “In addition to the time-tested advantage of being able
to create unique geometries, there are a host of other possibilities in varying degrees
of maturity, including cellular structures, gradient structure, directional properties,
on-the-fly in-build probing of the internal structure, etc.” Trying to mimic products
that are produced normally, creates an extra challenge for AM. It has to compete with
the performance of existing methods (Bourell et al., 2009, p.20-21). If products are
build that do not suffer from competition, it is more likely that a steadily improved
AM process will succeed.
Complementary products are the best way to gradually improve and create new
product types. On the other hand mimicking existing material properties is important
as well, since understanding of physical properties and how they can be formed in an
AM process will provide knowledge needed for improvement. The two approaches do
not exclude each other but have to develop in such a manner that they consolidate.
For concrete this means that the properties need to be well investigated in relation
to the AM techniques. What is going on during curing of concrete and how can it be
64
CONCRETE AM TECHNIQUES
controlled. The products as quoted can be more optimised like self-optimised three
structures, instead of the massive sections used in elements nowadays.
§ 5.5.1
Concrete products that benefit from an AM process
What kind of concrete elements should be manufactured with an AM technique?
As discussed before and in §2.2 prefabricated concrete elements are produced highly
automated and optimised. Generally there are several types of products as Eekhout
(1997) mentions;
•
Standardised products,
•
Systemized standardised products,
•
Standardised system products,
•
System products,
•
Special system products,
•
Systemized special products, and
•
Special products.
The AM technique should not be used as a substitution good of prefabricated
elements, but as a complementary production method to produce special elements.
The increase in performance of AM that can be expected will not be able to compete
S3
Super Smart Skin
In this conceptual vision the facade is made of a super
clever, thin, wrapping layer of additive manufactured
building skin. The skin is wrapped around the main
construction and the different ‘pads’ are ‘zipped’
together.
Fa
In
te
ca
de
gr
al
Pl
Sk
at
e
in
Pr
Pa
in
Strategic road map for Additive Manufacturing in Facade Design
The Super Smart Skin enables freeform design while it
can be formed to appear like any double-curved
surface designed. The skin contains internal
microstructures that can deform the pad in to a
curved surface. It uses the benefits of internal
structures to fulfil a variety of functions. Internal
mechanisms can be used to integrate all kind of
building physical functions like ventilation - provide by
micro fans -, sun shading - provided by little ‘eyes’ - or
insulation value - provided by a adaptive surface
which inflates adaptively to the circumstances.
ds
ting
Technology Road Map
The basic functions of a single pad, small or big sized,
needs to be (1) sealing the building (water, air,
energy...), (2) structural (dead load, form) and (3) one
or more additional functions. The pad could have a
‘mono-function’, like only ‘ventilation’ or ‘providing
visibility’ (transparency), or fulfil multiple functions
combined in one pad. The modularity of the facade
depends on the size of the pads.
in
te
Fa
rfac
es
Development line
ca
de
Co M
m ac
po hi
ne ne
nt
s
Legend
Fl
ex
Transfer in development
3D
The pads can ‘stitched’ to the building by a ‘spider
robot’ that zips the building skin around the main
structure. The functions of the skin can be mapped
freely to fulfil the desired functions where the benefit
most. Like putting heat gaining surfaces to the south
facade or (kinetic) energy generating surfaces in a
windy corner.
Step in development
Technology Bridge
The Facade Machine
sion
s
In this conceptual vision the whole facade is a
en
machine, made of ingenious integrated mechanisms
that fulfil all functions needed. The mechanisms make
the facade super adaptive and adaptable. Facade
elements could change form, function and properties
and the facade can ‘open’ itself for maintenance or
replacement, or even to let someone in.
Su
sp
Note:
Gra
de
d
Positions and concepts are indicative
This Road Map is a snapshot of the situation at a certain
time, from the authors perpective. Positions and concepts
can be differten for different stakeholders and industries.
The facade fittings could be adaptive: when
components have deviations in size, due to tolerances
or temperature, the ‘facade machine’ can adjust to it.
With the facade machine it is not necessary to have
doors, the facade just folds open whenever someone
wants to enter...
FE
M
co op
ns ti
tr m
uc iz
tion ed
s
RM
FiF
RT
Fully Integral Facade
In this conceptual vision the facade is made of a printed
graded-multi-material structure that fulfils all functions
in one continuous facade layer. The facade could eventually seamlessly go on, into a fully integral building.
RP
The ‘FiF’ vision mostly uses the benefits of ‘graded materials’ and ‘freeform design’ from the Additive Manufacturing aspect, and it covers most aspects from facade
design, although ‘freeform’ and ‘function integration’
are the most important in this concept.
Switch to ‘multi-functionals’
AM machines for RP, RT and RM
Process
pp
m orti
ou ve
ld
s
The FiF fully benefits from 3D CAD software with finite
element methods build into it. Engineers design these
facades with parametric models that can be fully
optimized for structural and functional aspects. For
example, structurally the facade can ‘mimic’ nature’s
solutions for structural optimization, like bone structures. For functional optimization one can think of a
graded material which functions as a hinge for opening
parts of the facade. One material than provides both
stiffness as flexibility.
at
e
M
ou
ld
in
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Fr
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fo
rm
Fa
su
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ou at
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Additive Manufacturing
Fr
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fo
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co op
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nt
s
The vision of the ‘Facade Machine’ mostly uses the
benefit of ‘internal structures’ from Additive
Manufacturing, and it covers ‘function integration’
and ‘adaptivity’ from Facade design.The machine can
be regarded as a ‘clock work’, precisely regulating the
functions of the facade. The mechanisms can provide
most of the building physical- / climate installations,
like ventilation and sun shading as well as other basic
functions like ‘opening’.
at
1:
fu 1 M
lls oc
ize, ku
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M
process side track concepts
Step 2
as
te
r
thesis of Nathan Volkers, “ The future of Additive Manufacturing in Facade Design”
April
2010
Ro
ad
M
> 25 Years
now
Th
is
Relative Timeline
ap
is
pa
rt
of
th
e
m
M
Nan
icro
o
Cr Pref
aft ab
ed Co
El nt
em ou
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ts
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em ac
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ru
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nt
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ct
st
ru
Step 1
ou
el
em
en
r Cr
pa aft
vi ed
lio
n
ts
process speed
Phase 3 - Durint the third phase the full benefits of Aditive
Manufacuturing technologies will become apparent. Designs
and developments which are now beyond our imagination will
become feasible and viable. Fully printed archicture is finally
possible.
Nan
ex o +
pe M
rim ac
en ro
ts
Volkers, 2010, p.109
1
Phase 2 - The second step will involve the development of
multi-material solutions, layered as well as (functionally)
graded, and transparent glass printing. Nano and macro
printed elements will be available. Most elements are
components in addition to conventional produced building
components.
Pr
(M inti
PV ng
’s) Ve
hi
cles
1:
Sc
er
pa
s
rt
pa
s
el
od
m
al
e
Phase 1 - The first step of the technical developments in
Additive Manufacturing will lead to intermediate sized
elements (10 um - 100 mm) that can be applied in addition to
existing products. There will experiments with all kind of new
processes, materials and scales, but the first applications will
have to be produced with currently available techniques and its
limitations.
ia
rt
l
s
Adv
an
ce
d
Pl
The Fully Integral Facade is the result of a complex mathematical 3D model that defines where structural
strength and other functions should be positioned. Mastering complex 3D modelling becomes a required skill for
designing facades or buildings. The future fully
integrated facade might be a complex formula and the
context and users define the parameters…
Figure 54 - Technology Roadmap by Volkers
(1)
65
with the existing production techniques in an economical way, but are important
to understand physical properties, as shown by Volkers’s Technology Roadmap
(figure 54 & Appendix A9). Therefore elements that can be produced with traditional
automated and optimised production techniques should not be reproduced the next
decades as mentioned before.
Products
The complementary production technique should focus on;
New product types;
•
Products with internal holes that cannot be produced otherwise.
Special forms (special products) that are very expensive due formwork, these can be
subdivided in;
•
Connections between standardised prefabricated products,
•
Individual products, or
•
Small series.
Priemus et al. (1971) divides the construction industry by production methods. What
kind of building techniques AM can be used for are indicated in red (figure 55).
constructing
material in solid
state
standard brick size
max. weight that
can be processed by
hand
mechanical installed
large construction
elements
casting
floors
standardized
formwork
in situ formwork
Industrial
constructing
prefabrication
Field of AM
traditional building
method
(1)
1
Figure 55 - Construction methods and the field where AM can manifest
Adapted from Priemus, et al., 1971, p.10
processable by hand
material in plastic
state
66
CONCRETE AM TECHNIQUES
§ 5.6
Environment: Material use, production and sustainability
The building’s components have different life spans (figure 58) (Brand, 1994, p.13).
To compare products and the LCA’s one can look at;
•
Amount of materials used (optimisation),
•
Material properties printing versus common techniques (e.g. structural
performance),
•
Embodied energy next to the product itself (transport),
•
Casting and mould embodied energy versus printing energy, and
•
Life span of the element.
The material concrete is new in the field of AM. Why would you print concrete instead
of a plastic? Dus Architects is printing in a bio-based plastic and are searching to
replace the plastic. Some experiments have been done with a cementitous granulate.
Advantage properties for constructing can be found in the facts that;
Concrete has a higher density and fire resistance than plastic. The main advantages
of concrete are its compressive strength, processability and the low costs. (Bio
based) plastics are for that reason less suitable to act like a thermal buffer. In
Figure 56 - Kamerprinter at Dus Architects
Figure 57 - Printed element at Dus Architects
67
addition, concrete can be considered more durable and because of thermal buffering
capacities it can be considered, due to the lower energy demand to maintain a stable
temperature, more suitable for indoor constructions in daily used buildings.
Stuff
Space plan
Services
Skin
Structure
Site
Figure 58 - Life span building components
(1)
The embodied energy of concrete is relative low if compared to other materials
(figure 59 & 60). Unfortunately recycling of concrete is hard. Alloys and metals can
be recycled easily. To minimise the consumption of raw materials optimisation is
1
Adapted from Brand, 1994, p.13
desired for concrete structures.
68
Embodied energy, primary production (MJ/kg)
CONCRETE AM TECHNIQUES
1000
Aluminum/silicon
composite
Aluminum carbide
/ silicon
carbide composite
Titanium alloys
Aluminum-poly-
ethylene sandwich
CFRP, epoxy matrix
CFRP, epoxy matrix (isotropic)
(isotropic)
100
Titanium alloys
Tungsten
alloysalloys
Tungsten
Magnesium
alloys
Magnesium
Tin
Tin
Carbon
Carbon fiberfibre
alloys
Metal
foam
Metal
foam
Ethylene
trafluoroethylene
Ethylene
tetrafluoroethylene
(ETFE)
(ETFE)
polyurethane
foam Polytetrafluoroethylene (PTFE)
ElastomericElastomeric
poluurethane
foam
Polytetrafluoroethylene (PTFE)
Aluminumalloy,
alloy, wrought
(6061, T4)
Aluminum
wrought
Glass fiber
Glass
fibre
(6061, T4)
GFRP, epoxy matrix (isotropic)
GlassGlass
ceramic
ceramic
GFRP, epoxy matrix
Zinc
alloys
Zinc
alloys
Polyester
Polyester
(isotropic)
Low carbon
steel steel
Low
carbon
Medium density fiberboard
parallel to board
Terracotta
Terracotta
Hemp
Hemp
10
Hardboard perpendicular
to boardto board
Hardboard perpendicular
Asbestos
fiber fibre
Asbestos
Bamboo
Bamboo
Common
brick
Common
brick
Concrete (structural
lightweight)
Concrete (structural
lightweight)
1
High performance concrete
High performance
concrete
Dense
concrete
Dense
concrete
Straw
bale
Straw
bale
0.1
Composites
Metals
Foams
Polymers
Ceramics
Wood
Embodied energy, primary production (MJ/m3)
Figure 59 - Embodied energy/kg (MJ/kg) (CES)
1e7
1e6
Tungsten alloysalloys
Tungsten
Aluminum / silicon
carbide composite
Titanium
Titanium alloysalloys
Aluminum-polyTin
CarbonCarbon
fibrefiber
Tin
Ethylene
tetrafluoroethylene (ETFE)
Ethylene
trafluoroethylene
(ETFE)
ethylene sandwich
Magnesium
Magnesium
alloys
100000
10000
Polytetrafluoroethylene (PTFE)
(PTFE)
Polytetrafluoroethylene
Zinc
Zincalloys
alloys
Lowcarbon
carbon
Low
steel steel
Glass fibre
Metal
foam
Metal foam
CFRP, epoxy matrix
alloys
(isotropic)
Aluminum
wrought (6061,
T4) T4)
Aluminum
alloy,alloy,
wrought
(6061,
GFRP, epoxy matrix
(isotropic)
Asbestos
fiber
Asbestos
fibre
Hemp
Hemp
Glass
ceramic
Glass ceramic
Common
brick
Common
brick
Elastomeric
polyurethanefoam
foam
Elastomeric
poluurethane
Medium density fiberboard
parallel to board
Bamboo
Bamboo
High performance
concrete
High performance
concrete
Concrete (structural
lightweight)
Concrete (structural
lightweight)
1000
Hardboard perpendicular
to board
to board
TerracottaHardboard perpendicular
Terracotta
Polyester
Polyester
Dense
concrete
Dense
concrete
100
Straw
bale
Straw
bale
10
Composites
Metals
Foams
Polymers
Ceramics
Wood
Figure 60 - Embodied energy/m3 (MJ/m3) (CES)
69
§ 5.6.1
Material usage
The amount of material used in an AM should be less than in a conventional process.
The material properties of Contour Crafting and Loughborough University used do
not match the desired characteristics in an element. Loughborough’s mixture has
a compressive strength of 110 MPa at 28 days (Le, et al., 2012b, p. 1231). The
40% binder in the mixture causes an increase in emission if compared to normal
concrete that contains only about twenty percent cement. 110 MPa compression
strength gives probabaly an over dimensioned element. In such a case the argument
of material efficiency in AM processes is not valid anymore. Contour Crafting performs
even worse if the structural strength of a 48 : 52 binder sand ratio gives only a
compressive strength of 18.6MPa.
The expected strength of concrete, shown in the grey bar of figure 61, shows the
expected relation between strength and the amount of cement. This needs to be
changed otherwise AM concrete performs less on their LCA due to its high cement
factors.
Strength (MPa)
High
Ex
p
ec
te
d
st
re
n
gt
hs
3D Concrete printing
Contour crafting
Low
Low
High
Cement (%)
Figure 61 - Material usage compared to the expected strength
70
CONCRETE AM TECHNIQUES
§ 5.7
Evaluation
Extruding with two extrusion nozzles, one with the final elements material and
another one with support material, is a hybrid solution that creates extra formwork
around vulnerable parts of the element. In the case where the formwork nozzle uses
a reusable material, there is no embodied energy lost in the formworks material. This
could be a new technique for processing concrete.
In the case of concrete in a 3D-printing process the cement should be bound by
water. It will be very hard to regulate the process due to capillary working of the
dry concrete mixture and the difference in aggregate sizes (Appendix A4). To print
concrete that fulfils literature’s demands, aggregates larger than sand should be used
to comply with the condition that a large part of the aggregate has a >4mm diameter.
To avoid problems with the 3-D printing process the resolution has to be bigger than
the largest aggregate size. Printing smooth surfaces will become difficult if only layers
are extruded on top of each other without direct postprocessing with for example
trowels like used in Contour Crafting. This is the reason why the concrete used for AM
needs to be defined. The aggregates are also in the layers and not between layers.
An anisotropic layered material will arise, even if the inter layer strength between
the layers is equal to the materials properties / strength (figure 53) since cracking
happens at the bounding of the cement paste and the aggregate material.
Extruding concrete through nozzles causes a lot of friction and wear to the extruder.
Decomposition of the mixture occurs which is probably the biggest problem (appendix
A3). Fabricating hollow core slab floor elements, the concrete is extruded using a
worm gear to compact and push the concrete through a nozzle. If a normal cylinder
is used to extrude, the water is pushed out of the mixture. The worm gear prevents
decomposing of the fresh concrete. The extruder moves because it is simply pushed
away during extrusion. The extruded hollow core slab element is hard enough (has
enough green strength) to cope with forces that are released. An advantage of this
particular extrusion process is that the aggregates are distributed equally, as it is
pressed through a die instead of a nozzle and because this slab is extruded in one
single layer. A variable die might be an idea to make simple columns with changing
sections.
71
§ 5.8
Points of improvement
Comparing printed and traditional in situ or prefabricated elements, some extremely
crucial properties for concrete are missing in AM processes that use concrete;
•
Substantial fraction of the aggregates >4mm
•
Reinforcement
•
Consistency
•
Surface quality
To improve the usefulness of the AM process, the following three properties should
be introduced for further investigation.
•
Aggregates to decrease the costs, which is traditionally one of the strengths of
concrete,
•
Aggregates to minimise the internal shrinkage,
•
Reinforcement to cope with tension forces,
•
Consistency to cope with tension and bending forces. Since the consistency of
the extruded filament has not changed compared to normal casted elements,
the concrete processing by printing makes it anisotropic. An anisotropic material
can be used and its anisotropy can be used in a beneficial way, but in that case
the direction of the loads should be in the correct direction. It is preferable to
eliminate the anisotropic behaviour because only than the widely used standard
calculation methods can still be used, and
•
Increased resolution to improve the surface quality.
In addition, other techniques and their advantageous properties can be combined
with AM. For example, lost moulds that are put in AM concrete elements during
fabrication as support and to facilitate internal voids. Multiple nozzles for different
materials are not used yet. If an additional material can be extruded, the support
can be build while the element itself is fabricated as well. In plastic AM this system
already exist and examples can be found in FDM printers that with dual extruders.
The kind of material used to build the support material influences the LCA of the
production process.
72
CONCRETE AM TECHNIQUES
§ 5.9
Conclusions AM of concrete
AM processes should not be used to replace evolved production techniques of
standard elements. Elements that make use of the capabilities of AM in a beneficial
way are a better option. Also because such a production process has not to compete
against other, existing techniques.
Uniform concrete with substantial sized aggregates and eventual internal
reinforcement is currently impossible to make. Other techniques to integrate them
need to be invented or other ways of material processing should led to new design
solutions.
Should AM adapt to our accepted way of designing or should our way of designing be
adjusted to AM capabilities? Both are an option, but in that case compromises have
to be made.
Production speed is limited by the speed of the extrusion head or nozzles in the roller.
Building large objects will cost a lot of time if a high resolution, because of surface
quality is desired.
The production techniques are important, but also the stakeholders. Two parties are
involved;
•
Designers that use the possibilities of these techniques
•
Engineers that build new equipment
Comparing the roadmap by Volkers (figure 54 & Appendix A9) to the technical
situation it is important that the AM of concrete keeps evolving. Before the desired
elements can be made, experiments need to be successfully carried out. Logically, the
start is always a simpler method and less complex regarding form. Now is the period
that the parameters have to be established and simpler objects should be fabricated
with the integration of some improvement. These improvements, like reinforcement,
isotropic material and lower environmental impact by lowering the amount of cement
in the fresh concrete mixture, increase the performance of the processes. When the
processes will be able to print more complex forms the mismatch between technique
and products also decreases.
73
74
6 Alternatives: other ceramic
materials and threats
While concrete is a composite material according to the literature, one of
the main materials in it, cement, is a ceramic. In addition to cement there
are other ceramic materials used in the construction industry;
•
Clay structures
•
Clay Bricks
•
Sand- lime bricks
•
Loam
For these materials an AM production method can be almost the same as
for concrete, i.e. support and workability of the material is still important,
but due to different material properties and behaviour they are worth
investigating.
Ceramic materials
Glasses
Glasses
Glassceramics
Clay
products
Structural
clay
products
Refractories
Whitewares
Figure 62 - Classification of ceramic materials
Fireclay
Abrasives
Silica
Cements
Basic
Advanced
ceramics
Special
(1)
The scheme above shows the classification of ceramic materials. The most
interesting for the construction industry are cement and the structural clay
products. Clay shows to be an alternative material, as well as threats for
AM of concrete. Such threats for AM of concrete can be found in advanced
subtractive processing techniques.
1
Adapted from Callister, 2007, p.461
formwork / moulding processes, that use AM in another way, but also from
75
§ 6.1
Clay
Plastic clay, a composition called hydroplasticity, can be shaped due to the water
molecules that covers the clay particles, which allow the layers of clay to move.
Figure 63 shows the kaolinite structure of clay.
The more water applied the more shrinkage will occur during drying and firing (figure
13). If clay dries, it hardens but is still soluble in water. The green ceramic bodies that
are formed can be fired afterwards. Firing is used to change the chemical bindings in
the clay. One of the reactions, that take place during firing at temperatures between
900 and 1400 0C, is called vitrification. Small glass particles are formed. Figure 64
shows a micrograph of a fired specimen (Callister, 2007, pp.463-481).
Materials based on clay have a lot of matching characteristics with concrete. Figures
•
Higher compressive strength,
•
Higher tensile strength,
•
Higher elastic limit,
•
Comparable young modulus,
•
Less thermal expansion, and
•
Higher embodied energy is.
Al2(OH)42+ Layer
Si4+
(Si2O5)2- Layer
Al3+
OH-
1
O2-
Callister, 2007, p.430 adapted from Hauth, W.E., 1951, p.140
65 till 70 show that clay compared to concrete has a;
Figure 63 - The structure of kaolinite clay
76
(1)
Glossy (rim) phase
Quartz grain
Crack in
quartz
grain
Feldspar
grain
Pore
Mullite needles
Figure 64 - Scanning electron micrograph of a fired porcelain specimen (1)
Brick (common,
hard)(2.25)
Brick (common,
hard)(2.25)
Compressive strength (MPa)
1000
Concrete (high(high
performance)
Concrete
performance)
Brick (common,
hard)(2.03)
Brick (common,
hard)(2.03)
Ceramic tiletile
Ceramic
100
Terracotta
Terracotta
High
density concrete
High
density
concrete
Concrete (ordinary
Portland)
Cement (ordinary
Portland)
10
Concrete (normal
(Portland (Portland
cement))
Concrete
(normal
cement)
Cement (Portland
blast furnace)
Cement
(Portland
blast furnace)
1
0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
2.4
2.5
Relative density
1
Callister, 2007, p.481
Figure 65 - Compressive strength compared to relative density (CES)
77
Tensile strength (MPa)
100
Brick (common,
hard)(2.25)
Brick (common,
hard)(2.25)
Concrete
(high
performance)
Concrete (high
performance)
Terracotta
Terracotta
Brick (common,
hard)(2.03)
Brick (common,
hard)(2.03)
10
Ceramic tile
Ceramic
tile
High density
High densityconcrete
concrete
Cement (Portland
furnace)
Cement (Portland
blast blast
furnace)
Cement (ordinary
Portland)
Concrete (ordinary
Portland)
1
Concrete (normal
(Portland
cement)) cement)
Concrete
(normal
(Portland
0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
2.4
2.5
2.4
2.5
Relative density
Yield strength (elastic limit) (MPa)
Figure 66 - Tensile strength compared to relative density (CES)
100
Brick (common,
hard)(2.25)
Brick (common,
hard)(2.25)
Terracotta
Terracotta
Brick (common,
hard)(2.03)
Brick (common,
hard)(2.03)
10
Cement (Portland
blastblast
furnace)
Cement (Portland
furnace)
High High
density
density concrete
concrete
Concrete
(high(high
performance)
Concrete
performance)
Ceramic tile
Ceramic tile
1
(ordinary
Portland)
Concrete Cement
(ordinary
Portland)
Concrete (normal (Portland cement))
Concrete
(normal (Portland cement)
0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
Relative density
Figure 67 - Yield strength compared to relative density (CES)
78
1.5
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
Young's modulus (GPa)
100
Concrete (ordinary
Portland)
Cement (ordinary
Portland)
Brick
(common,
hard)(2.25)
Brick (common,
hard)(2.25)
HighHigh
density
concrete
density concrete
Concrete
(high(high
performance)
Concrete
performance)
Cement (Portland
furnace)
Cement (Portland
blastblast
furnace)
10
Brick (common,
hard)(2.03)
Brick
(common,
hard)(2.03)
Concrete (normal
(Portland (Portland
cement))
Concrete
(normal
cement)
tile
Terracotta
Ceramic Ceramic
tileTerracotta
1
0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
2.4
2.5
Relative density
Figure 68 - Young’s modulus compared to relative density (CES)
Thermal expansion coefficient (µstrain/°C)
50
Cement
(Portland
blast furnace)
Cement (Portland
blast furnace)
High density
concrete
High
density
concrete
20
Concrete
performance)
Concrete
(high (high
performance)
Brick (common,
hard)(2.03)
Brick (common,
hard)(2.03)
Terracotta
Terracotta
10
Ceramic
Ceramic
tile
tile
Cement (ordinary Portland)
Concrete (ordinary Portland)
5
Cement (Portland blast furnace)
Concrete (normal
(Portland
cement))
Concrete (normal
(Portland
cement)
Brick (common,
hard)(2.25)
Brick
(common,
hard)(2.25)
2
Non-technical ceramics
Figure 69 - Thermal expansion coefficient (CES)
79
Compressive strength (MPa)
1000
Brick (common,
hard)(2.25)
Brick
(common,
hard)(2.25)
Brick
(common,
hard)(2.03)
Brick (common,
hard)(2.03)
Ceramic
Ceramic tile tile
Terracotta
100
Concreteperformance)
(high performance)
Concrete (high
Cement
(Portland
blast furnace)
Cement (Portland
blast furnace)
High density
concrete
High
density
concrete
Concrete (ordinary Portland)
Concrete (super sulfate cement)
10
1
0.1
0
5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 65000 70000 75000 80000 85000 90000 95000 10e4
Embodied energy, primary production (MJ/m3)
Figure 70 - Compressive strength compared to embodied energy of primary production (CES)
§ 6.1.1
AM of Clay
Erno Langenberg has shown the potentials of extruding a filament, drying and firing it
(figure 71 and 72). In addition to this there are other concepts that can be added to
80
(1)
1
Figure 71 - 3D printed clay elements
Langenberg, 2014
process clay. The next step is to refine this method. That can be done by;
ALTERNATIVES: OTHER CERAMIC MATERIALS AND THREATS
•
Increasing the resolution,
•
Introducing a new production technique, or
•
Combine different production techniques.
Weaving with clay filament can be used as an architectural application to produce
ceramic screens and façade elements. Such screens can be used as filters and
examples can be found in the Alhambra palace in Granada, where they were installed
between two rooms. The challenge in weaving a screen lies in the G-code that is
generated and describes the extrusion path. To extrude the filament an uninterrupted
path should be used. To finish the edges of a panel the extruded corner edges can
be cut off (Friedman, Kim, & Mesa, 2014, pp.262-267). Shrinkage is a problem and
firing large elements will cause cracking.
New techniques could be like the MX3D printing (§3.2.5), where the clay is instantly
baked after extrusion, but if multiple layers are applied on top of each other, there is
a weak bounding between them.
Combined techniques are probably more suitable if an isotropic material is desired.
The extra step, drying, in between raw material and the hardened state allows time
for additional editing. The green ceramic body can be CNC milled before firing. In
1
Langenberg, 2014
contrast to cementious materials, the chemical reaction starts during the baking and
Figure 72 - 3D printed brick system
(1)
81
not directly after mixing. There is no waste because the dried clay that comes off
during CNC can be reused. The production process would look like figure 73;
•
Extruding,
•
Drying (for an uniform dehumidification),
•
CNC milling,
The steps Extruding, drying and CNC milling can take place several times followed by;
•
Firing.
If support material is used, it should melt or burn during the firing and not react with
the clay itself.
Extrude
Measure shrinkage
Dry material
Clay
Dry
CNC mill and
sand
Fire
(Post process)
Figure 73 - Clay processing concept
82
ALTERNATIVES: OTHER CERAMIC MATERIALS AND THREATS
§ 6.2
Threats
The overall quality of the AM products influences the field where the products can
be used. The demand for high strength concrete will be of high importance in civil
engineering and the aesthetical aspect will be less important. In architecture it is the
other way around; the aesthetical part will be considered as most important. In the
building technology discipline both fields come together. From here a new technology
can be expanded in both directions;
•
A production technique that is focused on optimised shaped and reinforced
strong elements, or
•
A production method that involves aesthetical freeform objects.
For the AM techniques adding additional value to a product is important. Especially
since concrete is relatively cheap and waste during production do not cause high
losses. The waste that is created is a larger problem concerning the environment
and the LCA. Lowering the LCA is an example of added value. Next to the added
value, elements that can not be made otherwise or elements that economically
benefit from an AM process are interesting to be investigated. With the way threats,
traditional and standardized techniques are used in mind the scheme below shows
1
External origin
Adapted from Volkers, 2010, p.18
Internal origin
the most important advantageous and disadvantageous properties of AM in red. The
Strengths
Weaknesses
Geometric freedom
File to factory
No tooling
No inventory/labour costs
Sustainability
Freeform design
Minimum waste
Testing of unique products/certification
Costs per piece
Production time
Properties of materials/anisotropy
Accuracy
Finishing
Opportunities
Threats
Mass customization
Graded materials/Micro structures
Printing composites
Hybrid structures
Limited size/Macro scale
Mass production
Helpful
Harmful
Table 18 - SWOT AM
(1)
83
SWOT analysis is an economical driven prognosis. Nonetheless imitating of existing
products will be done with the AM techniques during the development, to validate
and compare product characteristics, but also to start from, while specific product
ideas are invented. Both fields in construction industry ask for a different approach.
These approaches have also different threats.
AM is a way of fabrication that is, as discussed in previous chapters, new in the
field of concrete processing. Concrete processing has been automated and optimised
over the last decades. Therefore it is hard to compete with existing techniques.
Standardized products are not a goal of AM yet. Added value is the most promising,
but such added value can also be obtained by other ways of processing concrete.
Complexity in form is one parameter in the discussion what technique should be
adopted as the final production process.
Using advanced production techniques for complete structures might not be the best
solution. Also the fabrication of formwork / moulds are subjected to the limitations of
an one phase production process like FDM. The best solution comes from combined
techniques. For example, when a mould is not only made with 3D printed or
CNC milled elements, but also carpentry elements are used for the simpler parts.
Printing complete moulds or elements is time intensive and therefore a combination
techniques can be used to produce formwork or a mould.
By using multiple techniques nearly all disadvantageous properties can be eliminated.
By printed formwork the resolution determines the surface quality of the casted
element. This can be compared to wood formwork that gives a certain relief. Concrete
plywood or metal does not give any relief on the concrete elements, depending on
the design, reliefs can easily be added in printed moulds.
Printing concrete directly skips a stage but also limits the possibilities. To print over
voids with a relatively liquid material is impossible, support material is needed in
the form of a support structure but a mould would be the easiest solution for this
problem.
Because concrete is hard to process in with AM new developed techniques are the
biggest threats and can be found in;
•
Printing advanced moulds,
•
Changing / adaptable mould systems, and
•
CNC subtractive manufacturing.
It becomes clear that complexity in form and size are next to costs determining
factors when a production method is chosen (table 18).
84
ALTERNATIVES: OTHER CERAMIC MATERIALS AND THREATS
§ 6.2.1
Printing advanced moulds
Instead of an one phase AM technique, concrete can be casted in a contra form. Such
a contra form can be made with help of an AM technique. The extra production step
provides advantageous but also disadvantageous properties and can not be used for
all kind of elements.
Advantageous properties
•
Isotropic material behaviour of the concrete that is casted in the moulds, and
•
Easy implementation of reinforcement.
Disadvantageous properties
•
Embodied energy in the mould,
•
Mould can not be reused if it needs to be broken to get the element out, and
•
Single material characteristic because of casting. Gradient materials can not be
casted easily.
General properties
•
Production speed depends on the time needed to produce the mould.
The important characteristics of AM and printing of advanced moulds are shown in
comparison to each other in the figures 74 & 75.
If moulds that cannot be re-used are printed, the customised or optimised elements
are using two production cycles. The product is not optimal anymore, if the production
process is taken into account, due to the use of extra labour and material. Removing
the formwork stage decreases the labour and embodied energy, but the freedom of
form (due to the missing support) and decreasing quality due to anisotropic behaviour
of the material does occur in concrete AM processes (chapter 5).
Freedom of form is one of the differences, but a very determinative one. When
Additive or Subtractive Manufacturing methods are used, the formwork’s form is not
important for a demoulding stage. Appendix A2 shows an ABS printed mould used to
cast an freeform surface element. It can be seen that the surface quality of the mould
is very important and determines the end result.
An approach to increase the performance of an advanced mould is to change the way
moulds are build and used for concrete casting. For example in the jewellery industry
reusable wax is used to make moulds for customized jewellery.
85
Sustainability
5
4.5
4
3.5
3
2.5
Surface and overall
quality
2
Speed
1.5
1
0.5
0
Geometric freedom
Size
Figure 74 - Characteristics of AM of concrete
Sustainability
5
4.5
4
3.5
3
2.5
Surface and overall
quality
2
Speed
1.5
1
0.5
0
Geometric freedom
Figure 75 - Characteristics of AM of a mould
86
Size
ALTERNATIVES: OTHER CERAMIC MATERIALS AND THREATS
§ 6.2.2
Changing / adaptable mould systems
Adaptable moulds can change their form within a certain range. All standardized
formwork is already an adaptable mould. By adding / removing parts, different forms
can be made within the boundary of the system. In this section adaptable moulds
refer to machines that can be programmed by computer. The mould can mechanically
adjusted to the desired form. For the systems Adapa and Roel Schippers use a mould
with a skin that can be adjusted within certain limits. It is capable of fluent forms
while rugged surfaces are not possible yet with this approach. For façade elements
that are fluently curved it is a good technique, but if a more complex form is desired
such adaptable moulds are not sufficient anymore. Figure 77 shows the corresponding
characteristics of a changing mould system
1
Adapa, 2013
Figure 76 - Adapa mould
87
Sustainability
5
4.5
4
3.5
3
2.5
Surface and overall
quality
2
Speed
1.5
1
0.5
0
Geometric freedom
Size
Figure 77 - Characteristics of a changing mould system
Sustainability
5
4.5
4
3.5
3
2.5
Surface and overall
quality
2
Speed
1.5
1
0.5
0
Geometric freedom
Figure 78 - Characteristics of CNC milling of concrete
88
Size
ALTERNATIVES: OTHER CERAMIC MATERIALS AND THREATS
§ 6.2.3
Milling of concrete
A Subtractive processes like milling of concrete elements has, like printing concrete
and extruding layers of concrete, to deal with the inhomogeneous properties of
concrete itself. The material that comes off during the milling stage, is reusable in
new fresh concrete, as aggregate. When a fine mortar is used the material will be
more homogeneous and the risk of parts flying of will decrease. The characteristics
are shown in figure 78.
The characteristics of the threats are showed in comparison to AM in table 19. Figure
79 shows an estimation of the energy distribution of time in each process
Additive Manufacturing
Casting (moulds)
Subtractive
Manufacturing
Material use
optimised
over constructed due
production limitations
optimised, but produces
waste material
Formwork / mould
no
yes
no
Openings
yes
yes
yes
Hollow parts
yes
no
yes with a lost formwork
no
aggregates
no (not yet)
yes
no (not recommended)
isotropic final
material
no (not yet)
yes
yes
surface quality
Low
Depends on resolution
Low - High
Depends on formwork /
mould quality
Medium - High
High, depends on
resolution
Freedom of form
High
Low - Medium
Medium - High
Points of attention
Quality of the stacked
layers
Demoulding
Particles that fly of during
CNC
Table 19 - 3 Concrete processing techniques and their characteristics
AM shows a lot of potential for freeform objects. Combined with a changeable print
chamber or a process with very rapid curing elements the production time does not
take considerably longer than competition. Energy consumption differs a lot with the
processes. Figure 80 shows the field where AM should operate in red, without being
hindered by the threats.
89
Pre processing
Production process
Post processing
AM process
Ideal AM process
Printing mould
Casting process
Demould
Cast conrtete block
CNC mill
Remove waste
Prinitng advanced moulds
CMC / subtractive
manufacturing
Preparing mould
Changing / adaptable mould
Demould
Casting process
Figure 78 - Energy and time distribution during production processes
Sustainability
5
4.5
4
3.5
3
2.5
Surface and overall
quality
2
Speed
1.5
1
0.5
0
Geometric freedom
Figure 79 - Advantages of AM
90
Size
ALTERNATIVES: OTHER CERAMIC MATERIALS AND THREATS
§ 6.3
Conclusion alternatives
The main threats for AM of concrete can be found in more traditional processing
techniques that are supported by AM. For example the AM of the formwork. The
traditional, over the centuries evolved, way of casting concrete gives an isotropic
material. It can be reinforced and the surface quality is determined by the surface
quality of the formwork / mould. The production of series can be easily achieved,
if the element’s form allows formwork that can be removed in one piece (or a few
pieces). The production time depends on the time to cast and cure in the formwork.
In case of AM of the concrete element the production speed is depending on the AM
technique and the corresponding speed of this technique. The way it is supported
also has its influence. If the element is supported locally and can be removed from
the ‘print chamber’ other elements can be printed directly afterwards. If the element
remains in the chamber to cure this has a high impact on the overall production
speed. The threats can be minimised if AM provides the technique that can produce
products with an added value. This is the part of concrete processing where AM
should be used. The part that other techniques can not provide for (figure 79).
Concrete itself is a challenging material to process using an AM production technique.
The chemical reaction taking place in this composite material leaves a lot of
opportunities for competitive ceramic materials that have comparable performance
regarding the Young’s modulus and compressive strength. Clay has the advantage
that it can be formed without the interference of a chemical reaction. The chemical
reaction happens during firing after the form has been defined. Unfortunately cracks
from baking can, like poor compacting does to concrete, influence the performance
of an element in a negative way. Especially large elements are vulnerable to cracking
during firing.
Both, the threats and the alternative materials, are based on the workability of
concrete in an AM process. Clay simply dries after extrusion and the materials that
are used to print the formwork, use a relatively easy phase change or adhesive to
apply the layers on top of each other. This shows again, that as mentioned before,
that the AM process should not be dictated to a material, but hat the AM process
should be developed around the material characteristics in the broadest sense of the
word.
91
II Design
92
7 Roadmap (printer concepts)
After evaluating the existing techniques in the previous chapter, new
designs and processes that improve the processing of concrete are the
focus of this chapter. A small summary and the context of the desired way
of designing leads to the roadmap. The roadmap is the outcome of the
research combined with the visions on how the concrete AM technique has
to evolve in order to use it in a beneficial way.
§ 7.1
Design methods
Before new production techniques can be elaborated on, the design methods and
desired characteristics of the designed object need to be known. For the design of
AM (concrete) products nature can be a large inspiration. Humans and trees have
optimised load bearing structures. The human skeleton has evolved over thousands
of years. Our bones are not solid but the internal structure consists of strands that
stabilize our bones (figure 80). Nature optimises more structures. Trees are a great
example. The loads that they have to deal with are distributed in an efficient way.
They have the ability to adapt to their environment.
This adaptability is illustrated by a tree that was placed against a handrail. The tree
uses a part of the rail to distribute his load. The bottom part of the trees trunk
is significantly thinner than the part that is on top of the rail. Figure 81 shows a
schematic force flow.
With this in mind optimised structures can be designed. However production
technologies are behind if compared to design methods and possibilities. Contour
crafting and 3D-Concrete printing extrude elements with simpler geometry. D-shape,
however it is not concrete, is able to 3D-print relative complex forms.
To design optimised elements with a Soft Kill Option (SKO) and Computer Aided
Optimisation software (CAO) to calculate the needed material and the location can
be used. CAO adds and removes material to spread the load on the component. SKO
takes design limits into account and it removes the not load bearing parts. The result
is an element with reduced weight but with the same performance (Mattheck, 1998,
p.261). The next step in an optimising process is to implement internal voids within
the structure. By increasing the diameter of the structural cores the moment of inertia
increases due to the location of the materials used. The voids within can be used to
implement services. Eventually software will determine the result based on the used
93
Figure 80 - Human hip bone texture
(1)
parameters. There is, regarding material use, an optimum. This can be calculated on
the base of parameters used in a parametric design program like Grasshopper.
§ 7.1.1
Parametric design method
Due to the parametric design it is possible to generate designs by changing the
input parameters. In the design of for example a façade cladding characteristics like
ventilation, sound absorption and heat exchanging can be integrated.
Mises stress
Figure 81 - Tree-Stone Friendship
94
Optimised
2
Non-optimised
(2)
1
Low
Siemer, P., 2008
Mattheck, C.,1998, pp. 96-97
High
If the points of fixation are fixated in a model, the Galápagos function in Grasshopper
can be used to optimise the geometric shape within the indicated parameters. These
models can be send to automated production processes. The interface for the future
vision techniques and the model needs to be made, but that is the field of computer
technology.
§ 7.2
Evolved and new techniques for concrete AM
The characteristics of concrete differ from most materials used for AM. The chemical
reaction and being a composite are of great importance in discussing the possibilities
of AM for concrete (table 21).
Mechanism
Constituent material
Phase change
Steel
Plastics
Drying
Clay
Chemical bonding
Gypsum
Instant
chemical reaction
Cement
Composite
Concrete
Smart materials
Table 20 - AM material properties
In the future vision, the characteristics of concrete will be adapted to the production
technique and vice versa. Concrete mixtures come in a lot of different varieties as
shown in figure 9. The Aggregate size determines the name and category, but next to
the composition and strength, workability and green strength can differ within each
category. For example, a high strength concrete with a high green strength can either
be normal concrete but also an UHPC.
Because either the material or the production technique has to be adapted to create
an satisfying result. The desired characteristics of the material are showed by “Zappie”
in table 21. Table 22 shows which characteristics a process should have to process
concrete that is commonly used.
The AM processes used for plastics are also opimised for the materials used. The
mechanisms behind the curing are most of the times simpler (table 20). Elaborating
the future visions into a concept printer, thus requires also a concrete expert to take
95
care of the right mixture.
Since technology is not able to print high quality massive elements, optimised
elements are even more challenging. To evolve the techniques to make that possible
a future vision is needed. The roadmap shows these visions. To obtain the dedsired
characteristics the production methods like Contour Crafting and 3D-Concrete printing
function as a basis to evolve the concrete AM techniques. New ways of processing
can be divided in four main groups;
•
•
Evolve existing techniques,
•
Combine Contour Crafting and Concrete Printing,
•
Improve D-Shape,
Hybrid techniques. To make use of the advantages of both techniques,
•
‘CNC mill/form’ the surface before/during hardening after it has been 3D
printed or extruded,
•
Print/extrude in a substance that partly supports the structure and takes a
part of the ‘gravity’, like NSTRMNT §3.2.5.,
Desired material
AM process like FDM
AM process like 3DP/
Polyjet
“Zappie” (new material)
Form of
element and
smoothness
- Resolution determine
surface quality
- Viscosity determines the
scale of a cantilever
- Resolution determine
surface quality
- Viscosity determines the
amount of support material
- Self smoothing
- Easy to shape
- High viscosity
Product
Layered material
Layered material
Becomes uniform
Composition
- Reinforcement between
layers is hard
- Extruding and distribute
aggregates is impossible
- Reinforcement needs to
be printed(welded)
-Print aggregates
themselves makes no sense
- No reinforcement needed
or fibres
- Reinforcement is also
between layers
Strengths
Differs
Differs
High strength
Difference
in strength
perpendicular
to workspace
- Bonding between the
layers due fixation of new
layer on old layer
- Bonding between the
layers due fixation of new
layer on old layer
Isotropic material
- Interlayer bounding
Curing
Has to cure before weight
of additional layer can be
handled
Has to cure before weight
of additional layer can be
handled
Fast curing
Treatment
- Easy to extrude
- Fast curing before next
layer
- Easy to apply
- Fast curing before next
layer
- Easy to extrude
- Self compacting
Viscosity
Green strength
Green strength
Green strength (less
hardening needed)
Additional
parameters
No formwork
Support material where
needed
Processable without
formwork
Table 21 - AM desired material properties
96
Roadmap
•
A nozzle that acts as support for the first seconds or activates an increased
reaction speed by use of heat or a gas as a catalyst. (MXRD §3.2.5),
•
A dissolving lost mould inside an element to embed voids within the AM element
without reducing speed because of the need of an increased resolution.
•
Implement new techniques in old processing techniques, and
•
New ideas
The threats of manufacturing a mould with an additive and subtractive technique can be
implemented in evolved AM techniques or used to support old processing techniques with
AM implementation.
Implementation of parts that are missing nowadays;
•
Print with larger aggregates instead of mortars,
•
Print different material compositions (gradient materials),
•
Larger reinforcement between the layers of the element, and
•
An uniform element with reinforcement aggregates and the same consistency.
The roadmap on the next page shows the existing and new concepts with their main
features. The feasibility of implementing the new features is described in the next section.
Desired production types
with existing materials
Concrete
UHPC
New technique printing
Form of
element and
smoothness
Surface quality determined
by mould
Surface quality determined
by mould
High resolution
Mechanical smoothing
Material
Uniform
Uniform
Isotropic material or
controlled anisotropy
Composition
- Reinforcement bars or
fibres
- Aggregates
No reinforcement needed
- Aggregates <2mm
Capable of reinforcing
Strengths
All strengths
High strength
Capable of high strengths
Difference
in strength
perpendicular
to workspace
Isotropic material
Isotropic material
Bond and compacts like
normal casted concrete
Curing
Dries at once in a ‘slow’
curing process
Dries at once in a ‘slow’
curing process
Depends on technique
Treatment
Compacting needed
Can be self compacting
Depends on technique
Viscosity
Differs
Liquid
Green strength not
necessary
Additional
parameters
Formwork needed
Formwork needed
No or little formwork needed
Table 22 - AM desired production properties
97
2015
- No aggregates
Changing die
Could contain additional
mixture information about;
Fibres
Aggregates
Retarders
Extruder without
trowels
Concrete consistency
and interlayer strength
Reinforcement
Additional
aggregates
Mixer
- Strong
- Freeform
Binding agent
Different materials
Print head and roller
Mix extra aggregates before
extrusion for efficient material
usage
Extruder
Nozzle
- Isotropic concrete
- Lost mould
Schwartz, 2013
Thin mould casting
Freeform
Print eco mould
Materia, 2013
AM mould technique
EZCT
(moulds by Voxeljet)
Mould
Support
material
Moulds
Concrete processing AM Concrete research
Dr. Dipl.-Ing. Holger Strauss (Hochschule
OWL)
Erno Langenberg (printing ceramic)
DUS Architecten (Canel House)
MX3D
NSTRMNT
Werner Sobek gradient beton
Stuttgart University
Mw. dr. ir. S.A.A.M. Fennis (CiTG TU-Delft)
ir. Siebe Bakker
Voxeljet
Sascha Hickert (Hochschule OWL)
Prof. Dipl.Ing. Matthias Michel
ir. Roel Schipper (CiTG TU-Delft)
dr.ir. Karel Vollers (BK TU-Delft)
Adapa (DK) MSc Eng Thomas Henriksen
Rieder Group (AT)
3D-Print techniques
that uses binders
Concrete
TU Eindhoven concrete printing
- prof.dr.ir. T.A.M. (Theo) Salet - support
material
- Rob Wolfs - Parameters and concrete
properties
TU Delft
- Evaluating techniques and searching
matching products
- Experiments with new concepts for AM
of concrete
Companies
Winsum new materials
EZCT / Voxeljet
BetaBram
Skanska
Advanced (AM) moulds
Related expertises
AM
Saxion
Breakthrough in 3D printing
Extude in elevated support
‘Print head’ and roller
- Not concrete
Implementation
Domus, 2013
Print concrete without
complete support (polyjet)
Techniques
Concrete mortar
3DP technique
D-Shape
Fresh concrete
AM with a support
material
‘Print head’
support material
Nozzle
Additive casting
Constituent material
Steel
Plastics
Drying
Clay
20
20
Chemical bonding
Gypsum
10
10
Instant
chemical reaction
Cement
Figure 82 - Roadmap
30
Micro Rapid
Manufacturing
0
10
20
30
40
50
60
70
80
90
100
Adapted from Buswell, et al., 2007, p.230
d
st
re
n
gt
h
s
3D Concrete printing
‘Desktop’ Rapid Manufacturing
0
0
Time to completion (Hours)
98
2
Freeform
Construction
1
40
Mechanism
30
3
50
te
40
4
Decreasing resolution with
increasing deposition rate
60
ec
50
70
Ex
p
60
Strength (MPa)
Progress of traditionally constructed wall
Phase change
Concrete
Existing
Construction
80
70
Deposition rate (m3/hr)
Percent complete (%)
Composite
High
90
80
Surface quality
Material usage
Version 22 January 2015 D. de Witte
100
Progress of 3D-printed wall
90
Contour crafting
Low
0
10
20
30
40
50
60
Resolution (mm3)
70
80
90
Reso
Curin
Cust
Developments
100
Extru
Mixer
Traditional concrete processing
Inter layer strength
Aggregates & reinforcement
Isotropy
Pultr
Nozzle
Support
Extrude in elevated support
- Missing support material
Extrude in mould
Contour Crafting, 2014
3D Concrete printing
Total custom
Fibre reinforcement
Mixture and composition
- No internal
reinforcement
G-code
Freeform and support
- Surface quality differs
- Compact concrete low
air bulbs
Increased
surface area
Changing die
Extruder with
trowels
Material
between
contours
Gradient materials
- Anisotropic
Shoot reinforcement
FDM technique
Contour crafting
Winsun new materials
Reinforcement
gun
Compacting
energy
Compact after extrusion
Characteristics
Roughen extruded surface
Initiatives
DEVELOPMENT
Pultrude fibres
FIELD OF AM
100
Adapted from Buswell, et al., 2007, p.229
Low
High
Cement (%)
CONCLUSION: FUTURE VISION
e.g using a non newtonian fluid
Multiple mixture extruder
Additional
aggregates
The multiple mixture
extruder mixus to obtain
the characteristics that
optimise the mixture
and material
composition
Fresh concrete
Mixer and
triple extruder
Polyjet concrete extrusion
Different materials
Print head and roller
Support
material
Polyjet in combination
with elevated support
printing increases the
resolution
Reinforcement
gun
Mixer
The extrusion head is used to
mix, extrude and reinforce.
Reinforcement is used for inter
layer strength and for load
distribution.
Reinforcement
fibres
Reinforcement gun
Isotropic concrete
Compacting
mixer
Shotcrete is used to
cover the reinforcement
with layers of concrete
Support net
On site customising of
standardised elements
Reinforcement shotcrete
Print with a low resolution the
desired form and use milling (or
lasers) as subtractive technique
to finish the element.
Use a (advanced) extrusion
head to print a layer and add /
cover the area around with
loose support material after the
extruded layer has been
covered with a protection layer.
The process is repeated till the
element is finished.
Aggregates
Reinforcement
Speed
Consistency
Consistency
Freeform
Speed
Surface quality
Orientated reinforcement
Controlled material composition
Less free form
More isotropic
Less material
Sanding
The protection layer
prevents dehydration of
the concrete
Formwork
Nozzle
Foam
Support
Shotcrete
layers
Standardized elements
can be customised on
site when the surface
binding is strong
enough by e.g.
roughning it
mechanically
Roughened
surface
G-code
Print or weld a support frame
that can be used as
reinforcement and to define the
geometry of the AM element. It
is the method that builds a layer
around a core. The net is
covered with concrete using
spray on.
Gradient material
Large structural elements
with different distribution
of aggregates and
composition. With or
without formwork.
Minimising printing time Consistency
Efficient support
Freeform
Controlled material composition
Freeform
Speed
Consistency
Extruded
concrete
Plaster
material
Support net spraying
Shotcrete
Advanced extruded
elements with
different densities are
extruded at once due
to multiple extrusion
points in the die. The
extruder head can be
used for different
process approaches
PRODUCTS
High surface quality
Less resolution needed
Faster printing process
Faster overall process
Laser
Freeform
Build around the reinforcement
Freeform
Fast process
High surface quality due post processing
Aggregates
Aggregates
Nozzle
(Mixed extrusion with) elevated support
printing
Resolution
Curing
Shotcrete
Surface quality
Reinforcement
and extra
surface
between
layers
Print mill sand
Customise
Speed
Reinforcement
Consistency
Fast
Reinforced
Can be automated easily
High quality concrete (extruded at once)
Surface quality
Instant
curing of
the outside
Aligned fibres
Controlled mixture
Inter layer strength
Smooth surface
Consistency
High furface quality elements
with reinforcement that do not
need to be finished.
Orientated fibre reinforced concrete
Extrusion
Changing die
Consistency
Core parts
Print in low resolution, to
increase production
speed. These elements
will be covered or
finished afterwards.
Surface quality
High resolution
concrete
Freeform
Freeform, high resolution
elements,
Joints of standarized
systems, and
3D refurbishment
elements
Reinforcement
Fibre
reinforcement
Speed
Instant dry extrusion/pultrusion
Advanced extruder
Freeform
Instant dry extrusion
Pultrusion
Combining extrusion
and curing
Instant curing of the
outside
Characteristics & Evaluation
ROADMAP: future vision
Hybrid techniques description
Interdisciplinarity
CONCRETE IN AN AM PROCESS
Mechanical Engineering
Computer
model
Generate
STL file
Generate
G-code
extrude
filament
Sensor
observes
extruded
filament
compare
to G-code
to correct
parallel code that
contains material
information
Material science
corrected
G-code
Building Technology
Architecture
Civil Engineering
Freeform concrete processing
This report examines the additive manufacturing (AM) of concrete, its possibilities, feasibility and advantages over existing techniques. Traditional
processing techniques are adapted to the characteristics of concrete and concrete does not let itself dictate how to behave. The possibilities for
products made with an additive process are endless, but just replacing existing production methods with additive ones is still impossible. Although
improved freeform production techniques are the aim of this research, this does not mean that more freedom in form is by definition the largest
improvement that AM can offer at the moment. From another point of view the implementation of additional functions in traditional products can
be of great value.
A roadmap envisions how the technique has to evolve in order to implement the characteristic properties of concrete. Product ideas and an
evaluation of the techniques shown in the roadmap are related to the developments to achieve an increase in speed, surface quality and strength
in the AM production technique, next to the requirements that have to be set regarding a matching fresh concrete mixture.
99
Version 22 January 2015 D. de Witte
Contour Crafting, 2014
Cement
Clay
Gypsum
Steel
Plastics
Drying
Instant
chemical reaction
Phase change
Chemical bonding
Constituent material
Mechanism
Inter layer strength
Aggregates & reinforcement
Isotropy
Surface quality
Material usage
Developments
ir. Siebe Bakker
Voxeljet
Moulds
Percent complete (%)
0
10
20
30
40
50
60
70
80
90
100
0
Binding agent
Concrete mortar
Extruder
Print head and roller
Different materials
Concrete consistency
and interlayer strength
Compacting
energy
10
20
30
40
50
60
Time to completion (Hours)
70
90
100
Adapted from Buswell, et al., 2007, p.230
Freeform
Reinforcement
Reinforcement
gun
Support
material
Nozzle
0
10
20
30
40
50
60
70
80
90
100
0
10
20
4
30
Micro Rapid
Manufacturing
Decreasing resolution with
increasing deposition rate
50
60
Resolution (mm3)
40
‘Desktop’ Rapid Manufacturing
1
3
70
Freeform
Construction
2
Existing
Construction
Traditional concrete processing
Mould
80
Could contain additional
mixture information about;
Fibres
Aggregates
Retarders
G-code
DEVELOPMENT
Thin mould casting
Shoot reinforcement
2: Development
80
Progress of traditionally constructed wall
Saxion
Breakthrough in 3D printing
TU Delft
- Evaluating techniques and searching
matching products
- Experiments with new concepts for AM
of concrete
TU Eindhoven concrete printing
- prof.dr.ir. T.A.M. (Theo) Salet - support
material
- Rob Wolfs - Parameters and concrete
properties
Progress of 3D-printed wall
Sascha Hickert (Hochschule OWL)
Prof. Dipl.Ing. Matthias Michel
ir. Roel Schipper (CiTG TU-Delft)
dr.ir. Karel Vollers (BK TU-Delft)
Adapa (DK) MSc Eng Thomas Henriksen
Rieder Group (AT)
Concrete processing AM Concrete research
‘Print head’ and roller
Extruder without
trowels
2015
Roughen extruded surface
1: Techniques
Concrete
Composite
Winsum new materials
EZCT / Voxeljet
BetaBram
Skanska
Companies
Werner Sobek gradient beton
Stuttgart University
Mw. dr. ir. S.A.A.M. Fennis (CiTG TU-Delft)
Dr. Dipl.-Ing. Holger Strauss (Hochschule
OWL)
Erno Langenberg (printing ceramic)
DUS Architecten (Canel House)
MX3D
NSTRMNT
- Lost mould
- Isotropic concrete
- Freeform
- Strong
- Not concrete
- Missing support material
Concrete
Schwartz, 2013
Materia, 2013
Domus, 2013
- No aggregates
- Compact concrete low
air bulbs
AM
Related expertises
AM mould technique
EZCT
(moulds by Voxeljet)
3DP technique
D-Shape
3D Concrete printing
Total custom
- No internal
reinforcement
Increased
surface area
Compact after extrusion
Print concrete without
complete support (polyjet)
Print eco mould
Extruder with
trowels
Deposition rate (m3/hr)
- Surface quality differs
Material
between
contours
3D-Print techniques
that uses binders
90
100
Implementation
Adapted from Buswell, et al., 2007, p.229
Pultrude fibres
Mixer
Fresh concrete
Mix extra aggregates before
extrusion for efficient material
usage
Additional
aggregates
Fibre reinforcement
Low
High
Low
Additive casting
AM with a support
material
Gradient materials
- Anisotropic
Advanced (AM) moulds
Characteristics
s
Initiatives
Strength (MPa)
Changing die
Extude in elevated support
Extrude in elevated support
Extrude in mould
th
ng
re
st
ed
FDM technique
Contour crafting
Winsun new materials
ct
pe
High
Contour crafting
3D Concrete printing
Resolution
Curing
Extrusion
Pultrusion
G-code
Customise
information
5: Additional
Cement (%)
Mixer
‘Print head’
support material
Nozzle
Nozzle
Support
Changing die
Mixture and composition
Freeform and support
Instant dry extrusion
Multiple mixture extruder
Polyjet concrete extrusion
Reinforcement shotcrete
FIELD OF AM
Ex
Shotcrete
parallel code that
contains material
information
extrude
filament
Computer
model
Roughened
surface
Sensor
observes
extruded
filament
compare
to G-code
to correct
Generate
G-code
Support
material
Print head and roller
Different materials
Mixer and
triple extruder
Fresh concrete
Generate
STL file
Shotcrete
Support net
Additional
aggregates
Instant curing of the
outside
corrected
G-code
Standardized elements
can be customised on
site when the surface
binding is strong
enough by e.g.
roughning it
mechanically
Shotcrete is used to
cover the reinforcement
with layers of concrete
Polyjet in combination
with elevated support
printing increases the
resolution
The multiple mixture
extruder mixus to obtain
the characteristics that
optimise the mixture
and material
composition
Combining extrusion
and curing
The protection layer
prevents dehydration of
the concrete
Building Technology
Foam
Civil Engineering
Material science
Laser
Shotcrete
layers
Support
Nozzle
Sanding
Nozzle
Reinforcement
fibres
Mixer
Reinforcement
gun
Instant
curing of
the outside
Changing die
Future vision
3: Conclusion:
Architecture
Mechanical Engineering
Interdisciplinarity
Print or weld a support frame
that can be used as
reinforcement and to define the
geometry of the AM element. It
is the method that builds a layer
around a core. The net is
covered with concrete using
spray on.
Support net spraying
Use a (advanced) extrusion
head to print a layer and add /
cover the area around with
loose support material after the
extruded layer has been
covered with a protection layer.
The process is repeated till the
element is finished.
(Mixed extrusion with) elevated support
printing
Print with a low resolution the
desired form and use milling (or
lasers) as subtractive technique
to finish the element.
Print mill sand
The extrusion head is used to
mix, extrude and reinforce.
Reinforcement is used for inter
layer strength and for load
distribution.
Orientated fibre reinforced concrete
e.g using a non newtonian fluid
High furface quality elements
with reinforcement that do not
need to be finished.
Instant dry extrusion/pultrusion
Fibre
reinforcement
CONCLUSION: FUTURE VISION
Hybrid techniques description
Characteristics & Evaluation
Consistency
Freeform
Freeform
Freeform
Reinforcement
Consistency
Speed
Speed
Speed
Surface quality
Surface quality
Consistency
Surface quality
Consistency
Aggregates
Freeform, high resolution
elements,
Joints of standarized
systems, and
3D refurbishment
elements
Freeform
Print in low resolution, to
increase production
speed. These elements
will be covered or
finished afterwards.
Core parts
Large structural elements
with different distribution
of aggregates and
composition. With or
without formwork.
Gradient material
Advanced extruded
elements with
different densities are
extruded at once due
to multiple extrusion
points in the die. The
extruder head can be
used for different
process approaches
Aligned fibres
Controlled mixture
Inter layer strength
Smooth surface
6: Description
4: Products
This report examines the additive manufacturing (AM) of concrete, its possibilities, feasibility and advantages over existing techniques. Traditional
processing techniques are adapted to the characteristics of concrete and concrete does not let itself dictate how to behave. The possibilities for
products made with an additive process are endless, but just replacing existing production methods with additive ones is still impossible. Although
improved freeform production techniques are the aim of this research, this does not mean that more freedom in form is by definition the largest
improvement that AM can offer at the moment. From another point of view the implementation of additional functions in traditional products can
be of great value.
A roadmap envisions how the technique has to evolve in order to implement the characteristic properties of concrete. Product ideas and an
evaluation of the techniques shown in the roadmap are related to the developments to achieve an increase in speed, surface quality and strength
in the AM production technique, next to the requirements that have to be set regarding a matching fresh concrete mixture.
Freeform concrete processing
High resolution
concrete
Extruded
concrete
Plaster
material
Formwork
PRODUCTS
Reinforcement
and extra
surface
between
layers
Compacting
mixer
Isotropic concrete
Reinforcement gun
Advanced extruder
CONCRETE IN AN AM PROCESS
Build around the reinforcement
Freeform
Fast process
High surface quality due post processing
Minimising printing time Consistency
Efficient support
Freeform
Controlled material composition
High surface quality
Less resolution needed
Faster printing process
Faster overall process
Aggregates
Orientated reinforcement
Controlled material composition
Less free form
More isotropic
Less material
Speed
Reinforcement
Consistency
Fast
Reinforced
Can be automated easily
High quality concrete (extruded at once)
Aggregates
Surface quality
Consistency
Reinforcement
Speed
Freeform
ROADMAP: future vision
100
On site customising of
standardised elements
Figure 83 - Roadmap
Techniques
ROADMAP (PRINTER CONCEPTS)
§ 7.3
Vision on AM of concrete
The roadmap is divided in 6 sections;
1
Techniques
2
Development
3
Conclusion: Future vision
4
Products
5
Preconditions
6
Description
Part 1 is a summary of the existing techniques described in chapter 5. Part 5 shows
information about the current techniques, preconditions and explains the motivation
behind the development and future visions with their resulting products. The
requirements that are set for a successful production technique are discussed in this
report. Part 6 shows a general description to clarify the future visions in context of
the report’s conclusions summarised in the roadmap.
Nozzle
- Lost mould
Schwartz, 2013
Thin mould casting
Print eco mould
Freeform
Mould
Support
material
Concrete
Moulds
Concrete processing AM Concrete research
Werner Sobek gradient beton
Stuttgart University
Mw. dr. ir. S.A.A.M. Fennis (CiTG TU-Delft)
ir. Siebe Bakker
Voxeljet
Sascha Hickert (Hochschule OWL)
Prof. Dipl.Ing. Matthias Michel
ir. Roel Schipper (CiTG TU-Delft)
dr.ir. Karel Vollers (BK TU-Delft)
Adapa (DK) MSc Eng Thomas Henriksen
Rieder Group (AT)
3D-Print techniques
that uses binders
AM
Dr. Dipl.-Ing. Holger Strauss (Hochschule
OWL)
Erno Langenberg (printing ceramic)
DUS Architecten (Canel House)
MX3D
NSTRMNT
TU Eindhoven concrete printing
- prof.dr.ir. T.A.M. (Theo) Salet - support
material
- Rob Wolfs - Parameters and concrete
properties
TU Delft
- Evaluating techniques and searching
matching products
- Experiments with new concepts for AM
of concrete
Companies
Winsum new materials
EZCT / Voxeljet
BetaBram
Skanska
Advanced (AM) moulds
Related expertises
Saxion
Breakthrough in 3D printing
AM with a support
material
Developments
Multiple mixture extruder
The multiple mixture
extruder mixus to obtain
the characteristics that
optimise the mixture
and material
composition
Fresh concrete
Mixer and
triple extruder
Existing
Construction
40
30
30
10
0
20
30
40
50
60
Time to completion (Hours)
70
80
90
100
Different materials
Print head and roller
Support
material
Polyjet in combination
with elevated support
printing increases the
resolution
Micro Rapid
Manufacturing
Sanding
(Mixed extrusion with) elevated support
printing
Shotcrete is used to
cover the reinforcement
with layers of concrete
Support net
Use a (advanced) extrusion
head to print a layer and add /
cover the area around with
loose support material after the
extruded layer has been
covered with a protection layer.
The process is repeated till the
element is finished.
The protection layer
prevents dehydration of
the concrete
0
10
20
Adapted from Buswell, et al., 2007, p.230
30
40
50
60
70
80
Resolution (mm3)
90
100
Low
Adapted from Buswell, et al., 2007, p.229
High
Reinforcement
Speed
Consistency
Consistency
Freeform
Speed
Surface quality
Minimising printing time Consistency
Efficient support
Freeform
Controlled material composition
Freeform
Speed
Consistency
Shotcrete
layers
Standardized elements
can be customised on
site when the surface
binding is strong
enough by e.g.
roughning it
mechanically
Roughened
surface
Print or weld a support frame
that can be used as
reinforcement and to define the
geometry of the AM element. It
is the method that builds a layer
around a core. The net is
covered with concrete using
spray on.
PRODUCTS
High surface quality
Less resolution needed
Faster printing process
Faster overall process
Formwork
Gradient material
Large structural elements
with different distribution
of aggregates and
composition. With or
without formwork.
Extruded
concrete
Plaster
material
Laser
Freeform
Build around the reinforcement
Freeform
Fast process
High surface quality due post processing
Consistency
Core parts
Print in low resolution, to
increase production
speed. These elements
will be covered or
finished afterwards.
Surface quality
High resolution
concrete
Freeform
Freeform, high resolution
elements,
Joints of standarized
systems, and
3D refurbishment
elements
Aggregates
Speed
Advanced extruded
elements with
different densities are
extruded at once due
to multiple extrusion
points in the die. The
extruder head can be
used for different
process approaches
Reinforcement
Compacting
mixer
Aggregates
Orientated reinforcement
Controlled material composition
Less free form
More isotropic
Less material
Aligned fibres
Controlled mixture
Inter layer strength
Smooth surface
Surface quality
Isotropic concrete
Consistency
Reinforcement gun
Support net spraying
Shotcrete
Interdisciplinarity
Computer
model
Generate
STL file
Generate
G-code
extrude
filament
Sensor
observes
extruded
filament
compare
to G-code
to correct
CONCRETE IN AN AM PROCESS
hs
Contour crafting
Low
Aggregates
Nozzle
Foam
Support
3D Concrete printing
‘Desktop’ Rapid Manufacturing
Surface quality
Nozzle
Print with a low resolution the
desired form and use milling (or
lasers) as subtractive technique
to finish the element.
ngt
2
Freeform
Construction
1
40
20
10
3
50
0
0
4
Decreasing resolution with
increasing deposition rate
60
10
Reinforcement
fibres
stre
70
20
ect
50
Exp
Progress of traditionally constructed wall
60
ed
80
70
Mixer
The extrusion head is used to
mix, extrude and reinforce.
Reinforcement is used for inter
layer strength and for load
distribution.
Mechanical Engineering
90
80
Concrete
Speed
Reinforcement
Consistency
Fast
Reinforced
Can be automated easily
High quality concrete (extruded at once)
Reinforcement
gun
High
Strength (MPa)
Progress of 3D-printed wall
90
Composite
Clay
Gypsum
Cement
Deposition rate (m3/hr)
Constituent material
Steel
Plastics
Chemical bonding
Instant
chemical reaction
100
100
Percent complete (%)
Mechanism
Phase change
Drying
Additional
aggregates
G-code
Inter layer strength
Aggregates & reinforcement
Isotropy
Surface quality
Material usage
Instant
curing of
the outside
Reinforcement
and extra
surface
between
layers
Resolution
Curing
Customise
Advanced extruder
Changing die
Print mill sand
Support
Mixer
Additive casting
Traditional concrete processing
Extrusion
Nozzle
‘Print head’
support material
Nozzle
Characteristics & Evaluation
Fibre
reinforcement
e.g using a non newtonian fluid
Polyjet concrete extrusion
Mix extra aggregates before
extrusion for efficient material
usage
Extruder
Instant dry extrusion/pultrusion
High furface quality elements
with reinforcement that do not
need to be finished.
Orientated fibre reinforced concrete
Reinforcement shotcrete
Binding agent
- Isotropic concrete
Extude in elevated support
- Freeform
Print head and roller
Instant curing of the
outside
On site customising of
standardised elements
Mixture and composition
Mixer
Different materials
Implementation
- Not concrete
- Strong
Materia, 2013
AM mould technique
EZCT
(moulds by Voxeljet)
Fresh concrete
Gradient materials
Print concrete without
complete support (polyjet)
Techniques
3DP technique
D-Shape
‘Print head’ and roller
Freeform and support
Reinforcement
Concrete mortar
Domus, 2013
Extrude in elevated support
- Missing support material
Additional
aggregates
Pultrusion
Instant dry extrusion
Changing die
Extruder without
trowels
Concrete consistency
and interlayer strength
Combining extrusion
and curing
Fibre reinforcement
Freeform
G-code
Could contain additional
mixture information about;
Fibres
Aggregates
Retarders
Extrude in mould
Contour Crafting, 2014
CONCLUSION: FUTURE VISION
Hybrid techniques description
Reinforcement
gun
Shotcrete
- Compact concrete low
air bulbs
Increased
surface area
Changing die
- No aggregates
3D Concrete printing
Total custom
DEVELOPMENT
Compacting
energy
Extruder with
trowels
Material
between
contours
- Surface quality differs
- No internal
reinforcement
Shoot reinforcement
- Anisotropic
Compact after extrusion
Characteristics
Roughen extruded surface
Initiatives
FDM technique
Contour crafting
Winsun new materials
Pultrude fibres
FIELD OF AM
ROADMAP: future vision
2015
Development
Version 22 January 2015 D. de Witte
§ 7.4
parallel code that
contains material
information
Material science
corrected
G-code
Building Technology
Architecture
Civil Engineering
Freeform concrete processing
This report examines the additive manufacturing (AM) of concrete, its possibilities, feasibility and advantages over existing techniques. Traditional
processing techniques are adapted to the characteristics of concrete and concrete does not let itself dictate how to behave. The possibilities for
products made with an additive process are endless, but just replacing existing production methods with additive ones is still impossible. Although
improved freeform production techniques are the aim of this research, this does not mean that more freedom in form is by definition the largest
improvement that AM can offer at the moment. From another point of view the implementation of additional functions in traditional products can
be of great value.
A roadmap envisions how the technique has to evolve in order to implement the characteristic properties of concrete. Product ideas and an
evaluation of the techniques shown in the roadmap are related to the developments to achieve an increase in speed, surface quality and strength
in the AM production technique, next to the requirements that have to be set regarding a matching fresh concrete mixture.
Cement (%)
Figure 84 - Roadmap: developments
The development is a process that takes place right now. Patents are requested
by the other initiatives, Which is the cause of that no publications with results are
available yet. General issues that can logically addressed to the development are;
•
The surface quality,
•
The inter layer strength,
•
The absence of reinforcement,
•
The position of the materials within the composition formed from filament,
•
The manufacturing speed, and
101
•
The freedom in form.
To overcome these challenging shortcomings the roadmap shows improvements for
them are showed in part 2 of the roadmap.
§ 7.4.1
Development in extrusion techniques
Techniques that look like FDM can be optimised by increasing the inter layer strength.
This can be done in several ways;
•
Roughen the extruded surface by extruding a surface like a mogul piste. The
increased surface area with the added z direction creates a stronger connection
between the layers.
•
Compact the layers after extrusion. Till a certain moment concrete can be
compacted. If those time intervals are regulated this can help to mix the layers
together, and
•
Mechanically connect the layers by shooting reinforcement through the extruded
of concrete.
By shooting reinforcement into the concrete, UHPC with controlled fibre alignment,
can be achieved. The fibres along the direction of extrusion cannot be embedded. To
embed the fibres with an extrusion process can be solved by embedding them along
the extrusion path.
In addition to the controlled positioning of fibres, an AM technique, in comparison
to standard casting, allows to adjust the mixtures density in real time. To make
lightweight porous concrete the extruder can mix additional granulates like expanded
glass balls or a chemical raising agent to the mixture just before it is extruded.
The G-code, normally used to describe the extruder’s path, can be linked to the
desired material properties and other parameters (§7.8). Those developments can be
accommodated and combined in an “advanced extruder head”. If the fresh concrete
mixture is too wet, using different mixtures with densities that differ, could start to
float on each other. The experiments in Appendix A8 shows the outcome of processing
mixtures with different densities.
A side track of the pultrusion is a die that can change its form. This allows to extrude
line-like elements with reinforcement and a changing section along its path. Rapid
curing can be embedded in such an extrusion process because no inter layer strength
is needed and the aggregates are equally distributed over the object. In the end
these techniques can also be combined, but experiments have to be done to evaluate
which combinations work best.
102
ROADMAP (PRINTER CONCEPTS)
Reinforcement
gun
Compacting
energy
Increased
surface area
Roughen extruded surface
Compact after extrusion
Shoot reinforcement
Figure 85 - Techniques to increase inter layer strength
Additional
aggregates
Fresh concrete
Mixer
Gradient materials
Additional
aggregates
Fresh concrete
Mixer and
triple extruder
Multiple mixture extruder
Figure 86 - Extrusion of different materials each layer or at once
103
Fibre
reinforcement
Changing die
Instant curing
of the outside
Pultrude fibres
Changing die
Instant dry extrusion /
pultrusion
Figure 87 - Reinforced extrusion techniques
§ 7.4.2
Developments in 3D-printing techniques
3D-printing techniques like D-Shape are time intensive, since all layers have to
be built separately, but it has the advantage of incorporated support material. To
develop this process it should become more like a Polyjet technique, a multi-material
technique without a binder, that uses concrete instead of powder and not a separate
binding agent. Polyjet allows to extrude only where the material is needed. Multiple
materials can be extruded at once, allowing to make (temporary) support structures
where needed. Another approach and development will be the elevated support
technique. This technique consists of printing or extruding a single layer of material
where after in the print chamber liquid / granular material is added to support the
path. This process repeats till the element is finished. Advantageous characteristics
are the decreased speed of adding support material and the ability to recycle the
support material. The elevated support method can take place on a platform that is
lowered. The support material will fill the outside of the chamber automatically, but
not the inside of the printed object. Print from the floor of the chamber is the second
option that avoids the need of a moving platform, which will be hard with in size
increasing elements. In this case the support needs to be selectively sprayed on top
of the existing layers, to prevent voids from being filled.
104
ROADMAP (PRINTER CONCEPTS)
Different materials
Different materials
Print head and roller
Print head and roller
Support
material
Print concrete without
complete support (polyjet /
3D-printing)
Polyjet concrete extrusion
with elevated extrusion
Figure 88 - PolyJet like techniques
Nozzle
Support
Extrude in elevated support
with moving platform
‘Print head’
support material
Nozzle
Extrude in elevated support
Figure 89 - Elevated support printing using an extrusion nozzle
105
§ 7.4.3
Implementation in traditional concrete processing
An advanced extruder (§7.6) which can mix the material instantly can be used in the
traditional concrete processing processes. It allows to additive cast in formwork. This
reduces environmental impact due to optimisation in material usage. Additionally,
standardized elements can be customized. Roughen the surface of a standardised
product in such a way that additional applied concrete will bind to the element to
customise it by adding additional layers of concrete.
Although shotcrete is used to cover the walls of a tunnel, it can also be used to make
a freeform element. Spraying layers of concrete on a reinforcement net will allow to
additive manufacture a freeform object. The reinforcement wire mesh acting as net
can be made using different technique including AM.
Mixer
Roughened
surface
Support net
Shotcrete
Extrude in mould
On site customizing of
standardized elements
Reinforcement shotcrete
Figure 90 - AM techniques implemented in traditional concrete processing processes
106
ROADMAP (PRINTER CONCEPTS)
Nozzle
Schwartz, 2013
Thin mould casting
Freeform
Print eco mould
- Lost mould
Mould
Support
material
Concrete
Moulds
Concrete processing AM Concrete research
Werner Sobek gradient beton
Stuttgart University
Mw. dr. ir. S.A.A.M. Fennis (CiTG TU-Delft)
ir. Siebe Bakker
Voxeljet
Sascha Hickert (Hochschule OWL)
Prof. Dipl.Ing. Matthias Michel
ir. Roel Schipper (CiTG TU-Delft)
dr.ir. Karel Vollers (BK TU-Delft)
Adapa (DK) MSc Eng Thomas Henriksen
Rieder Group (AT)
3D-Print techniques
that uses binders
AM
TU Eindhoven concrete printing
- prof.dr.ir. T.A.M. (Theo) Salet - support
material
- Rob Wolfs - Parameters and concrete
properties
TU Delft
- Evaluating techniques and searching
matching products
- Experiments with new concepts for AM
of concrete
Companies
Winsum new materials
EZCT / Voxeljet
BetaBram
Skanska
Advanced (AM) moulds
Related expertises
Dr. Dipl.-Ing. Holger Strauss (Hochschule
OWL)
Erno Langenberg (printing ceramic)
DUS Architecten (Canel House)
MX3D
NSTRMNT
Saxion
Breakthrough in 3D printing
Extude in elevated support
Mix extra aggregates before
extrusion for efficient material
usage
Extruder
- Isotropic concrete
AM with a support
material
‘Print head’
support material
Nozzle
Additive casting
100
Customise
Multiple mixture extruder
The multiple mixture
extruder mixus to obtain
the characteristics that
optimise the mixture
and material
composition
Fresh concrete
Mixer and
triple extruder
Concrete
40
30
30
10
0
20
30
40
50
60
Time to completion (Hours)
70
80
90
100
Different materials
Print head and roller
Support
material
Polyjet in combination
with elevated support
printing increases the
resolution
Micro Rapid
Manufacturing
Sanding
(Mixed extrusion with) elevated support
printing
Shotcrete is used to
cover the reinforcement
with layers of concrete
Support net
Use a (advanced) extrusion
head to print a layer and add /
cover the area around with
loose support material after the
extruded layer has been
covered with a protection layer.
The process is repeated till the
element is finished.
The protection layer
prevents dehydration of
the concrete
Support
0
10
20
30
40
Adapted from Buswell, et al., 2007, p.230
50
60
Resolution (mm3)
70
80
90
100
Low
Adapted from Buswell, et al., 2007, p.229
High
Aggregates
Orientated reinforcement
Controlled material composition
Less free form
More isotropic
Less material
Shotcrete
layers
Standardized elements
can be customised on
site when the surface
binding is strong
enough by e.g.
roughning it
mechanically
Roughened
surface
Print or weld a support frame
that can be used as
reinforcement and to define the
geometry of the AM element. It
is the method that builds a layer
around a core. The net is
covered with concrete using
spray on.
Reinforcement
Speed
Consistency
Consistency
Freeform
Speed
Surface quality
Minimising printing time Consistency
Efficient support
Freeform
Controlled material composition
Freeform
Speed
Consistency
Formwork
Gradient material
Large structural elements
with different distribution
of aggregates and
composition. With or
without formwork.
Extruded
concrete
Plaster
material
Laser
Freeform
Build around the reinforcement
Freeform
Fast process
High surface quality due post processing
Consistency
Core parts
Print in low resolution, to
increase production
speed. These elements
will be covered or
finished afterwards.
Surface quality
High resolution
concrete
Freeform
Freeform, high resolution
elements,
Joints of standarized
systems, and
3D refurbishment
elements
Speed
Advanced extruded
elements with
different densities are
extruded at once due
to multiple extrusion
points in the die. The
extruder head can be
used for different
process approaches
Reinforcement
Compacting
mixer
PRODUCTS
High surface quality
Less resolution needed
Faster printing process
Faster overall process
Aggregates
Aligned fibres
Controlled mixture
Inter layer strength
Smooth surface
Surface quality
Isotropic concrete
Consistency
Reinforcement gun
Support net spraying
Shotcrete
Interdisciplinarity
Computer
model
Generate
STL file
Generate
G-code
extrude
filament
Sensor
observes
extruded
filament
compare
to G-code
to correct
CONCRETE IN AN AM PROCESS
Freeform concrete processing
This report examines the additive manufacturing (AM) of concrete, its possibilities, feasibility and advantages over existing techniques. Traditional
processing techniques are adapted to the characteristics of concrete and concrete does not let itself dictate how to behave. The possibilities for
products made with an additive process are endless, but just replacing existing production methods with additive ones is still impossible. Although
hs
Contour crafting
Low
Aggregates
Nozzle
Foam
3D Concrete printing
‘Desktop’ Rapid Manufacturing
Surface quality
Nozzle
Print with a low resolution the
desired form and use milling (or
lasers) as subtractive technique
to finish the element.
ngt
2
Freeform
Construction
1
40
20
10
3
50
0
0
4
Decreasing resolution with
increasing deposition rate
60
10
Reinforcement
fibres
Mechanical Engineering
Existing
Construction
70
20
ect
50
Exp
Progress of traditionally constructed wall
60
Mixer
High
90
80
70
Speed
Reinforcement
Consistency
Fast
Reinforced
Can be automated easily
High quality concrete (extruded at once)
Reinforcement
gun
The extrusion head is used to
mix, extrude and reinforce.
Reinforcement is used for inter
layer strength and for load
distribution.
stre
Progress of 3D-printed wall
80
Composite
Clay
Gypsum
Cement
Deposition rate (m3/hr)
Constituent material
Steel
Plastics
Chemical bonding
Instant
chemical reaction
Percent complete (%)
Mechanism
Phase change
ed
100
90
Surface quality
Material usage
Strength (MPa)
Inter layer strength
Drying
Additional
aggregates
G-code
Aggregates & reinforcement
Isotropy
Instant
curing of
the outside
Reinforcement
and extra
surface
between
layers
Resolution
Curing
Developments
Advanced extruder
Changing die
Print mill sand
Support
Mixer
Traditional concrete processing
Extrusion
Nozzle
Extrude in elevated support
Binding agent
Implementation
- Freeform
Materia, 2013
Fresh concrete
Mixer
Print head and roller
Characteristics & Evaluation
Fibre
reinforcement
e.g using a non newtonian fluid
Polyjet concrete extrusion
Additional
aggregates
Different materials
Instant dry extrusion/pultrusion
High furface quality elements
with reinforcement that do not
need to be finished.
Orientated fibre reinforced concrete
Reinforcement shotcrete
Reinforcement
Gradient materials
Print concrete without
complete support (polyjet)
Techniques
‘Print head’ and roller
- Not concrete
Instant curing of the
outside
On site customising of
standardised elements
Concrete consistency
and interlayer strength
- Missing support material
- Strong
AM mould technique
EZCT
(moulds by Voxeljet)
Mixture and composition
Extruder without
trowels
Pultrusion
Instant dry extrusion
Changing die
Concrete mortar
Domus, 2013
3DP technique
D-Shape
Combining extrusion
and curing
Fibre reinforcement
Freeform
G-code
Could contain additional
mixture information about;
Fibres
Aggregates
Retarders
Extrude in mould
Contour Crafting, 2014
CONCLUSION: FUTURE VISION
Hybrid techniques description
Reinforcement
gun
Freeform and support
- Compact concrete low
air bulbs
Increased
surface area
Shotcrete
- No aggregates
Changing die
- No internal
reinforcement
3D Concrete printing
Total custom
DEVELOPMENT
Compacting
energy
Extruder with
trowels
Material
between
contours
- Surface quality differs
Shoot reinforcement
- Anisotropic
Compact after extrusion
Characteristics
Roughen extruded surface
Initiatives
FDM technique
Contour crafting
Winsun new materials
Pultrude fibres
FIELD OF AM
ROADMAP: future vision
2015
AM Techniques: Future vision
Version 22 January 2015 D. de Witte
§ 7.5
parallel code that
contains material
information
Material science
corrected
G-code
improved freeform production techniques are the aim of this research, this does not mean that more freedom in form is by definition the largest
improvement that AM can offer at the moment. From another point of view the implementation of additional functions in traditional products can
be of great value.
A roadmap envisions how the technique has to evolve in order to implement the characteristic properties of concrete. Product ideas and an
Building Technology
Architecture
Civil Engineering
evaluation of the techniques shown in the roadmap are related to the developments to achieve an increase in speed, surface quality and strength
in the AM production technique, next to the requirements that have to be set regarding a matching fresh concrete mixture.
Cement (%)
Figure 91 - Roadmap: future vision
The future vision is a mixture of the developed improvements and new technical
inventions. Also traditional concrete methods have been implemented in the AM
future visions. The visions can be split in three different approaches:
•
Extrusion/pultrusion,
•
3D-printing, and
•
Building layers around a core.
These categories are based on their development trajectory. The other way around
with the implementation of AM in the existing concrete processing is shown in the
development part. Extrude different and regulated concrete mixtures in a traditional
casting process (extrude in formwork).
The five visions with the highest potential for concrete processing are;
•
Elevated support printing,
•
Reinforcement / support net spraying,
•
Print mill sand / lasercut,
•
Instant curing extrusion / pultrusion, and
•
Fibre orientated reinforced UHPC
The development is performed by the competition as well. Its important to obtain
a leading role in the AM of concrete. The visions showed are one step ahead of the
competition. The new concepts are of great importance since, although it cannot be
verified, the pending patents from Contour crafting, 3D-concrete printing, D-Shape
will concern optimising their processes, and not about a complete change in their
concept. The future visions are a result of the analysis of existing techniques, the
alternatives and threats for AM of concrete and from an innovative point of view.
107
Name
Comparable existing
techniques involved
Category
Additive
Contour Crafting
Concrete filament is extruded on top of each
other. (§5.3.1)
Additive
Concrete Printing
Concrete filament is extruded on top of each
other. (§5.3.2)
Additive
D-Shape
3D-printing process that uses powder and a
binder (§5.3.3)
Additive
Instant curing extrusion
Using a nozzle that cures the outside of
the heat/
temporary support,
Change the diameter of the nozzle, allows to
extrude a changing form.
MX3D
Additive
Fibre orientated reinforced
concrete
Using an extrusion process and additional
machines to extrude and shoot fibres in the
concrete.
Next generation
extrusion
Mixed
Print mill sand
Finish the AM rough printed concrete by cnc
milling the surface
Milling the complete
form
Additive
Elevated support printing
Extrude a layer of concrete. The layer will be
supported by granular materials that can be
reused and are added during printing
D-Shape
Mixed
Support net layer spraying
Print or produce reinforcement nets that are
used to apply layers of shotcrete on.
-
Table 23 - new AM concepts comparison
108
Description
Techniques
Speed
Aggregates
Reinforcement
Mix different
material
compositions
Material isotropy
Internal voids
dissolving
material etc
Surface quality
ROADMAP (PRINTER CONCEPTS)
High
No
Yes, fibres
Maybe
Layered
Yes
Medium
High
No
Yes, fibres
Maybe
Layered
Yes
Low
Medium
No
No
Yes the layer
composition
No
No
Medium
High
Yes
Yes, fibres
Maybe
Material
behaves /
cures different
in the core
No
High
Medium
Yes
Yes,
orientation
controlled
fibres
Yes
Isotropic,
but can be
manipulated
No
Medium,
depends on
resolution
Medium
Yes, but not at
the surface
Yes, fibres
Maybe
Isotropic
Yes
High, but
aggregates can
spring of
Medium-High,
depending on
the resolution
used
Yes
Yes, fibres
Yes, if the
extrusion head
can mix
Isotropic
Inter layer
bounding is
important
Yes, but they
need to be fixed
in the concrete,
because
otherwise
support material
fills the voids
Depends on
resolution
Medium-High,
depending
on the (AM)
technique used
for the net
Yes
Yes
Yes
Isotropic
No, but hollow
elements can
be attached to
the net
Medium,
depends on
post processing
as well
109
Instant curing extrusion
Fibre
reinforcement
Changing die
Instant
curing of
the outside
Material waste
§ 7.5.1
Cement
Aggregates
Additives
Water
Fresh concrete
mixture
Extrude
Dry outside
Cure
(Post process)
Figure 91 - Instant curing extrusion / pultrusion
Concrete hardens due to a chemical reaction. By changing the composition and
by adding extra blowers to the extrusion head, the concrete can be cured on the
outside instantly. There is no support needed anymore after extrusion and the linelike elements becomes formwork for the core of the element. Attention needs to be
paid to the internal stress. The main advantage is that the element is extruded at
once. Because the die changes its form it is a continues process without layers. The
extruded concrete is isotropic and can contain larger aggregates.
Advantageous properties:
•
Reinforced,
•
Fast,
•
Can be automated easily, and
•
High quality concrete (extruded at once).
Disadvantageous properties;
•
110
Cracking due to internal stress concentrations.
ROADMAP (PRINTER CONCEPTS)
Fibre orientated reinforced concrete
Reinforcement
gun
Mixer
Reinforcement
fibres
Material waste
§ 7.5.2
Cement
Aggregates
Additives
Water
Fresh concrete
mixture
Extrude
Reinforce
(Post process)
Figure 92 - Fibre orientated reinforced concrete extrusion
Orientating the fibres in concrete has great potential. The fibres used nowadays are
randomly spread across such a fibre reinforced mixture. Therefore the needle like
reinforcement is everywhere instead of concentrated on the desired spots and in the
desired direction. In AM it can fulfil, in addition to the improved location controllability,
the function to generate the desired inter layer strength.
Advantageous properties:
•
Minimising printing time
•
Efficient support
•
Freeform
Disadvantageous properties;
•
Resolution determines surface quality
Figure 93 shows an example of fibre reinforced concrete. The fibres are concentrated
in the lower part of the element.
111
Figure 93 - Fibre reinforced concrete
112
ROADMAP (PRINTER CONCEPTS)
Print mill sand
Nozzle
Sanding
Material waste
§ 7.5.3
Cement
Aggregates
Additives
Water
Fresh concrete
mixture
Extrude
Mill
Sand
(Post process)
Figure 94 - Print mill sand
Subtractive manufacturing is the opposite of AM, but a combination of the two
methods leads to processes like print mill sand. First the geometry is printed quickly
in a low resolution, after curing the material will be removed by use of a subtractive
process. The surface quality can now be controlled by the subtractive process, for
which traditional milling tools or a laser can be used. Large aggregates have to be
avoided at the surface, since these can spring of and damage the surface.
Advantageous properties:
Better surface quality
Less resolution needed
Faster printing process
Faster overall process
Disadvantageous properties;
•
Waste during milling
113
§ 7.5.4
Elevated support printing
Foam
Support
Material waste
Nozzle
Cement
Aggregates
Additives
Water
Fresh concrete
mixture
Extrude
Coat concrete
Apply layer of
support material
Remove support material
(Post process)
Figure 95 - Elevated support printing
Elevated support printing can be even more advanced than described in the
developments. To prevent dehydration of the concrete a layer of, for example
biodegradable foam, will be applied after extrusion. This has to be done just before
the next layer of support material will be selectively sprayed around the extruded
layer of the element. This also prevents that the support material sticks to the
element (figure 97).
This technique combines FDM and 3DP. The extrusion head’s functions can be as
advanced as desired, because the elevated support does not affect the extruder.
Advantageous properties:
114
•
Minimising printing time
•
Efficient support
•
Freeform
•
Freedom in material composition
ROADMAP (PRINTER CONCEPTS)
Disadvantageous properties;
•
Print chamber is needed
Figure 96 - Elevated support printed concrete
Figure 97 - Elevated support printing resolution
115
Support net layer spraying
Shotcrete
layers
Material waste
§ 7.5.5
Laser
Cement
Aggregates
Additives
Water
Fresh concrete
mixture
Place support
net
Apply shotcrete
layers
(Post process)
Figure 98 - Reinforcement / support net layer spraying
Support net spraying is a method that builds a layer around a core. It uses a frame
that can also be used as reinforcement for defining the geometry of the AM element.
The net is covered with concrete using a spray on technique. The amount of layers
depends on the desired thickness. After the element has been cured it can be post
processed to improve the surface quality.
Advantageous properties:
116
•
Build around the embedded reinforcement.
•
Freeform
•
Optimised material usage
ROADMAP (PRINTER CONCEPTS)
§ 7.6
Advanced extruder
Reinforcement
gun
Isotropic
concrete
Compacting
mixer
Reinforcement
and extra
surface
between
layers
Figure 99 - Advanced extruder
The advanced extruder can be used as extrusion head in the future visions. It
combines the previously mentioned developments in such a way that the material
can be used in an optimised way. The inter layer strength, mixture and reinforcement
orientation can be controlled. When the way of processing the material through a
nozzle is controlled and combined with the right mixture the exact characteristics of
the extruder can be adapted to the AM process.
Next to the ability to print gradient materials, the advanced extruder has, like in
Contour Crafting, trowels that are used to smoothen the surface. In this way a smooth
surface can be obtained without a time intensive high resolution. It is a sort of direct
post processing that can also be used for compacting when the trowels vibrate.
An important instrument related to the advanced extruder is the G-code. It needs to
be extended with additional information like the composition (§7.8).
117
Nozzle
Schwartz, 2013
Thin mould casting
Print eco mould
Freeform
Mould
Support
material
Concrete
Moulds
Concrete processing AM Concrete research
Werner Sobek gradient beton
Stuttgart University
Mw. dr. ir. S.A.A.M. Fennis (CiTG TU-Delft)
ir. Siebe Bakker
Voxeljet
Sascha Hickert (Hochschule OWL)
Prof. Dipl.Ing. Matthias Michel
ir. Roel Schipper (CiTG TU-Delft)
dr.ir. Karel Vollers (BK TU-Delft)
Adapa (DK) MSc Eng Thomas Henriksen
Rieder Group (AT)
3D-Print techniques
that uses binders
AM
TU Eindhoven concrete printing
- prof.dr.ir. T.A.M. (Theo) Salet - support
material
- Rob Wolfs - Parameters and concrete
properties
TU Delft
- Evaluating techniques and searching
matching products
- Experiments with new concepts for AM
of concrete
Companies
Winsum new materials
EZCT / Voxeljet
BetaBram
Skanska
Advanced (AM) moulds
Related expertises
Dr. Dipl.-Ing. Holger Strauss (Hochschule
OWL)
Erno Langenberg (printing ceramic)
DUS Architecten (Canel House)
MX3D
NSTRMNT
Saxion
Breakthrough in 3D printing
Extude in elevated support
Mix extra aggregates before
extrusion for efficient material
usage
Extruder
Support
AM with a support
material
‘Print head’
support material
Nozzle
Mixer
Additive casting
Traditional concrete processing
Version 22 January 2015 D. de Witte
100
30
Different materials
Print head and roller
Support
material
Polyjet in combination
with elevated support
printing increases the
resolution
30
10
Instant
chemical reaction
Cement
Micro Rapid
Manufacturing
0
10
20
30
40
50
60
Time to completion (Hours)
70
80
90
100
Contour crafting
Low
0
10
20
Adapted from Buswell, et al., 2007, p.230
30
40
50
60
Resolution (mm3)
70
80
90
100
Adapted from Buswell, et al., 2007, p.229
Low
High
Isotropic concrete
Shotcrete is used to
cover the reinforcement
with layers of concrete
Support net
Use a (advanced) extrusion
head to print a layer and add /
cover the area around with
loose support material after the
extruded layer has been
covered with a protection layer.
The process is repeated till the
element is finished.
Reinforcement
Speed
Consistency
Consistency
Freeform
Speed
Surface quality
The protection layer
prevents dehydration of
the concrete
Minimising printing time Consistency
Efficient support
Freeform
Controlled material composition
Freeform
Speed
Consistency
PRODUCTS
High surface quality
Less resolution needed
Faster printing process
Faster overall process
Foam
Support
Formwork
Shotcrete
layers
Standardized elements
can be customised on
site when the surface
binding is strong
enough by e.g.
roughning it
mechanically
Roughened
surface
Print or weld a support frame
that can be used as
reinforcement and to define the
geometry of the AM element. It
is the method that builds a layer
around a core. The net is
covered with concrete using
spray on.
Gradient material
Large structural elements
with different distribution
of aggregates and
composition. With or
without formwork.
Extruded
concrete
Plaster
material
Support net spraying
Shotcrete
Laser
Freeform
Build around the reinforcement
Freeform
Fast process
High surface quality due post processing
Consistency
Core parts
Print in low resolution, to
increase production
speed. These elements
will be covered or
finished afterwards.
Surface quality
High resolution
concrete
Freeform
Freeform, high resolution
elements,
Joints of standarized
systems, and
3D refurbishment
elements
Aggregates
Speed
Advanced extruded
elements with
different densities are
extruded at once due
to multiple extrusion
points in the die. The
extruder head can be
used for different
process approaches
Reinforcement
Compacting
mixer
Aggregates
Orientated reinforcement
Controlled material composition
Less free form
More isotropic
Less material
Aligned fibres
Controlled mixture
Inter layer strength
Smooth surface
Surface quality
Reinforcement gun
Consistency
Aggregates
Nozzle
Interdisciplinarity
Computer
model
Generate
STL file
Generate
G-code
extrude
filament
Sensor
observes
extruded
filament
compare
to G-code
to correct
CONCRETE IN AN AM PROCESS
Freeform concrete processing
This report examines the additive manufacturing (AM) of concrete, its possibilities, feasibility and advantages over existing techniques. Traditional
processing techniques are adapted to the characteristics of concrete and concrete does not let itself dictate how to behave. The possibilities for
products made with an additive process are endless, but just replacing existing production methods with additive ones is still impossible. Although
3D Concrete printing
‘Desktop’ Rapid Manufacturing
0
0
Sanding
(Mixed extrusion with) elevated support
printing
hs
2
Freeform
Construction
1
40
Surface quality
Nozzle
Print with a low resolution the
desired form and use milling (or
lasers) as subtractive technique
to finish the element.
ngt
3
50
20
Concrete
4
Decreasing resolution with
increasing deposition rate
60
10
Reinforcement
fibres
Mechanical Engineering
Existing
Construction
70
20
ect
40
Exp
50
Deposition rate (m3/hr)
Progress of traditionally constructed wall
60
Mixer
High
90
80
70
Clay
Gypsum
Speed
Reinforcement
Consistency
Fast
Reinforced
Can be automated easily
High quality concrete (extruded at once)
Reinforcement
gun
The extrusion head is used to
mix, extrude and reinforce.
Reinforcement is used for inter
layer strength and for load
distribution.
stre
Progress of 3D-printed wall
80
Composite
Percent complete (%)
Constituent material
Steel
Plastics
Drying
Chemical bonding
ed
100
90
Surface quality
Material usage
Strength (MPa)
Inter layer strength
Mechanism
Mixer and
triple extruder
G-code
Aggregates & reinforcement
Isotropy
Phase change
The multiple mixture
extruder mixus to obtain
the characteristics that
optimise the mixture
and material
composition
Fresh concrete
Resolution
Curing
Customise
Developments
Additional
aggregates
Print mill sand
Nozzle
Extrude in elevated support
Binding agent
- Isotropic concrete
- Lost mould
Advanced extruder
Changing die
Instant
curing of
the outside
Orientated fibre reinforced concrete
Extrusion
Multiple mixture extruder
Mixer
Implementation
- Strong
Fresh concrete
Characteristics & Evaluation
Fibre
reinforcement
e.g using a non newtonian fluid
Polyjet concrete extrusion
Additional
aggregates
Print head and roller
Instant dry extrusion/pultrusion
High furface quality elements
with reinforcement that do not
need to be finished.
Reinforcement
and extra
surface
between
layers
Reinforcement shotcrete
Reinforcement
Different materials
Pultrusion
Instant curing of the
outside
On site customising of
standardised elements
Print concrete without
complete support (polyjet)
Techniques
‘Print head’ and roller
- Not concrete
Freeform and support
Concrete consistency
and interlayer strength
- Missing support material
- Freeform
Materia, 2013
AM mould technique
EZCT
(moulds by Voxeljet)
Mixture and composition
Extruder without
trowels
Instant dry extrusion
Changing die
Concrete mortar
Domus, 2013
3DP technique
D-Shape
Combining extrusion
and curing
Fibre reinforcement
Freeform
G-code
Could contain additional
mixture information about;
Fibres
Aggregates
Retarders
Extrude in mould
Contour Crafting, 2014
CONCLUSION: FUTURE VISION
Hybrid techniques description
Reinforcement
gun
Shotcrete
- No aggregates
- Compact concrete low
air bulbs
Increased
surface area
Changing die
- No internal
reinforcement
3D Concrete printing
Total custom
DEVELOPMENT
Compacting
energy
Extruder with
trowels
Material
between
contours
- Anisotropic
Gradient materials
- Surface quality differs
Shoot reinforcement
Characteristics
Roughen extruded surface
Initiatives
FDM technique
Contour crafting
Winsun new materials
Pultrude fibres
FIELD OF AM
ROADMAP: future vision
2015
Products
Compact after extrusion
§ 7.7
Material science
corrected
G-code
parallel code that
contains material
information
Architecture
improved freeform production techniques are the aim of this research, this does not mean that more freedom in form is by definition the largest
improvement that AM can offer at the moment. From another point of view the implementation of additional functions in traditional products can
be of great value.
A roadmap envisions how the technique has to evolve in order to implement the characteristic properties of concrete. Product ideas and an
Building Technology
Civil Engineering
evaluation of the techniques shown in the roadmap are related to the developments to achieve an increase in speed, surface quality and strength
in the AM production technique, next to the requirements that have to be set regarding a matching fresh concrete mixture.
Cement (%)
Figure 100 - Roadmap: products
The products that can be made with the new techniques should either be different
from existing concrete products or the process has to be more efficient so that the
production process is competitive, as described in chapter 6.
The products focus on freeform elements like façade cladding, small batch size with
different forms (for example corner solutions for standardized elements) or large
freeform extruded elements with embedded reinforcement. The reinforcement can
also be shot in the concrete, which allows the industry to produce fibre aligned
reinforced UHPC.
If the technique is used on site different densities of concrete can be applied using the
advanced extruder head, if the mixture is relatively earth dry. The material is placed
in such a way that over dimensioning or unnecessarily material usage is prevented.
An example of a product with internal structures like a human bone (figure 80)
can be seen in figures 102 and 103. This gypsum model is 3D printed. With this
AM technique it is possible to print at a very high resolution and to use this for the
internal structure. However it is faster and more economical to change the mixture,
using expanded glass balls or by using a raising agent. The internal voids shown
in figure 103 are made with a gypsum 3DP technology, but figure 104 shows foam
concrete that has nearly the same result. This is why different mixtures are more
suitable in a fast economic concrete extrusion process.
118
ROADMAP (PRINTER CONCEPTS)
Formwork
Extruded
concrete
Plaster
material
High resolution
concrete
Figure 101 - f.l.t.r. Gradient concrete in mould, an element that is finished afterwards and a freeform element
Products can be:
•
Gradient concrete elements (insulation and material efficiency),
•
Lower resolution freeform structures that are finished,
•
Freeform elements (economically small batch sizes), and
•
Freeform elements that can not be made otherwise (internal voids).
The hybrid production techniques have also a high potential at the moment, while
complete freedom in form without formwork is pursued. Combining different
techniques in such a way that only the beneficial properties are used shows its
potentials in AM casting in formwork. (figure 101 left). It adds extra functions to a
widely used product. These functions can be:
§ 7.7.1
•
Insulation (porous concrete in the middle),
•
Structural optimisation (material usage),
•
Controlled fibre reinforcement disposition without the need of pre-installed nets.
Gradient materialized composite elements
Gradient material elements can be obtained in different ways;
•
Printing the structure
•
By chemical reaction in the concrete that foams the concrete
•
By lightweight aggregates.
119
Figure 98 and 99 show a 3D-printed gypsum element with a gradient. This open
structure inside has been modelled in the computer and is not randomly like in the
foam concrete (figure 101) or concrete with expanded glass balls. For concrete the
randomly distributed voids to obtain the gradient are the best solution since printing
them needs a very high resolution and is time intensive.
Figure 102 (left) - Section of façade element with integrated heat exchanger (Computer model).
Figure 103 (right) - Printed gypsum model. of the integrated heat exchanger
Figure 104 - Foam concrete
120
ROADMAP (PRINTER CONCEPTS)
Figure 105 - Concrete core with expanded glass balls
§ 7.8
G-code
Printing with a composite that hardens according to a chemical reaction asks for
another extrusion approach. First of all a gradient material that is mixed just before
extrusion is new. If the material properties differ along the extrusion path, additional
information regarding the composition of the material and the filament thickness after
extrusion is needed. This information about the mixture can be saved in a parallel
G-code like temperature is done for an FDM process as illustrated in figure 106. In
plastic FDM the printer is calibrated for a certain material, with a certain filament
thickness. The layer thickness is known and the software adjusts the printer nozzle
according to these constant values. If the material composition differs along the
extrusion path, additional sensors to observe the extruded filament are necessary.
If the extruded element is not scanned before another layer is extruded, the model
can collapse. Using a continuously updated G-code is needed to process gradient
materials.
121
Computer
model
Generate
STL file
Generate
G-code
extrude
filament
Sensor
observes
extruded
filament
compare
to G-code
to correct
corrected
G-code
parallel code that
contains material
information
Figure 106 - Correcting G-code during extrusion
§ 7.9
Conclusions roadmap
The roadmap shows a clear representation of the current technical situation, the
expected developments, the relation between existing AM techniques and those
used for AM of concrete and a founded future vision with matching products. Most
important is the relation between the characteristics of concrete and the production
process. Concrete cannot be processed without adapting an AM process to it, as
its behaviour differs too much from, for example, plastics. The five visions show
how concrete can be processed in the future. It tries to solve the problem with
reinforcement, aggregates and the weak inter layer strength. The products that
match the production processes are divided in groups;
•
Elements that will be post processed,
•
High resolution free form elements, and
•
Elements casted with use of AM in formwork to create gradient materials
Although it is possible to print everything, it is important to use the technique
adequate. When there is no direct economical benefit, added value needs to be
pursued.
122
123
III Conclusions
124
8 Conclusions and
recommendations
§ 8.1
Conclusions
While answering the research questions, it became clear that the main challenge
of the AM of concrete is how the technique is used and the way the concrete is
processed. The roadmap shows a summary of the existing processes and how
they should evolve. The overall strength, inter layer strength, reinforcement and
the material composition are aspects that need to be developed first. The future
vision showed five techniques that respect the characteristics of concrete and
most sub-questions regarding the evolvement of the technique are answered
within these visions. The questions about how to implement the technique in
the building process are harder to answer, because a well functioning technique
as a freeform concrete processing principle does not exist yet. It is premature
to talk about specific characteristics of the elements and whether the AM should
take place at the building site or not, therefore a shift in research focus to
processes has to be made. Nonetheless, it can be assumed with certainty that
the production technique will develop in two directions in the near future. One
for large elements that only can be produced on site and on the other hand the
high resolution elements that need to be made in a controlled environment for
best results.
Requirements of products are nevertheless important to evolve the production
technique and to examine the designed production process. Attention need to be
paid that the AM technique is used adequate.
AM of concrete is a challenging field. The material and the manner of processing
are just a first stage. Considering that the strength of concrete is its price, the
prevailing approach to the AM of concrete, which consists of producing relatively
low strength elements by a lot of expensive cement, is ineffective. To improve
this the material and processing process needs to be integrated. Concrete differs
in many ways from the materials that are commonly used in AM processes, due
to the chemical reaction involved.
The way concrete is processed by initiatives such as Contour Crafting, 3D-Concrete
printing impose on concrete a production technique that looks like Fused Deposit
Melting. D-Shape uses just like 3D-printing a binding agent. All those methods do
not use concrete as described in literature, but rather as a substitute for normal
concrete in order to sell it. The material and the process should be changed to
get the best results, but as far as information is available that is not done yet.
The findings in this thesis indicate that to get the best results the materials and
125
processes used in present AM methods need to be changed and more aligned.
The possibilities for products made with an additive process are endless, but to
improve existing production methods with the use of additive ones, does not mean
that more freedom in form is the largest improvement. From another point of view
implementation of functions in traditional products can be even more valuable. An
example is the integration of insulation in the core of casted walls, using AM to
extrude these porous cores in between of the water tight and load bearing slabs.
Freeform elements can also be made using an advanced moulding technique. Internal
gradient properties cannot made otherwise.
Added value is the aim that should be pursued in an AM process. AM has a great
potential for the concrete industry, but the application is in some cases less visible,
since implementation of functions is not always as visible as freeform geometry.
Mechanical Engineering
Material science
Building Technology
Architecture
Figure 107 - AM of concrete as interdisciplinary subject
126
Civil Engineering
CONCLUSIONS AND RECOMMENDATIONS
§ 8.2
Recommendations
Although this thesis has described various difficulties, printing concrete remains
a viable technique, however it still requires a lot of research. Especially to make
it economically feasible it is important to be able to compete with traditional and
more advanced concrete processing techniques, including approaches that leads to
freeform concrete elements as well: in particular the AM of moulds.
The roadmap shows how AM of concrete should evolve. Milling, printing support
structures, using different approaches for support and pultrusion with an adaptable
die are part of the roadmap. The main conclusion is that production techniques need
to be combined for processing the composite material.
However this is a vision and the final processing methods could differ. A collaboration
between mechanical engineering, civil engineering, material science, architecture
and building technology in the middle of them to coordinate would be the best way
to share knowledge and get the desired result:
•
A machine capable of the requirements - Mechanical engineering,
•
The right mixture (Properties and reinforcement) - Civil engineering /
Material science,
•
Architectural products that benefit most from the possibilities that this
technique has to offer - Architecture,
•
Structural products that benefit most from the possibilities that this
technique has to offer - Civil engineering, and
•
A life cycle assessment - Civil engineering, Material science and Architecture.
In a time where everyone is trying to obtain patents it is important to get at the same
level of knowledge. Now is the time to join forces to gather and share the knowledge
available within the university.
The recommendations are mostly about the way a project like this should be
organised. The subject is very broad and gives room for multiple faculties to join.
However collaboration is a key factor, it is also important that ideas and concepts are
validated by producing elements and testing them.
127
128
Appendices
Appendix 1 - Experiment with layered concrete
Appendix 2 - Printed mould
Appendix 3 - Decomposition of concrete mixture
Appendix 4 - Capillary action 3D-printing with water
Appendix 5 - Extruding on bentonite
Appendix 6 - Aligned fibre reinforcement
Appendix 7 - Elevated support printing
Appendix 8 - Gradient concrete
Appendix 9 - Technology roadmap by Volkers
129
A1
Experiment with layered concrete
Test layered concrete BEAmix 135
Using 150/150/150mm cubes to look at the difference between layered and single
volume casted elements.
Experiment:
Casting 8 elements with BEAmix 135
2 compacted cubes with concrete
2 not compacted 5 layers (30mm each) concrete cube
2 compacted 5 layers (30mm each) concrete cube
The time interval between the layers is 5 minutes to simulate a layered extrusion
process, and determine if the open time next to the layers influences the concrete’s
strength.
After curing the concrete will has been tested on compressive strength.
Figure A1 (left) - Casted cubes
Figure A2 (right) - De-moulded cubes
compacted cube
layered compacted
cube
layered cube
7 day strength (27 may 2014)
28.58MPa
28.41MPa
23.2MPa
28 days strength
?
?
?
surface
smooth
smooth
rough
consistency
normal
normal
with voids
Table A1 - Strength demoulded cubes
Tension strength is normally 10% of the compressive strength
Flexural strength is approximately 15% of the compressive strength
130
APPENDICES
A2
Printed mould
To test the surface quality BEAmix 135 has been casted on a 3D printed ABS element
placed inside an 150/150/150 mould. The surface shows the relief of the resolution
of the printed mould, although it had been sanded and treated with diluted acetone.
There is also a lot of capillary voids in the mixture that showed up at the surface.
Either the mixture was too wet or more compacting had been needed. Demoulding
was hard due the 90 degrees angles and the stacked filaments that acted as hooks.
2 - 5 degrees tapered walls would ease the de-moulding like a ring shaped cake.
Figure A3 (left) - Part of the mould printed out of ABS
Figure A4 (right) - Before and after sanding the mould a little
Figure A5 (left) - Cured concrete with locked mould
Figure A6 (right) - De-moulded element
Printing advanced moulds has also to do with these design limitations, limiting the
freedom in form.
131
A3
Decomposition of the concrete mixture
Figure A5 (left) - Mortar extruder
Figure A6 (right) - Extrusion of mortar with bentonite
The sealant gun applies to much force on the thick mortar to be extruded well. The
mixture decomposes and the sealant gun gets clogged. Mortar mixed with bentonite
does not clog the sealant gun and forms can be extruded easily, but hardens slowly.
A4
Capillary action 3D-printing with water
Figure A7 (left) - Spraying water on concrete mix
Figure A8 (right) - Brittle concrete after drying
Spraying water on spread concrete should only bind the concrete that gets wet.
Because it is not mixed well the capillary action the concrete becomes brittle. The
water/cement factor is too low, but the air that is normally removed during mixing and
compacting is still within the cured concrete and is the main cause of the brittleness.
132
APPENDICES
A5
Extruding on bentonite
Bentonite is a material used to prevent excavations from collapsing. The muddy
substance is poured in the cavity till the desired depth is reached. After the excavation
concrete is poured in the cavity. The density of concrete is higher and the bentonite
will float on the concrete.
By changing the amount of water the density of the bentonite mixture can be adapted.
Concrete with a normal density of 2250 kg/m3 remains to heavy to float on bentonite.
Although bentonite has some surface tension the concrete sinks if a thick layer of
concrete is applied.
Figure A9 (left) - Concrete with bentonite as support material
Figure A10 (right) - Layered concrete with rough surface
The experiment is repeated with sand. The way of processing differs. Was bentonite
orinting meant like NSTRMNT (§3.2.5), printing with sand is a combination of 3DP
and an FDM process.
133
A7
Aligned fibre reinforcement
To examine whether it is possible and how fibre reinforced concrete would look
like, formwork has been used. The fibres are concentrated in the bottom part of
the concrete. Figures A11, A12 and A13, show the formwork and casted concrete
element.
Figure A11 (left) - Formwork with fibres
Figure A12 (right) - Concrete cube with fibre reinforcement
Figure A12 - Close-up fibres
A7
Elevated support printing
Elevated support printing has been tested with a concrete mortar. The mortar
consisted of 30% cement and 70% sand. After the first layer was extruded, sand
was added as support material. After a few layers the small concrete dome’s roof was
closed (figures A13, A14 and A15) Unfortunately the sealant gun still gets clogged
rapidly. Despite that the method works. If an advanced extruder is used freeform
elements can be made easily.
134
APPENDICES
Figure A13 (left) - First layer
Figure A14 (right) - Supported layer
Figure A14 (left) - Finished dome
Figure A15 (right) - ‘demoulded’ element
Figure A16 (left) - Bottom of the element
Figure A17 (right) - Resolution of extrusion process
135
A8
Gradient concrete
3 types of gradient concrete were made. One of them was casted at once (figure
A18) the last two were casted with 30 minutes between the outside and inside of the
element (figures A19 and A20). The elements are not tested, but show to be rigid.
The mixture used for the element in figure A20 contained less cement for the core. It
is more porous but sticks well together.
Figure A18 (left) - Two types of concrete casted at once
Figure A19 (right) - Two types of concrete casted with 30 minutes in between
Figure A20 - Two types of concrete casted with 30 minutes in between.
136
APPENDICES
137
Technology roadmap by Volkers
in
s
tin
g
Technology Road Map
Strategic road map for Additive Manufacturing in Facade Design
In
Fa
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Legend
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Development line
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Step in development
en
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RM
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Phase 3 - Durint the third phase the full benefits of Aditive
Manufacuturing technologies will become apparent. Designs
and developments which are now beyond our imagination will
become feasible and viable. Fully printed archicture is finally
possible.
Relative Timeline
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Phase 2 - The second step will involve the development of
multi-material solutions, layered as well as (functionally)
graded, and transparent glass printing. Nano and macro
printed elements will be available. Most elements are
components in addition to conventional produced building
components.
en
nt
ts
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er
ls
ia
l
1:
Sc
er
pa
s
rt
pa
ku
p
els
od
m
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Phase 1 - The first step of the technical developments in
Additive Manufacturing will lead to intermediate sized
elements (10 um - 100 mm) that can be applied in addition to
existing products. There will experiments with all kind of new
processes, materials and scales, but the first applications will
have to be produced with currently available techniques and its
limitations.
ia
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Positions and concepts are indicative
This Road Map is a snapshot of the situation at a certain
time, from the authors perpective. Positions and concepts
can be differten for different stakeholders and industries.
Step 2
APPENDICES
S3
Super Smart Skin
In this conceptual vision the facade is made of a super
clever, thin, wrapping layer of additive manufactured
building skin. The skin is wrapped around the main
construction and the different ‘pads’ are ‘zipped’
together.
In
Fa
c
te
ad
e
gr
al
Pla
Sk
te
in
Pr
Pa
d
in
s
tin
g
The Super Smart Skin enables freeform design while it
can be formed to appear like any double-curved
surface designed. The skin contains internal
microstructures that can deform the pad in to a
curved surface. It uses the benefits of internal
structures to fulfil a variety of functions. Internal
mechanisms can be used to integrate all kind of
building physical functions like ventilation - provide by
micro fans -, sun shading - provided by little ‘eyes’ - or
insulation value - provided by a adaptive surface
which inflates adaptively to the circumstances.
Fle
x in
te
Fa
c
r fa
ce
s
ad
Co e M
m a
po ch
ne ine
nt
s
The basic functions of a single pad, small or big sized,
needs to be (1) sealing the building (water, air,
energy...), (2) structural (dead load, form) and (3) one
or more additional functions. The pad could have a
‘mono-function’, like only ‘ventilation’ or ‘providing
visibility’ (transparency), or fulfil multiple functions
combined in one pad. The modularity of the facade
depends on the size of the pads.
3D
The pads can ‘stitched’ to the building by a ‘spider
robot’ that zips the building skin around the main
structure. The functions of the skin can be mapped
freely to fulfil the desired functions where the benefit
most. Like putting heat gaining surfaces to the south
facade or (kinetic) energy generating surfaces in a
windy corner.
The Facade Machine
sio
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In this conceptual vision the whole facade is a
Gr
ad
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Su
sp
en
machine, made of ingenious integrated mechanisms
that fulfil all functions needed. The mechanisms make
the facade super adaptive and adaptable. Facade
elements could change form, function and properties
and the facade can ‘open’ itself for maintenance or
replacement, or even to let someone in.
co
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The vision of the ‘Facade Machine’ mostly uses the
benefit of ‘internal structures’ from Additive
Manufacturing, and it covers ‘function integration’
and ‘adaptivity’ from Facade design.The machine can
be regarded as a ‘clock work’, precisely regulating the
functions of the facade. The mechanisms can provide
most of the building physical- / climate installations,
like ventilation and sun shading as well as other basic
functions like ‘opening’.
co
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The facade fittings could be adaptive: when
components have deviations in size, due to tolerances
or temperature, the ‘facade machine’ can adjust to it.
With the facade machine it is not necessary to have
doors, the facade just folds open whenever someone
wants to enter...
FiF
Fully Integral Facade
In this conceptual vision the facade is made of a printed
graded-multi-material structure that fulfils all functions
in one continuous facade layer. The facade could eventually seamlessly go on, into a fully integral building.
The ‘FiF’ vision mostly uses the benefits of ‘graded materials’ and ‘freeform design’ from the Additive Manufacturing aspect, and it covers most aspects from facade
design, although ‘freeform’ and ‘function integration’
are the most important in this concept.
Switch to ‘multi-functionals’
AM machines for RP, RT and RM
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The FiF fully benefits from 3D CAD software with finite
element methods build into it. Engineers design these
facades with parametric models that can be fully
optimized for structural and functional aspects. For
example, structurally the facade can ‘mimic’ nature’s
solutions for structural optimization, like bone structures. For functional optimization one can think of a
graded material which functions as a hinge for opening
parts of the facade. One material than provides both
stiffness as flexibility.
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The Fully Integral Facade is the result of a complex mathematical 3D model that defines where structural
strength and other functions should be positioned. Mastering complex 3D modelling becomes a required skill for
designing facades or buildings. The future fully
integrated facade might be a complex formula and the
context and users define the parameters…
139
140
Additional information
Literature
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mega-scale rapid manufacturing for construction. Automation in
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Figures
[2]
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[4]
Ashby, M., Shercliff, H., & Cebon, D. (2007). Materials: engineering,
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[17,18]
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[37,38]
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Facade design: a strategic roadmap towards a preferable
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[55]
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Samson Uitgeverij NV.
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Tables
[1,2,4]
Berg, v. d., P., Buist, W., Souwerbren, C., & de Vree, R. T. (1995).
Betontechnologie (C. Souwerbre Ed.). ‘s-Hertogenbosch:
Stichting BetonPrisma.
[12]
Volkers, J. N. (2010). The Future of Additive Manufacturing in
Facade design: a strategic roadmap towards a preferable
future. Delft University of Technology, Delft.
[14] Lim, S., Buswell, R. A., Le, T. T., Austin, S. A., Gibb, A. G., & Thorpe,
T. (2012). Developments in construction-scale additive
manufacturing processes. Automation in construction, 21,
262-268.
145
Glossary
146
3DP
3D-printing
AM
Additive Manufacturing
CC
Contour Crafting
Earth dry
Fresh concrete with a very low water cement ratio
FDM
Fused Deposition Modelling
Filament
Line-like material used to extrude
Fresh concrete
Mixed ingredients of the composite before curing
G-code
Code that describes the path of an extrusion head
Green ceramic body
Dried clay element
Green strength
High strength at early life of concrete
LCA
Life Cycle Assessment
LS
Laser Sintering
Plasticizer
Additive in fresh concrete to make it more workable
Polyjet
An AM process that uses multiple nozzles to build a model
Retarder
Additive in fresh concrete to make cure more slowly
Silica
Fine powder that also binds the mixture
Shotcrete
Concrete that is sprayed against objects
SLA
Stereolithography
UHPC
Ultra High Performance Concrete
UHPFRC
Ultra High Performance Fibre Reinforced Concrete
WCR
Water Cement Ratio
Workability
The ease of processing the material
Zappie
A material that has only advantageous properties. This material is used often in
the AE+T department
,seitilibissop sti ,etercnoc fo )MA( gnirutcafunam evitidda eht senimaxe troper sihT
stcudorp rof seitilibissop ehT .seuqinhcet gnitsixe revo segatnavda dna ytilibisaef
noitcudorp gnitsixe gnicalper tsuj tub ,sseldne era ssecorp evitidda na htiw edam
noitcudorp mrofeerf devorpmi hguohtlA .elbissopmi llits si seno evitidda htiw sdohtem
ni modeerf erom taht naem ton seod siht ,hcraeser siht fo mia eht era seuqinhcet
ssecorp MA na ni etercnoC
gnissecorp etercnoc merto
feerF
tiW ed sinneD
ssecorp MA na ni
.tnemom eht ta reffo nac MA taht tnemevorpmi tsegral eht noitinfied yb si mrof
lanoitidart ni snoitcnuf lanoitidda fo noitatnemelpmi eht weiv fo tniop rehtona morF
.eulav taerg fo eb nac stcudorp
tnemelpmi ot redro ni evlove ot sah euqinhcet eht woh snoisivne pamdaor A
eht fo noitaulave na dna saedi tcudorP .etercnoc fo seitreporp citsiretcarahc eht
na eveihca ot stnempoleved eht ot detaler era pamdaor eht ni nwohs seuqinhcet
txen ,euqinhcet noitcudorp MA eht ni htgnerts dna ytilauq ecafrus ,deeps ni esaercni
.erutxim etercnoc hserf gnihctam a gnidrager tes eb ot evah taht stnemeriuqer eht ot
This report examines the additive manufacturing (AM) of concrete, its possibilities,
feasibility and advantages over existing techniques. The possibilities for products
made with an additive process are endless, but just replacing existing production
methods with additive ones is still impossible. Although improved freeform production
techniques are the aim of this research, this does not mean that more freedom in
form is by definition the largest improvement that AM can offer at the moment.
From another point of view the implementation of additional functions in traditional
products can be of great value.
A roadmap envisions how the technique has to evolve in order to implement
the characteristic properties of concrete. Product ideas and an evaluation of the
techniques shown in the roadmap are related to the developments to achieve an
to the requirements that have to be set regarding a matching fresh concrete mixture.
Dennis de Witte | Concrete in an AM process Freeform concrete processing
increase in speed, surface quality and strength in the AM production technique, next
Concrete in an AM process
Freeform concrete processing
Dennis de Witte
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