STONE Newsletter on stone decay

STONE Newsletter on stone decay
ISSN 1754-1026
STONE
No 2 - Aug 2007
Newsletter on stone decay
Abstracts from SWAPNET 2007 & Workshop on
Limestone Decay and Conservation (Malta, 24-26 May)
Contents:
Foreword
Abstracts SWAPNET 2007 & Workshop on Limestone Decay:
Pg 2
Malta: buildings, materials and deterioration
J. Cassar
Pg 3
A geotechnical approach to the formation of the 'cart ruts' of Malta
D. Mottershead, A. Pearson, M. Schaefer
Pg 5
The influence of environmental change in the formation of the 'cart ruts' at Naxxar
D. Mottershead, P. Farres, A. Pearson
Pg 7
Particulate induced short-term modification of temperature and moisture loss from two common UK building stones
Pg 9
D. E. Searle , D.J. Mitchell
Conditions of quantitative repeat photography at the Ashmolean Museum, Oxford
M. J. Thornbush
Pg 11
Surface characterisation of stone structures by HD laser reflectance
J. R. Scott, M. E. Young
Pg 13
Resistance based measurement method for measuring moisture movement in building stone
S. Srinivasan, M. Gomez-Heras, P.A.M. Basheer, B.J. Smith, K.T.V. Grattan, T. Sun, H.A. Viles
Pg 15
Provenance determination of marbles from Czech quarries: a complex analytical approach
A. Šastná, R. Pøikryl
Pg 17
Historic lime mortars: potential effects of local climate on the evolution of binder morphology and composition
K.R. Dotter
Pg 19
Egg shell lime based mortar and criteria of compatibility with a porous limestone
K. Beck, X. Brunetaud, J.D. Mertz, J.P. Bigas, M. Al-Mukhtar
Pg 21
Improving Conservation Practices: An On-line Database of Building Stone in Use for Northern Ireland
C. Adamson, J. Curran, M. Francis, B.J. Smith, P. Warke, J. Savage, D. Stelfox
Pg 22
New insights on the use of crystallization inhibitors as a potential treatment for preventing salt weathering of biocalcarenites
Pg 24
E. Ruiz-Agudo, C.V. Putnis, C. Rodriguez-Navarro
Porous limestone decay; the role of mineralogical changes in crust formation
A. Török
Pg 26
The origins and significance of rapid surface stabilisation of building limestones
B.J. Smith, A. Török, J.J. McAlister, M. Gomez-Heras, H.A. Viles, B. Emery P.A.M. Basheer
Pg 28
Decay in Oxford limestone: observational units and jumping edges
M. Gomez-Heras, B.J. Smith, H.A. Viles
Pg 30
Identifying facies with different weathering properties in Malta's Lower Globigerina Limestone
T. Zammit, J. Cassar, A.J. Vella, A.Torpiano
Pg 32
The influence of design requirements on the durability of porous building stones used in façades. A case study
A. Bernabeu, M.A. García del Cura
Pg 34
Santa Engrácia National Pantheon (Portugal): the Stones and Pathologies
C. Figueiredo, L. Aires-Barros, A. Dionísio, F. Correia, C. M. Soares, M.J. Neto, L.V. Mendonça, J.S. Rodolfo
Pg 36
On site evaluation of "mechanical-physical" properties of the Maastricht limestone
S. Rescic, F. Fratini, P. Tiano
Pg 38
Conservation state of bioclastic limestones: Los Reales Alcázares (Royal Fortress) Palace of Seville (Spain)
C. Vazquez-Calvo, M.J. Varas, R. Fort, M. Alvarez de Buergo
Pg 40
The decay of the calcarenite utilised in the Etruscan tombs of S. Cerbone necropolis (Populonia-Italy)
F. Fratini, E. Pecchioni, P. Pallecchi
Pg 41
Decay forms of limestones used as building materials in Greek monuments
M. Stefanidou
Pg 43
Pore structure and durability of natural stones: a case study
C. Figueiredo, R. Folha, A. Dionísio, A. Maurício, C. Alves, L. Aires-Barros
Pg 45
Weathering effect in urban environment: a case study of a French porous limestone
K. Beck, M. Al-Mukhtar, I. Rannou, X. Brunetaud
Pg 47
Relationship between the durability and fabric of Hungarian porous limestones, a laboratory testing approach
A. Török, Z. Pápay
Pg 49
Physical changes of porous Hungarian limestones related to silica-acid-ester consolidant treatments
Z. Pápay, A, Török
Pg 51
Recording weathering and decay
Ongoing and newly funded projects
News
Pg 53
Pg 56
Pg 57
Contact and submissions:
Dr. M. Gomez-Heras
[email protected]
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No 2 - Aug 2007
Foreword:
This second issue of the newsletter includes the abstracts of the Stone Weathering and Pollution
NETwork (SWAPNET) 2007 & Workshop on bioclastic limestone decay and conservation
organized during 24-26 May by the UK EPSRC “The Limestone Project”, together with Heritage
Malta.
The venue could have not been more appropriate for this event; a historic building completely built
in limestone which hosts Heritage Malta's Conservation Division in Bighi, Malta. This 17th century
villa, later converted into a Royal Navy Hospital, is located between Rinella Bay and Kalkara Creek
and has amazing views to the Grand Harbour.
The event brought together over 60 participants from 11 countries to discuss various issues related
to stone decay, from material characterization to the development of new techniques and protective
strategies.
While the first day of the meeting covered a wide range of stone decay issues, within the framework
of the Stone Weathering and Atmospheric Pollution Network (SWAPNET), the emphasis of the
second day was on limestone decay and conservation, with presentations of the EPSRC
Limestone Project jointly run by Queen’s University of Belfast, Oxford University and City University
of London.
The grand finale of the meeting was an extensive field trip in which the participants had the
opportunity to study the geology of the island at Dingli cliffs, explore the specific conservation
challenges of the World Heritage Site temples of Hagar Qim and Mnajdra and gain insights into the
stone production industry of Malta in a “Globigerina Limestone” quarry at Mqabba/Qrendi.
This meeting also marked the start of this newsletter now circulated to over 550 persons. We
encourage you to send material for future issues of the newsletter, as well as suggestions as to how
its contents could be improved.
MGH & BJS
2
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No 2 - Aug 2007
3
Malta: buildings, materials and deterioration
J. Cassar
University of Malta
Institute for Masonry and Construction Research
Contact e-mail: [email protected]
Buildings
Existing buildings in the Maltese Islands range from
complex megalithic prehistoric temples, to
impressive Baroque buildings and fortifications built
by the Knights of St John, to modern edifices, built of
the local Globigerina Limestone.
The oldest buildings, the prehistoric temples, were
built during the period 3600 - 2400 BC. In the
Mediterranean this is the period which falls between
the Neolithic and the Bronze Age. The best preserved
temple complexes are those of Hagar Qim, Mnajdra,
Tarxien and Ggantija, which are recognised as
UNESCO World Heritage Sites.
Figure 1: One of the elaborate decorated doorways in
Globigerina Limestone in the old city of Mdina (a) and
map of the Maltese islands, showing the main quarry
areas, and Valletta (b).
Materials
The material used in the construction of these ancient
structures is the readily available and abundant local
stone: Globigerina Limestone and Coralline
Limestone. The mode of construction is megalithic,
with stones up to 6.40m long being utilised to build a
series of adjacent curved apses. The external walls
were built of Coralline Limestone, when this material
was readily available in outcrop in the vicinity of the
building site. This material is in fact much used in the
Ggantija temples on the smaller island of Gozo. The
Globigerina Limestone, on the other hand, was much
more widely used in the temples, especially for
internal walls and decorative elements. In some of the
temples, such as that of Hagar Qim, this has also been
used for external walls, as no Coralline Limestone is
here easily available. Globigerina Limestone is also
the material much used by the Knights of St John: the
fortified city of Valletta, is built of Globigerina
Limestone. Even the old capital city, Mdina, is
constructed out of this honey coloured soft limestone.
Mdina, also fortified, possesses palaces and
churches, decorated with elaborate gateways and
doorways (Figure 1a). This limestone is today still
much utilised for building in the Maltese Islands.
Active quarries are to be found mainly to the South of
the main island (Figure 1b).
Composition and properties
Globigerina Limestone is composed of > 90%
calcite. The Insoluble Residue consists primarily of
quartz and clay minerals (Cassar, 2002). It has a very
fine texture, containing numerous microfossils
(planktonic and bentonic foraminiferans), primarily
globigerinae from which the name Globigerina
Limestone derives. The Total Porosity reaches values
up to 41% and the Absorption Capacity is of 20 - 24%
by weight and 34 - 37% by volume; the Saturation
Index is of a maximum of 89% (Vannucci et al.,
1994). During total immersion, the stone will absorb
15% by weight of water in the first 10 minutes.
Deterioration
The main forms of deterioration seen in the Maltese
Islands are alveolisation and powdering (Figure 2).
Many Globigerina Limestone elements in buildings
of all ages also however present a very sound and
compact surface. Causes of deterioration include
intrinsic properties of the material. One can usually
distinguish between the different types of
Globigerina Limestone only after weathering has set
in. Preliminary studies have shown that different
types of Globigerina Limestone have a different pore
size distribution. Environmental causes also play a
great part in the deterioration of these materials; these
include temperature changes, wind, insolation,
humidity, pollution and in particular the presence of
soluble salts. The local environment is typically
Mediterranean, and the air is heavily contaminated
with soluble salts. Other lesser causes of
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No 2 - Aug 2007
4
And a more or less plain surface has developed and
the edges of the blocks become rounded.
The size, orientation and number of bioturbation
which occur also condition the form, extent and depth
of the alveoli thus formed.
References
Cassar, J. & Vannucci, S., 2001. “Petrographical and chemical
research on the stone of the megalithic temples.” In: Malta
Archaeological Review, 5, pp. 40-45.
Figure 3: Pronounced deterioration, including alveolar
weathering (honeycombing) of Globigerina Limestone
deterioration include the clay fraction in Globigerina
Limestone, although small, contains smectite and
illite-smectite, which are expandable minerals
(Cassar and Vannucci, 2001).
A model for the damage processes, initially
suggested by Vannucci et al. (1994) and Fitzner et al.
(1996), distinguished five phases of the damage
development, a model which has been reproposed by
Rothert et al. (2007) as follows:
· Phase 1: the formation of a superficial crust by reprecipitation of dissolved calcite.
· Phases 2 and 3: back-weathering of the stone
surface through the formation of neighbouring
cavities which can be traced back to cracking and/or
partial loss of the crust owing to mechanical stress
provoked by salt crystallization.
· Phase 4: material loss and the formation of alveoli
are very pronounced. Connection of the alveoli
occurs. The septa of the honeycomb structure are
severely back-weathered, but are still recognizable.
· Phase 5: this is the final deterioration state. The
septa of the honeycombs are totally back-weathered
Cassar, J., 2002. “Deterioration of the Globigerina Limestone of
the Maltese Islands.” In: Siegesumnd, S., Weiss, T., &
Volbrecht, A. (eds) Natural Stone, Weathering Phenomena,
Conservation Strategies and Case Studies. Geological Society,
London, Special Publication, 205, pp. 33-49.
Farrugia, P., 1993 “Porosity and related properties of local
building stone.” B.E. & A. dissertation, University of Malta,
unpublished.
Fitzner, B., Heinrichs, K. & Volker, M., 1996. “Model for salt
weathering at Maltese Globigerina Limestones.” In: Zezza, F.
(ed.) Origin, Mechanisms and Effects of Salt on Degradation of
Monuments in Marine and Continental Environments.
Proceedings, European Commission Research Workshop on
Protection and Conservation of the European Cultural Heritage,
Bari, Italy. Research Report, 4, pp. 333-344.
Rothert, E., Eggers, T., Cassar, J., Ruedrich, J., Fitzner, B., &
Siegesmund, S 2007,. “Stone properties and weathering
induced by salt crystallization of Maltese Globigerina
Limestone.” In: Prikryl, R., & Smith, B.J. (eds) Building Stone
Decay: From Diagnosis to Conservation. Geological Society,
London, Special Publication, 271, pp. 189-198.
Vannucci, S., Alessandrini, G., Cassar, J., Tampone, G. &
Vannucci, M. L., 1994. “The prehistoric megalithic temples of
the Maltese Islands: causes and processes of deterioration of
Globigerina Limestone.” (I templi megalitici preistorici delle
isole maltesi: cause e processi di degradazione del Globigerina
Limestone.) In: Fassina, V., Ott, H. & Zezza, F. (eds)
Conservation of Monuments in the Mediterranean Basin.
Proceedings of the 3rd International Symposium, Venice, Italy,
Sopritendenza di Beni Artistici e Storici di Venezia, Italy, pp.
555-565.
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No 2 - Aug 2007
A geotechnical approach to the formation of the 'cart ruts' of Malta
D. Mottershead, A. Pearson, M. Schaefer
University of Portsmouth, Dept of Geography, Lion terrace, Buckingham Building, Portsmouth, UK.
Contact e-mail: [email protected]
The intriguing problem of the origins of the Maltese
cart ruts has hitherto been approached almost
exclusively from the perspective of archaeology,
whereas the application of geomorphology has been
very limited. Geomorphology can make a distinctive
contribution to the study of cart-ruts, which are, in
essence, small-scale erosional landforms.
Previous interpretations of the ruts have been made
by Gracie (1954), Trump (1993), and Venturi and
Tanta (1994), amongst others. Hughes (1999)
provides an excellent summary of the research issues.
An interesting experimental approach was taken by
the BBC (1955). Notably, focused quantitative
information has been lacking, as has consideration of
the material properties of the rock surface and issues
of force and resistance.
The ruts are paired grooves incised into the bedrock
surface. Their outstanding characteristic is the
remarkable constancy of gauge of ca 1.40 m. Depth
varies both across a profile pair, and along their
course, up to a maximum of ca 0.6m. Rut width is
variable from 40 mm up to 150 mm or more. They
exhibit crossing and diverging patterns, and
commonly occur in swarms, often related to a major
landscape feature.
Ruts are erosional forms. This is the major focus of
geomorphology, hence geomorphology is an
appropriate perspective from which to approach their
formation. In this context, erosion processes and
material properties have been hitherto little
considered. Here we present observations of
properties and process, in combination with some
geotechnical concepts.
Overall, the nature of the tractive force responsible
for rut formation remains unresolved, with major
questions remaining as to whether they were eroded
by sliding runners or rolling wheels. The objectives
of this paper are therefore:
1. to examine the geotechnical properties of the rock
surface.
2. to consider force/ resistance relationships, and
3.to reverse engineer a vehicles capable of eroding
the ruts.
Values of uniaxial compressive strength of rock
obtained from the rutted surfaces are variable,
ranging from medium strength to very weak rock.
Point hardness values show that the rock is much
weaker, and therefore more erodible, when saturated.
These values permit the calculation of
stress/resistance relations between vehicle and rock
surface.
The contact between a vehicle and underlying
surface is through the wheel or runner. Assuming a
wheel, its width (or footprint) is indicated by the
narrowest rut cross section. Assuming a two wheeled
vehicle, plane surfaces of both wheel and rock,
perfect clean contact, then the mass of the vehicle
required to cause the rock to fail is given by:
M=
4 wls max
3(9.81)
Where w,l = are width and length respectively of the
wheel/rock contact (m), assumed as 0.04,
0.02 respectively
M = mass of vehicle (kg)
smax = uniaxial compressive strength of
surface rock, as observed (MPa)
For different samples of the local limestones, this
yields values of 0.4 - 9.1 tonnes for the mass of a
vehicle required to cause failure by compression of
the saturated rock surface.
The assumption of perfect plane and clean contacts
is, however, rarely justified under field conditions.
Small surface irregularities and solid particles cause
local stress concentrations at the microscale. A stress
concentration factor of 10 is commonly utilised in
this situation, thus reducing the critical load by a
factor of 10. Estimates of the volume of timber
required to contract a two-wheeled cart of
dimensions to fit the ruts suggest that about 250 kg
would be required. These calculations suggest that he
mass of a cart alone would be sufficient to erode the
rock surface in the case of the weaker rocks present at
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No 2 - Aug 2007
the rut sites, whereas the strongest rock observed
would be damaged by a cart with a minimum load of
0.665 tonnes.
Thus, under wet conditions, when these rocks are at
their most erodible, the passage of a cart alone would
be sufficient to erode the weaker rock surfaces. A load
of just over half a tonne would initiate erosion of the
harder rocks. This in turn implies that the wheeled
vehicular traffic employed would have been able to
carry loads of a small number of tonnes certainly
capable of carrying the quarried rocks at the Clapham
Junction quarries, or moderate volumes of soil or
other commodities.
Similar calculations indicate that a sledge with
runners of 2m length, would require a mass of up to
91 tonnes in order to fail the rocks by compression. It
is very unlikely that such a vehicle could readily slide
6
under such a load, because of high friction, or even
be constructed with timber with a clearance height of
0.6m to carry that load.
References
B B C . 1 9 5 5 . B u r i e d Tr e a s u r e : 2 . Tw o M a l t e s e
Mysteries:13.06.55. BBC Information & Archives: CC 052379.
Gracie, H.S. 1954. The ancient cart-tracks of Malta. Antiquity
28: 91-8.
Hughes, K.J. 1999 Persistent features from a palaeo-landscape:
the ancient tracks of the Maltese Islands. Geographical Journal
165.1, 62-278.
Trump, D.H. 1993. Malta: An Archaeological Guide. Valletta,
Malta: Progress Press.
Ventura, F. and Tanti, T. 1994. The cart tracks at San Pawl tattarga, Naxxar. Melita Historica 11.3: 219-40.
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No 2 - Aug 2007
The influence of environmental change in the formation of the 'cart ruts' at Naxxar
D. Mottershead, P. Farres, A. Pearson
University of Portsmouth, Dept of Geography, Lion terrace, Buckingham Building, Portsmouth, UK.
Contact e-mail: [email protected]
Geomorphological processes of erosion and
deposition cause environmental change. Historical
geomorphology interprets evidence of past
environments and reveals how an environment may
have changed through time. Various authors have
suggested that environmental change in the form of
soil erosion has been a significant factor in Maltese
prehistory (Hughes 1999, Parker & Rubinstein 1984,
Trump 1993).
The planform of the Naxxar ruts can be considered at
two scales. At the macroscale they describe a large
hairpin bend traversing the lower slope of the Upper
Coralline Limestone escarpment, crossing the
contours obliquely towards a gap in the scarp. At the
immediately local scale, however, their relations with
the bedrock topography raise questions about their
specific routes across the exposed rock surfaces. At
one point a pair of ruts cuts through a bedrock step
0.5m in height, despite the fact that a much easier
route nearby offers a ramped climb up the same step.
Nearby, one track of a pair of ruts intersects a vertical
shaft descending several metres down into the rock;
at the same point a diverging pair of ruts appears to
offer a by-pass route around the shaft, although
ultimately unsuccessful because it does not take a
sufficiently wide deviation.
In difficult terrain such as this, it would be sensible
for the ancient carters to adopt the most energyefficient route. The relationships noted above,
however, suggest that the tracks do not take the
Time Nature of surface
optimum route in relation to the obstacles presented
by the bedrock topography. This then raises the
question as to whether the tracks were initiated on the
present ground surface, or whether there has been
significant environmental change between the
establishment of the routes, and the present state of
the surface.
Within sight of the cart ruts themselves, a quarry
section exposes the relationships between the relief
of the bedrock surface (rockhead relief), sediment
infill and the present ground surface. This section
traverses a valley floor eroded into the Upper
Coralline escarpment, a site that favours both the
accumulation and preservation of sediment from the
laterally convergent valleyside slopes. It serves as an
analogue for nearby rock surfaces from which
surficial sediment has been removed.
Rockhead relief (Fig.1) is shown to be highly
irregular, with a tabular morphology pitted with
broad basins >2 m across and near-vertical shafts up
Route selection
Surface development
t0
Smooth ground surface over soil;
occasional rises and hollows.
Variable vegetation cover.
Route selection favours less
densely vegetated areas on a
uniform ground surface.
Ruts develop in the silt/clay soil,
with graded floors, and will attract
subsequent traffic.
t1
Knolls and plateaux of bedrock
appear, separated by soil-filled
hollows carrying rutted trackways.
Traffic will follow existing ruts on
to the intermittent bedrock
outcrops.
Bedrock outcrops start to become
rutted. Hollows deepen as the
sticky clay is walked out by passing
t2
Irregular surface of bedrock widely
exposed, revealing hollows and
deep shafts.
Rutted tracks become laterally
uneven; deep shafts need bypassing.
Bedrock surface hardens and
fossilises.
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No 2 - Aug 2007
to >2m deep. these are filled with unbedded
sediments dominated by clay and fine silt, identical in
granulometry and clay minerals to insoluble residue
derived from the local bedrock. The surface layer
suggests that it additionally contains windblown
material.
Figure 1 also presents an interpretation of how the
surface, assuming an initial overall soil cover, would
develop through time under conditions of
progressive erosion. At time t0, the ground surface is
formed exclusively of soil, with a covering of natural
vegetation, varying perhaps in magnitude and
density. At time t1, tabular areas of bedrock become
exposed, separated by sediment-filled areas
indenting the bedrock surface. Vehicular tracks pass
both over soil and rock surfaces, initiating rut erosion
in bedrock where it is now exposed. At time t2,
continuing erosion of the depressions causes them to
become hollowed out and difficult to traverse. This
sequence of changing conditions is summarised in
Table 1.
8
This model contends that the ruts are initiated on a
soil cover. Environmental change though progressive
erosion of that cover creates changes in the form and
nature of the ground surface. The vehicle tracks thus
become superimposed on to the bedrock surface, and
subsequently incised into it, in ways which are
discordant to the local topography of the rockhead
relief.
References
Hughes, K.J. 1999 Persistent features from a palaeo-landscape:
the ancient tracks of the Maltese Islands. Geographical Journal
165.1, 62-278.
Parker, R. and Rubinstein, M. 1984 The cart-ruts on Malta and
Gozo. Malta: Gozo Press.
Trump, D.H. 1993. Malta: An Archaeological Guide. Valletta,
Malta: Progress Press.
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Particulate induced short-term modification of temperature and moisture loss from two
common UK building stones.
1
D. E. Searle , D.J. Mitchell
2
1 School of Engineering and the Built Environment, University of Wolverhampton, UK.
2 School of Applied Sciences, University of Wolverhampton, UK.
Contact e-mail: [email protected]
A
C
C
B
B
D
A
D
B
C
D
A
occur from the change in surface albedo due to the
presence of particulate. All samples were coated with
coal and diesel particulates both separately and in
combination as shown in Figure 1
Drying study: Differences were observed in the rate
of moisture loss after the different particulate
treatments had been applied. There was evidence,
some of it strong (P<0.010), that the rate of moisture
loss was increased on the diesel treated limestone
samples during the first two hours of drying (Figure
2).
5
Mean moisture loss, n=3 (g)
Urban particulate pollution that results from the use
of fossil fuels has a long history of affecting stone
buildings and monuments in the UK. Where the
nature of the particulate itself has evolved from being
coal derived industrial and domestic sources to being
dominated from those resulting from vehicular
sources, primarily diesel, they both have negative
effects. Movement of moisture and variation of
temperature an important role in weathering
processes either directly in the form of insolation
weathering and wetting/drying cycles or indirectly
by facilitating the movement of salts and enhancing
chemical processes.
4
3
2
1
0
A: Untreated Portland Limestone.
B: Portland Limestone + diesel particulate
(coverage: 0.38 mg cm-2).
C: Portland Limestone + coal particulate
(coverage: 0.38 mg cm-2).
D: Portland Limestone + coal/diesel combination,
50:50 ratio (coverage: 0.38 mg cm-2).
Figure 1: Treated samples used for rate of drying study,
showing colour differences due to treatment.
A comparative experimental design was used, which
compared the mass of water loss and temperature
variations, over time, between stone samples with
different particulate treatments. The experiment was
carried out under controlled environmental
conditions, designed to simulate a set of `average`
meteorological conditions in a typical UK urban
centre. In particular, an attempt was made to explore
any changes in the rate of moisture loss that might
0
5
10
15
20
25
Time (Hours)
Portland Limestone - diesel (pre-treatment)
Portland Limestone - diesel (post treatment)
Figure 2: Treated samples used for rate of drying study,
showing colour differences due to treatment.
Surface temperature study: Figure 3 represents
surface temperature logged at five-minute intervals
over an approximate 24-hour period. Post hoc
analysis of the ANOVA's for the Portland Limestone
showed strong evidence (P<0.010) that the dieselcoated samples have higher surface temperatures
than both the control and the other treatments, under
the same environmental conditions. Excess mean
surface temperatures of approximately +2.2ºC,
+1.8ºC and +1ºC were recorded for the diesel
treatment, when compared to the control, coal and
coal/diesel combination, respectively.
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No 2 - Aug 2007
After the 23-hour heating period, the heat source was
removed and surface temperatures were continued to
be monitored at five-minute intervals for an
approximate period of 40 minutes. The values
obtained for each sample group and the rate of heat
loss is shown in Figures 4. The diesel treatment
appears to be losing heat at a greater rate than the
other sample groups in the initial stages of cooling.
40,0
Temp (oC)
35,0
Increase the thermal absorption of the surface. The
diesel coated Portland Limestone samples are
considerably darker than the other sample groups.
Predictably this resulted in the lower albedo and
hence the significantly higher (P<0.05) temperatures
seen on these samples.
The temperature differences obtained between the
untreated and the diesel coated Portland samples
were around 2-3ºC. The enhanced temperatures seen
on the diesel-coated samples correspond to the
significantly increased (P<0.05) moisture loss
observed in the first few hours of heating. In addition
they heated up quicker, maintained higher surface
temperatures and cooled down quicker than the other
sample groups.
30,0
Untreated control
diesel (post treatment)
coal (post treatment)
coa/diesle (post treatment)
25,0
5
10
15
20
Time (hours)
Figure 3: Mean surface temperature of Portland
Limestone samples under a radiant heat source.
When light absorbing particles such as diesel or coal
particulate accumulate on a surface, a reduction
occurs in the amount of solar electromagnetic
radiation reflected from the surface. This can also be
termed as a reduction in the reflection coefficient,
solar reflectance or albedo of the surface, which will
Untreated control
diesel (post treatment)
coal (post treatment)
coal/diesel (post treatment)
35,0
25
Temp (oC)
0
25,0
heating
sw itched
off
15,0
23,0
23,5
24,0
Time (hours)
Figure 4:
Mean surface temperature of Portland
Limestone samples after removal of heat source.
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No 2 - Aug 2007
11
Conditions of quantitative repeat photography at the Ashmolean Museum, Oxford
M. J. Thornbush
School of Geography, University of Oxford. Oxford University Centre for the Environment, Oxford, UK.
Contact e-mail: [email protected]
The paper examines the quantitative use of repeat
photography (rephotography) using simple digital
cameras. It provides a review of colorimetric
research in which reflectance is used to assess
changes in surface soiling (e.g., Pio et al., 1998;
Grossi et al., 2003) and also considers chromametric
instruments employed in these studies, including
chromameters (e.g., Minolta CR200 used by Urzì and
Realini, 1998 and Minolta CR-300 by Prieto et al.,
2004), spectrophotometers (e.g., Minolta CM-2002
by Fort et al., 2000 and Minolta CM2600D by
Franceschi et al., 2006), and other portable systems
(e.g., Dr Lange Colorpen used by Feliu et al., 2005).
Other instruments being used in image-based
quantitative research include video cameras (e.g.,
static grey-tone CCD images for a quantitative
texture analysis by Maurício and Figueiredo, 2000
and to capture brightness differences of pixels in
greyscale of various polished rock specimens by
Erdogan, 2000), and photographic cameras (e.g.,
photography employed by Durán-Suárez et al., 1995
and by Searle, 2001, who included a large greyscale
in photographs of building façades for calibration).
Thornbush and Viles have various published studies
in the area of quantitative rephotography in central
Oxford, UK. In 2004, they introduced a histogrambased approach to measuring areal surface soiling
and patterns on stone discs (Thornbush and Viles,
2004a, 2004b). Subsequently, from a detailed
archival study at Magdalen College in Oxford,
Thornbush and Viles (2005) discovered that it was
very difficult to quantify soiling of surfaces through
the use of archival photographs chiefly because they
lack fixed vantage points that are close-up. More
recently, Thornbush and Viles (2007) used
photographs with greyscale calibration for
measuring changes in the dimensions of decay
features (namely, blisters) at Worcester College,
Oxford. Thornbush and Viles (in press a) used a
qualitative approach because of the uncertainty
around greyscale calibration. However Thornbush
(in press b) confirmed that the greyscale calibration
of images improves the comparability of colour
measurements with spectrophotometric data. She
also tested for different lighting conditions and
concluded that overcast conditions are best for
quantitative photography rather than images taken
under a clear sky.
With this background in mind, a case study of the
Ashmolean Museum located in central Oxford is
presented with quantitative rephotography as the
selected methodology for this study.
Digital
photographs were taken under different outdoor
lighting conditions (clear vs. overcast sky) at the
southern façade of the Ashmolean Museum in the
spring of 2005 and subsequently in 2007.
Spectrophotometric data taken in the winter of 2006
were used to calibrate the photographs and Lab Color
images were processed in Adobe Photoshop (Version
7.0) for histogram-based measurements of soiling at
the façade scale.
The results convey that the southern façade of the
building appeared darker in 2005, with a lower L*
(lightness ranging from black = 0% to white = 100%)
value, especially at the east elevation. After being
cleaned in 2006/7, the building façade becomes
brighter and both elevations have a similar
colouration. Findings also show that L* values are
more affected by outdoor lighting conditions than
chromatic values a* (ranging from red = 0% to green
= 100%) and b* (ranging from blue = 0% to yellow =
100%) that are mostly unaffected.
In conclusion, the method presented in this paper can
be used to measure surface colour change at the
façade (building) scale to quantify levels of soiling
(black-white) as well as color changes (e.g., greening
indicated by an increase in a* or yellowing after
cleaning will increase b*). Though outdoor lighting
seems to affect surface lightness, colour parameters
are not very affected by different outdoor lighting
conditions. Some problems still need address, such
as the effect of architectural features (e.g. columns)
and glare from windows as well as calibration using
only 3 points and taken only at the west elevation, a
limited temporal range of 2 years of survey, and the
use of different cameras. These problems will be
thoroughly examined in future research, including
application to a plain façade (without any
architectural features or windows); an examination
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of the impact of using different cameras (both nikon
digital cameras namely, 950 and S4); possibly testing
another calibration procedure that is fast, simple, and
easy to use; and applying this method to measure
biological growths and track the colonization of
surfaces.
References
Durán-Suárez, J., García-Beltrán, A., and Rodríguez-Gordillo,
J., 1995. Colorimetric cataloguing o f s t o n e m a t e r i a l s
(biocalcarenite) and evaluation of the chromatic effects of
different restoring agents. Science of the Total Environment,
167: 171-180.
Erdogan, M., 2000. Measurement of polished rock surface
brightness by image analysis method. Engineering Geology, 57:
65-72.
Feliu, M.J., Edreira, M.C., Martin, J., Calleja, S., and Ortega, P.,
2005. Study of various interventions in the façades of a
historical building methodology proposal, chromatic and
material analysis. Color Research and Application, 30: 382390.
Fort, R., Mingarro, F., Lüpez de Azcona, M.C., and Rodriguez
Blanco, J., 2000. Chromatic parameters as performance
indicators for stone cleaning techniques. Color Research and
Application, 25: 442-446.
Franceschi E, Letardi P, and Luciano G., 2006. Colour
measurements on patinas and coating system for outdoor bronze
monuments. Journal of Cultural Heritage, 7:166-170.
Grossi, C.M., Esbert, R.M., Díaz-Pache, F., and Alonso, F.J.,
2003. Soiling of building stones in u r b a n e n v i r o n m e n t s .
Building and Environment, 38: 147-159.
Maurício, A. and Figueiredo, C., 2000. Texture analysis of greytone images by mathematical morphology: a non-destructive
tool for the quantitative assessment of stone decay.
Mathematical Geology, 32: 619-642.
Pio, C.A., Ramos, M.M., and Duarte, A.C., 1998. Atmospheric
aerosol and soiling of external surfaces in an urban
environment. Atmospheric Environment, 32: 1979-1989.
12
Prieto, B., Silva, B., and Lantes, O., 2004. Biofilm
quantification on stone surfaces: comparison of various
methods. Science of the Total Environment, 333: 1-7.
Searle, D.E., 2001. The Comparative Effects of Diesel and Coal
Particulate Matter on the Deterioration of Hollington Sandstone
and Portland Limestone. D.Phil. thesis, University
of
Wolverhampton.
Thornbush, M. and Viles, H., 2004a. Integrated digital
photography and image processing for the quantification of
colouration on soiled surfaces in Oxford, England. Journal of
Cultural Heritage, 5(3): 285-290.
Thornbush, M.J. and Viles, H.A., 2004b. Surface soiling pattern
detected by integrated digital photography and image
processing of exposed limestone in Oxford, England. In: SaizJimenez, C. (ed.), Air Pollution and Cultural Heritage, pp. 221224. A.A. Balkema Publishers, London.
Thornbush, M. and Viles, H., 2005. The changing façade of
Magdalen College, Oxford: Reconstructing long-term soiling
patterns from archival photographs and traffic records. Journal
of Architectural Conservation, 11(2): 40-57.
Thornbush, M.J. and Viles, H.A., 2007. Photo-based decay
mapping of replaced stone blocks on the boundary wall of
Worcester College, Oxford. In: Pøikryl, R. and Smith, B.J.
(eds.), Building Stone Decay: From Diagnosis to
Conservation, pp. 69-75. Geological Society, London, Special
Publications, 271.
Thornbush, M.J. and Viles, H.A., in press a. What can repeat
photography tell us about soiling and decay of roadside walls
over a six-year period?: A study combining qualitative
comparisons
and image processing techniques. Building
and Environment.
Thornbush, M., in press b. Grayscale calibration of outdoor
photographic surveys of historical stone walls in Oxford,
England. Color Research and Application.
Urzì, C. and Realini, M., 1998. Colour changes of Noto's
calcareous sandstone as related to its colonisation by
microorganisms. International Biodeterioration and
Biodegradation, 42: 45-54.
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13
Surface characterisation of stone structures by HD laser reflectance
J. R. Scott, M. E. Young
Scott Sutherland School of Architecture and Built Environment, Robert Gordon University, Aberdeen, UK.
Contact e-mails: [email protected], [email protected]
Building Information Management and visualisation
tools have created, with the introduction of laser
scanners, an opportunity to rapidly and accurately
render large spaces and building facades into 3-d
through the creation of dense point clouds of surface
data. These tools allow the surveyor to render space
internally and externally with precision by creating
an object where the information is determined by
surface reflectance and can be exactly measured.
This, arguably, makes quantifying soiling patterns,
roughness, colour, tooling and other factors,
possible. Over time, visualisation tools can be used to
determine the rate of change of physical
characteristics which affect surface reflectance.
Laser scanning technology has the potential to
contribute much more information than simple
physical modelling to the development of
maintenance stratagems for building facades. Further
investigations are required to develop the full
potential of visualisation tools in the field of building
surveying. This research will be using a Leica HDS
3000 laser scanner for characterising surfaces of
stone buildings with the aim of determining how a
range of factors influence reflectance: e.g.
roughness, porosity, moisture levels, colour, soiling,
grain size, shape and orientation.
The local building material in Aberdeen is granite. It
is used for over 95% of buildings constructed before
1945. Aberdeenshire granites were produced from a
few granite masses. The two most important units are
the “Aberdeen Granite”, source of Rubislaw granite
and the “Kemnay Granite”. Rubislaw and Kemnay
granites are muscovite-biotite granites with low
porosity and negligible permeability. Loanhead
granite was also quarried within the city from
superficial, weathered deposits and has extensive
development of secondary muscovite along grain
boundaries. Loanhead granite is weak and
significantly more permeable than Rubislaw and
Kemnay granites.
Many of the city centre buildings date from the 1820s
to the 1890s and these are constructed of good quality
granite from deep quarries - granite it is the
predominant local building material and is used for
(a) A sandstone block, (b) point cloud data showing
elevation of points above reference plan and (c) the
surface elevation map derived from this data.
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structural stonework, cladding and paving. While
many buildings remain in sound condition, surface
deterioration of the granite is becoming particularly
noticeable in Aberdeen city centre. There is an
association between the degree of decay & traffic
volumes, implying that vehicle pollution, perhaps in
conjunction with sea salts, may be a primary cause of
deterioration. Comparing the condition of facades in
polluted and unpolluted areas shows that granite
buildings in more polluted streets are in a
significantly worse condition than those elsewhere.
Initial investigations to establish the potential of laser
scanning suggests that useful data may be obtained
from reflection intensity data. The intensity has the
potential to yield useful information about surface
characteristics as distinctions can be made between
clean, soiled and decayed granite surfaces.
Manipulation of the colour display of intensity can
highlight particular areas. Further investigations are
required to determine the full potential of this
information. Interpreting differences in intensity is
complex and information may be affected by factors
such as differences in intensity ranges between scans.
But the data have the potential to yield useful
information about surface characteristics. This could
be useful for quantifying surface coverage of decay
or soiling types or for getting information from areas
which are difficult to access.
Point cloud information provides a 3-dimensional
representation of surfaces and has great potential for
calculating the amount and rate of surface erosion.
By defining a reference plane the point cloud can
show the elevation of points relative to this plane and
14
the point cloud can be used to define a stone or
building surface, producing a surface elevation map.
By defining a high point and a reference plane we can
calculate the volume of stone which is missing below
that surface by this means it should be possible to
calculate how much material has been lost from
eroded stone blocks and to follow the progress of
stone decay by scanning the same areas over a period
of time.
While the technique seems likely to yield useful
information on the amount of stone decay and surface
loss on granite buildings there is still a good deal of
work to be done to establish a sound methodology
measuring, for instance, the degree of error in
measurements and the methodology for defining the
reference plane from which calculations will be
made.
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Resistance based measurement method for measuring moisture movement in building stone
S.Srinivasan1,2, M. Gomez-Heras2, P.A.M. Basheer1, B.J. Smith2, K.T.V. Grattan3, T. Sun3, H.A. Viles4
1 School of Civil Engineering, 2 School of Geography, Archaeology & Palaeoecology. Queen’s University Belfast, UK.
3 School of Engineering and Mathematical Sciences, City University, London, UK.
4 Oxford University Centre for the Environment. Oxford University, UK.
Contact e-mail: [email protected]
Although much research has concentrated on the
deleterious effects of atmospheric pollution on stone
and other masonry materials, the locally significant
contribution of salts derived from rising groundwater
(figure 1) has received relatively less attention. Yet, it
is likely to be much more pervasive than pollutionspecific decay and will continue irrespective of
improvements in air quality. Therefore it is important
to monitor the water ingress and moisture movement
in order to control the degradation processes in
building stones.
method the change in electrical resistance due to
capillary rise of water was measured between two
electrodes embedded in stone. The electrodes were
made of stainless steel pin of 1.3mm diameter and
50mm in length sleeved to expose 5mm of tip (as
shown in figure 2 b). Along with the pair of electrodes
a thermistor was also placed to monitor temperature
changes at the vicinity of electrodes inside stone. The
electrical resistance between the pair of electrodes
was measured with the help of an LCR Data Bridge
and switching from one electrode pair to another was
carried out using a switch unit (figure 2 a). The data
logging was done using Datataker DT80.
a
b
Figure 1: Groundwater rise and associated salts can lead
to complex patterns of decay close to ground level.
One of the methods of monitoring the moisture
ingress in concrete is by using electrical resistance
method, for example the system developed by
McCarter et al. (1995). This system was adapted and
modified for monitoring the stone masonry. In this
Figure 2: Experimental
setup for monitoring the
capillary suction using
electrical resistance method
(a). Stainless steel
electrodes along with
thermistor (b).
The electrodes were oriented in two different
directions, parallel and perpendicular to the moisture
front in an attempt to compare the performance of the
two orientations because in most of the earlier work
done in concrete the electrodes were embedded
perpendicular to the moisture front, whereas in the
case of masonry structures there are practical
difficulties with this orientation.
In this paper, the scientific basis and the construction
of electrodes for monitoring moisture are described
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and the results of the experimental investigations are
presented and discussed. In figure 3a the electrical
resistance versus time plot for the two orientations
are similar and figure 3 b shows the time at which the
moisture front reached the electrodes (spikes in the
graph) for the two orientations. Based on these results
it can be concluded that the electrodes oriented
parallel could successfully monitor the moisture
a
Perpendicular orientation
ingress, but further work is needed to compare the
two arrangements.
References
McCarter W.J. et al. (1995) Properties of concrete in the cover
zone: developments in monitoring techniques., Magazine of
Concrete Research, 47, No. 172, Sept., 243-251
b
Parallel orientation
10.00
Perpendicular orientation
Parallel orientation
0.40
Differentiation of Electrical Resistance
9.00
Electrical Resistance (ohms)
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No 2 - Aug 2007
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
0
200
400
600
800
1000
Time (mins)
1200
1400
1600
1800
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
-0.15 0
200
400
600
800
1000
1200
1400
-0.20
Time(mins)
Figure 3: Data of electrical resistance as measured between the electrodes (a) and rate of change of resistance with time (b)
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17
Provenance determination of marbles from Czech quarries: a complex analytical approach
A. Šastná, R. Pøikryl
Institute of Geochemistry, Mineralogy and Mineral Resources,
Faculty of Science, Charles University in Prague, Albertov 6, 128 43, Prague 2, Czech Republic.
Contact e-mail: [email protected]
Czech Republic is rich in numerous varieties of
crystalline marbles that have been used on local
monuments from early medieval times. Similarity in
macroscopic appearance and overall mineralogical
composition do not allow precise sourcing of the
material without use of more complex analytical
approaches. Another limitation is low amount of
material from monuments available for the analysis
which restricts the selection of analytical techniques.
Based on previous results the combination of
geochemical and mineralogical-petrographic
methods (stable isotopes (SIRA), optical microscopy
(OM), cathodoluminescence (CL), image analysis
(IA)) was applied to crystalline limestones (i.e. true
marbles) from the Czech Republic. As it turned out
the unconventional methods (e.g. Raman
microspectrometry (RM) or physical properties like
magnetic susceptibility (MS)) are very useful for the
provenance studies concerning impure calcite or
dolomite marbles.
The study has been conducted on selected samples
from different metamorphic units of the Bohemian
Massif (Figure 1). Mineralogical-petrographic
characteristics of sampled marbles permit a
distinction in terms of macroscopic and microscopic
description of different types of marbles from
quarries i.e. identification of structure, average size,
area, shape, zoning, chemical and volume
composition of carbonate grains (OM, CL, IA).
Stable isotope ratio analysis of carbonates in the
groundmass and genetically different secondary
Figure 1: A simplified geological map of the Bohemian Massif with sampled areas (1-Krkonoše-Jizera Terrane, 2-Lugicum
and Silesicum, 3-Moldanubian zone and Moravicum 4-Kutná Hora Crystalline Complex and Sedlèany-Krásná Hora
metamorphic “Islet”.
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veins proved that C and O isotope data can vary
significantly within one sample. The oxygen isotopic
shifts in secondary veins of studied marbles are most
likely caused by exchanges with metamorphic,
magmatic or even meteoric fluids. sotopic analysis
requires only minute quantities of material, which is
the main advantage of this method. From d13C and
d18O carbonate veins the danger of an erroneous
determination of provenance of marble artefacts is
evident (especially small artefacts, where the
groundmass is undistinguishable from veins). Raman
microspectrometry is very useful method for samples
containing metamorphosed organic matter.
Structural information of the carbonaceous matter
allowed discrimination among different types of
“graphitic“ marbles with various degree and type of
metamorphism. Three general types of Raman
spectra confirm differences between well-ordered
carbonaceous matter including graphite of highergrade regional metamorphosed marbles and rather
amorphous organic compounds (disordered
carbonaceous matter) of low-grade regional
metamorphosed (Figure 2, b) and contact
metamorphosed marbles. The majority of studied
marbles exhibits low values of the bulk magnetic
susceptibility, with the exception of those from
Raspenava (Krkonoše-Jizera Terrane) (Figure 2, a),
Horní Lipová (Silesicum) and Skoupý (SedlèanyKrásná Hora metamorphic “Islet”) in which
a
18
magnetite or pyrrhotite are present. The bulk
magnetic susceptibility measurement is useful
additional method for provenance studies, when
marbles with different magnetic characteristics are
compared. The majority of pure white marbles is
diamagnetic and therefore this method based on
physical properties of samples is redundant for them.
For provenance studies the most important factors
are (a) the amount of a sampled material from
historical artefacts and (b) the sort of analytical
techniques and their predicative ability. The results
obtained indicate, that the most effective and
discriminant way to search for the origin of pure
white marbles is the combination of petrographic
methods with the stable isotope analysis. The optical
microscopy with the combination of the image
analysis (fabric, grain size, mineralogical
composition etc.) is probably the best first step in an
attempt to determine the provenance. After that
cathodoluminescence with the isotope geochemistry
may be used. The uconventional methods (e.g.
Raman microspectrometry (RM) or physical
properties like magnetic susceptibility (MS)) are
very useful for impure calcite or dolomite marbles
which include silicates, magnetic minerals and/or the
organic matter transformed due to various degree of
metamorphism.
b
Figure 2: Different types of marbles from the Krkonoše-Jizera Terrane (Bohemian Massif, Czech Republic). A Dolomite
marble with serpentine veins (ophicalcite) and magnetite from Raspenava. B “Graphitic” marble with calcite veins from
Horní Hanychov. The real slabs size is 15 x 10 cm (lenght x width).
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19
Historic lime mortars: potential effects of local climate on the evolution of binder
morphology and composition
K. R. Dotter
School of Geography, Queen's University Belfast, Belfast, UK.
Contact e-mail: [email protected]
This work explores some preliminary observations
on potential effects of local climate conditions on the
evolution of binder morphology and composition or
mineralogy of historic lime mortars. By examining
the effect of climate on lime mortars, conservators
can improve identification and condition assessment
of historic lime mortars, better understand causes of
damage and decay attributed to previous mortar
repairs, and formulate better conservation mortars to
improve protection and conservation of our
architectural heritage.
Lime mortar samples were collected from a group of
buildings of similar age, but from three distinct
climate regions, to investigate possible changes in
lime mortar due to climatic conditions. The climate
regions and their associated buildings are:
· Arid Desert - Three buildings (c. 1900) at Fort Bliss
U.S. Army Air Defense Artillery Center in El Paso,
Texas, USA.
· Tropical Wet - Phillips House (c. 1840) in Bay St.
Louis, Mississippi, USA.
· Humid Subtropical/Continental - Two houses (c.
1840 and c. 1900) in Staunton, Virginia, USA, and the
Grandma Moses House (c. 1840) in Verona, Virginia,
USA.
Figure 1. Black voids of desiccation cracks as seen in an
Arid Desert climate sample (BSE).
Another set of mortar samples was collected from
buildings in similar climates, but of significantly
older ages, to look at climate-related temporal
changes. These include:
·
Humid Continental, 16th century - Cesis
Castle (c. 1540) in Cesis, Latvia.
·
Maritime Temperate, 16th - 17th century Bonamargy Friary (built c. 1500, second phase c.
1620; documented fire in 1584) near Ballycastle,
Northern Ireland, UK.
The samples were then prepared for the selected
analytical techniques. Small pea-sized chunks of
samples were mounted onto metal stubs and gold
sputter-coated for scanning electron microscopy with
energy-dispersive spectra analysis (SEM-EDS).
Blocks were vacuum-impregnated with blue-dyed
epoxy, and then thin sectioned for polarised light
microscopy (PLM) and point count analysis.
Afterwards, the thin sections were carbon-coated for
backscattered electron imaging (BSE).
Regarding the climate region samples, the analyses
reveal some intriguing results. Point counts show the
percentage of total porosity comprised by desiccation
cracks increased with increasing aridity. The Arid
Desert samples average 65% and the Humid
Subtropical/Continental samples average 58%,
whereas the Tropical Wet samples average 22% total
porosity from desiccation cracks. Lime binders cure
through carbonation, which is facilitated by exposure
to moisture. Lack of moisture, due to climatic or
enclosed conditions, encourages drying-out and
formation of desiccation cracks in the lime binder
(Figure 1). While this may in part be attributed to
construction techniques, these results indicate there
exists a correlation between climate and desiccation
crack porosity. SEM-EDS analysis shows the
presence of environmental contaminants, in this case
chloride, is related to climate as well. The samples
from the Tropical Wet climate have a significantly
higher percentage of chloride in their chemical
composition. Moisture percolating through the
binder deposits various contaminants. This can
impact the mineralogy of the binder by encouraging
growth of destructive minerals, such as calcium or
sodium chloride. SEM-EDS analysis also highlights
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a unique characteristic of lime mortars: autogenous
healing. The calcium-based mineralogy of lime
binders facilitates filling of microcracks. Water
percolates through the binder, dissolving calcite
which eventually reprecipitates along the flow path.
If enough atmospheric moisture is present, this selfhealing mechanism allows buildings to absorb and
adjust to stress caused by settlement, or even
experience traumatic events such as mild
earthquakes, without sacrificing long-term stability.
Figure 2. Entrenched pores with increased cementation,
believed to cause liesegang band-like weathering (Cesis
sample, BSE).
When applied to the temporal samples, further
interesting results arise from the analyses. PLM and
SEM-EDS reveal changes in crystal morphology
over time. Small, anhedral to euhedral crystals (25mm) become larger and more platy (10-20mm) with
age. BSE analysis reveals mineral enrichment along
pore networks. Over time, pore waters deposit
minerals in the interstices of the medium through
which it passes. This leads to localised enrichment
along pore paths, shown in the BSE image as light
grey aureoles around black voids in the binder
(Figure 2). This can lead to concentric zoning, similar
to Liesegang bands, of more highly cemented
20
areas alternating with less cemented areas within
lime mortar and render over time, which results in a
distinctive weathering pattern (Figure 3). Analysis
also reveals growth of new mineral species within the
mortars as age progresses, leading to a series of
secondary cements such as euhedral calcite and
acicular magnesite or hydromagnesite. Finally, the
X
analysis results reveal the presence of organicsourced vesicles (hair, straw, etc.). When subjected to
fire, organic fillers like hair and straw exceed their
ashing point temperature. The ash is then washed out,
either through natural weathering or sample
preparation, leaving behind distinctively shaped
vesicles.
From this research, we can draw several preliminary
conclusions. Climate likely influences the evolution
of lime mortars by increasing the quantity and extent
of desiccation cracks in more arid environments;
altering the porosity distribution; and sourcing
contaminants which alter mineralogy. Climate also
impacts temporal variations by affecting binder
crystal morphology; entrenching pore networks; and
facilitating or impeding growth of secondary
cements. Ongoing research seeks to better explain
these research results, and to further explore the roll
of local climate on mortar morphology and
mineralogy.
Figure 3. Liesegang band-like weathering of render (wall
in Mdina).
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21
Egg shell lime based mortar and criteria of compatibility with a porous limestone
K. Beck1, X. Brunetaud1, J.D. Mertz2, J.P. Bigas3, M. Al-Mukhtar1
1 Centre de Recherche sur la Matière Divisée, Université d'Orléans - CNRS-CRMD, France.
2 Laboratoire de Recherche sur les Monuments Historiques, LRMH. Champs-sur-Marne, France.
3 Laboratoire Mécanique et Matériaux de Génie Civil, Université de Cergy-Pontoise, France.
Contact e-mail: [email protected]
This publication deals with the criteria of
compatibility of an appropriate lime-based mortar for
use with a porous limestone. Indeed, it is well known
that the decay process of stones in monuments also
depends on the type of mortar used. So, the
compatibility of mortars with stones remains a key
factor in the restoration and preservation of
monuments. The studied building stone is the white
tuffeau, which is commonly used in most of the
monuments built along the Loire valley in France
(Loire Castles). This porous limestone (porosity
about 45%) is very sensitive to atmospheric
conditions (pollution, salts, water movements…).
Mortars studied in this work are composed of a
powder resulting from the sawing of Tuffeau as
aggregate in order to develop the quarry waste (stone
powder). Moreover, the use of stone powder is
interesting in order to improve compatibility with the
tuffeau stone used.
limestones masonries. figure 1 shows the stage of the
egg shell lime manufacture. egg shells are heated
1000 °c (calcination temperature) then are hydrated
with water at the extinction stage.
The different parameters influencing the stonemortar compatibility are the aesthetic aspect (color,
texture…), the chemical compatibility (soluble salt
content, pH…), the mechanical properties
(compressive strength, tensile strength, adhesion
force…), and especially the water transfer properties
(water retention capacity, capillary absorption, water
permeability, vapour permeability…). Water transfer
properties and mechanical behaviour of the mortars
are optimized at the formulation step. Based on these
studies, some key guidelines are provided to ensure
that a mortar that is compatible with the properties of
tuffeau can be prepared and used for construction and
restoration of monuments.
Different binders can be used for the formulation of
mortar as commercial limes (hydraulic lime NHL2 or
hydrated lime CL90) and an original egg shell lime.
The very fine part of the stone powder provides clay
minerals and reactive silica that interact with
hydrated lime as pozzolanic reaction that produce CS-H and C-S-A-H. As a consequence, a mix between
hydrated lime and the stone powder results in
properties comparable with those of a natural
hydraulic lime.
Commercial hydrated lime is generally obtained
starting from very pure limestones. But, the egg
shells are domestic waste which can develop a new
source of calcium carbonate. The originality of this
work is the use of calcined egg shell as hydrated lime
in order to produce a restoration mortar for
Figure 1: stages of the lime manufacture from egg shells
STONE
22
No 2 - Aug 2007
Improving Conservation Practices: An On-line Database of Building Stone in Use for
Northern Ireland
1
2
2
1
1
2
2
C. Adamson , J. Curran , M. Francis , B.J. Smith , P. Warke , J. Savage , D. Stelfox
1 School of Geography, Archaeology & Palaeoecology. Queen’s University Belfast, UK.
2 Consarc Design Group, Belfast, UK.
Contact e-mail: [email protected]
Conservation of our stone-built heritage is a complex
process requiring expert knowledge and skilled
workmanship. In Northern Ireland there is a lack of
authoritative data on how natural stone performs as a
building material and this can lead to poor choices for
repair strategies.
The Natural Stone Database Project will produce a
free online website for architects, building owners,
and conservation professionals providing
comprehensive information on the characteristics
and availability of local stone for monuments and
listed buildings throughout Northern Ireland.
Surveying, Sampling & Analysis
Quarries
Built Heritage
Buildings
Monuments
BUILDING STONE
DATABASE FOR
NORTHERN IRELAND
Website
Publications
Specifier’s Checklist
Guidelines for Repairs
imported stone in Northern Ireland, and how
different stone types weather, both over time, and in
different environments.
The website goes live in December 2007 and to
demonstrate the project in action this paper gives an
overview of the various types of local limestone.
There are a range of limestones in Northern Ireland,
from the Cretaceous Ulster White Limestone of
County Antrim, to the yellow Dolomitic Cultra
Limestone of County Down. However by far the
most widely used, and arguably the most durable, are
the Carboniferous Limestones of the South and West
of the Province. These fall into two geographic and
lithological groups. The Armagh Limestones and the
dark grey Fermanagh/Tyrone Limestone types.
Armagh Limestone
Armagh Limestone is probably the most well
recognised of Northern Ireland’s limestones. It is a
Carboniferous, fossiliferous limestone varying in
colour from pale grey to purplish red and was used
extensively in Armagh City and the surrounding
areas in the 18th and 19th centuries. The majority of
the main stone quarries are still active, although
largely used for aggregate. Armagh limestone shows
little decay over time, with only mild weathering
along stylolites and where fossils are present, and
occasional mortar damage where cement pointing
has been used.
Seminars and Workshops
Figure 1: Diagrammatic summary of the Natural Stone
Database Project
The project includes surveys of listed stone
buildings, monuments, and quarries (both active and
inactive) across the 6 counties of Northern Ireland,
collecting GPS co-ordinates, architectural
information, photographs, and stone samples from all
sites (where possible). Stone tests are performed on
collected samples (BS EN Tests, XRD, FTIR, and
Probe permeametry. This will provide a
comprehensive overview of the use of local and
Figure 2: Carganamuck Quarry, Armagh
STONE
23
No 2 - Aug 2007
Fermanagh/Tyrone Carboniferous Limestones
Castle Espie Limestone
There are several Carboniferous limestone
formations in Fermanagh and Tyrone, including the
Dartry Limestone formation and the Ballyshannon
Limestone formation. In all the formations the
limestone is grey and often rich in fossils. It weathers
to varying degrees, in most cases it is very durable but
occasionally it can be found to flake and scale heavily
with isolated hollowing out of blocks. Several
quarries are still actively used for aggregate, many
more quarries are now disused.
Castle Espie Carboniferous limestone was quarried
outside Comber, County Down and mainly used for
lime production. It is occasionally seen as dressing
stone on older buildings and monuments, and as
headstones in local graveyards. It is distinctively pink
to red in colour, often with visible fossils. It is
reasonably durable over time, occasional blocks
show heavy flaking.
Figure 5: Dressing on Louginisland Church Ruins
Cultra Limestone
Figure 3: Belleek Porcelain Factory, Co. Fermanagh
Ulster White Limestone
Also known as Antrim Chalk this Cretaceous
limestone is fine-grained, white, and very hard.
Antrim chalk is very brittle, fractures heavily in situ
and contains numerous bands of flint nodules. Thus it
is generally unsuitable for building but is
occasionally seen as quarry-faced stone blocks on
buildings along the Co. Antrim coast and in
Moneymore (Co. Londonderry). It is no longer
quarried for dimension stone.
A less commonly used pale yellow to orange
dolomitic limestone formed in the Permian age.
Cultra limestone was quarried along the shoreline at
Cultra, County Down. It is generally pale yellow in
colour and may contain fossils. It weathers poorly,
including scaling and flaking, loss of face, and
caverning. Used as dressing on Holywood Priory and
Carrickfergus Castle.
a
b
Figure 6: heavy decay on Carrickfergus Castle. Dressing
on Holywood Priory
Figure 4: Chalk, Co. Antrim
Overall it can be seen that the building limestones of
Northern Ireland demonstrate a range of
characteristics and a varied responses on exposure to
different environmental conditions. The main two
types make very durable building stone, the latter
three are more suitable as stone dressing, the least
durable of which is the Cultra Limestone.
STONE
No 2 - Aug 2007
24
New insights on the use of crystallization inhibitors as a potential treatment for preventing
salt weathering of biocalcarenites.
1
2
1
E. Ruiz-Agudo , C.V. Putnis , C. Rodriguez-Navarro
1 Dept. Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002 Granada, Spain.
2 Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Germany.
Contact e-mail: [email protected]
Introduction
The potential use of crystallization inhibitors
(phosphonates) as a new means to halt and/or
mitigate the damaging effects of Na and Mg sulfate
crystallization within a natural porous medium has
been studied using a biomicritic limestone
(biocalcarenite) from Granada (Spain). These
additives, in contrast with previous works that have
indicated their role as effective inhibitors of epsomite
and mirabilite crystallization (Ruiz-Agudo et al.
2006a,b), seem to act as crystallization promoters
when a calcitic support is present. This could be
interpreted in terms of additive-mediated (templateassisted) heterogeneous nucleation of salts on the
carbonate substratum at a very low supersaturation,
which results in a significant reduction in
crystallization pressure and in the damage undergone
by the stone. Additionally, the additive layer formed
on the calcitic support acts a barrier that protects
mineral surfaces against dissolution by saline
solutions. Experimental evidences of such a layer are
given by means of atomic force microscopy (AFM)
studies.
Rodriguez-Navarro et al. (2002). Crystallization
experiments were performed in the absence and in
the presence of the phosphonate
diethylenetriaminepentakis (methylphosphonic
acid) (DTPMP).
Materials and methods
The damaging effects of sodium and magnesium
sulfate crystallization within a natural porous
medium were studied using a biomicritic limestone
(biocalcarenite). Such a porous limestone was
selected as model material for salt crystallization
tests because it is commonly used in the sculptural
and architectural heritage and it has well-known salt
weathering problems (Rodriguez-Navarro and
Doehne 1999). The biocalcarenite was quarried in the
Santa Pudia area (15 km SW from Granada, Spain). It
is buff colored, quite porous (ca. 30 % on average)
and easy to quarry and carve. These characteristics
led to its extensive use in the Andalusian's
architectural and sculptural heritage (RodriguezNavarro 1994). Salt crystallization tests were carried
out in a controlled environment (20±2ºC, and 45±5%
relative humidity). Saturated sulfate solutions were
let to flow-through, evaporate and crystallize in the
porous stone, following the methodology outlined by
Figure 1. Macroscale sulfate crystallization tests using
calcarenite slabs: a) pure saturated Na2SO4 solution and
with 1 mM DTPMP and b) pure saturated MgSO4 solution
and with 10 mM DTPMP. Note the reduction in damage in
the presence of the additive (images on the right side),
especially in the case of MgSO4.
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No 2 - Aug 2007
Rodriguez-Navarro et al. (2002). Crystallization
experiments were performed in the absence and in
the presence of the phosphonate
diethylenetriaminepentakis (methylphosphonic
acid) (DTPMP).
Figure 2. Schematic representation of the fosfonate layer
formed on calcite surfaces.
Results and discussion
A reduction in crystallization damage occurred in the
presence of phosphonates (DTPMP) if compared
with the control sodium sulfate solution (Figure 1a).
MgSO4 crystallization in limestone was also
investigated, with similar results (Figure 1b).
Efflorescence growth is not promoted in the presence
of this additive. These observations suggest that
crystallization inhibition does not take place within
the limestone pores, as occurred in batch
crystallization experiments (Ruiz-Agudo et al
2006a,b). In contrast, crystallization promotion took
place. This could be explained by considering that the
additives formed a template following adsorption
and/or precipitation on the calcite grains of the stone.
Such template (schematically depicted in Figure 2)
contributed to the heterogeneous nucleation of
epsomite at very low supersaturation. this effect
results in a significant reduction in crystallization
pressure and a minimization of the damage
undergone by the stone, as it was observed in
macroscopic crystallization tests. This model has
been considered previously to explain mineral
formation assisted by macromolecules (Jiang et al,
2005). The formation of such additive “film” or
“template” on calcite crystals exposed to the solution
with additive was observed by means of AFM
(Figure 3).
25
Conclusions
Organic additives, particularly phosphonates, were
found to promote both sodium and magnesium
sulfate crystallization when a porous calcareous
support is present. This is considered to be due to
template-assisted heterogeneous nucleation of these
salts directed by phosphonate molecules adsorbed on
calcite surfaces. Such results open new perspectives
in preventing salt damage affecting building stone, as
this template effect apparently contribute to: a) the
protection of the calcite surface against chemical
weathering induced by salts, and b) the reduction of
salt crystallization damage. Work is in progress to
elucidate if such protection model works in the case
of various saline systems other than sulfates.
Acknowledgments
This work has been financially supported by the
European Commission VIth Framework Program,
under Contract No. SSP1-CT-2003-501571, and by
the research group NRM-179 (Junta de Andalucía,
Spain). The AFM used is in the Institut für
Mineralogie (Westfälische Wilhelms-Universität
Münster, Germany). The research at Münster
University is supported by the Deutsche
Forschungsgemeinschaft (DFG).
References
Jiang, H.; Liu, X.; Zhang, G.; Li, Y. (2005) Kinetics and
Template Nucleation of Self-Assembled Hydroxyapatite
Nanocrystallites by Chondroitin Sulfate. J. Biol. Chemistry,
280: 42061-42066
Rodriguez-Navarro C, Doehne E (1999) Salt weathering:
influence of evaporation rate, supersaturation and
crystallization pattern. Earth Surf. Processes Landf. 24:191209
Rodriguez-Navarro C (1994) Causas y mecanismos de
alteración de los materiales calcáreos de las catedrales de
Granada y Jaén. PhD, University of Granada, Spain.
Rodriguez-Navarro C, Linares-Fernandez L, Doehne E,
Sebastian-Pardo E (2002) Effects of ferrocyanide ions on NaCl
crystallization in porous stone. J. Cryst. Growth 243:503516
Ruiz-Agudo, E.; Rodríguez-Navarro, C. (2006a) The use of
additives (phosphonates) as inhibitors for the crystallization of
magnesium sulfate. In Fort, R.; Alvarez de Buergo, GomezHeras, Vazquez-Calvo, C. (Eds.) Heritage, Weathering and
Conservation. Balkema.
Figure 3. AFM deflection images of a) normal calcite
surface during dissolution by Na2SO4 1M; dissolution by
saturated Na2SO4 solution in the presence of b) 0.5 mM
and c) 30 mM DTPMP. Note the layer that covers the
calcite surface in the presence of additive.
Ruiz-Agudo, E.; Rodriguez-Navarro, C.; Sebastián-Pardo, E.
(2006b). Sodium Sulfate Crystallization in the Presence of
Phosphonates: Implications in Ornamental Stone Conservation.
Cryst. Growth Des., 6(7):1575-1583.
STONE
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26
Porous limestone decay; the role of mineralogical changes in crust formation
A. Török
Department of Construction Materials & Engineering Geology, Budapest University of Technology and Economics,
Hungary.
Contact e-mail: [email protected]
Hungarian porous Miocene limestones show a wide
range of fabrics. From the various lithologies found
in monuments a fine-grained, a medium-grained
oolitic and a coarse-grained bioclastic, were studied
in the urban environment of Budapest. The
weathering features and forms were mapped on
ashlars of public buildings. The surface alteration is
characterized by the presence of white (thin and
thick) and black (laminar and framboidal)
weathering crusts (Fig. 1). Flaking, scaling and
blistering are common crust detachment forms
(Török 2002). The exposed weaker surface below the
crusts often shows granular disintegration (Fig. 1d).
crust zone. The crust is also characterized by silt sized
quartz grains and high amount of organic carbon.
Gypsum was detected both in the crust and below.
Dark grey gypsum crystals contain organic carbon
and dust inclusions (Fig. 3).
Figure 2: Average mineralogical composition of
framboidal black crusts (others include silt sized quartz
particles, feldspars and clay minerals).
Figure 1: Common weathering forms of porous limestone:
framboidal black crust (a), scaling laminar black crust (b),
white crust and secondary black crust (c) white crusts on
severely damaged ashlars, that shows granular
disintegration (d).
Crust detachment is initiated by opening up of microfissures that develop below the cemented crust zones.
The most sensitive stone type is the fine-grained
limestone which appears to be less durable than its
coarse-grained counterpart. The analyses have
demonstrated that the air pollution related gypsum
crystallisation with combination of freeze/thaw
weathering lead to crust detachment with rates
strongly controlled by the micro-fabric of limestone
substrate.
To assess the processes of crust formation and
detachment, description of lithologies and associated
weathering features were combined with microfabric and mineralogical analyses. Mineralogical
analyses have shown that gypsum accumulates in the
crust zone. In framboidal black crusts the
contribution of gypsum to crusts is more than 60%
(Fig. 2).
Thin and thick weathering crusts were also identified
by microscope. A textural change is marked by pore
occluding calcite and reduction of porosity in the
Figure 3: Microscopic image of black crust formed on
oolitic limestone. Note the gypsum crystals few
millimetres below the surface in the pores.
STONE
No 2 - Aug 2007
To conclude, Hungarian porous limestones are very
sensitive to surface degradation. The decay features
that were observed on the monuments in Budapest
(Fig. 2) are similar to ones of the porous limestones of
other cities (Smith & Viles 2006). The most common
weathering forms are black and white crusts. The
crust removal and stability is strongly controlled by
limestone fabric and by extrinsic factors such as
climate and air pollution. In Budapest both of these
have a very negative effect on crust stability although
after crust removal two main scenarios can take
place: i) stabilization of the surface by a
secondary/tertiary crust or ii) rapid surface loss due
to granular disintegration. The flaking, scaling is
initiated by micro-crack formation within the stone.
The micro-cracks are formed at the boundary layer
between the host porous limestone and the cemented
crust due to mineralogical changes that cause
differences in mechanical properties, porosity and
thermal behavior of crust and host rock.
27
The financial support of Bolyai János Research
Grant (BO/233/04) and the Hungarian Science
Foundation (OTKA, K63399) are acknowledged.
References
Smith, B.J, Viles H. 2006. Rapid catastrophic decay of building
limestones: Thoughts on causes, effects and consequences. In:
Fort, R, Alvarez de Buego M., Gomez-Heras M. & VazquezCalvo C. (Eds): Heritage Weathering and Conservation, Taylor
& Francis/Balkema, London. Vol. I, 191-197.
Török Á 2002. Oolitic limestone in polluted atmospheric
environment in Budapest: weathering phenomena and
alterations in physical properties. In: Siegesmund, S., Weiss, T.,
S., Vollbrecht, A (Eds.) Natural Stones, Weathering Phenomena,
Conservation Strategies and Case Studies. Geological Society,
London, Special Publications 205, 363-379.
STONE
No 2 - Aug 2007
28
The origins and significance of rapid surface stabilisation of building limestones
B. Smith1, A. Török2, J.J. McAlister1, M. Gomez-Heras1, H.A. Viles3, B. Emery3 P.A.M. Basheer4
1 Weathering Research Group, Queen’s University Belfast, UK.
2 Technical University Budapest, Hungary.
3 Rock Breakdown laboratory, Oxford University Centre for the Environment. Oxford University, UK.
4 Structural Materials Research Group, Queen's University Belfast, UK
Previous decay models of bioclastic limestones in
polluted, salt-rich environments have indicated that,
after the initial formation of a superficial gypsum
crust, stonework is prone to retreat as the crust and
outer layer of stone eventually spall. Following
delamination, decay pathways can diverge. Under
certain conditions, a positive feedback is established
whereby the stone continues to retreat through
granular disaggregation and/or multiple flaking to
create surface hollows within which, for example,
deposited salts are preferentially retained. Indeed,
previous studies (e.g. Smith et al. 2002) have
suggested that the key to understanding the rapid
retreat of sandstones in polluted environment is the
continued supply of salts that drive rapid retreat
mechanisms and, with it, the conditions that trigger
associated positive feedbacks
repetition of this 'healing' and delamination process
has been shown to produce stonework with patchy
remnants of several generations of gypsum crust.
Ultimately, however, repeated spalling can produce a
complex surface topography that encourages
localised rapid retreat.
Figure 2: Surface stabilization and regrowth of a gypsum
crust following contour scaling of an oolitic limestone, St
Mattias Church, Budapest.
Figure 1: Rapid retreat through granular disintegration of
a bioclastic limestone in the salt-rich, maritime
environment of Mallorca
In contrast, preliminary studies of limestones from
Cities such as Budapest and Oxford suggest a greater
significance for the rapidity with which spalled
surfaces 'heal' through the regrowth of a surface
gypsum crust, and the importance of the factors that
control crust growth in determining whether rapid,
catastrophic decay of limestones is initiated and
maintained (Smith and Viles 2006).
The stabilisation created by these crusts is, however,
only temporary and eventually it too can delaminate.
Figure 3: Scanning electron micrograph of a gypsum crust
from St Matthias Church Budapest illustrating the
incorporation of large quantities of wind blown dust.
Thus, to understand the decay of this class of building
stones requires not only an understanding of the
processes responsible for rapid decay, but also the
more subtle processes and feedbacks that promote
rapid stabilisation of spalled surfaces.
STONE
No 2 - Aug 2007
This presentation examines the conditions required
for this stabilisation through a study of oolitic
limestones in the still-polluted city of Budapest and
the city of Oxford, where levels of particulate
pollution have been significantly reduced over the
last forty years (Anthill and Viles, 1999). Results
from Budapest indicate the significance for crust
formation of the rapid deposition of atmospheric dust
rich in calcium carbonate, and its rapid
transformation to gypsum in a sulphur-rich
atmosphere (Smith et al. 2003).
Crusts can also contain significant amounts of
fibrous organic debris that might act as a framework
within and onto which loose dust particles could
possibly be trapped and held prior to incorporation
into a protective surface crust.
The factors allowing surface crusts to form rapidly on
new and newly exposed limestone are however
complex and involve the interplay of a range of geoenvironmental factors, the properties and
depositional characteristics of surface dusts as well
as the nature and properties of any surface biological
colonisation. A selection of the possible factors are
tabulated below.
Geo-Environmental factors controlling surface
gypsum crust formation
· Surface chemistry/mineralogy.
· Variable atmospheric chemistry (short- mediumand long-term).
· Variable dust deposition rates/flux (shortmedium- and long-term).
· Variable dust chemistry.
· Façade topography, aspect.
· Exposure to rainwash (amount, frequency,
intensity).
· Drying rate (Radiation balance, E/T, windspeed).
· Surface colonisation organics.
· Surface wash in/wash out
The role of surface dust deposition in gypsum crust
formation
· Surface insulation (physical and chemical
intermediary at the stone atmosphere interface)
· Direct source of gypsum.
· Indirect source of gypsum (post-depositional
transformation).
· Large specific surface.
· Crystallisation nuclei.
· Catalysing reactions.
· Chemical weathering, breakdown, phase
transformations.
29
The role of 'organics' in gypsum crust formation
· Adhesive surface coatings.
· Depositional framework.
· Modification of surface chemistry.
· Biochemical processing of inorganic materials.
The dry, dusty, pollution-rich conditions currently
experienced in Cities such as Budapest are redolent
of those previously experienced in Oxford, where the
burning of coal as a fuel was widespread and intense
and where stonework was universally masked by
black gypsum encrustations. Preliminary
observations suggest that the reduction of particulate
pollution, whilst resulting in generally cleaner
buildings, has also been associated with a greater
prevalence of the rapid, catastrophic retreat that has
in turn required widespread replacement of
weathered stone.
Thus, whilst there are undoubtedly many other
factors to be taken into account, there is possibly
some virtue in viewing Budapest as a temporal
analogue for understanding the conditions that
prevailed in Oxford prior to the introduction of cleanair legislation. Conversely, the subsequent response
of stone in Oxford to reduced particulate deposition
could provide an insight into the future decay and
intervention that will be required in cities such as
Budapest as levels of pollution are gradually reduced.
One possible implication of these observations is that
under certain circumstances, a reduction in pollution
could conceivably accelerate, rather than curtail rates
of stone decay.
References
Antill, S.J. & Viles, H.A. 1999. Deciphering the impacts of
traffic on stone decay in Oxford: Some preliminary
observations from old limestone walls. In M.S. Jones & R.D.
Wakefield (eds) Aspects of stone weathering, decay and
conservation: 28-42. London: Imperial College Press.
Smith, B.J. & Viles, H.A. 2006. Rapid, catastrophic decay of
building limestones: Thoughts on causes, effects and
consequences. In: R. Fort González, M. Alvarez de Buergo and
M. Gómez-Heras, (eds) Heritage Weathering and Conservation.
Taylor and Francis, London, pp. 191-197.
Smith, B.J., Török, A., McAlister, J.J. & Megarry, Y. 2003.
Observations on the factors influencing stability of building
stones following contour scaling: a case study of oolitic
limestones from Budapest, Hungary. Building and
Environment, 38: 1173-1183.
Smith, B.J., Turkington, A.V., Warke, P.A,. et al. 2002.
Modelling the rapid retreat of building sandstones. A case study
from a polluted maritime environment. Geological Society of
London Special Publication, 205: 339-354.
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30
Decay in Oxford limestone: observational units and jumping edges
M. Gomez-Heras1, B.J. Smith1, H.A. Viles2
1 Weathering Research Group, Queen’s University Belfast, UK.
2 Rock Breakdown laboratory, Oxford University Centre for the Environment. Oxford University, UK.
Contact e-mail: [email protected]
When the decay of building stones is studied, one of
the first decisions to be taken is the 'observational
unit' to be employed. These can range from a mineral
(e.g. Weiss et al., 2002) or an individual stone (e.g.
Rothert et al., 2007) to the whole building (e.g. Warke
et al., 2003), depending on the purpose of the
exercise. In doing this, continuous results can be
translated into discrete units that allow, for example,
the state of decay of a building to be mapped and its
evolution to be understood.
buildings constructed of oolitic limestone in Oxford.
It is shown how, especially where mortar joints are
very thin, facades can behave organically and pattern
of decay are seen to evolve in ways that are not
necessarily related to individual stones. For example,
surface gypsum crusts are often seen to form across a
complete façade in response to a general exposure to
atmospheric pollution. However, once formed, these
continuous crusts facilitate the spread of decay
phenomena, such as contour scales, and allow them
to 'jump' from one block to another (Figure 1).
The observational unit selected also affects to the
conservation strategies. For example, the
replacement of individual stones could be favoured
when the focus lays on the individual stones and the
interaction between blocks are neglected. This
approach may lead to the acceleration of decay if the
newer blocks interfere with the equilibrium of the
whole façade (Figure 2). In these cases, maintenance
strategies allowing to keep dynamic equilibrium
surfaces may be advisable, as the façades are
therefore allowed to evolve organically (Figure 3).
50 cm
Figure 1: Section of the former perimeter wall of the
Sheldonian Theatre (Oxford), which shows patchy
detachment of the outer layer hardened by a gypsum crust.
In some areas, this crust is observed to jump over the edges
of the individual stones, forming a continuous layer of
gypsum crust.
The selection of the observational unit conditions
necessarily the interpretation of the research results
as it places the focus of the observation on a specific
scale. An unfortunate consequence of this
'discretization' is, however that many investigations
treat buildings and structures as the sum of their
individual parts. Thus, it is normal practice to treat
individual stones as confined elements, relatively
isolated from their surroundings by a mortar layer. In
doing this, studies ignore the possible interactions
between adjacent units and the decay synergies that
derive from these interactions. This presentation,
explores these synergies through a study of historic
Figure 2: Oxford college wall where the replacement of
individual blocks has accelerated the decay of the
remaining blocks. The subsequent decay spreads from one
block to the other in a continuous way.
As a consequence, it is important to be flexible when
selecting observational units and, even where
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31
individual blocks are the most obvious units they
may not necessarily be the most appropriate.
This research is part of the EPSRC project
EP/D008603/1.
References
Rothert, E. et al., 2007. Stone properties and weathering
induced by salt crystallization of Maltese Globigerina
Limestone, Building Stone Decay: From Diagnosis to
Conservation. Geological Society Special Publication, pp. 189198.
Warke, P.A., Curran, J.M., Turkington, A.V. and Smith, B.J.,
2003. Condition assessment for building stone conservation: a
staging system approach. Building and Environment, 38(9-10):
1113-1123.
Figure 3: Recently restored buttress of St Stephen’s
Cathedral in Vienna. The restoration has left an irregular
“dynamic equilibrium” surface.
Weiss, T., Siegesmund, S. and Fuller (Jr), E.R., 2002. Thermal
stresses and microcracking in calcite and dolomite marbles via
finite element modelling. In: S. Siegesmund, T. Weiss and A.
Vollbrecht (Editors), Natural stone, weathering phenomena,
conservation strategies, and case studies. Geological Society
special publication ; no. 205. Geological Society, London, pp.
89-102.
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32
Identifying facies with different weathering properties in Malta's Lower Globigerina
Limestone
1
1
2
1
T. Zammit , J. Cassar , A.J. Vella , A.Torpiano
1 Institute for Masonry and Construction Research, University of Malta, Msida, Malta.
2 Department of Chemistry, University of Malta, Msida, Malta.
Contact e-mail: [email protected]
Geologically the Maltese Islands are characterized
by a slightly tilted stratigraphy composed of five
sedimentary rock formations (Table 1), formed over a
period of 25 million years during the Oligocene and
Miocene epochs of the Tertiary period (Pedley et al.,
2002). The distinct rock types are a result of varying
marine environments in which they were formed.
The generic Maltese terms Franka and Soll have been
used, since time immemorial, to distinguish between
the 'good' and the 'bad' weathering varieties of this
stone type.
Past research on these two stone types has indicated
that Soll is a physically denser and mechanically
stronger stone type, with a total porosity less than that
of Franka variety, but with a higher percentage of
micro-pores (Saliba, 1990), (Farrugia, 1993),
(Muscat, 2006). Geochemical and mineralogical
analyses have also indicated that there are significant
differences in the non-carbonate fraction of the two
stone types (Vella et al. 1997). Indications are that
Soll has a richer non-carbonate content, with higher
concentrations of quartz and phyllosilicates (Cassar,
1999).
Figure 1: Typical weathered Lower Globigerina
Limestone quarry face.
The main source of Malta's building stone is the
Lower Globigerina Limestone member, which is a
typical bioclastic limestone. It has been used as a
building stone for over 5000 years. Its apparent
homogenous appearance on extraction is no
indication of the notably variable weathering
behaviour it exhibits with time. Bearing testimony to
this are old and abandoned quarry faces which
exhibit beds of badly weathered stone, alternating
with thicker beds of less weathered stone.
The durability of these stone types against the
processes of weathering was investigated in separate
research efforts (Vannucci et al., 1994), (Fitzner et
al., 1996). Direct observation, together with chemical
and petrographical analyses of weathered stone
samples, were compared with accelerated testing
techniques employing the method of salt-loading of
freshly quarried samples (Rothert et al., 2007). From
this research, a deterioration process was identified,
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involving; a) high soluble salt concentrations within
the stone, b) the dissolution and re-precipitation of
calcite to form a thin superficial crust, and c) the
eventual lifting and loss of the crust to expose an
already deteriorated surface. These studies also
confirmed that stone types with different weathering
properties are thus characterized by different micropore size distributions.
However, it was also thought that other empirical
'indicators' could be used to distinguish between
these two stone types. In this respect, work has been
ongoing at the University of Malta for the past 20
years to try to determine whether geochemical
indicators can be used to distinguish between the two
main Lower Globigerina Limestone types. The result
of this research was the strengthening of the
hypothesis that characterizing 'good' from 'bad'
quality building stone extracted from the Lower
Globigerina Limestone member may be achieved by
way of geochemical composition. Particularly
promising results were obtained by measuring the
Acid Insoluble Residue. (Cassar and Vella, 2003)
Current research is focused on the physically
measurable parameter of Total Insoluble Residue
(TIR), as well as verification of Total Porosity values
and Pore Size Distribution.
The initial testing programme has utilized the
selected cores originally forming part of the “Mineral
Resource Assessment” (Wardell Armstrong, 1996)
and will also include stone samples taken from both
active and disused quarries.
References
Cassar, J., (1999), “Geochemical and Mineralogical
Characterisation of the Lower Globigerina Limestone of the
Maltese Islands with special reference to the “soll” facies”. Ph D
Thesis, University of Malta, unpublished.
Cassar J. & Vannucci S., (2001), “Petrographical and chemical
research on the stone of the megalithic temples”. In: Malta
Archaeological Review, Issue 5, pp. 40 45.
Cassar, J., & Vella, A.J., (2003), “Methodology to identify badly
weathering limestone using geochemistry: case study on the
33
Lower Globigerina Limestone of the Maltese Islands”. In:
Quarterly Journal of Engineering Geology and Hydrogeology,
36, pp. 85-96.
Farrugia, P., (1993),“Porosity and Related Properties of Local
Building Stone”. B.E & A (Hons.) Dissertation, University of
Malta, unpublished
.
Fitzner, B., Heinrichs K. & Volker M., (1996) “Model For Salt
Weathering at Maltese Globigerina Limestones”. In: Zezza, F.
(ed.) “Origin, Mechanisms and Effects of Salts on Degradation
of Monuments in Marine and Continental Environments”,
Proceedings, European Commission Research Workshop on
Protection and Conservation of the European Cultural Heritage,
Bari, Italy. Research Report No. 4, pp. 331-344.
Muscat, M., (2006), “The Behaviour of Franka and Soll
Globigerina Limestone with respect to Salt Weathering and
Possible Solutions”. B.E.& A. Dissertation, University of
Malta, unpublished.
Pedley, M, Hughes Clarke, M, & Galea, P, (2002), “Limestone
Isles in a Crystal Sea. The Geology of the Maltese Islands”. Peg
Publications, Malta.
Rothert, E., Eggers, T., Cassar, J., Ruedrich, J., Fitzner, B., &
Siegesmund, S., (2007), “Stone properties and weathering
induced by salt crystallization of Maltese Globigerina
Limestone”. In: Prikryl, R. & Smith, B. J. (eds) Building Stone
Decay; From Diagnosis to Conservation, Geological Society,
London. Geological Society, London, Special Publications,
271, pp. 189198. Saliba, J., (1990), “The shear strength of
Globigerina Limestone”. B.E & A (Hons.) Dissertation,
University of Malta, unpublished.
Vannucci, S., Alessandrini, G., Cassar, J., Tampone, G., &
Vannucci, M. L. (1994). "The prehistoric, megalithic temples of
the Maltese islands : causes and processes of deterioration of
Globigerina Limestone". (I templi megalitici preistorici delle
isole maltesi: cause e processi di degradazione del Globigerina
Limestone.) In : Fassina, V., Ott, H. & Zezza, F. (eds)
Conservation of Monuments in the Mediterranean Basin.
Proceedings of the 3rd International Symposium,Venice, Italy,
Sopritendenza di Beni Artistici e Storici di Venezia, Italy, pp.
555565.
Vella A. J., Testa S., & Zammit C., (1997), “Geochemistry of the
Soll Facies of the Lower Globigerina Limestone Formation,
Malta”. Research article in: Xjenza: 2:1, pp. 27-33.
Wardell Armstrong, (1996), “Mineral resource assessment for
the Planning Authority of Malta”. 5 Volumes, unpublished,
limited circulation document.
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34
The influence of design requirements on the durability of porous building stones used in
façades. A case study
1,2
1,3
A. Bernabéu , M.A. García del Cura
1 Laboratorio de Petrología Aplicada, Unidad Asociada CSIC-UA. Universidad de Alicante. Spain.
2 Dpto. Ciencias de la Tierra y del Medio Ambiente. Universidad de Alicante. Spain.
3 Instituto de Geología Económica CSIC-UCM. Madrid, Spain.
Contact e-mail; [email protected]
The widespread use of porous limestone, such as in
paving and cladding is well-known. Although much
research has been carried out on factors that influence
the degradation process of this type of porous stone,
little mention has been made of design requirements.
In this study, we highlight the importance of such
requirements for this specific usage given the
considerable influence that they exert on the
durability of these stones. For this purpose, two
examples of a biocalcarenite (Novelda stone) used,
on the one hand, in new construction and, on the
other, in a historic building are presented.
The studied stone is extracted from the Vinalopó
Medio area (Alicante, Eastern Spain) and has been
used as a building stone since the 13th century (Fort
et al., 2002). The stone contains foraminifera (which
are often filled by glauconite and/or siliceous
cement) and the terrigenous fraction is comprised of
quartz, feldspars, micas, dolostones and other rock
fragments. Both interparticle and intraparticle
porosity are variable, and the connected porosity
(Hg) ranges from 13 to 20 % in different commercial
varieties.
buildings, particularly in stones situated near the
ground, where the capillary rise effect is most
pronounced.
The efflorescence in samples collected from the
weathered façade was studied. The composition of
this efflorescence is related to the location of the
building and environmental conditions. Data
obtained from the salt crystallization test were
compared with the studied materials.
Example 1 is a new building in which the stone is near
a green area (Figure 1). The stone studied has a
connected porosity (Hg) of 13 % and the most
abundant pore size interval (62 %) is 0,1 - 0,01 m.
This latter characteristic greatly influences resistance
to salt crystallization, as has been observed in the salt
crystallization test.
The efflorescence was studied on the inner and
external surfaces of the samples collected from the
weathered façade, using SEM both in BSE and SE
mode.
On the inner surface, gypsum, sodium and potassium
chloride were observed. In samples collected near
green areas, sodium nitrates were identified by EDX
analysis (figure 2). On the external surface, abundant
gypsum efflorescence was identified (figure 3).
Figure 1: Example 1; Novelda stone in a new building.
University of Alicante.
In the examples studied, much deterioration can be
observed. Among the different decay forms observed
in this location, we can highlight: (a) efflorescence
and salt crusts; (b) superficial flaking; (c) loss of
material and (d) granular disintegrationThis type of
decay is noticeable in both historical and new
Figure 1: Efflorescence (Inner surface).
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35
The salt efflorescence present in the samples studied
corresponds mainly to sulphates and chlorides.
Proximity to green areas increases the weatherability
of this type of stone and causes the presence of salts,
such as sodium nitrate and potassium chlorides. Salt
presence is related to climatic conditions.
Figure 3: Efflorescence (external surface).
In this case, the decay observed is due to granular
disintegration and the presence of organic material.
In figure 5, details of SEM images from the external
surface of the collected sample can be seen.
The decay observed in stone at this location can be
predicted by a salt crystallization test, i.e. the
continuous partial immersion test Results obtained
from this test, mainly as regards appearance, are
extremely similar to those observed in the decayed
stone.
The second case study is a historic building in Madrid
in which Novelda stone was used (Gómez-Heras &
Fort; 2004) (Figure 4). The connected porosity (Hg)
of this stone is 19 % and pore size distribution reveals
two predominant pore size intervals: (45 %) 10-1 m,
and (34 %) 1- 0,1 m.
Figure 4: External façade
of the Almudena
Cathedral Crypt, Madrid
and detail of sample.
Figure 5: SEM images efflorescences.
This work has been partially supported by S0505MAT/000094 project of the CAM
References
Benavente, D., García del Cura, M.A., Bernabéu, A., Ordóñez,
S. (2001). Engineering Geology 59, 313 - 325.
As conclusion to this study, we can point out:
The decay observed in porous stones used in building
façades is due not only to the petrophysical properties
of the stone and the climatic conditions, but also to
the location of the materials on the façade itself and
the positioning method used.
Charola, A.E., Pühringer, J. & Steiger, M. (2007).
Environmental Geology 52, 339-352.
Fort, R., Bernabéu, A., García del Cura, M.A., López de
Azcona, M.C., Ordóñez, S. & Mingarro, F. (2002). Materiales
de Construcción 52, 19-32
Gómez-Heras, M.; Fort González, R. (2004)Materiales de
Construcción, 54 (274), 31-47.
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36
Santa Engrácia National Pantheon (Portugal): the Stones and Pathologies
C. Figueiredo1, L. Aires-Barros1, A. Dionísio1, F. Correia1, C.M. Soares2, M.J. Neto2, L.V. Mendonça3, J.S. Rodolfo3
1 Center of Petrology and Geochemistry, CEPGIST, IST, Lisbon, Portugal.
2 Faculdade de Letras, Lisboa, Portugal.
3 SPY Building Inspecção de Edifícios, Portugal.
Contact e-mail: [email protected]
Some results obtained in the framework of the
Research Project “SOLIS: Santa Engrácia National
Pantheon (Portugal): building campaigns, quarries
exploited and stones used” are presented. This
Portuguese monument (Fig. 1), located in eastern
part of the historical centre of Lisbon and in the
vicinity of the Tagus River, presents some peculiar
aspects: its location, its baroque architecture
Figure 1: General view of Santa
Pantheon
Engrácia-National
(premature example in Portugal) and its historical
vicissitudes, mainly the circumstance of it has been
unachieved until the 20th century. Besides, it does not
exist an exhaustive and actual monographic study
contemplating all the building and restoration
campaigns and even fewer studies about the stones
used or the conservation state of the monument.
Identification of monument's stones, their
provenance (recent and ancient quarries), their
pathologies and the most probable causes were
achieved through an innovative approach of History
of Art and Geosciences. The main stone type used as
structural as well as ornamental stone is a Cretaceous
limestone exploited in quarries located in the
surrounding of Lisbon and known locally as “Lioz”.
Figure 2: Inside of National Pantheon: general view of the
paving and chapels, showing the play of colours created
by the various ornamental stones used.
Figure 3: Details of the main weathering forms identified on the outside walls.
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Other limestone types like “Encarnadão”, “ Amarelo
de Negrais”, “Negro de Mem Martins” and “Azul de
Sintra” and the “Ruivina” marble were essentially
applied in decorative elements, like panel lining,
vaulting panels, paving and tombs (Fig. 2). The
stones used in Santa Engrácia church are, in general,
of very good quality and resistant to weathering.
Only the limestone varities “Encarnadão” and the
less pure ones (“Negro de Mem Martins” and
“Amarelo de Negrais”) with a low clay matrix
content represent moderate to good quality
dimension stones and are quite prone to weathering.
Detailed survey of stone decay phenomena was
carried out outside and inside the National Pantheon
37
and several weathering forms have been identified.
Outside should be referred the presence of
vegetation in specific areas of the façades, a
brownish surface deposit covering protected zones
and fissuring and cracking of stones of some
columns, balconies and balustrades (Fig. 3). Inside
(Fig. 4), physical-mechanical weathering forms
(deformation, fissuring and cracking, differential
degradation, flaking, scaling and spalling), prevail,
mainly related to the differential settlement of the
building, rising damp, rain water infiltration and the
occurrence of soluble salts (gypsum, thenardite and
niter).
Figure 4: Details of the main weathering forms identified on the inside walls.
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38
On site evaluation of "mechanical-physical" properties of the Maastricht limestone
S. Rescic, F. Fratini, P. Tiano
Institute for Conservation and Promotion of Cultural Heritage, CNR-ICVBC, Sesto Fiorentino, (Florence) Italy.
Contact e-mail: [email protected]
In this paper the physical characteristics and the
cohesion of the weathered Maastricht limestone
(Tongeren Cathedral, Belgium) compared to the
unweathered material coming from the Sibbe quarry
(Holland) have been studied.
This material has been widely used from Middle Age
to the Renaissance period and it characterises the
architecture of Limburg in both sides of the Meuse
river but also the architecture of the XVI century of
some cities in central Holland (Utrecht,
Zaltbommel). At present it is mainly used for
restoration purposes.
Today the Maastricht limestone is quarried in Sibbe,
(Holland) in an underground quarry which extends
over an area of approximately 100 hectares. The
Maastricht Sibbe variety is very homogeneous and
layering is rarely observed. The excavation is
performed using ordinary motor-operated chain
saws.
Fossil content and petrographic characteristics which
determine slight differences in the compressive
strength (Fig. 1).
Despite the poor mechanical characteristics, the
material shows a good durability with remarkable
frost resistance. This is mainly due to the type of
porosity but also to the formation, particularly in the
Sibbe variety, of a protective "skin" through a process
of dissolution of unstable aragonite from serpulids
and precipitation of calcite in the pores of the external
layer (Dreesen &, Dusar, 2004; Dubelaar et al.,
2006). The decay develops mainly through
detachment of the crust (Fig. 2).
a
b
Figure 1. Thin section image PPL
The Maastricht limestone
The Maastricht limestone is a soft bioclastic
calcarenite of Upper Cretaceous age belonging to the
Maastricht Formation outcropping in southern
Limburg between Belgium and The Netherlands.
Four main varieties are distinguished according to
Figure 2. Tongeren Cathedral: particular of a crust formed
on an old ashlar (a) and substituted ashlars (b).
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Methods
- determination of the total open porosity (helium and
mercury picnometers method);
- determination of the water porosity (hydrostatic
balance method- ISO 6783:1982);
- pore size distribution (Hg porosimeter);
- capillary water absorption (UNI 10859);
- “cohesion” through DFMS (Drilling Force
Measurement System).
39
- total open porosity decreases from 50% to 47%.
- mesopores (.0037<r<150)mm decrease from 49%
to 42%
- pore size distribution shows a shift towards the
pores of lower dimension (Fig. 3)
- capillary absorption shows a decrease of about 50%
(Fig. 4)
- “cohesion” measurements (DFMS)3 show the
presence, in the weathered material, of a hardened
layer about 2mm thick (Fig. 5).
Discussion
Figure 3. Pore size distribution
Figure 4. Capillary water absorption curves
The weathering of the Maastricht limestone develops
through formation of a “hard layer” which physical
characteristics and cohesion are the following:
- thickness of about 2mm;
- “cohesion” 20 times higher than the underlying
material and the quarry material;
- decrease of capability to absorb water through
capillarity;
- The total open porosity of the weathered material up
to a depth of 1cm shows only a slight decrease which
is mainly due to a decrease of the bigger pores (pore
radius 32-64mm) but we may calculate that the
approximate value of the porosity of the “hard layer”
is 35%
The pore size distribution shows a low amount of
pores with radius around 1mm and this justifies the
good frost resistance. The strong physical and
mechanical differences of the ''hard layer” with
respect to the substrate give rise to the formation of a
discontinuity that favours its detachment.
Acknowledgements
European Project: Contract n°EVK4-CT-200200080 Dias
References
Dreesen, R. & Dusar, M. (2004): “Historical Building stones in
the province of Limburg (NE Belgium): role of petrography in
provenance and durability assessment”, Materials
Characterization 53: 273-287.
Figure 5. DFMS drilling outlines
Results
Striking differences can be emphasized between the
quarry material and the weathered material from the
Cathedral:
C. W. Dubelaar, M. Dusar, R. Dreesen, W.M. Felder, T.G.
Nijland (2006): “Maastricht limestone: A regionally significant
building stone in Belgium and The Netherlands. Extremely
weak, yet time resistant”, Proceedings of the International
Conference on Heritage, Weathering and Conservation, HWC
2006, 21-24 June 2006, Madrid -Spain, (1) 9-14.
Fratini F., Rescic s., Tiano P. (2006): “A new portable system for
determining the state of conservation of monumental stones”,
Materials and Structures, vol 39, n.2, (2006), 139-147.
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40
No 2 - Aug 2007
Conservation state of bioclastic limestones: Los Reales Alcázares (Royal Fortress) Palace of
Seville (Spain)
1
1,2
1
C. Vazquez-Calvo , M.J. Varas , R. Fort , M. Alvarez de Buergo
1
1 Instituto de Geología Económica (CSIC-UCM), Madrid, Spain.
2 Facultad de Ciencias Geológicas, Dpto. Petrología y Geoquímica (UCM), Madrid, Spain.
Contact e-mail: [email protected]
a)
This work presents part of the previous studies for the
restoration of the Façade of Don Pedro I of the
“Reales Alcázares” in the city of Seville (Spain)
(figure 1a). The construction of the “Reales
Alcázares” began in 913, in the time of the Muslim
ruler Abd Ar Rahman III, in the Mudejar style. The
façade of Don Pedro I dates back to the 14th century
and it was built in Mudejar style, too.
The location, characterization and decay condition
mapping of the different stone types were carried out.
The existence of two types of limestone can be
stressed among the other different materials
characterised in the façade (brick, render, ceramic,
marbles). These two types of limestone conform the
most important part of the façade, as both are the
building material of the ashlars of the façade and the
arabesques that adorn it.
The first of these stones was commonly called Tosca
stone (figure 1b) and was used in the ashlars of the
façade corresponding to the ground floor. The second
one is locally known as Palomera stone (figure 1c),
and was used for the ashlars corresponding to the
intermediate and top floor and for the arabesques.
The state of conservation of these two limestones is
different.
The Tosca stone is a biosparrudite (Folk 1959) from
the Upper Miocene. It has been used in some others
Sevillian buildings as the Cathedral. This stone
doesn’t show severe decay processes and its main
problems are related to surface soiling. It also shows
some material loss in the socle.
The Palomera stone is a biomicrite according to Folk
(1959). The main decay forms that can be observed in
Palomera stone are flaking, granular dissaggregation
and small cracks. These pathologies generate
unstable surfaces of the stone that in turn will cause
the detachment of areas of the surface with the
subsequent loss of the morphology of the arabesques.
Real and bulk densities, compactness, open porosity,
water saturation coefficient and total porosity were
determined for both stone types. The results show
b)
c)
Figure 1. a) Don Pedro I façade at Los Reales Alcázares
Palace (Seville, Spain). Images of the Tosca limestone (b)
and of the Palomera limestone (c) at the façade
the relation between the different decay rates and the
properties of each stone type. The performance of
Palomera stone is worse than the Tosca’s. The
relation is shown, for instance, in the porosity
accessible to mercury values, which show that Tosca
stone is less porous than the Palomera stone.
Nevertheless, the porosity value on the samples
changes depending on where in the façade the tested
specimens were sampled and on the decay processes
that each specific block has undergone; those
Palomera stone blocks that are protected by the
arabesques and therefore less affected by decay
processes, show a lower porosity than those forming
the arabesques relieves, which are much more
exposed.
The results obtained in this study were used as a
guideline for the future restorations works that will
be carried out on the façade
References
Folk, R. L. (1959). "Practical petrographic classification of
limestone." AAPG Bulletin 43: 1-38.
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41
The decay of the calcarenite utilised in the Etruscan tombs of S. Cerbone necropolis
(Populonia-Italy)
1
2
3
F. Fratini , E. Pecchioni , P. Pallecchi
1 Institute for Conservation and Promotion of Cultural Heritage, CNR-ICVBC, Sesto Fiorentino, (Florence) Italy.
2 Earth Science Department, University of Florence, Florence, Italy.
3 Supervision for Archaeological Heritage of Tuscany, Laboratory of Analyses, Florence, Italy.
In this abstract the decay morphologies of the
calcarenite used in the Etruscan tombs of the S.
Cerbone Necropolis are presented (Figure 1). The
study was possible also thanks to the recent discovery
of the supply quarries sited close to the necropolis.
medium geomechanical characteristics. The material
shows an evident crossed lamination with an ochre
colour, rough aspect and a high porosity. It can be
easily quarried and shaped in regular blocks (Figure
3).
The site
Populonia was a seaport of Etruria, originally
connected to Volterra but later turning into a
flourishing independent mining centre where the iron
coming from the Elba mines and those sited near
“Campiglia” was processed. The necropolis ranging
from the Villanovan period (9th century BC) to the
middle of the 3rd century BC, was explored first in
1908. The archaeologists found the tombs buried in a
deep layer of iron slags because particularly after the
V century BC, the top of the tumulus tombs, were the
site of the iron furnaces.
Figure 2. Macroscopical aspect of the Pietra Panchina
Historical use of the material
This material has been used along the Tuscan coast in
the following times:
Etruscan (Poulonia necropolis), Roman (Luni, Pisa,
Lucca), high Middle Ages (Lucca), the building stone
of Volterra since Middle Ages, the stone of Leghorn
(since the XVI century). At present it is not quarried.
In the necropolis it is used as rectangular blocks in the
external surface of the cylindrical drums (crepidine)
of the tumulus and of the Aedicula tomb (Figure 4).
Figure 1. Necropolis of Populonia
The material
Along the Tuscan coast the stone is traditionally
named as “Pietra Panchina”. It is a medium high
grained calcarenite of upper Pleistocene age
(Tirrenian) formed through cementation, in a littoral
environment, of an eolian sand made of quartz and
organogenic fragments during a regressive phase.
The degree of cementation is medium-low with
Analytical Methods
thin section optical microscopy;
mineralogical composition through XRD;
determination of the total open porosity (helium and
mercury picnometers method);
determination of the water saturation index (UNI
Normal 7/81).
STONE
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42
with increase of the roughness in the
exposedsurfaces, formation of residual reddish to
dark brown superficial films, alveolisation on the
surfaces exposed to wind.
The alteration processes in general do not
compromise the cohesion of the stone and it is
possible to affirm that there is not so much difference
between the sound material from the quarry and the
weathered stone (Fig. 5), even if an increase of the
open porosity can be observed (Table 1).
As a matter of fact the superficial decay is balanced
by the continuous precipitation of calcite from the
rising damp which is able to cement the
decohesioned material on the stone surface. This
process can explain way the Pietra Panchina shows a
good durability and sometimes increase its
compactness after exposition.
Figure 3. Rectangular blocks in quarry site
Figure 4. Aedicola Tomb called Bronzetto dell'Offerente
(530-540a.C.)
Figure 5. Pietra Panchina after weathering exposition
The weathering
The material shows generally a good durability even
if macroscopic alteration morphologies can be
observed: differential erosion in presence of
laminations, formation of wide cavities inside the
material when portions characterised by a low
cementation are present, dissolution of the cement
Barbi L., Leggeri B., Nencioni S., Manganelli Del Fa C.,
Pecchioni E. (1991) "La Tomba dei Carri: indagine e proposte
per la conservazione", Arkos Notizie GOR, 15, BE-MA
Editrice, Milano, 11-28.
Cortemiglia G.C., Mozzanti R., Parea G.C. (1983) "Geologia
della Baia di Baratti (Livorno, Toscana) e della sua spiaggia"
Geog. Fis. Dinam. Quat.,6, 148-173.
Table 1: Physical characteristics
Real density Bulk density Total open
porosity (%)
(g/cm3)
(g/cm3)
References
Saturation
index (%)
Quarry
2.68 ± 0.01
1.99 ± 0.07
26 ± 2
63 ± 4
Weathered
material
2.70 ± 0.02
1.84 ± 0.04
32 ± 2
68 ± 3
Fedeli F., Galiberti A., Romualdi A. (1993) "Populonia e il suo
territorio, profilio storico-archeologico" Ed. All'insegna del
Giglio Firenze, 92-107.
Lezzerini M. (2005) "Mappatura delle pietre presenti nella
facciata della Chiesa di San Frediano (Pisa, Italia)", Atti Soc.
Tosc. Sci. Nat. Mem. Seria A, 110, 43-50.
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43
Decay forms of limestones used as building materials in Greek monuments
M. Stefanidou
Civil Engineering Department, Laboratory of Building Materials, Aristotle University of Thessaloniki, Greece.
Contact e-mail: [email protected]
Limestone is one of the most commonly found stones
in building construction in Greece is due to its ability
to be cut and shaped easily, its “warm” colour and its
abundance. Whole structures such as castles, palaces
and fortresses were built only with limestone blocks
or limestone pieces combined with other types of
stone.
In the present paper two types of limestone (a
biogenic limestone and a travertine) used in
construction of monuments are tested and analyzed
in terms of their physical, mechanical and micro
structural characteristics in order to record their
properties. Their exposure to different environmental
conditions and the pathology forms that they have
presented are also recorded.
The possibility of their replacement is approached
either by supplement the missing parts by finding a
comparable new stone or by applying an artificial
stone.
contact with waves (especially those being in the
coast yard) and indirect though the wind action. The
stone is exposed to different deterioration actions
such as:
- soluble salts
- wind
- sunlight
- sea
The alteration forms that are present are:
- alveolus
- irregular material loss- disintegration
- efflorescence
- exfoliation
- bio-deterioration
- black crust
The compressive strength of the stone ranges 0.514MPa while the open porosity ranges 10-25%.
In the archaeological site of Loggos on the other
hand, travertine chronological is positioned to
Pleistocene. The site is placed in a rural environment,
is open with significant temperature variations.
Figure 1. The medieval city of Rhodes.
The stone of the monuments of the medieval city of
Rhodes is petrographically characterized as biogenic
limestone from the local deposits. Its genesis dates
back to the High Pliocene- Low Pleistocene and
consists of rounded fossils joined together with
microsparitic calcitic binder.
The monuments of Rhodes are exposed to marine
environment and they are affected both by direct
Figure 1. The archaeological site of Loggos
The main problems of the stones presented in the site
of Logos are:
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No 2 - Aug 2007
- cracks in stone samples probably due to frost action,
- biological growth,
-colour alteration of stones due to black crust
deposition.
The compressive strength of the stone ranges 1.010MPa while the open porosity ranges 18-22%.
The use of new compatible stone from the ancient
quarries seems impossible as there legislation is
strict. In case of producing artificial stone, the results
of the analysis of the authentic stones are giving the
guidelines for the selection of the raw materials and
the percent that both binders and aggregates are
mixed. From laboratory results seems possible the
production of compatible artificial stone.
44
Results
Limestone is by nature a soft material. Different
decay patterns are observed in lime stones exposed to
different environments. Material loss in the form of
alveolus- degradation and salts are present in the case
of marine environment while cracks due to frost and
loss of material due to biogenic deterioration in the
case of rural environment. In both cases black crust
are present.
Measures against humidity and direct contact with
water may assist towards the direction of protecting
the stones. Their exposure to aggressive
environments seems unavoidable. Our concerns are
to extent their serviceability and retain the authentic
stones in the historic structures.
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45
Pore structure and durability of natural stones: a case study
C. Figueiredo1, R. Folha1, A. Dionísio1, A. Maurício1, C. Alves2, L. Aires-Barros1
1 Center of Petrology and Geochemistry, CEPGIST, IST, Lisbon, Portugal.
2 Centro de Investigação Geológica, Ordenamento e Valorização de Recursos, DCT, University of Minho, Braga, Portugal
Contact e-mail: [email protected]
Some preliminary data obtained, in the framework of
the research Project PORENET-Pore-Structure
Geometry Measurement, Visualization and
Modelling of some Portuguese, Ornamental and
Building Limestones, on pore structures (fluid
transport related properties) and durability (salt
crystallization tests) of limestones are presented. The
pore network is one of the most significant
petrographical components governing the durability
of natural stones. The pore space represents the
preferred area for physical, chemical and biological
weathering processes.
The data presented refer to two commercial varieties
of Portuguese Dimensional Stones (“Semi-rijo” (SR)
and “Moca Creme” (MC)) (Figures 1 and 2). These
stones are both calciclastic limestones widely used
mainly in pavement and cladding inside and outside
buildings. They represent different facies exploited
from the same Bathonian age (Middle Jurassic)
“Valverde” formation belonging to the Limestone
Massif of Estremadura (Mesocenozoic Occidental
Border of Portugal). While the “Semi-rijo” (SR) is a
light beige oolitic, calciclastic limestone, scarcely
bioclastic, the “Moca Creme” (MC) is a beige
limestone, in general, coarsely calciclastic and
abundantly bioclastic. In thin sections, the “Semirijo” (SR) could be classified as fossiliferous
pelmicrosparite/ grainstone and the “Moca Creme”
(MC) as biopelintrasparite/ grainstone.
The methodological approach used to characterize
the pore-structure geometry is based on the combined
application of classical and modern methods and
techniques usually used in the context of fluid flow
studies in engineering, hydrology, sedimentology,
and petroleum industry such as: optical microscopy,
Scanning Electron Microscopy (SEM) and Mercury
Injection Porosimetry (MIP). Besides, fluid
migration physical tests (including open and free
porosity, capillary imbibition, Hirschwald
coefficient) were also performed on core samples of
the limestones, according to European (prEN 1936;
NP EN 1936. 2001) and French (N FB 10-504. 1973)
Standards. Based on the Portuguese Standard NP EN
12370 (2001), the resistance of the limestones to salt
crystallization was also determined.
Regarding the pore system, both varieties (SR and
MC) are moderately porous stones and have an open
porosity accessible to water ranging, respectively,
from 11.2 % to 12.8 % and from 12.1 % to 12.9 %.
The pore network structure is, for both stones,
composed mainly by micropores (pore radius < 7,
5µm) that comprise more than 90 percent of the total
space invaded by mercury injection. The hirschwald
coefficients are, in general, higher than 80 %,
suggesting predominance of freely interconnected
and uniformly distributed pores. The “Moca Creme”
(MC) shows lower values for the capillary kinetic
Figure 1: “Semi-rijo” (SR): Cutting plane showing the
most common aesthetic characteristics.
Figure 2: “Semi-rijo” (SR): Cutting plane showing the
most common aesthetic characteristics.
STONE
No 2 - Aug 2007
46
parameters A (mass increase by area by square root of
time) and B (height of capillary rise by square root of
time), that range, respectively, from 0.143 g.cm-2.h1/2 to 0.256 g·cm-2·h-1/2 and from 0.7872 cm·h-1/2 to
-1/2
1.9029 cm·h . “Semi-rijo” samples have values of A
-2 -1/2
-2 -1/2
ranging from 0.1812 g·cm ·h to 0.2782 g·cm ·h
-1/2
and B ranging from 1.5721 cm·h to 2.0938 cm·h-1/2
(Figures 3 and 4). Based on the durability tests, the
“Moca Creme” seems to be less resistant to salt
crystallization than “Semi-rijo” (Figures 5 and 6).
These results seem to be related with the free porosity
accessible to water at 48 hours (N48, %).
Figure 3: “Semi-rijo” (SR): Water absorption by capillary
action on samples cut ¦ (H) and - (V) to the bedding planes.
Figure 5: “Semi-rijo” (SR): cubic samples before (a) and
after (b) the salt crystallization tests.
Figure 4: “Moca Creme” (MC): Water absorption by
capillary action on samples cut ¦ (H) and - (V) to the
bedding planes.
Figure 6: “Moca Creme” (MC): cubic samples before (a)
and after (b) the salt crystallization tests.
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47
Weathering effect in urban environment: a case study of a French porous limestone
K. Beck, M. Al-Mukhtar, I. Rannou, X. Brunetaud
Centre de Recherche sur la Matière Divisée, Université d'Orléans - CNRS-CRMD, Orléans, France.
Contact e-mail: [email protected]
This publication deals with a case study of a highly
porous limestone taken in urban environment. The
studied building stone is the white tuffeau, which is
commonly used in most of the monuments built
along the Loire valley in France (Loire Castles). This
porous limestone (porosity about 45%) is very
sensitive to atmospheric conditions (pollution, salts,
water movement, …). The studied stone sample
comes from a building site of restoration in the centre
town of Orleans.
thin slice sampling
100
gypsum
calcite
quartz
crystal orientation effect
90
Diffraction relative intensity (%)
according to two processes: traditional XRD analysis
on the stone powder obtained every 5 mm starting
from external surface and original XRD analysis on
the whole sample (thin slice of solid stone) with
displacements of beam (analyzer) every 0.1 mm in
order to detect mineralogical modifications more
precisely.
80
70
60
50
40
30
20
10
0
0
2
4
6
8
10
Depth (mm)
Figure 1: Changes in the relative phase diffraction
intensity with stone depth.
The weathering effect is analysed according to the
depth of the stone by several complementary
techniques of characterization in a multi-scales
approach: mechanical resistance (compressive
strength test), capillary absorption (imbibition test),
mercury intrusion porosimetry (MIP), chemical
analysis (ICP, ATG), SEM image analysis, X-ray
diffraction (XRD).
The visual aspect of the weathered stone shows the
presence of a black crust in the outside surface.
Below the black crust, a number of microscopic
cracks can be observed on 2 mm from the stone
surface. Nevertheless, the deterioration process is not
limited to this visible surface zone. Indeed, the result
of mineralogical characterization reveals that the
gypsum content decreases from a high value at the
surface (black crust) to much lower values in the
depth of the stone. XRD analysis are carried out
Figure 2: Elementary cartography by EDX analysis (Si,
Ca, S.
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Results of XRD analysis on the bulk sample are
presented in figure 1. Considering only the three
main mineralogical phases (calcite, quartz and the
gypsum which is a product of weathering), the
variation of the relative proportions of these three
phases can be evaluated. The quartz content is overall
stable according to the depth, but the calcite content
and the gypsum content changes.The proportion of
gypsum highly decreases within the first two
millimetres, and then continues to decrease slightly.
These measurements were confirmed by several
quantitative analyses (ICP, TGA) and are in
agreement with the elementary cartography made by
EDX analysis on SEM images (figure 2).
Moreover, this sample is characterized by the
presence of an orange edging located at a regular
48
depth of 20 mm. This edging is constituted by fine
orange particles of organic origin naturally present in
the stone but accumulated because of the water
movements at this distance from outside surface.
Mineralogical analysis shows that gypsum is only
detected in this zone limited to 20 mm of depth which
can be considered as the weathered zone.
Finally, the zone highly degraded by the microscopic
cracks is limited to 2 mm of depth with a high gypsum
content. Moreover, results obtained allowed to
conclude that in the urban environment in which this
stone was used, water movement and weathering
effect are dependant and limited to 20mm from the
outside surface of this highly porous limestone.
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49
Relationship between the durability and fabric of Hungarian porous limestones, a
laboratory testing approach
A. Török, Z. Pápay
Department of Construction Materials & Engineering Geology, Budapest University of Technology and Economics,
Hungary.
Contact e-mail: [email protected]
The Miocene porous limestones are the most
common dimension stones of Budapest. Most of
these buildings are now showing signs of
deterioration, which is caused by air-pollution, salt
crystallization and freeze-thaw. Four types of porous
limestones; a fine-grained, two medium-grained and
a coarse-grained bioclastic were studied. The
porosity values were between 20 % (coarse
bioclastic) and 36% (fine-grained).
Cyclic freeze-thaw tests and salt crystallization tests
were performed under laboratory conditions to
understand the mechanism of decay and the
behaviour of lithotypes. Cylindrical specimens with
diameter of 40 mm and height of app. 40 mm to 80
mm were used for the tests. Specimens were divided
into analytical groups on the basis of non-destructive
tests (density, ultrasonic sound velocity). For sodium
sulphate tests 14 m% of Na2SO4.10H2O solution
was used according to EN 12370. The samples were
immersed for 24 hours and than dried at 105 °C and
cooled down at room temperature. The weight loss
was recorded after each cycle. Water saturation tests,
and 5 to 10 freeze-thaw cycles (6 hours of freeze and
6 hours of thaw) were also applied. Changes in
weight, in tensile- and uniaxial compressive strength
(UCS) as well as in ultrasonic sound velocities were
recorded.
lithotypes. Samples of fine-grained limestone
damaged the most.
Comparing the salt-crystallization tests and freezethaw simulations it seems that salt caused a
significant weight loss and some samples were
entirely damaged after 4 cycles (Fig. 1).
Simulation experiments have shown that there is a
drop in strength values from air dry to water saturated
and to freeze-thaw experienced samples. Similar
trend was observed when average tensile strength
values of air dry, water saturated and freeze-thaw
conditioned specimens were compared (Fig. 2 and 3).
Figure 2: Compressive strength after freeze-thaw cycles
Freeze-thaw tests and salt weathering tests caused
micro-cracking and granular disintegration on most
Figure 1: Material loss after freeze-thaw and sulphatecrystallization cycles for fine-grained and mediumgrained limestone
Figure 3: Tensile strength after freeze-thaw cycles
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These experiments pointed out the importance of
laboratory simulations in stone durability
assessment. Test results have also demonstrated that
various decay processes such as salts or freeze-thaw
cycles can result in very similar decay patterns,
50
including the formation of micro-cracks and
detachment of damage layers. Our observations also
proved that there are many similarities between the
behaviour and decay mechanism of Hungarian and
other porous limestones.
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51
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Physical changes of porous Hungarian limestones related to silica-acid-ester consolidant
treatments
Z. Pápay, A, Török
Department of Construction Materials & Engineering Geology, Budapest University of Technology and Economics,
Hungary.
Contact e-mail: [email protected]
Porous limestones are widely used in the monuments
of Hungary, and are often treated by stone
consolidants on site during restoration works. Two
types of porous Miocene limestones from Sóskút
were treated with dilute and concentrated silica-acidester under laboratory conditions. The aim of the
experiments was to assess the performance of the
consolidant.
(EN 1936:2000) were measured before and after the
treatment of specimens to detect the physical
changes. Efficiency of Type A and Type B silica-acidester consolidant was evaluated by comparing the
uniaxial strength (Brazilian test) of untreated and
silica acid ester treated specimens.
Two types of porous Miocene limestones (a mediumgrained oolitic type and fine grained more micritic
variety) were used for tests (Fig. 1).
The test results are summarized in Table 1. It shows
the differences in properties related to consolidation
tests. The amounts of silica gel precipitated in the
pores of the two limestone types are only a few
percent - 3.75 V% and 3.23 V% in medium-grained
and 5.19 V% and 4.03 V% in fine-grained limestone despite the 23% and 37% of effective porosity of
medium-grained of fine-grained limestone,
respectively.
Table 1: Changes in selected physical properties due to
consolidation (in percentage)
Apparent
density
Ultrasonic
velocity
Open
porosity
Tensile
strength
Treated with
type A
+3.78 %
+ 6.67 %
- 16.22 %
+ 22.54 %
Treated with
type B
+2.61 %
+ 11.36 %
- 13.97 %
+ 36.89 %
Treated with
type A
+8.69 %
+ 7.42 %
- 13.95 %
+ 19.70 %
Treated with
type B
+6.26 %
+ 14.62 %
- 10.85 %
+ 25.76 %
Treated specimens
Mediumgrained
limestone
Figure 1: Fabric and microscopic image of mediumgrained (a,c)and fine-gained (b,d) limestone
Cylindrical specimens of 40 mm in diameter and 20
mm of height were divided into groups on the basis of
non-destructive tests (density, ultrasonic sound
velocity). The specimens were consolidated by using
vacuum impregnation. The applied silica-acid-ester
consolidant is well-known and widely used. A diluted
and a concentrated form were used. Type A consisted
of 100 m% of silica-acid-ester, while Type B
consisted of 20 m% of silica-acid-ester. The solvent
for the latter one was aliphatic carbohydrate. In the
presence of water silica-acid-ester transforms to
silica gel, which fills the pores and forms silicate
bonds between the particles. Ultrasonic sound
velocity (EN 14579:2005), density and open porosity
Finegrained
limestone
The densities of the two limestones have increased
when the consolidants were applied. Type A
consolidant caused larger increase in density than the
dilute one (Type B, Table 1). The effective porosity
values show a drastic decrease which is in the order of
10 to 16% indicating that silica gel preferentially
occluded connected pores. The highest increase in
tensile strength was recorded for medium-grained
limestone treated by Type B consolidant (+ 36,89 %).
There is a 63% difference in the affectivity of Type B
and Type A since the letter one only caused a 22,54 %
of increase in strength. The same tendency is
observed at fine-grained limestone (Table 1).
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No 2 - Aug 2007
It seems that the diluted silica acid ester strengthen
these porous limestones more effectively. A fairly
good correlation was found between ultrasonic sound
velocity and tensile strength measured on treated and
non-treated specimens (Fig. 2).
Consolidation by silica acid ester increased the
density, the ultrasonic sound velocity and decreased
the porosity of the medium- and the fine-grained
limestone. When the two consolidating agents are
compared the one, which contains diluted silica acid
ester (Type B) increased the tensile strength more
effectively than concentrated one (Type A). The
tensile strength of the consolidated porous
limestones can be estimated by measuring ultrasonic
sound velocity.
52
Figure 2: Correlation of ultrasonic sound velocity and
tensile strength
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53
Recording wathering and decay:
Case hardening of bioclastic
limestone through absorption
of mortar into ashlar blocks
(Sliema, Malta)
(Picture: M. Gomez-Heras)
Alveolar weathering
exploiting a combination of
surface hardening and
complex patterns of
bioturbation leading
ultimately to a cavernous
“latticework” decay of
complete blocks (Victoria,
Gozo, Malta).
(Picture: M. Gomez-Heras)
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54
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Combination of alveolar
weathering and casehardening through
absorption of mortar leading
to catastrophic decay of
individual ashlar blocks
(Fortress of the Knights of St
John, Rhodes, Greece).
(Picture: B. J. Smith)
A detail of the walls of Victoria in Gozo,
revealing hard Portland cement repair mortar
standing proud as the softer limestone blocks it
surrounds decay more rapidly.
(Picture: K. R. Dotter)
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55
Example of marine karst on
the coast of Sliema (Malta) solution pans modified by
salt action.
(Picture: M. Gomez-Heras)
Outcrop on the north coast of
the island of Gozo showing
different erosion patterns in
Miocene units in the Maltese
archipelago: raised wave-cut
platform of Middle
Globigerina limestone and
mesa showing a harder softer - harder stone
succession of Limestone and
grey marl belonging to the
Upper Globigerina
Limestone Member.
(Picture: M. Gomez-Heras)
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NEWLY FUNDED PROJECTS:
The impact of climate change on weathering in
urban environments: prediction and mitigation.
One of the main impacts on the west of Scotland of
changes in the UK climate will be an increase in
average temperature and the intensity of rainfall. The
potential effect of these changes on the historic
landscape within urban and rural environments has
received very little attention. Most of the work
carried out to date has focused on adapting buildings
and categorising the decay to facades rather than
assessing how to preserve the stone and prevent
further deterioration. This project will examine past
and present-day stone decay in order to predict how it
will change with the climate. The project partners are
Historic Scotland and the British Geological Survey
and they will bring to this study their invaluable
expertise in conservation of buildings and
monuments and the geological background and
sources of Scottish sandstones.
56
X-rays penetrate through the rock the technique
captures the millimeter scale 3D structure of the
sandstones. Preliminary results obtained from two
Glasgow stones courtesy of Iain Young and Cheryl
Wood at the University of Abertay are shown below.
From the tomography images (left hand side) the
software calculates the volume of each pore and sorts
them by size. The graphs illustrate the degree of
connectivity of each pore from the two areas in each
stone sample that have been analysed. The data show
that the near-surface weathered areas are surprisingly
more permeable than the interior of the sandstones
reflecting the complex nature of the decay processes
on the millimeter-scale.
These initial results have helped to show the
multifaceted nature of Scottish sandstone decay and
the need for much more detailed investigations,
which will be undertaken within this project.
Contact details:
Laura Duthie,
Department of Geographical and Earth Sciences,
Gregory Building,
University of Glasgow,
Glasgow G12 8QQ.
[email protected]
Three of the key objectives of the research are to:
· Clarify the mechanisms of weathering from
mineralogical, geochemical and microbiological
perspectives.
· Quantify the rates of weathering at the present-day
in the recent past and also to predict how these will
change in the future.
· Assess a range of strategies to prevent or slow
further decay.
In this project we will study weathered sandstones
from buildings of different ages, principally in
Glasgow, and undertake experiments on recently
quarried rocks of equivalent mineralogy and
petrophysical characteristics. One technique which
has proved to be of particular use in quantifying the
porosity and permeability of the sandstones is X-ray
tomography. Using high resolution X-rays together
with advanced software, the technique enables
calculation of the porosity, permeability, fluid
intrusion and retention, and other properties. As the
Preliminary results of high resolution X-rays tomography, as
described in the text.
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NEWS
57
Job oportunities:
Two mid-term (17 and 10 months) and 3 shortterm (6 months) research and training stages.
CSIC, Spain.
Funding oportunities:
Conservation guest scholar grants
The J Paul Getty Trust invites applications for its
conservation guest scholar grants. This program at
the Getty Conservation Institute supports new ideas
and perspectives in the field of conservation, with an
emphasis on the visual arts, including sites, buildings
and objects, and the theoretical underpinning of the
field.
These grants are for established conservators,
scientists and professionals who have attained
distinction in conservation and allied fields and who
wish to pursue scholarly research in an
interdisciplinary manner across traditional
boundaries.
Scholars are in residence at the Getty Center for three
to nine consecutive months. A monthly stipend of
$3,500 is awarded, up to a maximum of $31,500.
Deadline: November 2007
Further information:
http://www.getty.edu/grant/research/
COST Open Call for proposals to support
scientific and technical collaboration in Europe
COST invites researchers throughout Europe to
submit proposals for research networks and use this
unique opportunity to exchange knowledge and to
embark on new European perspectives.
COST’s main objective is to stimulate new,
innovative and interdisciplinary scientific networks
in Europe. COST activities (Actions) are carried out
by research teams to strengthen the foundations for
building scientific excellence in Europe. This
continuous call is thematically open. Proposals
playing a precursor role for other European
programmes involving young groups’ ideas are
especially welcome.
Deadline: 30th September 2007
Further information:
Http://www.cost.esf.org/index.php?id=721
The topics and positions are the following:
1 . M O RTA R S A N D C O N C R E T E I N
MONUMENTS (17 months). Instituto Eduardo
Torroja de Ciencias de la Construccion (IETCC),
Madrid, Spain.
2. ASSESSMENT OF THE DURABILITY OF
BUILDING STONES BY MEANS OF NONDESTRUCTIVE TECHNIQUES (10 months).
Instituto de Geología Economica (IGE), Madrid,
Spain.
3 . C H R O M AT I C D E T E R I O R AT I O N O F
NATURAL AND ARTIFICIAL MATERIALS IN
FAÇADES (6 months). Instituto Eduardo Torroja de
Ciencias de la Construccion (IETCC), Madrid,
Spain.
4. ATOMIC FORCE MICROSCOPY FOR THE
STUDY OF CULTURAL HERITAGE ASSET
SURFACES (6 months). Instituto de Ciencia de
Materiales (ICMSE), Sevilla, Spain.
5. DEGRADATION AND CONSERVATION
TECHNIQUES OF ARCHITECTURAL
HERITAGE (6 months). Instituto de Geología
Economica (IGE), Madrid, Spain.
Eligibility:
This action supports the initial training of
researchers, typically during the first four year of
their research careers, starting at the date of obtaining
the degree which would formally entitle them to
embark on a doctorate. We are looking for young and
highly motivated individuals with a M Sc in Geology
(positions 1, 2 and 5), Material Sciences (position 3),
and Chemistry or Physics (position 4). Other related
specializations will be also considered. The
candidates should have a strong background and
currently undertaking studies in a subject area similar
to that of the training site. A high level of English skill
is required.
The applications should include experience in the
field of research, aptitude of the candidate to carry
out an individual training/mobility project, capability
for integration in a research team, potential for
STONE
58
No 2 - Aug 2007
excellence, impact and the benefit of the proposed
training to the individual fellow’s research career and
their origin country, academic degree obtained and
date, list of scientific publications and participation
in congresses, willingness to carry out an intense
research training programme, and potential interest
in a multidisciplinary research based on Cultural
Heritage.
The positions are not available to Spanish or EU
citizens with residence in Spain, but to EU citizens.
Contact:
Candidates are invited to send an application letter
indicating the position requested, a European CV and
two reference letters to the project coordinator: Prof.
Dr. C. Saiz-Jimenez, Instituto de Recursos Naturales
y Agrobiologia, Apartado 1052, 41080 Seville,
Spain. Email: [email protected]
It is essential to reveal the fundamental mechanisms
leading to salt damage, to identify the key parameters
controlling the process, and to use this knowledge for
the development of new methods for repair and
maintenance.
This conference addresses the problems of saltinduced decay on buildings and sculptures from a
scientific and as well as a practical perspective.
Restoration and conservation techniques for salt
contaminated structures and objects are also in focus.
The conference provides a forum forpractitioners and
scientists to present and discuss recent findings
within the field.
Key dates
Deadline for submission of abstracts: 1 October 2007
Acceptance of abstracts: 1 December 2007
Deadline for registration and submission of full
papers: 1 June 2008
Deadline:
1st September 2007, extended to 15th September
2007 only in the case that not applications be received
for a position.
Further information:
http://www.swbss.dk
Education:
Forthcoming events:
Joint II level master course and PhD:
Salt weathering on buildings and stone sculptures
Economics and techniques for the conservation of
the architectural and environmental heritage
sciences for conservation, economics and
creativity - SCEC
University of Nova Gorica
Universita Iuav di Venezia
Universita degli Studi di Udine
Universita degli Studi di Napoli
Federico II
Soluble salts are a principal agent of decay of porous
building materials. The crystallization of soluble
salts can cause characteristic pitting, powdering and
exfoliation of surfaces. This is particularly damaging
to decorated masonry surfaces and sculpture on
buildings.
The course in “Economics and Techniques for the
Conservation of the Architectural and Environmental
Heritage - SCEC” has been jointly established by the
University of Nova Gorica, Università IUAV di
Venezia, Università di Napoli Federico II and in
collaboration with Università degli Studi di Udine.
The duration of the Master programme is one year. It
features a preliminary common instruction period
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No 2 - Aug 2007
which further divides in two specialisations:
“Techniques and Materials in Conservation of the
Architectural Heritage” (technical issues of
conservation), and “Managerial Science and
Economics of the Cultural Heritage” (economic
aspects of conservation).
Students that successfully accomplish the master
course may be admitted to the PhD. In this case the
PhD lasts two years, for a total duration of three
years.
The official language is English. Lectures are in
English and Italian.
The first year of the programme includes three
educational periods:
- The 1st period (12 credits) is obligatory for the two
specializations (see below) and focuses on theoreticmethodological issues and the knowledge of
architectural and environmental heritage (preparing
the scientific education of the second and third
period).
- The 2nd period (28 credits) is divided into two
specializations:
“Techniques and Materials in Conservation of the
Architectural Heritage”
“Managerial Science and Economics of the Cultural
Heritage”
59
Recently listed publications on stone
decay:
Papers:
(As listed in ISI-Thompson database)
Bonazza A, Brimblecombe P, Grossi CM, et al. Carbon in black
crusts from the Tower of London. Environmental Science &
Technology 41 (12): 4199-4204 JUN 15 2007.
Cardell C, Sanchez-Navas A, Olmo-Reyes FJ, et al. Powder Xray thermodiffraction study of mirabilite and epsomite
dehydration. Effects of direct IR-irradiation on samples.
Analytical Chemistry 79 (12): 4455-4462 JUN 15 2007.
Grossi CM, Brimblecombe P, Harris I. Predicting long term
freeze-thaw risks on Europe built heritage and archaeological
sites in a changing climate. Science of The Total Environment
377 (2-3): 273-281 MAY 15 2007.
Thornbush MJ, Viles HA. Simulation of the dissolution of
weathered versus unweathered limestone in carbonic acid
solutions of varying strength. Earth Surface Processes and
Landforms 32 (6): 841-852 MAY 2007.
Brai M, Camaiti M, Casieri C, et al. Nuclear magnetic resonance
for cultural heritage. Magnetic Resonance Imaging 25 (4): 461465 MAY 2007.
Giordano R, Teixeira J, Triscari M, et al. Porosimetric and
particle-size measurements by small-angle neutron scattering.
European Journal of Mineralogy 19 (2): 223-228 MAR-APR
2007.
Books and Special Issues:
- The 3rd period (20 credits) includes thesis
elaboration, tutoring and stage (if required).
The accomplishment of the Masters (MsC), which
requires total attendance of courses, and final
evaluation, will assign 60 university credits (CFU);
the Doctoral Programme will assign 180 credits
(CFU).
A certificate of attendance will be issued after each
period.
Beginning of courses
End of courses
Thesis defense
Application deadlines
October 2007
February 2008
Sept.or Dec. 2008
15 September 2007
Further information:
http://www.p-ng.si/en/academic-programmes/6500/
Programme Director:
Sasa Dobricic e-mail: [email protected]
Prikryl, R., Smith, B.J. (Eds), 2007. Building Stone Decay:
From Diagnosis to Conservation. Geological Society, London,
Special Publications, 271
Special issue on salt decay. Environmental Geology 52(2)
March 2007 (Edited by M. Steiger & S. Siegesmund)
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