UNIFIED FACILITIES CRITERIA (UFC) SOIL STABILIZATION FOR PAVEMENTS

UNIFIED FACILITIES CRITERIA (UFC) SOIL STABILIZATION FOR PAVEMENTS
UFC 3-250-11
16 January 2004
UNIFIED FACILITIES CRITERIA (UFC)
SOIL STABILIZATION FOR
PAVEMENTS
APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED
UFC 3-250-11
16 January 2004
UNIFIED FACILITIES CRITERIA (UFC)
SOIL STABILIZATION FOR PAVEMENTS
Any copyrighted material included in this UFC is identified at its point of use.
Use of the copyrighted material apart from this UFC must have the permission of the
copyright holder.
U.S. ARMY CORPS OF ENGINEERS (Preparing Activity)
NAVAL FACILITIES ENGINEERING COMMAND
AIR FORCE CIVIL ENGINEER SUPPORT AGENCY
Record of Changes (changes are indicated by \1\ ... /1/)
Change No.
Date
Location
This UFC supersedes TM 5-822-14, dated 25 October 1994. The format of this UFC does not
conform to UFC 1-300-01; however, the format will be adjusted to conform at the next revision.
The body of this UFC is the previous TM 5-822-14, dated 25 October 1994.
1
UFC 3-250-11
16 January 2004
FOREWORD
\1\
The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides
planning, design, construction, sustainment, restoration, and modernization criteria, and applies
to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordance
with USD(AT&L) Memorandum dated 29 May 2002. UFC will be used for all DoD projects and
work for other customers where appropriate. All construction outside of the United States is
also governed by Status of forces Agreements (SOFA), Host Nation Funded Construction
Agreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA.)
Therefore, the acquisition team must ensure compliance with the more stringent of the UFC, the
SOFA, the HNFA, and the BIA, as applicable.
UFC are living documents and will be periodically reviewed, updated, and made available to
users as part of the Services’ responsibility for providing technical criteria for military
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Engineering Command (NAVFAC), and Air Force Civil Engineer Support Agency (AFCESA) are
responsible for administration of the UFC system. Defense agencies should contact the
preparing service for document interpretation and improvements. Technical content of UFC is
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UFC are effective upon issuance and are distributed only in electronic media from the following
source:
•
Whole Building Design Guide web site http://dod.wbdg.org/.
Hard copies of UFC printed from electronic media should be checked against the current
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AUTHORIZED BY:
______________________________________
DONALD L. BASHAM, P.E.
Chief, Engineering and Construction
U.S. Army Corps of Engineers
______________________________________
DR. JAMES W WRIGHT, P.E.
Chief Engineer
Naval Facilities Engineering Command
______________________________________
KATHLEEN I. FERGUSON, P.E.
The Deputy Civil Engineer
DCS/Installations & Logistics
Department of the Air Force
______________________________________
Dr. GET W. MOY, P.E.
Director, Installations Requirements and
Management
Office of the Deputy Under Secretary of Defense
(Installations and Environment)
2
ARMY TM 5-822-14
AIR FORCE AFJMAN 32-1019
SOIL STABILIZATION FOR PAVEMENTS
APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED
DEPARTMENT OF THE ARMY, THE NAVY, AND THE AIR FORCE
OCTOBER 1994
TM 5-822-14/AFJMAN 32-1019
REPRODUCTION
AUTHORIZATION/RESTRICTIONS
This manual has been prepared by or for the Government and, except
to the extent indicated below, is public property and not subject to
copyright.
Copyrighted material included in the manual has been used with the
knowledge and permission of the proprietors and is acknowledged as
such at point of use. Anyone wishing to make further use of any
copyrighted material, by itself and apart from this text, should seek
necessary permission directly from the proprietors.
Reprints or republications of this manual should include a credit
substantially as follows: “‘Joint Departments of the Army and Air
Force, USA, TM 5-822-14/AFMAN 32-8010, Soil Stabilization for
Pavements,” 25 October 1994.
If the reprint or republication includes copyrighted material, the
credit should also state: ‘Anyone wishing to make further use of
copyrighted material, by itself and apart from this text, should seek
necessary permission directly from the proprietors.”
TM 5-822-14/AFJMAN 32-1019
A
TECHNICAL MANUAL
NO. 5-822-14
AIR FORCE MANUAL
NO. 32-1019
HEADQUARTERS
DEPARTMENTS OF THE ARMY,
AND THE AIR FORCE
WASHINGTON, DC, 25 October 1994
SOIL STABILIZATION FOR PAVEMENTS
1.
CHAPTER
CHAPTER
2.
3.
CHAPTER
4.
CHAPTER
CHAPTER
5.
Paragraph
Page
INTRODUCTION
Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Uses of Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-1
1-2
1-3
1-4
1-5
1-1
1-1
1-1
1-1
1-1
SELECTION OF ADDITIVE
Factors to be Considered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Use of Stabilized Soils in Forst Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thickness Reduction for Base and Subbase Courses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2-1
2-2
2-3
2-1
2-2
2-4
DETERMINATION OF STABILIZER CONTENT
Stabilization with Portland Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stabilization with Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stabilization with Lime-Fly Ash (LF) and Lime Centment-Fly Ash (LCF) . . . . . . . . . . . . . . . . . .
Stabilization with Bitumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stabilization with Lime-Cement and Lime-Bitumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lime Treatemt of Expansive Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3-1
3-2
3-3
3-4
3-5
3-6
3-1
3-3
3-5
3-6
3-8
3-8
DETERMINATION OF STABILIZER CONTENT
Construction with Portland Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Construction with Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Construction with Lime-Fly Ash (LF) and Lime-Cement-Fly Ash (LCF) . . . . . . . . . . . . . . . . . . .
Construction with Bitumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-1
4-2
4-3
4-4
4-1
4-10
4-20
4-20
QUALITY CONTROL
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cement Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lime Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lime-Fly Ash (LF) and Lime-Cement-Fly Ash (LCF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bituminous Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-1
5-2
5-3
5-4
5-5
5-1
5-1
5-1
5-2
5-2
APPENDIX A.
REFERENCES
A-1
APPENDIX
B.
pH TEST ON SOIL-CEMENT MIXTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B-1
APPENDIX
C.
DETERMINATION OF SULFATE IN SOILS, GRAVIMETRIC METHOD . . . . . . . . . . . . . . .
C-1
APPENDIX D.
pH TEST TO DETERMINE LIME REQUIREMENTS FOR LIME
STABILIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D-1
List of Figures
Figure
2-1.
3-1.
4-1.
4-2.
4-3.
4-4.
4-5.
4-6.
4-7.
4-8.
4-9.
4-10.
4-11.
Gradation triangle for aid in selecting a commercial stabilizing agent.
Chart for the initial determination of lime content.
Transverse single-shaft mixer processing soil cement in place. Multiple passes are required.
Multiple-transverse-shaft mixer mixing soil, cement, and water in one pass.
Windrow-type traveling pugmill mixing soil-cement from windrows of soil material.
Twin-shaft, continuous-flow central mixing plant mixing soil, cement, and water.
Batch-type central plant used for mixing soil-cement.
Rotary-drum central mixing plant.
Bulk portland cement being transferred pneumatically from a bulk transport truck to a job
truck.
Mechanical cement spreader attached to a job dump truck spreading cement in regulated
quantities.
Windrow-type mechanical spreader is used to place cement on the top of a slightly flattened
windrow of borrow soil material.
Sketch of soil-cement processing operations with windrow-type traveling pugmill.
Plan for processing with windrow-type traveling pugmill.
2-2
3-4
4-2
4-2
4-2
4-2
4-2
4-2
4-3
4-3
4-3
4-5
4-6
APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED
i
TM 5-822-14/AFJMAN 32-1019
List of Figures (cont*d)
Page
Figure
4-12.
4-13.
4-14.
4-15.
4-16.
4-17.
4-18.
4-19.
4-20.
4-21.
4-22.
4-23.
4-24.
4-25.
4-26.
4-27.
4-28.
4-29.
4-30.
4-31.
4-32.
4-33.
4-34.
4-35.
4-36.
4-37.
4-38.
4-39.
4-40.
4-41.
4-42.
4-43.
4-44.
4-45.
4-46.
4-47.
4-48.
4-49.
4-50.
4-51.
4-52.
4-53.
4-54.
4-55.
4-56.
4-57.
4-58.
C-1.
Sketch of soil-cement processing operations with multiple-transverse-shaft traveling mixing
machine.
Plan for processing with multiple-transverse-shaft traveling mixing machine.
Sketch of soil-cement processing operations with single-transverse shaft mixers.
In-place mixing of lime with existing base and paving material on city street.
Off-site mixing pads for Mississippi River levee repair project.
Deep stabilization after lime spreading the plow cuts 24 inches deep.
Root plow for scarifying to a depth of 18 inches.
Scarifying existing clay subgrade with lime on city street project.
Lime-treated gravel with lime fed by screw conveyor.
Lime-cement-fly ash aggregate base course.
Enclosed soil holds lime for adding to marginal crushed stone base material.
Lime slurry pressure injection (LSPI) rig treating a failed highway slope.
Application of lime by the bag for a small maintenance project.
Application of lime by a bulk pneumatic truck.
Bulk pneumatic truck spreading lime from bar spreader.
Distribution of quicklime from mechanical spreader on city street.
Spreading of granular quicklime.
Slurry mixing tank using recirculating pump for mixing hydrate and water.
Jet slurry mixing plant.
Spreading of lime slurry.
Recirculation pump on top of a 6,000-gallon wagon agitates slurry.
Grader-scarifier cutting slurry into stone base.
Portabatch lime slaker.
Watering of lime-treated clay on airport project.
Mixing with a disc harrow.
Rotary mixer.
Train of rotary mixers.
Rotary mixer on primary road project.
Self-propelled sheepsfoot roller.
Double sheepsfoot roller.
Pneumatic roller completes compaction of LCF base.
Vibrating roller completes compaction of subgrade.
Windrow-type pugmill travel plant.
Hopper-type pugmill travel plant.
Multiple rotary mixer.
A processing chamber of a multiple rotary mixer.
Single-shaft rotary mixer with asphalt supply tank.
Single-shaft rotary mixer without asphalt.
Mixing with motor grader.
Distributor applying asphalt.
Spreading and compacting train.
Stationary cold-mix plant.
Flow diagram of a typical cold-mix continuous plant.
Spreading cold mix with conventional paver.
Spreading cold mix with full-width cutter-trimmer modified for paving.
Jersey spreader.
Towed-type spreader.
Example standard curve for spectrophotometer.
4-6
4-7
4-8
4-11
4-11
4-11
4-11
4-11
4-12
4-12
4-12
4-12
4-13
4-13
4-13
4-13
4-15
4-16
4-16
4-16
4-16
4-16
4-16
4-18
4-18
4-18
4-18
4-18
4-19
4-19
4-20
4-20
4-21
4-21
4-21
4-21
4-22
4-22
4-22
4-22
4-25
4-26
4-26
4-26
4-26
4-27
4-27
C-3
List of Tables
Table
2-1.
2-2.
2-3.
3-1.
3-2.
3-3.
3-4.
3-5.
3-6.
3-7.
3-8.
ii
Guide for selecting a stabilizing additive.
Minimum unconfined compressive strength for cement, lime, lime-cement, and lime-cementfly ash stabilized soils.
Durability requirements.
Gradation requirements for cement stabilized base and subbase courses.
Cement requirements for various soils.
Gradation requirements for lime stabilized base and subbase courses.
Gradation requirements for fly ash stabilzed base and subbase courses.
Recommended gradations for bituminous stabilized subgrade materials.
Recommended gradations for bituminous stabilized base and subbase materials.
Emulsified asphalt requirements.
Swell potential of soils.
2-3
2-4
2-4
3-1
3-2
3-3
3-5
3-7
3-7
3-8
3-9
TM
5-822-14/AFJMAN
32-1019
CHAPTER 1
INTRODUCTION
1-1. Purpose. This manual establishes criteria
for improving the engineering properties of soils
used for pavement base courses, subbase courses,
and subgrades by the use of additives which are
mixed into the soil to effect the desired improvement. These criteria are also applicable to
roads and airfields having a stabilized surface
layer.
1-2. Scope. This manual prescribes the appropri-
ate type or types of additive to be used with
different soil types, procedures for determining a
design treatment level for each type of additive,
and recommended construction practices for incorporating the additive into the soil. It applies to all
elements responsible for Army and Air Force
pavement and design construction.
1-3. References. Appendix A contains a list of
references used in this manual.
1-4. Definitions.
a. Soils. Naturally occurring materials that are
used for the construction of all except the surface
layers of pavements (i.e., concrete and asphalt) and
that are subject to classification tests (ASTM D
2487) to provide a general concept of their engineering characteristics.
b. Additives. Manufactured commercial products
that, when added to the soil in the proper quantities, improve some engineering characteristics of
the soil such as strength, texture, workability, and
plasticity. Additives addressed in this manual are
limited to portland cement, lime, flyash, and bitumen.
c. Stabilization. Stabilization is the process of
blending and mixing materials with a soil to
improve certain properties of the soil. The process
may include the blending of soils to achieve a
desired gradation or the mixing of commercially
available additives that may alter the gradation,
texture or plasticity, or act as a binder for cementation of the soil.
d. Mechanical stabilization. Mechanical stabilization is accomplished by mixing or blending soils
of two or more gradations to obtain a material
meeting the required specification. The soil blending may take place at the construction site, a
central plant, or a borrow area. The blended
material is then spread and compacted to required
densities by conventional means.
e. Additive stabilization. Additive stabilization
is achieved by the addition of proper percentages
of cement, lime, fly ash, bitumen, or combinations
of these materials to the soil. The selection of type
and determination of the percentage of additive to
be used is dependent upon the soil classification
and the degree of improvement in soil quality
desired. Generally, smaller amounts of additives
are required when it is simply desired to modify
soil properties such as gradation, workability, and
plasticity. When it is desired to improve the
strength and durability significantly, larger quantities of additive are used. After the additive has
been mixed with the soil, spreading and compaction are achieved by conventional means.
f. Modification. Modification refers to the stabilization process that results in improvement in
some property of the soil but does not by design
result in a significant increase in soil strength and
durability.
1-5. Uses of Stabilization. Pavement design is
based on the premise that minimum specified
structural quality will be achieved for each layer
of material in the pavement system. Each layer
must resist shearing, avoid excessive deflections
that cause fatigue cracking within the layer or in
overlying layers, and prevent excessive permanent
deformation through densification. As the quality
of a soil layer is increased, the ability of that layer
to distribute the load over a greater area is
generally increased so that a reduction in the
required thickness of the soil and surface layers
may be permitted.
a. Quality improvement. The most common improvements achieved through stabilization include
better soil gradation, reduction of plasticity index or swelling potential, and increases in durability and strength. In wet weather, stabilization
may also be used to provide a working platform
for construction operations. These types of soil
quality improvement are referred to as soil modification.
b. Thickness reduction. The strength and stiffness of a soil layer can be improved through the
use of additives to permit a reduction in design
thickness of the stabilized material compared with
an unstabilized or unbound material. Procedures
for designing pavements that include stabilized
soils are presented in TM 5-822-5/AFM 88-7,
Chap. 3, TM 5-825-2/AFM 88-6, Chap. 2, TM
1-1
TM 5-822-14/AFJMAN 32-1019
5-825-3/AFM 88-6, Chap. 3. The design thickness
of a base or subbase course can be reduced if the
stabilized material meets the specified gradation,
1-2
strength, stability, and durability requirements
indicated in this Technical Manual for the particular type of material.
TM
5-822-14/AFJMAN
32-1019
CHAPTER 2
SELECTION OF ADDITIVE
2-1. Factors to be Considered. In the selection
of a stabilizer, the factors that must be considered
are the type of soil to be stabilized, the purpose for
which the stabilized layer will be used, the type of
soil improvement desired, the required strength
and durability of the stabilized layer, and the cost
and environmental conditions.
a. Soil types and additives. There may be more
than one candidate stabilizer applicable for one
soil type, however, there are some general guidelines that make specific stabilizers more desirable
based on soil granularity, plasticity, or texture.
Portland cement for example is used with a variety of soil types; however, since it is imperative
that the cement be mixed intimately with the
fines fraction (< .074 mm), the more plastic materials should be avoided. Generally, well-graded granular materials that possess sufficient fines to
produce a floating aggregate matrix (homogenous
mixture) and best suited for portland cement stabilization. Lime will react with soils of medium to
high plasticity to produce decreased plasticity,
increased workability, reduced swell, and increased strength. Lime is used to stabilize a
variety of materials including weak subgrade soils,
transforming them into a “working table” or
subbase; and with marginal granular base materials, i.e., clay-gravels, “dirty” gravels, to form a
strong, high quality base course. Fly ash is a
pozzolanic material, i.e. it reacts with lime and is
therefore almost always used in combination with
lime in soils that have little or no plastic fines. It
has often been found desirable to use a small
amount of portland cement with lime and fly ash
for added strength. This combination of limecement-flyash (LCF) has been used successfully in
base course stabilization. Asphalt or bituminous
materials both are used for waterproofing and for
strength gain. Generally, soils suitable for asphalt
stabilization are the silty sandy and granular
materials since it is desired to thoroughly coat all
the soil particles.
b. Selection of candidate additives. The selection
of candidate/stabilizers is made using figure 2-1
and table 2-1. The soil gradation triangle in figure
2-1 is based upon the soil grain size characteristics and the triangle is divided into areas of soils
with similar grain size and therefore pulverization
characteristics. The selection process is continued
with table 2-1 which indicates for each area
shown in figure 2-1 candidate stabilizers and
restrictions based on grain size and/or plasticity
index (PI). Also provided in the second column of
table 2-1 is a listing of soil classification symbols
applicable to the area determined from figure 2-1.
This is an added check to insure that the proper
area was selected. Thus, information on grain size
distribution and Atterberg limits must be known
to initiate the selection process. Data required to
enter figure 2-1 are: percent material passing the
No. 200 sieve and percent material passing the
No. 4 sieve but retained on the No. 200 (i.e., total
percent material between the No. 4 and the No.
200 sieves). The triangle is entered with these two
values and the applicable area (1A, 2A, 3, etc.) is
found at their intersection. The area determined
from figure 2-1 is then found in the first column
of table 2-1 and the soil classification is checked
in the second column. Candidate stabilizers for
each area are indicated in third column and
restrictions for the use of each material are presented in the following columns. These restrictions
are used to prevent use of stabilizing agents not
applicable for the particular soil type under consideration. For example, assume a soil classified as a
SC, with 93 percent passing the No. 4 and 25
percent passing the No. 200 with a liquid limit of
20 and plastic limit of 11. Thus 68 percent of the
material is between the No. 4 and No. 200 and the
plasticity index is 9. Entering figure 2-1 with the
values of 25 percent passing the No. 200 and 68
percent between the No. 4 and No. 200, the
intersection of these values is found in area 1-C.
Then going to the first column of table 2-1, we
find area 1-C and verify the soil classification, SC,
in the second column. From the third column all
four stabilizing materials are found to be potential
candidates. The restrictions in the following columns are now examined. Bituminous stabilization
is acceptable since the PI does not exceed 10 and
the amount of material passing the No. 200 does
not exceed 30 percent. However it should be noted
that the soil only barely qualifies under these
criteria and bituminous stabilization probably
would not be the first choice. The restrictions
under portland cement indicate that the PI must
be less that the equation indicated in footnote b.
Since the PI, 9, is less than that value, portland
cement would be a candidate material. The restrictions under lime indicate that the PI not be less
than 12 therefore lime is not a candidate material
for stabilization, The restrictions under LCF stabi2-1
TM
5-822-14/AFJMAN
32-1019
PERCENT BY WEIGHT, FINES
(MATERAIL PASSING NO. 200 SIEVE)
Figure 2-1.
Gradation triangle for aid in selecting a commercial stabilizing agent.
lization indicate that the PI must not exceed 25,
thus LCF is also a candidate stabilizing material.
At this point, the designer must make the final
selection based on other factors such as availability of material, economics, etc. Once the type of
stabilizing agent to be used is determined, samples
must be prepared and tested in the laboratory to
develop a design mix meeting minimum engineering criteria for field stabilization.
2-2. Use of stabilized soils in Frost Areas.
a. Frost considerations. While bituminous, portland cement, lime, and LCF stabilization are the
most common additives other stabilizers may be
used for pavement construction in areas of frost
design but only with approval obtained from the
HQUSACE (CEMP-ET), Washington, DC 203141000 or the appropriate Air Force Major Command.
2-2
b. Limitations. In frost areas, stabilized soil is
only used in one of the upper elements of a
pavement system if cost is justified by the reduced
pavement thickness. Treatment with a lower degree of additive than that indicated for stabilization (i.e., soil modification) should be used in frost
areas only with caution and after intensive tests,
because weakly cemented material usually has
less capacity to endure repeated freezing and
thawing than has firmly cemented material. A
possible exception is modification of a soil that will
be encapsulated within an impervious envelope as
part of a membrane-encapsulated-soil-layer pavement system. A soil that is unsuitable for encapsulation due to excessive moisture migration and
thaw weakening may be made suitable for such
use by moderate amounts of a stabilizing additive.
Materials that are modified should also be tested
to ascertain that the desired improvement is dura-
TM
5-822-14/AFJMAN
32-1019
Table 2-1. Guide for selecting a stabilizing additive.
ble through repeated freeze-thaw cycles. The improvement should not be achieved at the expense
of making the soil more susceptible to ice segregation.
c. Construction cutoff dates. Materials stabilized with cement, lime, or LCF should be constructed early enough during the construction
season to allow the development of adequate
strength before the first freezing cycle begins. The
rate of strength gain is substantially lower at 50
degrees Fahrenheit than at 70 or 80 degrees
Fahrenheit. Chemical reactions will not occur
rapidly for lime-stabilized soils when the soil
temperature is less than 60 degrees Fahrenheit
and is not expected to increase for one month, or
cement-stabilized soils when the soil temperature
is less than 40 degrees Fahrenheit and is not
expected to increase for one month. In frost areas,
it is not always sufficient to protect the mixture
from freezing during a 7-day curing period as
required by the applicable guide specifications,
and a construction cutoff date well in advance of
2-3
TM
5-822-14/AFJMAN
32-1019
lime, LF, and LCF are indicated in tables 2-2
and 2-3, respectively. For bituminous stabilized
materials to qualify for reduced thickness, they
must meet strength requirements in TM 5-825-21
AFM 88-6, Chap. 2. All stabilized materials except those treated with bitumen must meet minimum durability criteria to be used in pavement
structures. There are no durability criteria for
bituminous stabilized materials since it is assumed
that they will be sufficiently waterproof if properly
designed and constructed.
the onset of freezing conditions (e.g. 30 days) may
be essential.
2-3. Thickness Reduction for Base and Subbase
Courses. Stabilized base and subbase course mate-
rials must meet certain requirements of gradation, strength, and durability to qualify for reduced layer thickness design. Gradation requirements are presented in the sections covering design with each type of stabilizer. Unconfined
compressive strength and durability requirements
for bases and subbases treated with cement,
Table 2-2. Minimum unconfined compressive strength for cement, lime, lime-cement, and lime-cement-fly ash stabilized soils
Minimum Unconfined Compressive strength, psia
Stabilized Soil Layer
Base course
Subbase course, select material or subgrade
Flexible pavement
Rigid pavement
750
250
500
200
a
Unconfined compressive strength determined at 7 days for cement stabilization and 28 days for lime, lime fly ash, or lime-cement-fly
ash stabilization.
Table 2-3. Durability requirements
Type
of Soil Stabilized
Granular, PI < 10
Granular, PI > 210
Silt
Clays
2-4
Maximum Allowable Weight Loss After 12 Wet-Dry or
Freeze-Thaw Cycles Percent of Initial Specimen Weight
11
8
8
6
TM
5-822-14/AFJMAN
32-1019
CHAPTER 3
DETERMINATION OF STABILIZER CONTENT
3-1. Stabilization with Portland Cement. Portland cement can be used either to modify and
improve the quality of the soil or to transform the
soil into a cemented mass with increased strength
and durability. The amount of cement used will
depend upon whether the soil is to be modified or
stabilized.
a. Types of portland cement. Several different
types of cement have been used successfully for
stabilization of soils. Type I normal portland cement and Type IA air-entraining cements were
used extensively in the past and gave about the
same results. At the present time, Type II cement
has largely replaced Type I cement as greater
sulfate resistance is obtained while the cost is
often the same. High early strength cement (Type
III) has been found to give a higher strength in
some soils. Type III cement has a finer particle
size and a different compound composition than do
the other cement types. Chemical and physical
property specifications for portland cement can be
found in ASTM C 150.
b. Screening tests for organic matter and sulfates. The presence of organic matter and/or sulfates may have a deleterious effect on soil cement.
Tests are available for detection of these materials
and should be conducted if their presence is suspected.
(1) Organic matter. A soil may be acid, neutral, or alkaline and still respond well to cement
treatment. Although certain types of organic matter, such as undecomposed vegetation, may not
influence stabilization adversely, organic compounds of lower molecular weight, such as nucleic
acid and dextrose, act as hydration retarders and
reduce strength. When such organics are present
they inhibit the normal hardening process. A pH
test to determine the presence of organic material
is presented in appendix B. If the pH of a 10:1
mixture (by weight) of soil and cement 15 minutes
after mixing is at least 12.0, it is probable that
any organics present will not interfere with normal hardening.
(2) Sulfates. Although sulfate attack is known
to have an adverse effect on the quality of hardened portland cement concrete, less is known
about the sulfate resistance of cement stabilized
soils. The resistance to sulfate attack differs for
cement-treated coarse-grained and fine-grained
soils and is a function of sulfate concentrations.
Sulfate-clay reactions can cause deterioration of
fine-grained soil-cement. On the other hand, granular soil-cements do not appear susceptible to
sulfate attack. In some cases the presence of small
amounts of sulfate in the soil at the time of
mixing with the cement may even be beneficial.
The use of sulfate-resistant cement may not improve the resistance of clay-bearing soils, but may
be effective in granular soil-cements exposed to
adjacent soils and/or ground water containing high
sulfate concentrations. A procedure for determining the percent SO4 is presented in appendix C.
The use of cement for fine-grained soils containing
more than about 1 percent sulfate should be
avoided.
c. Water for hydration. Potable water is normally used for cement stabilization, although sea
water has been found to be satisfactory.
d. Gradation requirements. Gradation requirements for cement stabilized base and subbase
courses are indicated in table 3-1.
e. Cement content for modification of soils.
(1) Improve plasticity. The amount of cement
required to improve the quality of the soil through
modification is determined by the trial-and-error
approach. If it is desired to reduce the PI of the
soil, successive samples of soil-cement mixtures
Table 3-1. Gradation requirements for cement stabilized base and subbase courses
Sieve Size
Percent Passing
Base
1½ in.
¾ in.
No. 4
No. 40
No. 200
100
70-100
45-70
10-40
0-20
Subbase
1½ in.
No. 4
No. 40
No. 200
100
45-100
10-50
0-20
Type Course
3-1
TM 5822-14/FJMAN 32-1019
must be prepared at different treatment levels and
the PI of each mixture determined. The Referee
Test of ASTM D 423 and ASTM D 424 procedures
will be used to determine the PI of the soil-cement
mixture. The minimum cement content that yields
the desired PI is selected, but since it was determined based upon the minus 40 fraction of the
material, this value must be adjusted to find the
design cement content based upon total sample
weight expressed as
A = 100BC
(eq 3-1)
where
A = design cement content, percent total
weight of soil
B = percent passing No. 40 sieve size, expressed as a decimal
C = percent cement required to obtain the
desired PI of minus 40 material, expressed as a decimal
(2) Improve gradation. If the objective of modification is to improve the gradation of a granular
soil through the addition of fines then particle-size
analysis (ASTM D 422) should be conducted on
samples at various treatment levels to determine
the minimum acceptable cement content.
(3) Reduce swell potential. Small amounts of
portland cements may reduce swell potential of
some swelling soils. However, portland cement
generally is not as effective as lime and may be
considered too expensive for this application. The
determination of cement content to reduce the
swell potential of fine-g-rained plastic soils can be
accomplished by molding several samples at various cement contents and soaking the specimens
along with untreated specimens for 4 days. The
lowest cement content that eliminates the swell
potential or reduces the swell characteristics to the
minimum is the design cement content. Procedures
for measuring swell characteristics of soils are
found in MIL-STD-621A, Method 101. The cement
content determined to accomplish soil modification
should be checked to see whether it provides an
unconfined compressive strength great enough to
qualify for a reduced thickness design in accordance with criteria established for soil stabilization.
(4) Frost areas. Cement-modified soil may also
be used in frost areas, but in addition to the
procedures for mixture design described in (1) and
(2) above, cured specimens should be subjected to
the 12 freeze-thaw cycles prescribed by ASTM D
560 (but omitting wire-brushing) or other applicable freeze-thaw procedures. This should be followed
by determination of frost design soil classification
by means of standard laboratory freezing tests. If
cement-modified soil is used as subgrade, its frostsusceptibility, determined after freeze-thaw cy3-2
cling, should be used as the basis of the pavement
thickness design if the reduced subgrade design
method is applied.
f. Cement content for stabilized soil. The following procedure is recommended for determining the
design cement content for cement-stabilized soils.
(1) Step 1. Determine the classification and
gradation of the untreated soil following procedures in ASTM D 422 and D 2487, respectively.
(2) Step 2. Using the soil classification select
an estimated cement content for moisture-density
tests from table 3-2.
Table 3-2. Cement requirements for various soils
Soil Classification
Initial Estimated
Cement Content
percent dry weight
GW, SW
GP, GW-GC, GW-GM, SW-SC, SW-SM
GC, GM, GP-GC, GP-GM, GM-GC, SC,
SM, SP-SC, SP-SM, SM-SC, SP
CL. ML, MH
CH
9
11
(3) Step 3. Using the estimated cement content, conduct moisture-density tests to determine
the maximum dry density and optimum water
content of the soil-cement mixture. The procedure
contained in ASTM D 558 will be used to prepare
the soil-cement mixture and to make the necessary
calculations; however, the procedures outlined in
MIL-STD 621, Method 100 (CE 55 effort), or
ASTM D 1557 will be used to conduct the moisture
density test.
(4) Step 4. Prepare triplicate samples of the
soil-cement mixture for unconfined compression
and durability tests at the cement content selected
in step 2 and at cement contents 2 percent above
and 2 percent below that determined in step 2.
The samples should be prepared at the density and
water content to be expected in field construction.
For example, if the design density is 95 percent of
the laboratory maximum density, the samples
should also be prepared at 95 percent. The samples
should be prepared in accordance with ASTM D
1632 except that when more than 35 percent of the
material is retained on the No. 4 sieve, a 4-inchdiameter by &inch-high mold should be used to
prepare the specimens. Cure the specimens for 7
days in a humid room before testing. Test three
specimens using the unconfined compression test
in accordance with ASTM D 1633, and subject
three specimens to durability tests, either wet-dry
(ASTM D 559) or freeze-thaw (ASTM D 560) tests
as appropriate. The frost susceptibility of the
TM
treated material should also be determined as indicated in appropriate pavement design manuals.
(5) Step 5. Compare the results of the unconfined compressive strength and durability tests
with the requirements shown in tables 2-2 and
2-3. The lowest cement content which meets the
required unconfined compressive strength requirement and demonstrates the required durability is
the design cement content. If the mixture should
meet the durability requirements but not the
strength requirements, the mixture is considered
to be a modified soil. If the results of the specimens tested do not meet both the strength and
durability requirements, then a higher cement
content may be selected and steps 1 through 4
above repeated.
3-2. Stabilization with lime. In general, all
lime treated finegrained soils exhibit decreased
plasticity, improved workability and reduced volume change characteristics. However, not all soils
exhibit improved strength characteristics. It
should be emphasized that the properties of soillime mixtures are dependent on many variables.
Soil type, lime type, lime percentage and curing
conditions (time, temperature, moisture) are the
most important.
a. Types of lime. Various forms of lime have
been successfully used as soil stabilizing agents for
many years. However, the most commonly used
products are hydrated high-calcium lime, monohydrated dolomitic lime, calcitic quicklime, and dolomitic quicklime. Hydrated lime is used most often
because it is much less caustic than quicklime,
however, the use of quicklime for soil stabilization
has increased in recent years mainly with slurrytype applications. The design lime contents determined from the criteria presented herein are for
hydrated lime. If quicklime is used the design lime
contents determined herein for hydrated lime
should be reduced by 25 percent. Specifications for
quicklime and hydrated lime may be found in
ASTM C 977.
b. Gradation requirements. Gradation requirements for lime stabilized base and subbase courses
are presented in table 3-3.
c. Lime content for lime-modified soils. The
amount of lime required to improve the quality of
a soil is determined through the same trial-anderror process used for cement-modified soils.
d. Lime content for lime-stabilized soils. The
following procedures are recommended for determining the lime content of lime stabilized soils.
(1) Step 1. The preferred method for determining an initial design lime content is the pH test.
In this method several lime-soil slurries are pre-
5-822-14/AFJMAN
32-1019
Table 3-3. Gradation requirements for lime stabilized base
and subbase courses
Sieve Size
Percent Passing
Base
1½ in.
¾ in.
No. 4
No. 40
No. 200
100
70-100
45-70
10-40
0-20
Subbase
1½
No.
No.
No.
100
45-100
10-50
0-20
Type Course
in.
4
40
200
pared at different lime treatment levels such as 2,
4, 6, and 8 percent lime and the pH of each slurry
is determined. The lowest lime content at which a
pH of about 12.4 (the pH of free lime) is obtained
is the initial design lime content. Procedures for
conducting the pH test are indicated in appendix
D. An alternate method of determining an initial
design lime content is by the use of figure 3-1.
Specific values required to use figure 3-1 are the
PI and the percent of material passing the No. 40
sieve.
(2) Step 2. Using the initial design lime content conduct moisture-density tests to determine
the maximum dry density and optimum water
content of the soil lime mixture. The procedures
contained in ASTM D 3551 will be used to prepare
the soil-lime mixture. The moisture density test
will be conducted following procedures in
MIL-STD 621 Method 100 (CE 55 effort) or ASTM
D 1557.
(3) Step 3. Prepare triplicate samples of the
soil lime mixture for unconfined compression and
durability tests at the initial design lime content
and at lime contents 2 and 4 percent above design
if based on the preferred method or 2 percent
above at 2 percent below design if based on the
alternate method. The mixture should he prepared
as indicated in ASTM D 3551. If less than 35
percent of the soil is retained on the No. 4 sieve,
the sample should be approximately 2 inches in
diameter and 4 inches high. If more than 35
percent is retained on the No. 4 sieve, samples
should be 4 inches in diameter and 8 inches
high. The samples should be prepared at the
density and water content expected in field construction. For example, if the design density is
95 percent of the laboratory maximum density,
the sample should be prepared at 95 percent
density. Specimens should be cured in a sealed
container to prevent moisture loss and lime carbonation. Sealed metal cans, plastic bags, and so
forth are satisfactory. The preferred method of
curing is 73 degrees F for 28 days. Accelerated
3-3
TM 5-822-14/AFJMAN 32-1019
Figure 3-1. Chart for the initial determination of lime content.
curing at 120 degrees F for 48 hours has also been
found to give satisfactory results; however, check
tests at 73 degrees for 28 days should also be
conducted. Research has indicated that if accelerated curing temperatures are too high, the pozzolanic compounds formed during laboratory curing
could differ substantially from those that would
develop in the field.
(4) Step 4. Test three specimens using the
unconfined compression test. If frost design is a
consideration, test three specimens to 12 cycles of
freeze-thaw durability tests (ASTM D 560) except
wire brushing is omitted. The frost susceptibility
of the treated material should be determined as
indicated in appropriate design manuals.
3-4
(5) Step 5. Compare the results of the unconfined compressive strength and durability tests
with the requirements shown in tables 2-2 and
2-3. The lowest lime content which meets the
unconfined compressive strength requirement and
demonstrates the required durability is the design
lime content. The treated material also must meet
frost susceptibility requirements as indicated in
the appropriate pavement design manuals. If the
mixture should meet the durability requirements
but not the strength requirements, it is considered
to be a modified soil. If results of the specimens
tested do not meet both the strength and durability requirements, a higher lime content may be
selected and steps 1 through 5 repeated.
TM 5-822-14/AFJMAN 32-1019
3-3. Stabilization with Lime-Fly Ash (LF) and
Lime-Cement-Fly Ash (LCF). Stabilization of
coarse-grained soils having little or no tines can
often be accomplished by the use of LF or LCF
combinations. Fly ash, also termed coal ash, is a
mineral residual from the combustion of pulverized coal. It contains silicon and aluminum compounds that, when mixed with lime and water,
forms a hardened cementitious mass capable of
obtaining high compressive strengths. Lime and
fly ash in combination can often be used successfully in stabilizing granular materials since the fly
ash provides an agent, with which the lime can
react. Thus LF or LCF stabilization is often appropriate for base and subbase course materials.
a. Types of fly ash. Fly ash is classified according to the type of coal from which the ash was
derived. Class C fly ash is derived from the
burning of lignite or subbituminous coal and is
often referred to as “high lime” ash because it
contains a high percentage of lime. Class C fly ash
is self-reactive or cementitious in the presence of
water, in addition to being pozzolanic. Class F fly
ash is derived from the burning of anthracite or
bituminous coal and is sometimes referred to as
“low lime” ash. It requires the addition of lime to
form a pozzolanic reaction.
b. Evaluation of fly-ash. To be acceptable quality
fly ash used for stabilization must meet the requirements indicated in ASTM C 593.
c. Gradation requirements. Gradation requirements for LF and LCF stabilized base and subbase
course are indicated in table 3-4.
Table 3-4. Gradation requirements for fly ash
stabilized base and subbase courses
Sieve Size
Percent Passing
Base
2 in.
¾ in.
3/8 in.
No. 4
No. 8
No. 16
No. 200
100
70-100
50-80
35-70
25-55
10-45
0-15
Subbase
1½ in.
No. 4
No. 40
No. 200
100
45-100
10-50
0-15
Type Course
d. Selection of lime-fly ash content for LF and
LCF mixtures. Design with LF is somewhat different from stabilization with lime or cement. For a
given combination of materials (aggregate, fly ash,
and lime), a number of factors can be varied in the
mix design process such as percentage of lime-fly
ash, the moisture content, and the ratio of lime to
fly ash. It is generally recognized that engineering
characteristics such as strength and durability are
directly related to the quality of the matrix material. The matrix material is that part consisting of
fly ash, lime, and minus No. 4 aggregate fines.
Basically, higher strength and improved durability
are achievable when the matrix material is able to
“float” the coarse aggregate particles. In effect,
the fine size particles overfill the void spaces
between the coarse aggregate particles. For each
coarse aggregate material, there is a quantity of
matrix required to effectively fill the available
void spaces and to “float” the coarse aggregate
particles. The quantity of matrix required for
maximum dry density of the total mixture is
referred to as the optimum fines content. In LF
mixtures it is recommended that the quantity of
matrix be approximately 2 percent above the
optimum fines content. At the recommended fines
content, the strength development is also influenced by the ratio of lime to fly ash. Adjustment of
the lime-fly ash ratio will yield different values of
strength and durability properties.
(1) Step 1. The first step is to determine the
optimum fines content that will give the maximum density. This is done by conducting a series
of moisture-density tests using different percentages of fly ash and determining the mix level that
yields maximum density. The initial fly ash content should be about 10 percent based on dry
weight of the mix. It is recommended that material larger than ¾ in. be removed and the test
conducted on the minus ¾ in. fraction. Tests are
run at increasing increments of fly ash, e.g. 2
percent, up to a total of about 20 percent. Moisture
density tests should be conducted following procedures indicated in MIL-STD 621, Method 100 (CE
55 effort) and ASTM D 1557. The design fly ash
content is then selected at 2 percent above that
yielding maximum density. An alternate method
is to estimate optimum water content and conduct
single point compaction tests at fly ash contents of
10-20 percent, make a plot of dry density versus
fly ash content and determine the fly ash content
that yields maximum density. The design fly ash
content is 2 percent above this value. A moisture
density test is then conducted to determine the
optimum water content and maximum dry density.
(2) Step 2. Determine the ratio of lime to fly
ash that will yield highest strength and durability.
Using the design fly ash content and the optimum
water content determined in step 1, prepare triplicate specimens at three different lime-fly ash
ratios following procedures indicated in MIL-STD
621 Method 100 (less effort) or ASTM D 1557. Use
LF ratios of 1:3, 1:4, and 1:5. If desired about 1
3-5
TM 5-822-14/AFJMAN 32-1019
percent of portland cement may be added at this
time.
(3) Step 3. Test three specimens using the
unconfined compression test. If frost design is a
consideration, subject three specimens to 12 cycles
of freeze-thaw durability tests (ASTM D 560) except wire brushing is omitted. The frost susceptibility of the treated material shall also be determined as indicated in appropriate design manual.
(4) Compare the results of the unconfined
compressive strength and durability tests with the
requirements shown in tables 2-2 and 2-3. The
lowest LF ratio content, i.e., ratio with the lowest
lime content which meets the required unconfined
compressive strength requirement and demonstrates the required durability, is the design LF
content. The treated material must also meet frost
susceptibility requirements as indicated in the
appropriate pavement design manuals. If the mixture should meet the durability requirements but
not the strength requirements, it is considered to
be a modified soil. If the results of the specimens
tested do not meet both the strength and durability requirements, a different LF content may be
selected or additional portland cement used and
steps 2 through 4 repeated.
e. Selection of cement content for LCF mixtures.
Portland cement may also be used in combination
with LF for improved strength and durability. If it
is desired to incorporate cement into the mixture,
the same procedures indicated for LF design
should be followed except that, beginning at step
2, the cement shall be included. Generally, about 1
to 2 percent cement is used. Cement may be used
in place of or in addition to lime however, the total
tines content should be maintained. Strength and
durability tests must be conducted on samples at
various LCF ratios to determine the combination
that gives best results.
3-4. Stabilization with Bitumen. Stabilization
of soils and aggregates with asphalt differs greatly
from cement and lime stabilization. The basic
mechanism involved in asphalt stabilization of
fine-grained soils is a waterproofing phenomenon.
Soil particles or soil agglomerates are coated with
asphalt that prevents or slows the penetration of
water which could normally result in a decrease in
soil strength. In addition, asphalt stabilization can
improve durability characteristics by making the
soil resistant to the detrimental effects of water
such as volume. In noncohesive materials, such as
sands and gravel, crushed gravel, and crushed
stone, two basic mechanisms are active: waterproofing and adhesion. The asphalt coating on the
cohesionless materials provides a membrane which
3-6
prevents or hinders the penetration of water and
thereby reduces the tendency of the material to
lose strength in the presence of water. The second
mechanism has been identified as adhesion. The
aggregate particles adhere to the asphalt and the
asphalt acts as a binder or cement. The cementing
effect thus increases shear strength by increasing
cohesion. Criteria for design of bituminous stabilized soils and aggregates are based almost entirely on stability and gradation requirements.
Freeze-thaw and wet-dry durability tests are not
applicable for asphalt stabilized mixtures.
a. Types of bituminous stabilized soils.
(1) Sand bitumen. A mixture of sand and
bitumen in which the sand particles are cemented
together to provide a material of increased stability.
(2) Gravel or crushed aggregate bitumen. A
mixture of bitumen and a well-graded gravel or
crushed aggregate that, after compaction, provides
a highly stable waterproof mass of subbase or base
course quality.
(3) Bitumen lime. A mixture of soil, lime, and
bitumen that, after compaction, may exhibit the
characteristics of any of the bitumen-treated materials indicated above. Lime is used with material
that have a high PI, i.e. above 10.
b. Types of bitumen. Bituminous stabilization is
generally accomplished using asphalt cement, cutback asphalt, or asphalt emulsions. The type of
bitumen to be used depends upon the type of soil
to be stabilized, method of construction, and
weather conditions. In frost areas, the use of tar as
a binder should be avoided because of its hightemperature susceptibility. Asphalts are affected
to a lesser extent by temperature changes, but a
grade of asphalt suitable to the prevailing climate
should be selected. As a general rule, the most
satisfactory results are obtained when the most
viscous liquid asphalt that can be readily mixed
into the soil is used. For higher quality mixes in
which a central plant is used, viscosity-grade
asphalt cements should be used. Much bituminous
stabilization is performed in place with the bitumen being applied directly on the soil or soilaggregate system and the mixing and compaction
operations being conducted immediately thereafter. For this type of construction, liquid asphalts,
i.e., cutbacks and emulsions, are used. Emulsions
are preferred over cutbacks because of energy
constraints and pollution control efforts. The specific type and grade of bitumen will depend on the
characteristics of the aggregate, the type of construction equipment, and climatic conditions. Generally, the following types of bituminous materials
will be used for the soil gradation indicated:
TM
(1) Open-graded aggregate.
(a) Rapid- and medium-curing liquid asphalts RC-250, RC-800, and MC-3000.
(b) Medium-setting asphalt emulsion MS-2
and CMS-2.
(2) Well-graded aggregate with little or no
material passing the No. 200 sieve.
(a) Rapid and medium-curing liquid asphalts RC-250, RC-800, MC-250, and MC-800.
(b) Slow-curing liquid asphalts SC-250 and
SC-800.
(c) Medium-setting and slow-setting asphalt
emulsions MS-2, CMS-2, SS-1, and CSS-1.
(3) Aggregate with a considerable percentage
of fine aggregate and material passing the No. 200
sieve.
5-822-14/AFJMAN
32-1019
(a) Medium-curing liquid asphalt MC-250
and MC-800.
(b) Slow-curing liquid asphalts SC-250 and
SC-800.
(c) Slow-setting asphalt emulsions SS-1,
SS-01h, CSS-1, and CSS-lh.
The simplest type of bituminous stabilization is
the application of liquid asphalt to the surface of
an unbound aggregate road. For this type of
operation, the slow- and medium-curing liquid
asphalts SC-70, SC-250, MC-70, and MC-250 are
used.
c. Soil gradation. The recommended soil gradations for subgrade materials and base or subbase
course materials are shown in tables 3-5 and 3-6,
respectively.
Table 3-5. Recommended gradations for bituminousstabilized subgrade materials
Sieve Size
Percent Passing
3 in.
No. 4
No. 30
No. 200
100
50-100
38-100
2-30
Table 3-6. Recommended gradations for bituminous-stabilized base and subbase materials
Sieve Size
1½-in.
l-in.
¾-in.
M-in.
3/8-in.
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
No. 200
1½ in.
Maximum
100
84±
76 ±
66 ±
59 ±
45 ±
35 ±
27 ±
20 ±
14 ±
9 ±
1-in.
Maximum
100
83 ±
73 ±
64 ±
48 ±
36 ±
28 ±
21 ±
16 ±
11 ±
5 ±
9
9
9
9
9
9
9
9
7
5
5 ± 2
d. Mix design. Guidance for the design of
bituminous-stabilized base and subbase courses is
contained in TM 5-822-8/AFM 88-6, Chap. 9. For
subgrade stabilization, the following equation may
be used for estimating the preliminary quantity of
cutback asphalt to be selected:
p =
0.02(a) + 0.07(b) + 0.15(c) + 0.20(d)
(100 - S)
X
100 (eq 3-2)
where
p = percent cutback asphalt by weight of dry
aggregate
a = percent of mineral aggregate retained on
No. 50 sieve
b = percent of mineral aggregate passing No.
50 sieve and retained on No. 100 sieve
9
9
9
9
9
9
9
7
5
2
¾-in.
Maximum
½-in.
Maximum
100
82 ± 9
72 ± 9
54 ± 9
41 ± 9
32 ± 9
24 ± 9
17 ± 7
12 ± 5
5 ± 2
100
83 ± 9
62 ± 9
47 ± 9
36 ± 9
28 ± 9
20 ± 7
14 ± 5
5 ± 2
c = percent of mineral aggregate passing No.
100 and retained on No. 200 sieve
d = percent of mineral aggregate passing No.
200
S = percent solvent
The preliminary quantity of emulsified asphalt to
be used in stabilizing subgrades can be determined
from table 3-7. The final design content of cutback
or emulsified asphalt should be selected based
upon the results of the Marshal Stability test
procedure (MIL-STD 620A). The minimum Marshall Stability recommended for subgrades is 500
pounds. If a soil does not show increased stability
when reasonable amounts of bituminous materials
are added, the gradation of the soil should be
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Table 3-7. Emulsified asphalt requirements
Pounds of Emulsified Asphalt per 100 pound of Dry Aggregate at Percent Passing No. 10 Sieve
Percent Passing
No. 200 Sieve
<50
60
70
80
90
100
0
2
4
6
8
10
12
14
16
18
20
22
24
25
6.0
6.3
6.5
6.7
7.0
7.2
7.5
7.2
7.0
6.7
6.5
6.3
6.0
6.2
6.3
6.5
6.7
7.0
7.2
7.5
7.7
7.5
7.2
7.0
6.7
6.5
6.3
6.4
6.5
6.7
7.0
7.2
7.5
7.7
7.9
7.7
7.5
7.2
7.0
6.7
6.5
6.6
6.7
7.0
7.2
7.5
7.7
7.9
8.2
7.9
7.7
7.5
7.2
7.0
6.7
6.9
7.0
7.2
7.5
7.7
7.9
8.2
8.4
8.2
7.9
7.7
7.5
7.2
7.0
7.1
7.2
7.5
7.7
7.9
8.2
8.4
8.6
8.4
8.2
7.9
7.6
7.5
7.2
7.3
modified or another type of bituminous material
should be used. Poorly graded materials may be
improved by the addition of suitable tines containing considerable material passing the No. 200
sieve. The amount of bitumen required for a given
soil increases with an increase in percentage of the
liner sizes.
3-5. Stabilization with Lime-Cement and LimeBitumen. The advantage in using combination
stabilizers is that one of the stabilizers in the
combination compensates for the lack of effectiveness of the other in treating a particular aspect or
characteristics of a given soil. For instance, in clay
areas devoid of base material, lime has been used
jointly with other stabilizers, notably portland
cement or asphalt, to provide acceptable base
courses. Since portland cement or asphalt cannot
be mixed successfully with plastic clays, the lime
is incorporated into the soil to make it friable,
thereby permitting the cement or asphalt to be
adequately mixed. While such stabilization practice might be more costly than the conventional
single stabilizer methods, it may still prove to be
economical in areas where base aggregate costs
are high. Two combination stabilizers are considered in this section: lime-cement and limeasphalt.
a. Lime-cement. Lime can be used as an initial
additive with portland cement or the primary
stabilizer. The main purpose of lime is to improve
workability characteristics mainly by reducing the
plasticity of the soil. The design approach is to add
enough lime to improve workability and to reduce
the plasticity index to acceptable levels. The design lime content is the minimum that achieves
3-8
desired results. The design cement content is
arrived at following procedures for cement stabilized soils presented in paragraph 3-1.
b. Lime-asphalt. Lime can be used as an initial
additive with asphalt as the primary stabilizer.
The main purpose of lime is to improve workability characteristics and to act as an anti-stripping
agent. In the latter capacity, the lime acts to
neutralize acidic chemicals in the soil or aggregate
which tend to interfere with bonding of the asphalt. Generally, about 1-2 percent lime is all that
is needed for this objective. Since asphalt is the
primary stabilizer, the procedures for asphalt stabilized materials as presented in paragraph 3-4
shall be followed.
3-6. Lime Treatment of Expansive Soils. Expansive soils as defined for pavement purposes are
those that exhibit swell in excess of three percent.
Expansion is characterized by heaving of a pavement or road when water is imbibed in the clay
minerals. The plasticity characteristics of a soil
often are a good indicator of the swell potential as
indicated in table 3-8. If it has been determined
that a soil has potential for excessive swell, lime
treatment may be appropriate. Lime will reduce
swell in an expansive soil to greater or lesser
degrees depending on the activity of the clay
minerals present. The amount of lime to be added
is the minimum amount that will reduce swell to
acceptable limits. Procedure for conducting swell
tests are indicated in MIL-STD 621 Method 101 or
ASTM D 1883. The depth to which lime should be
incorporated into the soil is generally limited by
the construction equipment used. However, 2 to 3
feet generally is the maximum depth that can be
treated directly without removal of the soil.
TM 5-822-14/AFJMAN 32-1019
Table 3-8. Swell potential of soils
Liquid Limit
>60
50-60
<50
Plasticity Index
Potential Swell
>35
25-35
<25
High
Marginal
Low
3-9
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CHAPTER 4
CONSTRUCTION PROCEDURES
4-1. Construction with Portland Cement.
a. General construction steps. In soil-cement construction the objective is to thoroughly mix a
pulverized soil material and cement in correct
proportions with sufficient moisture to permit
maximum compaction. Construction methods are
simple and follow a definite procedure:
(1) Initial preparation
(a) Shape the area to crown and grade.
(b) If necessary, scarify, pulverize, and prewet the soil.
(c) Reshape to crown and grade.
(2) Processing
(a) Spread portland cement and mix.
(b) Apply water and mix.
(c) Compact.
(d) Finish.
(e) Cure.
b. Mixing equipment. Soil, cement, and water
can be mixed in place using traveling mixing
machines or mixed in a central mixing plant. The
types of mixing equipment are
(1) Traveling mixing machines.
(a) Flat-transverse-shaft type:
1 Single-shaft mixer (fig 4-1).
2 Multiple-shaft mixer (fig 4-2).
(b) Windrow-type pugmill (fig 4-3).
(2) Central mixing plants.
(a) Continuous-flow-type pugmill (fig 4-4).
(b) Batch-type pugmill (fig 4-5).
(c) Rotary-drum mixers (fig 4-6).
Whatever type of mixing equipment is used, the
general principles and objectives are the same.
Some soil materials cannot be sufficiently pulverized and mixed in central mixing plants because of
their high silt and clay content and plasticity.
Almost all types of soil materials, from granular to
fine grained, can be adequately pulverized and
mixed with transverse-shaft mixers. The exception
is material containing large amounts of highly
plastic clays. These clays may require more mixing effort to obtain pulverization. Revolving-blade
central mixing plants and traveling pugmills can
be used for nonplastic to slightly plastic granular
soils. For coarse, nonplastic granular materials, a
rotary-drum mixer can provide a suitable mix;
however, if the material includes a small amount
of slightly plastic fines, mixing may not be adequate.
c. Equipment for handling and spreading cement. There are a number of methods of handling
cement. On mixed-in-place construction using traveling mixing machines, bulk cement is spread on
the area to be processed in required amounts by
mechanical bulk cement spreaders (fig 4-7). Bag
cement is sometimes used on small jobs. Cement
spreaders for mixed-in-place construction are of
two general types: those that spread cement over
the soil material in a blanket (fig 4-8) and those
that deposit cement on top of a partially flattened
or slightly trenched windrow of soil material (fig
4-9). Cement meters on continuous-flow central
mixing plants are of three types: the belt with
strikeoff, screw, or vane. Cement for batch-typepugmill mixers and rotary drum-mixers is batchweighed.
d. Construction. Construction with soil cement
involves two steps-preparation and processing.
Variations in these steps, dictated by the type of
mixing equipment used, are discussed in this
chapter. Regardless of the equipment and methods
used, it is essential to have an adequately compacted, thorough mixture of pulverized soil material and other proper amounts of cement and
moisture. The completed soil-cement must be adequately cured.
(1) Preparation. Before construction starts,
crown and grade should be checked and any fine
grading should be completed. Since there is little
displacement of material during processing, grade
at the start of construction will determine final
grade to a major extent. If borrow material is to be
used, the subgrade should be compacted and
shaped to proper crown and grade before the
borrow is placed. Any soft subgrade areas should
be corrected. To avoid later costly delays, all
equipment should be carefully checked to ensure it
is in good operating condition and meets construction requirements of the job. Guide stakes should
be set to control the width and guide the operators
during construction. Arrangements should be
made to receive, handle, and spread the cement
and water efficiently. The number of cement and
water trucks required depends on length of haul,
condition of haul roads, and anticipated rate of
production. For maximum production, an adequate
cement and water supply is essential. The limits of
the different materials and their corresponding
cement requirements should be established by the
project engineer. Prewetting by adding moisture
before cement is applied often saves time during
actual processing. Friable granular materials,
4-1
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Figure 4-1. Transverse single-shaft mixer processing
soil-cement in place. Multiple passes are required.
Figure 4-2. Multiple-transverseshaft mixer mixing soil,
cement, and water in one pass.
Figure 4-3. Windrow-type traveling pugmill mixing
soil-cement from windrows of soil material.
4-2
TM 5-822-14/AFJMAN 32-1019
Figure 4-7. Bulk portland cement being transferred
pneumatically from a bulk transport truck to a job truck.
Figure 4-8. Mechanical cement spreader attached to a
job dump truck spreading cement in regulated quantities.
Figure 4-9. Windrow-type mechanical spreader placing
cement on windrow.
which are most commonly used, require little or no
scarification or pulverization. Silty and clayey
soils may require extra effort to pulverize them,
particularly if they are too dry or too wet. Soils
that are difficult to pulverize when dry and brittle
can be broken down readily if water is added and
allowed to soak in; whereas, sticky soils can be
pulverized more easily when they have been dried
out a little. Most specifications require that the
soil material be pulverized sufficiently so that at
the time of compaction 100 percent of the soilcement mixture will pass a l-inch sieve and a
minimum of 80 percent will pass a No. 4 sieve,
exclusive of any gravel or stone. Gravel or stone
should be no more than 2-inches maximum size.
The final pulverization test should be made at the
conclusion of mixing operations. When borrow
material is specified, it should be distributed on an
accurately graded, well-compacted roadway in an
even layer or uniform windrow, depending on the
type of mixing equipment to be used. It should be
placed by weight or volume as required by the
specifications.
(2) Processing. For maximum efficiency and to
meet specification time limits, a day’s work should
be broken down into several adjacent sections
rather than one or two long sections. This procedure will result in maximum daily production and
will prevent a long stretch of construction from
being rained out in case of a sudden severe
rainstorm.
(a) Handling and spreading cement. Bulk
cement is normally trucked to the jobsite in bulk
transport trucks or shipped to the nearest railroad
siding in enclosed hopper cars. Compressed air or
vibrators are used to loosen the cement in the
hopper cars during unloading. Transfer to cement
trucks is done pneumatically or by a screen or belt
conveyor. The trucks are usually enclosed or fitted
with canvas covers. The cement is weighed in
truckloads on portable platform scales or at a
nearby scale. Soil materials that contain excessive
amounts of moisture will not mix readily with
cement. Sandy soils can be mixed with a moisture
content at optimum or slightly above; whereas,
clayey soils should have a moisture content below
optimum when cement is spread. Cement should
not be applied onto puddles of water. If the soil
material is excessively wet, it should be aerated to
dry it before cement is applied. Handling and
spreading procedures for different types of equipment are presented below.
1. Mechanical cement spread, mixed-inplace construction. A mechanical cement spreader
is attached to the dump truck. As the truck moves
forward, cement flows through the spreader, which
4-3
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regulates the quantity of cement placed on the
prepared soil. To obtain a uniform cement spread,
the spreader should be operated at a constant,
slow speed and with a constant level of cement in
the hopper. A true line at the pavement edge
should be maintained with a string line. The
mechanical spreader must have adequate traction
to produce a uniform cement spread. Traction can
be aided by wetting and rolling the soil material
before spreading the cement. When operating in
loose sands or gravel, slippage can be overcome by
the use of cleats on the spreader wheels or by
other modifications; sometimes, the spreader is
mounted on a tractor or high lift. The mechanical
cement spreader can also be attached directly
behind a bulk cement truck. Cement is then
moved pneumatically from the truck through an
air separator cyclone that dissipates the air pressure, and falls into the hopper of the spreader.
Forward speed must be slow and even. Sometimes
a motor grader or loader pulls the truck to maintain this slow, even forward speed. Pipe cement
spreaders attached to cement transport trucks
have been used in some areas with variable
results. Improvements in this type of equipment
are being made.
2. Bagged-cement spread, mixed-in-place
construction. When bags of cement are used on
small jobs, a simple but exact method for properly
placing the bags is necessary. The bags should be
spaced at approximately equal transverse and
longitudinal intervals that will ensure the proper
percentage of cement. Positions can be spotted by
flags or markers fastened to chains at proper intervals to mark the transverse and longitudinal rows.
When the bags are opened, the cement should be
dumped so that it forms fairly uniform transverse
windrows across the area being processed. A spiketooth harrow, a nail drag, or a length of chain-link
fence can be used to spread the cement evenly.
The drag should make at least two round trips
over the area to spread the cement uniformly.
3. Cement application, central-mixingplant construction. When a continuous-flow central
mixing plant is used, the cement is usually metered onto the soil aggregate and the two materials are carried to the pugmill mixer on the main
feeder belt. Variations in moisture and in gradation of the soil aggregate will result in variations
in the amount of material being fed onto the
feeder belt. A high bulkhead placed in front of the
soil hopper will help to obtain a more uniform flow
through the soil material feeder. The chance of
loss of cement due to wind can be minimized by
the use of a small plow attachment that will form
a furrow for the cement in the soil aggregate.
4-4
After the cement is added, a second plow attachment a little farther up on the main feeder belt
closes the furrow and covers the cement. A cover
on the main feeder belt will also minimize cement
loss due to wind. One of three types of cement
meters-belt, screw, or vane-can be used to proportion the cement on a volumetric basis. Each
requires a 450- to 750-pound capacity surge tank
or hopper between the cement silo and the cement
feeder. This tank maintains a constant head of
cement for the feeder, thus providing a more
uniform cement discharge. Compressed air of 2- to
4-pounds per square inch pressure should be used
to prevent arching of cement in the silo and the
surge tank. Portable vibrators attached to the
surge tank can be used instead of air jets. A
positive system should be included to stop the
plant automatically if the cement flow suddenly
stops. The correct proportion of cement, soil material, and water entering the mixing chamber must
be determined by calibrating the plant before
mixing and placing operations begin.
(b) Mixing and application of water. Procedures for applying water and mixing depend on
the type of mixing machine used. A thorough
mixture of pulverized soil material, cement, and
water must be obtained. Uniformity of the mix is
easily checked by digging trenches or a series of
holes at regular intervals for the full depth of
treatment and inspecting the color of the exposed
soil-cement mixture. Uniform color and texture
from top to bottom indicate a satisfactory mix; a
streaked appearance indicates insufficient mixing.
Proper width and depth of mixing are also important. Following are methods of applying water and
mixing for the different types of mixing machines.
1. Windrow-type traveling mixing machine. Windrow-type traveling mixing machines
will pulverize friable soil materials. Other soils,
however, may need preliminary pulverizing to
meet specification requirements. This is usually
done before the soil is placed in windrows for
processing. The prepared soil material is bladed
into windrows and a proportion pulled along to
make them uniform in cross section. When borrow
materials are used, a windrow spreader can be
used to proportion the material. Nonuniform windrows cause variations in cement content, moisture
content, and pavement thickness. The number and
size of windrows needed depend on the width and
depth of treatment and on the capacity of the
mixing machine. Cement is spread on top of the
partially flattened or slightly trenched, prepared
windrow. The mixing machine then picks up the
soil material and cement and dry-mixes them with
the first few paddles in the mixing drum. At that
TM
point water is added through spray nozzles and the
remaining paddles complete the mixing. A strikeoff attached to the mixing machine spreads the
mixed soil-cement. If a motor grader is used to
spread the mixture and a tamping roller is used
for compaction, the mixture should first be loosened to ready it for compaction. If two windrows
have been made, the mixing machine progresses
350 to 500 feet along one windrow and then is
backed up to process the other windrow for 700 to
1,000 feet. The cement spreading operation is kept
just ahead of the mixing operation. Water is
supplied by tank trucks. A water tank installed on
the mixer will permit continuous operation while
5-822-14/AFJMAN
32-1019
the tank trucks are being switched. As soon as the
first windrow is mixed and spread on one section
of the roadway, it is compacted. At the same time
a second windrow is being mixed and spread. It in
turn is then compacted. Finishing of the entire
roadway is completed in one operation. Water
requirements are based on the quantity of soil
material and cement per unit length of windrow.
See figures 4-10 and 4-11 for construction sequences for windrow-type operations.
2. Multishaft traveling mixing machine.
Since most multi-shaft traveling mixing machines
have a high-speed pulverizing rotor, preliminary
pulverization is usually unnecessary. The only
preparation required is shaping the soil material
Figure 4-10. Sketch of soil-cement processing operations with windrow-type traveling pugmill.
4-5
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2 WINDROWS
3 WINDROWS
Figure 4-11. Plan for processing with windrow-type
traveling pugmill.
to approximate crown and grade. If an old roadbed
is extremely hard and dense, prewetting and scarification will facilitate processing. Processing is
done in lanes 350 to 500 feet long and as wide as
the mixing machine. Cement is spread on the soil
material in front of the mixing machine. Cement
spreading should be completed in the first working
lane and under way in the second lane before
mixing operations are begun. This ensures a fullwidth cement spread without a gap between lanes
and keeps spreading equipment out of the way of
mixing equipment. See figures 4-12 and 4-13 for
an illustration of the construction sequence.
3. Single-shaft traveling mixing machine.
Soil-cement construction with single-shaft traveling mixers differs from the preceding examples in
that more than one mixing pass is required. The
basic principles and objectives are the same, however. Shaping, scarifying, and pulverizing the
roadway are the first steps of preparation, as
described previously in this chapter. Since most
single-shaft traveling mixers were not designed to
scarify, the soil material may need to be loosened
with a scarifier. Prewetting the soil material is
common practice. Applying water at this stage of
Figure 4-12. Sketch of soil-cement processing operations with multiple-transverse-shaft traveling mixing machine.
4-6
TM
2 LANES
3 LANES
Figure 4-13. Plan for processing with
multiple-transverse-shaft traveling mixing machine.
construction saves time during actual processing
operations because most of the required water will
already have been added to the soil material. In
very granular materials, prewetting prevents cement from sifting to the bottom of the mix by
causing it to adhere more readily to the sand and
gravel particles. Mixing the soil material and
cement is easier if the moisture content of the raw
material is two or three percentage points below
optimum. However, very sandy materials can be
mixed even if the moisture content is one or two
percentage points above optimum. Moisture should
be applied uniformly during prewetting. By mixing it into the soil material, evaporation losses are
reduced. Because of the hazard of night rains,
some prefer to do the prewetting in the early
morning. After scarifying and prewetting, the
loose, moist soil material is shaped to crown and
grade. Cement is spread by a mechanical cement
spreader or from bags. Occasionally, the prewet
soil material becomes compacted by cementspreading equipment. In such cases, mixing can be
hastened by loosening the material again after
cement is spread, usually with the scarifier on a
motor grader. The scarifier teeth should be set so
that the cement will flow between them and not be
carried forward or displaced by the scarifier frame.
The mixer picks up the soil material and cement
5-822-14/AFJMAN
32-1019
and mixes them in place. Water, supplied by a
tank truck, is usually applied to the mixture by a
spray bar mounted in the mixing chamber, or it
can be applied ahead of the mixer by water
pressure distributors. The soil material and cement must be sufficiently blended when water
contacts the mixture to prevent the formation of
cement balls. The number of mixing passes depends on the type of soil material and its moisture
content and on the forward speed of the mixer. See
figure 4-14 for construction sequences.
(c) Central mixing plant. Central mixing
plants are often used for projects involving borrow
materials. The basic principles of thorough mixing,
adequate cement content, proper moisture content,
and adequate compaction apply. Friable granular
borrow materials are generally used because of
their low cement requirements and ease in handling and mixing. Pugmill-type mixers, either
continuous flow or batch, or rotary-drum mixers
are used for this work. Generally the twin-shaft
continuous-flow pugmill is used on highway
projects. Facilities for efficiently storing, handling,
and proportioning materials must be provided at
the plant. Quantities of soil material, cement, and
water can be proportioned by volume for weight.
Mixing is continued until a uniform mixture of
soil material, cement, and water is obtained. To
reduce evaporation losses during hot, windy conditions and to protect against sudden showers, haul
trucks should be equipped with protective covers.
To prevent excessive haul time, not more than 60
minutes should elapse between the start of moistmixing and the start of compaction. Haul time is
usually limited to 30 minutes. The mixed soilcement should be placed on the subgrade without
segregation in a quantity that will produce a
compacted base of uniform density conforming to
the specified grade and cross section. The mixture
should be spread to full roadway width either by
one full-width spreader or by two or more spreaders operating in staggered positions across the
roadway. Less preferable is the use of one piece of
spreading equipment operating one lane at a time
in two or more lanes. No lane should be spread so
far ahead of the adjoining lane that a time lapse of
more than 30 minutes occurs between the time of
placing material in adjoining lanes at any location. The subgrade should be damp when the
soil-cement is placed. Bituminous pavers have
been used for spreading soil-cement although modification may be necessary to increase volume
capacity before they can be used. Compaction
equipment should follow immediately behind the
spreader. When compacting the first lane, a narrow compacted ridge should be left adjacent to the
4-7
TM 5-822-14/AFJMAN 32-1019
Figure 4-14. Sketch of soil-placement processing operations with single-transverse-shaft mixers.
second lane to serve as a depth guide when placing
the mix in the second lane. Water spray equipment should be available to keep the joint areas
damp. The amount of water needed to bring the
soil-cement mixture to required moisture content
in continuous-flow-type mixing plants is based on
the amount of soil material and cement coming
into the mixing chamber per unit of time. The
amount of water required in batch-type central
mixing plants is similarly calculated, using the
weights of soil material and cement for each batch.
(3) Compaction. The principles governing compaction of soil-cement are the same as those for
compacting the same soil materials without cement treatment. The soil-cement mixture at optimum moisture should be compacted to maximum
density and finished immediately. Moisture loss by
evaporation during compaction, indicated by a
greying of the surface, should be replaced with
light applications of water. Tamping rollers are
4-8
generally used for initial compaction except for the
more granular soils. Self-propelled and vibratory
models are also used. To obtain adequate compaction, it is sometimes necessary to operate the
rollers with ballast to give greater unit pressure.
The general rule is to use the greatest contact
pressure that will not exceed the bearing capacity
of the soil-cement mixture and that will still
“walk out” in a reasonable number of passes.
Friable silty and clayey sandy soils will compact
satisfactorily using rollers with unit pressures of
75 to 125 pounds per square inch. Clayey sands,
lean clays, and silts that have low plasticity can
be compacted with 100- to 200-pounds per square
inch rollers. Medium to heavy clays and gravelly
soils required greater unit pressure, i.e., 150 to
300 pounds per square inch. Compacted thickness
up to 8 or 9 inches can be compacted in one lift.
Greater thicknesses can be compacted with equipment designed for deeper lifts. When tamping
TM 5-822-14/AFJMAN 32-1019
rollers are used for initial compaction, the mixed
material must be in a loose condition at the start
of compaction so that the feet will pack the bottom
material and gradually walk out on each succeeding pass. If penetration is not being obtained, the
scarifier on a motor grader or a traveling mixer
can be used to loosen the mix during start of
compaction, thus allowing the feet to penetrate.
Vibratory-steel-wheeled rollers and grid and segmented rollers can be used to satisfactorily compact soil-cement made of granular soil materials.
Vibratory-plate compactors are used on nonplastic
granular materials. Pneumatic-tired rollers can be
used to compact coarse sand and gravel soilcement mixtures with very little plasticity and
very sandy mixtures with little or no binder
material, such as dune, beach, or blow sand. Some
permit rapid inflation and deflation of the tires
while compacting to increase their versatility.
Pneumatic-tired rollers pulled by track-type tractors equipped with street plates can be used to
compact cohesionless sand mixtures. The weight
and vibration of the tractor aid in compaction.
Heavy three-wheeled steel rollers can be used to
compact coarse granular materials containing little or no binder material. Gravelly soils that
contain up to about 20 percent passing the No. 200
sieve and have low plasticity are best suited for
compaction with these rollers. Tandem-steelwheeled rollers are often used during final rolling
to press down or set rock particles and to smooth
out ridges. There are two general types of road
cross section: trench and featheredge. Both can be
built satisfactorily with soil-cement. In trench-type
construction, the shoulder material gives lateral
support to the soil-cement mixture during compaction. In the featheredge type of construction, the
edges are compacted first to provide some edge
stability while the remaining portion is being
compacted. The edge slope should not be steeper
than 2:1 to facilitate shaping and compacting.
Shoulder material is placed after the soil-cement
has been finished. Occasionally, during compaction
and finishing, a localized area may yield under the
compaction equipment. This may be due to one or
more causes: the soil-cement mix is much wetter
than optimum moisture; the subsoil may be wet
and unstable; or the roller may be too heavy for
the soil. If the soil-cement mix is too damp, it
should be aerated with a cultivator, traveling
mixer, or motor grader. After it has dried to near
optimum moisture, it can be compacted. For best
results, compaction should start immediately after
the soil material, cement, and water have been
mixed. Required densities are then obtained more
readily; there is less water evaporation; and daily
production is increased.
(4) Finishing. There are several acceptable
methods for finishing soil-cement. The exact procedure depends on equipment, job conditions, and
soil characteristics. Regardless of method, the fundamental requirements of adequate compaction,
close to optimum moisture, and removal of all
surface compaction planes must be met to produce
a high quality surface. The surface should be
smooth, dense, and free of ruts, ridges, or cracks.
When shaping is done during finishing, all smooth
surfaces, such as tire imprints and blade marks,
should be lightly scratched with a weeder, nail
drag, coil spring, or spiketooth harrow to remove
cleavage or compaction planes from the surface.
Scratching should be done on all soil-cement mixtures except those containing appreciable quantities of gravel. The surface should be kept damp
during finishing operations. Steel-wheeled rollers
can be used to smooth out ridges left by the initial
pneumatic-tired rolling. Steel-wheeled rollers are
particularly advantageous when rock is present in
the surface. A broom drag can sometimes be used
advantageously to pull binder material in and
around pieces of gravel that have been set by the
steel-wheeled roller. Instead of using a steel roller,
surfaces can be shaved with the motor grader and
then rerolled with a pneumatic-tired roller to seal
the surface. Shaving consists of lightly cutting off
any small ridges left by the finishing equipment.
Only a very thin depth is cut and all material
removed is bladed to the edge of the road and
wasted. The final operation usually consists of a
light application of water and rolling with a
pneumatic-tired roller to seal the surface. The
finished soil-cement is then cured.
(5) Curing. Compacted and finished soilcement contains sufficient moisture for adequate
cement hydration. A moisture-retaining cover is
placed over the soil-cement soon after completion
to retain this moisture and permit the cement to
hydrate. Most soil-cement is cured with bituminous material, but other materials such as waterproof paper of plastic sheets, wet straw or sand,
fog-type water spray, and wet burlap or cotton
mats are entirely satisfactory. The types of bituminous materials most commonly used are RC-250,
MC-250, RT-5, and emulsified asphalt SS-1. Rate
of application varies from 0.15 to 0.30 US gallons
per square yard. At the time of application, the
soil-cement surface should be free of all dry, loose
and extraneous material. The surface should also
be moist when the bituminous materials are applied. In most cases a light application of water is
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placed immediately ahead of the bituminous application.
(6) Construction joints. After each day’s construction, a transverse vertical construction joint
must be formed by cutting back into the completed
soil-cement to the proper crown and grade. This is
usually done the last thing at night or the first
thing the following morning, using the toe of the
motor-grader blade or mixer. The joint must be
vertical and perpendicular to the centerline. After
the next day’s mixing has been completed at the
joint, it must be cleaned of all dry and unmixed
material and retrimmed if necessary. Mixed moist
material is then bladed into the area and compacted thoroughly. The joint is left slightly high
until final rolling when it is trimmed to grade
with the motor grader and rerolled. Joint construction requires special attention to make sure the
joints are vertical and the material in the joint
area is adequately mixed and thoroughly compacted. When bituminous material is used as a
curing agent, it should be applied right up to the
joint and sanded to prevent pickup.
(7) Multiple-layer construction. When the specified thickness of soil-cement base course exceeds
the depth (usually 8 or 9 inches compacted) that
can be compacted in one layer, it must be constructed in multiple layers. No layer should be less
than 4 inches thick. The lower layer does not have
to be finished to exact crown and grade, nor do
surface compaction planes have to be removed
since they are too far from the final surface to be
harmful. The lower layer can be cured with the
moist soil that will subsequently be used to build
the top layer-which can be built immediately, the
following day, or some time later. With mixed-inplace construction, care must be taken to eliminate any raw-soil seams between the layers.
e. Special construction problems.
(1) Rainfall. Attention to a few simple precautions before processing will greatly reduce the
possibility of serious damage from wet weather.
For example, any loose or pulverized soil should be
crowned so it will shed water, and low places in
the grade where water can accumulate should be
trenched so the water will drain off freely. As
shown by the construction of millions of square
yards of soil-cement in all climates, it is unlikely
that rainfall during actual construction will be a
serious problem to the experienced engineer or
contractor. Usually construction requires the addition of water equivalent to 1 to 1½ inches of rain.
If rain falls during cement-spreading operations,
spreading should be stopped and the cement already spread should be quickly mixed into the soil
mass. A heavy rainfall that occurs after most of
4-10
the water has already been added, however, can be
serious. Generally, the best procedure is to obtain
rapid compaction by using every available piece of
equipment so that the section will be compacted
and shaped before too much damage results. In
such instances it may be necessary to complete
final blading later; any material bladed from the
surface is wasted. After the mixture has been
compacted and finished, rain will not harm it.
(2) Wet soils. Excessively wet material is difficult to mix and pulverize. Experience has shown
that cement can be mixed with sandy materials
when the moisture content is as high as 2 percent
above optimum. For clayey soils, the moisture
content should be below optimum for efficient
mixing. It may be necessary to dry out the soil
material by aeration. This can be done by using
single-shaft traveling mixers with the hood in a
raised position, or by cutting out the material with
the tip of a motor grader blade and working and
aerating with a disc. The maintenance of good
crown and surface grade to permit rapid runoff of
surface water before soil-cement processing is the
best insurance against excessive amounts of wet
material.
(3) Cold weather. Soil-cement, like other
cement-using products, hardens as the cement
hydrates. Since cement hydration practically
ceases when temperatures are near or below freezing, soil-cement should not be placed when the
temperature is 40 degrees F or below. Moreover, it
should be protected to prevent its freezing for a
period of 7 days after placement, and until it has
hardened, by a suitable covering of hay, straw, or
other protective material.
4-2. Construction with lime.
a. Lime stabilization methods. Basically, there
are three recognized lime stabilization methods;
in-place mixing, plant mixing, and pressure injection.
(1) In-place mixing.
(a) In-place mixing may be subdivided into
three methods: mixing lime with the existing
materials already a part of the construction site or
pavement (fig 4-15); off-site mixing in which lime
is mixed with borrow and the mixture is then
transported to the construction site for final manipulation and compaction (fig 4-16); and mixing
in which the borrow source soil is hauled to the
construction site and processed as in the first
method.
(b) The following procedures are for in-place
mixing:
One increment of lime is added to clays or
granular base materials that are easy to pulverize.
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Figure 4-15. In-place mixing of lime with existing base
and paving material on city street.
Figure 4-17. Deep stabilization after lime spreading
the plow cuts 24 inches deep.
Figure 4-16. Off-site mixing pads for Mississippi River
levee repair project.
The material is mixed and compacted in one
operation, and no mellowing period is required.
One increment of lime is added and the
mixture is allowed to mellow for a period of 1 to 7
days to assist in breaking down heavy clay soils.
(The term mellow refers to the reaction of the lime
on clay to make it more friable and easier to
pulverize.)
One increment of lime is added for soil modification and pulverization before treatment with
cement or asphalt.
One increment of lime is added to produce a
working table. Proof rolling is required instead of
pulverization and density requirements.
Two increments of lime are added for soils
that are extremely difficult to pulverize. Between
the applications of the first and second increments
of lime, the mixture is allowed to mellow.
(c) Deep stabilization may be accomplished
by one of two approaches.
One increment of lime is applied to modify soil
to a depth of 24 inches (fig 4-17 through fig 4-19).
Greater depths are possible but to date have not
been attempted. A second increment of lime is
Figure 4-18. Root plow for scarifying to a depth of 18 inches.
Figure 4-19. Scarifying existing clay subgrade with lime on
city street project.
added to the top 6 to 12 inches for complete
stabilization. Plows and rippers are used to break
down the large clay chunks in the deep treatment.
Heavy disc harrows and blades are also used in
pulverization of these clay soils. In frost zones, the
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TM 5-822-14/AFJMAN 32-1019
use of small quantities of lime for soil modification
under some circumstances may result in a frost
susceptible material that in turn can produce a
weak sublayer.
One increment of lime is applied for complete
stabilization to a depth of 18 inches. Mechanical
mixers are now available to pulverize the limeclay soil to the full depth by progressive cuts as
follows: first-pass cut to a depth of 6 inches, second
to 9 inches, third to 12 inches, fourth to 15 inches,
and then a few passes to a depth of 18 inches to
accomplish full pulverization. The full 18 inches is
compacted from the top by vibratory and conventional heavy rollers.
(2) Plant mixing. The plant-mix operation usually involves hauling the soil to a central plant
where lime, soil, and water are uniformly mixed
and then transported to the construction site for
further manipulation (fig 4-20 through fig 4-22).
The amount of lime for either method is usually
predetermined by test procedures. Specifications
may be written to specify the actual strength gain
required to upgrade the stabilized soil, and notations can be made on the plans concerning the
estimated percent of lime required. This note
should also stipulate that changes in lime content
may be necessary to meet changing soil conditions
encountered during construction.
(3) Pressure injection. Pressure injections of
lime slurry to depths of 7 to 10 feet, for control of
swelling and unstable soils on highways (fig 4-23)
and under building sites, are usually placed on
5-foot spacings, and attempts are made to place
horizontal seams of lime slurry at 8- to 12-inch
intervals. The top 6- to 12-inch layer should be
completely stabilized by conventional methods.
b. Construction steps.
Figure 4-21. Lime-cement-fly ash aggregate base course.
Figure 4-22. Enclosed soil holds lime for adding to
marginal crushed stone base material.
Figure 4-23. Lime slurry pressure injection (LSPI) rig
treating a failed highway slope.
Figure 4-20. Lime-treated gravel with lime fed by
screw conveyor.
4-12
(1) Soil preparation. The in-place subgrade soil
should be brought to final grade and alignment.
The finished grade elevation may require some
adjustment because of the potential fluff action of
the lime-stabilized layer resulting from the fact
that some soils tend to increase in volume when
mixed with lime and water. This volume change
TM
may be exaggerated when the soil-lime is remixed
over a long period of time, especially at moisture
contents less than optimum moisture. The fluff
action is usually minimized if adequate water is
provided and mixing is accomplished shortly after
lime is added. For soils that tend to fluff with
lime, the subgrade elevation should be lowered
slightly or the excess material trimmed. Trimming
can usually be accomplished by blading the material onto the shoulder of embankment slopes. The
blading operation is desirable to remove the top
0.25 inch because this material is not often well
cemented due to lime loss experienced during
construction. Excess rain and construction water
may wash lime from the surface, and carbonation
of lime may occur in the exposed surface. If dry
lime is used, ripping or scarifying to the desired
depth of stabilization can be accomplished either
before or after lime is added (fig 4-19). If the lime
is to be applied in a slurry form, it is desirable to
scarify prior to the addition of lime.
(2) Lime application.
(a) Dry hydrated lime. Dry lime can be
applied either in bulk or by bag. The use of bagged
lime is generally the simplest but also the most
costly method of lime application. Bags of 50
pounds are delivered in dump or flatbed trucks
and placed by hand to give the required distribution (fig 4-24). After the bags are placed they are
slit and the lime is dumped into piles or transverse windrows across the roadway. The lime is
then levelled either by hand raking or by means of
a spike-tooth harrow or drag pulled by a tractor or
truck. Immediately after, the lime is sprinkled to
reduce dusting. The major disadvantages of the
bag method are the higher costs of lime because of
bagging costs, greater labor costs, and slower
operations. Nevertheless, bagged lime is often the
most practical method for small projects or for
projects in which it is difficult to utilize large
equipment. For large stabilization projects, particularly where dusting is no problem, the use of
bulk lime has become common practice. Lime is
delivered to the job in self-unloading transport
trucks (fig 4-25). These trucks are large and
efficient, capable of hauling 15 to 24 tons. One
type is equipped with one or more integral screw
conveyors that discharge at the rear. In recent
years pneumatic trucks have increased in popularity and are preferred over the older auger-type
transports. With the pneumatic units the lime is
blown from the tanker compartments through a
pipe or hose to a cyclone spreader to a pipe
spreader bar-mounted at the rear (fig 4-26).
Bottom-dump hopper trucks have also been tried,
but they are undesirable because of difficulty in
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32-1019
unloading and obtaining a uniform rate of discharge. With the auger trucks, spreading is handled by means of a portable, mechanical-type
spreader attached to the rear (fig 4-27) or through
metal downspout chutes or flexible rubber boots
extending from the screw conveyors. The mechanical spreaders incorporate belt, screw, rotary vane,
or drag-chain conveyors to distribute the lime
uniformly across the spreader width. When boots
or spouts are used instead, the lime is deposited in
windrows; but because of lime’s lightness and
flowability, the lime becomes distributed rather
uniformly across the spreading lane. Whether mechanical spreaders, downspouts, or boots are used,
the rate of lime application can be regulated by
varying the spreader opening, spreader drive
speed, or truck speed so that the required amount
of lime can be applied in one or more passes. With
the pneumatic trucks, spreading is generally handled with a cyclone spreader mounted at the rear,
which distributes the lime through a split chute or
with a spreader bar equipped with several large
downspout pipes. Finger-tip controls in the truck
cab permit the driver to vary the spreading width
by adjusting the air pressure. Experienced drivers
can adjust the pressure and truck speed so that
accurate distribution can be obtained in one or two
passes. When bulk lime is delivered by rail, a
variety of conveyors can be used for transferring
the lime to transport trucks; these include screw,
belt, or drag-chain conveyors, bucket elevators,
and screw elevators. The screw-type conveyors are
most commonly used, with large diameter units of
10- to 12-inches being recommended for high-speed
unloading. To minimize dusting, all types of conveyors should be enclosed. Rail-car unloading is
generally facilitated by means of poles and mechanical or air-type vibrators. Lime has also been
handled through permanent or portable batching
plants, in which case the lime is weigh-batched
before loading. Generally, a batch plant setup
would only be practical on exceptionally large jobs.
Obviously, the self-unloading tank truck is the
least costly method of spreading lime, because
there is no rehandling of material and large
payloads can be carried and spread quickly.
(b) Dry quicklime. Quicklime may be applied in bags or bulk. Because of higher cost,
bagged lime is only used for drying of isolated wet
spots or on small jobs. The distribution of bagged
quicklime is similar to that of bagged hydrate,
except that greater safety emphasis is needed.
First, the bags are spaced accurately on the area
to be stabilized, and, after spreading, water is
applied and mixing operations started immediately. The fast watering and mixing operation
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TM 5-822-14/AFJMAN 32-1019
Figure 4-27. Distribution of quicklime
from mechanical spreader on city street.
Figure 4-24. Application of lime by the bag
for a small maintenance project.
Figure 4-25. Application of lime by a bulk pneumatic truck.
Figure 4-26. Bulk pneumatic truck spreading lime
from bar spreader.
4-14
helps minimize the danger of burns. Quicklime
may be applied in the form of pebbles of approximately 3/8 inch, granular, or pulverized. The first
two are more desirable because less dust is generated during spreading. Bulk quicklime may be
spread by self-unloading auger or pneumatic transport trucks, similar to those used for dry hydrate.
However, because of its coarser size and higher
density, quicklime may also be tailgated from a
regular dump truck with tailgate opening controls
to ensure accurate distribution (fig 4-28). Because
quicklime is anhydrous and generates heat on
contact with water, special care should be taken
during stabilization to avoid lime burns. Where
quicklime is specified, the contractor should provide the engineer with a detailed safety program
covering precautions and emergency treatment
available on the jobsite. The program should include protective equipment for eyes, mouth, nose,
and skin, as well as a first-aid kit containing an
eyeball wash. This protective equipment should be
available on the jobsite during spreading and
mixing operations. The contractor should actively
enforce this program for the protection of the
workers and others in the construction area.
(c) Slurry method. In this method either
hydrated lime or quicklime and water are mixed
into a slurry. With quicklime, the lime is first
slaked and excess water added to produce the
slurry.
(d) Slurry made with hydrated lime. This
method was first used in the 1950s and is currently very popular, especially where dust from
using dry lime is a problem. The hydrated limewater slurry is mixed either in a central mixing
tank (fig 4-29), jet mixer (fig 4-30), or in a tank
truck. The slurry is spread over the scarified
roadbed by a tank truck equipped with spray bars
(fig 4-31 and fig 4-32). One or more passes may be
TM
Figure 4-28. Spreading of granular quicklime.
required over a measured area to achieve the
specified percentage based on lime solids content.
To prevent runoff and consequent nonuniformity of
lime distribution that may occur under certain
conditions, it may be necessary to mix the slurry
and soil immediately after each spreading pass (fig
4-33). A typical slurry mix proportion is 1 ton of
lime and 500 gallons of water, which yields about
600 gallons of slurry containing 31 percent lime
solids. At higher concentrations there is difficulty
in pumping and spraying the slurry. Forty percent
solids is a maximum pumpable slurry. The actual
proportion used depends on the percentage of lime
specified, type of soil, and its moisture condition.
When small lime percentages are required, the
slurry proportions may be reduced to 1 ton of lime
per 700 to 800 gallons of water. Where the soil
moisture content is near optimum, a stronger lime
concentration would normally be required. In
plants employing central mixing, agitation is usually accomplished by using compressed air and
recirculating pump, although pugmills have also
been used. The most typical slurry plant incorporates slurry tanks large enough to handle whole
tank truck loads of hydrated lime of approximately
20 tons. For example, on one job two 15,000 gallon
tanks, 10 feet in diameter by 26 feet in length,
were used, each fitted with an 8-inch perforated
air line mounted along the bottom. The air line
was stopped 18 inches short of the end wall,
thereby providing maximum agitation in the limefeeding zone. A typical batch consisted of 10,000
gallons of water (charged first) and 20 tons of lime,
producing about 12,000 gallons of slurry in less
than 25 minutes. Loading of the tank trucks was
handled by a standard water pump, with one
slurry tank being unloaded while the slurry was
being mixed in the other tank. On another job the
contractor used a similar tank and air line, but, in
addition, a 4-inch recirculating pump was used for
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32-1019
mixing; the same pump loaded the tank trucks. To
keep the lime from settling, the contractor devised
a hand-operated scraper fitted with air jets. The
newest and most efficient method of slurry production, which eliminates batching tanks, involves
the use of a compact jet slurry mixer. Water at 70
pounds per square inch and hydrated lime are
charged continuously in a 65:35 (weight) ratio into
the jet mixing bowl where slurry is produced
instantaneously. The mixer and auxiliary equipment can be mounted on a small trailer and
transported to the job readily, giving great flexibility to the operation. In the third type of slurry
setup, measured amounts of water and lime are
charged separately to the tank truck, with the
slurry being mixed in the tank either by compressed air or by a recirculating pump mounted at
the rear. The water is metered and the lime
proportioned volumetrically or by means of weight
batchers. Both portable and permanent batching
plants are used. Mixing with air is accomplished
at the plant. The air jets are turned on during the
loading operation, and remain on until the slurry
is thoroughly mixed which takes about 10 to 15
minutes. The use of a recirculating pump, however, permits mixing to occur during transit to the
job. Usually, 2-, 3-, or 4-inch pumps are used in
this operation, with the slurry being recirculated
through the tank by means of a perforated longitudinal pipe extending the length of the tank and
capped at one end. Spreading from the slurry
distributors is effected by gravity or by pressure
spray bars, the latter being preferred because of
better distribution. The use of spray deflectors is
also recommended for good distribution. The general practice in spreading is to make either one or
two passes per load. However, several loads may
be needed in order to distribute the required
amount of lime. The total number of passes will
depend on the lime requirement, optimum moisture of the soil, and type of mixing employed.
Windrow mixing with the grader generally requires several passes.
(e) Double application of lime. In some areas
where extremely plastic, gumbo clay (PI 50+)
abounds, it may prove advantageous to add the
requisite amount of lime in two increments to
facilitate adequate pulverization and obtain complete stabilization. For example, 2 or 3 percent
lime is added first, partially mixed, then the layer
is sealed and allowed to cure for up to a week. The
remaining lime is then added preparatory to final
mixing. The first application mellows the clay and
helps in achieving final pulverization, and the
second application completes the lime-treatment
process.
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5-822-14/AFJMAN
32-1019
Figure 4-29. Slurry mixing tank using recirculating pump
for mixing hydrate and water.
Figure 4-32. Recirculation pump on top of
6,000-gallon wagon agitates the slurry.
a
Figure 4-30. Jet slurry mixing plant.
Figure 4-33. Grader-scarifier cutting slurry into stone base.
Figure 4-34. Portabatch lime slaker.
Figure 4-31. Spreading
of lime slurry.
(f) Slurry made with quicklime. A recent
unit developed for making lime slurry from quicklime is the Portabatch Slaker (fig 4-34). This unit
consists of a lo-foot diameter by 40-foot tank that
incorporates a 5-foot diameter single shaft agitator
turned by a 100-horse power diesel engine. The
batch slaker can handle 20 to 25 tons of quicklime
and about 25,000 gallons of water, producing
the slurry in about 1 to 1.5 hours. Because of the
4-16
exothermic action of quicklime in water, the slurry
is produced at a temperature of about 185 degrees
F.
(g) Some of the advantages and disadvantages of dry hydrated lime are as follows:
1 Advantages:
Dry lime can be applied two or three
times faster than a slurry.
Dry lime is very effective in drying out
soil.
2 Disadvantages:
Dry lime produces a dusting problem
that makes its use undesirable in
urban areas.
TM
The fast drying action of the dry lime
requires an excess amount of water
during the dry, hot seasons.
(h) Some of the advantages and disadvantages of dry quicklime are as follows:
1. Advantages:
More economical as it contains approximately 25 percent more available
lime.
Greater bulk density for smaller-sizes
silos.
Faster drying action in wet soils.
Faster reaction with soils.
Construction season can be extended, in
both spring and fall, because of faster
drying.
2. Disadvantages:
Field hydration less effective than commercial hydrators, producing a
coarser material with poorer distribution in soil mass.
Quicklime requires more water than
hydrate for stabilization, which may
present a problem in dry areas.
Greater susceptibility to skin and eye
burns.
(i) Some of the advantages and disadvantages of slurry lime are as follows:
1. Advantages:
Dust-free application is more desirable
from an environmental standpoint.
Better distribution is achieved with the
slurry.
In the lime slurry method, the lime
spreading and sprinkling operations
are combined, thereby reducing job
costs.
During summer months slurry application prewets the soil and minimizes
drying action.
The added heat when slurry is made
from quicklime speeds drying action,
which is especially desirable in cooler
weather.
2. Disadvantages:
Application rates are slower. High capacity pumps are required to achieve
acceptable application rates.
Extra equipment is required, therefore,
costs are higher.
Extra manipulation may be required for
drying purposes during cool, wet, humid weather, which could occur during the fall, winter, and spring construction season.
5-822-14/AFJMAN
32-1019
Not practical for use with very wet
soils.
(3) Pulverization and mixing. To obtain satisfactory soil-lime mixtures adequate pulverization
and mixing must be achieved. For heavy clay soils
two-stage pulverization and mixing may be required, but for other soils one-stage mixing and
pulverization may be satisfactory. This difference
is primarily due to the fact that the heavy clays
are more difficult to break down.
(a) Two-stage mixing. Construction steps in
two-stage mixing consist of preliminary mixing,
moist curing for 24 to 48 hours (or more), and final
mixing or remixing. The first mixing step distributes the lime throughout the soil, thereby facilitating the mellowing action. For maximum chemical
action during the mellowing period, the clay clods
should be less than 2 inches in diameter. Before
mellowing the soil should be sprinkled liberally to
bring it up to at least two percentage points above
optimum moisture in order to aid the disintegration of clay clods The exception to excess watering
would be in cool, damp weather when evaporation
is at a minimum. In hot weather, however, it may
be difficult to add too much water. After preliminary mixing, the roadway should be sealed lightly
with a pneumatic roller as a precaution against
heavy rain, because the compacted subgrade will
shed water, thereby preventing moisture increases
that might delay construction. Generally, in 24 to
48 hours the clay becomes friable enough so that
desired pulverization can be easily attained during
final mixing. Additional sprinkling may be necessary during final mixing to bring the soils to
optimum moisture or slightly above (fig 4-35). In
hot weather more than optimum moisture is
needed to compensate for the loss through evaporation. Although disc harrows (fig 4-36) and grader
scarifiers are suitable for preliminary mixing,
high-speed rotary mixers (fig 4-37 to fig 4-39) or
one-pass travel plant mixers (fig 4-15) are required for final mixing. Motor graders are generally unsatisfactory for mixing lime with heavy
clays.
(b) One-stage mixing. Both blade and rotary
mixing, or a combination, have been used successfully in projects involving granular base materials.
However, rotary mixers are preferred for more
uniform mixing, finer pulverization, and faster
operation. They are generally required for highly
plastic soils that do not pulverize readily and for
reconstructing worn-out roads in order to pulverize
the old asphalt.
(c) Blade mixing. When blade mixing is
used in conjunction with dry lime, the material is
generally bladed into two windrows, one on each
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TM 5-822-14/AFJMAN 32-1019
Figure 4-35. Watering of lime-treated clay on airport project.
Figure 4-36. Mixing with a disc harrow.
Figure 4-37. Rotary mixer.
Figure 4-38. Train of rotary mixers.
4-18
Figure 4-39. Rotary mixer on primary road project.
side of the roadway. Lime is then spread on the
inside of each windrow or down the center line of
the road. The soil is then bladed to cover the lime.
After the lime is covered, the soil is mixed dry by
blading across the roadway. After dry mixing is
completed, water is added to slightly above the
optimum moisture content and additional mixing
is performed. To ensure thorough mixing by this
method, the material should be handled on the
mold board at least three times. When blade
mixing is used with the slurry method, the mixing
is done in thin lifts that are bladed to windrows.
One practice is to start with the material in a
center windrow, then blade aside a thin layer after
the addition of each increment of slurry, thereby
forming side windrows. The windrowed material is
then bladed back across the roadway and compacted, provided that its moisture content is at
optimum. A second practice is to start with a side
windrow, then blade in a thin 2-inch layer across
the roadway, add an increment of lime, and blade
this layer to a windrow on the opposite side of the
road. On one job this procedure was repeated
several times until all the material was mixed and
bladed to the new windrow. Because only one-half
of the lime had been added at this time, the
process was repeated, moving the material back to
the other side. This procedure is admittedly slow,
but it provides excellent uniformity.
(d) Central mixing. Premixing lime with
granular base materials is becoming popular on
new construction projects, particularly where submarginal gravels are used. Because the gravel has
to be processed anyway to meet gradation specifications, it is a relatively simple matter for the
contractor to install a lime bin, feeder, and pugmill at the screening plant. On one project a small
pugmill was installed at the head pulley of the
collecting belt conveyor (fig 4-20) and at another
operation a larger pugmill plant was utilized (fig
4-21). The general practice is to add the optimum
TM
moisture at the pugmill, thereby permitting immediate compaction after laydown. Figure 4-22
shows a crushed-stone plant where lime was added
to upgrade a clay bearing crushed stone.
(e) Pulverization and mixing requirements.
Pulverization and mixing requirements are generally specified in terms of percentages passing the
1½-inch or 1-inch screen and the No. 4 sieve. Typical requirements are 100 percent passing the 1
inch, and 60 percent passing the No. 4 sieve,
exclusive of nonslaking fractions. However, in
some applications the requirements are relaxed.
For example, the South Dakota Highway Department only requires 100 percent passing the 1.5
inch screen with no requirement for the No. 4
sieve. Other specifications may only require 40 to
50 percent passing the No. 4 sieve. In certain
expedient construction operations, formal requirements are eliminated and the “pulverization and
mixing to the satisfaction of the engineer” clause
is employed.
(4) Compaction. For maximum development of
strength and durability, lime-soil mixtures should
be properly compacted. Many agencies require at
least 95 percent of ASTM D 698 density for
subbase and 90 percent for bases. Some agencies
have required 95 percent ASTM D 1557 maximum
density. Although such densities can be achieved
for more granular soil-lime mixtures, it is difficult
to achieve this degree of compaction for limetreated, fine-grained soils. If a thick soil-lime lift is
to be compacted in one lift, many specifications
require 95 percent of ASTM D 698 maximum
density in the upper 6 to 9 inches, and lower
densities are accepted in the bottom portion of the
lift. To achieve high densities, compacting at
approximately optimum moisture content with appropriate compactors is necessary. Granular soillime mixtures are generally compacted as soon as
possible after mixing, although delays of up to 2
days are not detrimental, especially if the soil is
not allowed to dry out and lime is not allowed to
carbonate. Fine-grained soils can also be compacted soon after final mixing, although delays of
up to 4 days are not detrimental. When longer
delays (2 weeks or more) cannot be avoided, it may
be necessary to incorporate a small amount of
additional lime into the mixture (0.5 percent) to
compensate for losses due to carbonation and
erosion. Various rollers and layer thicknesses have
been used in lime stabilization. The most common
practice is to compact in one lift by first using the
sheeps-foot roller (fig 4-40 and fig 4-41) until it
“walks out,” and then using a multiple-wheel
pneumatic roller (fig 4-42). In some cases, a flat
wheel roller is used in finishing. Single lift com-
5-822-14/AFJMAN
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paction can also be accomplished with vibrating
impact rollers (fig 4-43) or heavy pneumatic rollers, and light pneumatic or steel rollers used for
finishing. When light pneumatic rollers are used
alone, compaction is generally done in thin lifts
usually less than 6 inches. Slush rolling of granular soil-lime mixtures with steel rollers is not
recommended. During compaction, light sprinkling
may be required, particularly during hot, dry
weather, to compensate for evaporation losses.
(5) Curing. Maximum development of
strength and durability also depends on proper
curing. Favorable temperature and moisture conditions and the passage of time are required for
curing. Temperatures higher than 40 degrees F to
50 degrees F and moisture contents around optimum are conducive to curing. Although some
specifications require a 3- to 7-day undisturbed
curing period, other agencies permit the immediate placement of overlaying paving layers if the
compacted soil-lime layer is not rutted or distorted
by the equipment. This overlying course maintains
Figure 4-40. Self-propelled sheepsfoot roller.
Figure 4-41. Dougle sheepsfoot roller.
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obtain adequate proportioning and mixing. With
LCF, it also should be noted that the presence of
cement requires that the stabilized mixture be
compacted as soon as possible.
4-4. Construction with Bitumen. Bituminous
Figure 4-42. Pneumatic roller completes compaction
of LCF base.
Figure 4-43. Vibrating roller completes compaction of subgrade.
the moisture content of the compacted layer and is
an adequate medium for curing. Two types of
curing can be employed: moist and asphaltic
membrance. In the first, the surface is kept damp
by sprinkling with light rollers being used to keep
the surface knitted together. In membrane curing,
the stabilized soil is either sealed with one shot of
cutback asphalt at a rate of about 0.10 to 0.25
gallons per square yard within 1 day after final
rolling, or primed with increments of asphalt
emulsion applied several times during the curing
period. A common practice is to apply two shots
the first day and one each day thereafter for 4
days at a total rate of 0.10 to 0.25 gallons per
square yard. The type of membrane used, amount,
and number of shots vary considerably. Usually, it
is difficult to apply more than 0.2 gallons of
asphalt prime because the lime-stabilized layer is
relatively impervious after compaction.
4-3. Construction with Lime-Fly Ash (LF) and
Lime-Cement-Fly Ash (LCF). Construction proce-
dures for LC and LCF are similar to those used for
lime stabilization. Although both field in place and
central plant mixing may be used with LF and
LCF, the latter procedure is recommended to
4-20
stabilization can involve either hot-mix or cold-mix
materials. Bitumen and aggregate or soil can be
blended in place or in a central plant. Construction procedures presented in this manual are for
cold-mix materials mixed in place or in a central
plant. Construction procedures for hot-mix hot-laid
materials are similar to those used for asphalt
concrete and applicable standard construction procedures should be followed when these materials
are involved.
a. Equipment for Mixed-in-Place Materials. Some
pieces of equipment used for mixed-in-place bituminous stabilization are similar to those used in
standard construction and will not be described
here. These include water distributors, compaction
equipment, and windrow sizers. Only equipment
especially associated with or having special features applicable to bituminous stabilization will be
discussed.
(1) Mixing equipment.
(a) Travel plants. Travel plants are selfpropelled pugmill plants that proportion and mix
aggregates and asphalt as they move along the
road. There are two general types of travel plants:
one that moves through a prepared aggregate
windrow on the roadbed, adds and mixes the
asphalt as it goes and discharges to the rear a
mixed windrow ready for aeration and spreading
(fig 4-44) and one that receives aggregate into its
hopper from haul trucks, adds and mixes asphalt,
and spreads the mix to the rear as it moves along
the roadbed (fig 4-45). Certain features and performance capabilities are common to all travel
plants, enabling them to operate effectively and to
produce a mix meeting design and specification
criteria. To begin, the tracks or wheels on which
the machine moves must be so sized, designed, and
positioned that they do not damage or rut the
surface on which it operates when the plant is
fully loaded. The basic purpose of the travel plant
is to mix asphalt and aggregate. Some machines
are equipped with devices that maintain the
proper proportions automatically. Others, however,
require that a uniform speed be maintained to
ensure uniform proportioning. Regardless of the
type, the manufacturer’s recommended procedures
for calibrating and operating the travel plant
should be followed carefully. Finally, the efficient
travel plant should be capable of thoroughly mixing the asphalt and aggregates, uniformly dispers-
TM 5-822-14/AFJMAN 32-1019
Figure 4-44. Windrowtype pugmill travel plant.
and fig 4-47), but most have only one. Some single
shaft mixers are equipped with a system that adds
asphalt by spraying it into the mixing chamber as
the machine moves ahead, with the amount of
spray being synchronized with the travel speed (fig
4-48). Other machines, however, must be used in
conjunction with an asphalt distributor that sprays
asphalt on to aggregates immediately ahead of the
mobile mixer (fig 4-49). Both types of machine
have the common capability of effecting a smooth
bottom cut and then blending the material with
asphalt into the mixture specified. But each type
individually is marked by certain devices and
features that enable it to perform. Machines with
built-in asphalt feeding must have the capability
for accurate metering and blending of asphalt into
the in-place materials in synchronization with a
continuous forward movement. Furthermore, they
must have spray bars that will distribute the
liquid uniformly across the mixer’s width. They
must be equipped with controls for both depth of
cutting and processing and for spreading the
mixed material being laid out behind. Rotary
mixers without asphalt spraying equipment generally feature controls that permit adjustment of
cutting depth to at least a lo-inch adjustment of
tail board and adjustment of the hood itself for
aeration purposes.
Figure 4-45. Hopper-type pugmill travel plant.
ing the asphalt and adequately coating the aggregate particles, thus producing a mixture that is
uniform in color. Hopper travel plants, and in
some cases, windrow plants, require devices for
ensuring accurate controls of the flow of aggregates from the hopper to the pugmill so that
correct mix proportions are maintained. Feed of
asphalt to the pugmill similarly requires accurate
calibration. Typically, a positive displacement
pump is utilized to deliver asphalt to the mixing
chamber via a spray bar.
(b) Rotary-type mixers. Rotary or mechanical
on-site mixing is accomplished by what is essentially a mobile mixing chamber mounted on a
self-propelled machine. Within the chamber, usually about 7 feet wide and open at the bottom, are
one or several shafts transverse to the roadbed, on
which are mounted tines or cutting blades that
revolve at relatively high speed. As the machine
moves ahead, it strikes off behind it a uniform
course of asphalt-aggregate mixture. Some rotary
mixers have up to four shafts or rotors (fig 4-46
Figure 4-46. Multiple rotary mixer.
Figure 4-47. A processing chamber of a multiple rotary mixer.
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Figure 4-48. Single-shaft rotary mixer with
asphalt supply tank.
Figure 4-50. Mixing with motor grader.
Figure 4-49. Single-shaft rotary mixer without asphalt.
(c) Motor graders. Blade mixing is the onsite mixing of asphalt and in-place materials on
the roadbed by a motor grader (fig 4-50). The
asphalt is applied directly ahead of the motor
grader by an asphalt distributor. For most effective blade mixing, the motor grader should have a
blade at least 10 feet long, and should have a
wheelbase of at least 15 feet. Motor graders used
for final layout and finishing of the surface should
be equipped with smooth, rather than treaded,
pneumatic tires. Scarifier or plow attachments
may be mounted before, behind, or both before and
behind the blade.
(d) Asphalt distributor. The asphalt distributor is a key piece of equipment in cold mix
construction, particularly when rotary pulverizer
mixers without built-in asphalt feed are used, or
when blade mixing is utilized. The asphalt distributor, either truck, or trailer-mounted, consists of
an insulated tank, self-contained heating system, a
pump, and a spray bar and nozzles through which
the liquid asphalt is applied under pressure onto
the prepared aggregate materials (fig 4-51). Asphalt distributors range in performance and capability, with some capable of spreading up to 15 feet
4-22
Figure 4-51. Distributor applying asphalt.
at controlled rates to as high as 3 gallons per
square yard. It is important to keep an adequate
supply of asphalt at or near the jobsite to avoid
delays. In rural areas, it may be advisable to have
an asphalt supply truck at the project.
(2) Spreading equipment. Some cold mixes
may be spread to the required depth without
aeration. Generally, these are open-graded mixes,
placed under climatic conditions that will allow
evaporation of moisture or volatiles within a reasonable time. They may be spread by a travel
plant, from windrows by motor grader or by large
multipurpose equipment, such as a cutter-trimmerspreader. On the latter machine, guidance and
grade are electronically controlled by sensors that
take reference from wires stretched along one or
both sides of the roadway.
b. Mixed-in-Place Construction.
(1) Windrows. Several types of cold-mix construction require that the aggregates be placed in
TM
windrows prior to mixing and spreading. If windrows are to be used, the roadway must be cleared
of all vegetation to a width sufficient to accommodate both windrow and traffic while the mixture
cures. Because the thickness of the new pavement
is directly proportional to the amount of aggregate
in the windrow(s), accurate control and measurement of the volume of the windrowed material is
necessary. Usually, there is not enough loose material on the road surface to use in the road mix. In
this case, it is best to blade the loose material onto
the shoulder rather than perform the several
operations that are necessary to blend it with the
material brought in from other sources. Sometimes, however, incorporating the existing material on the roadbed into the mixture is considered
practical, if it is uniform and enough is available.
When this is done, the loose aggregate must first
be bladed into a windrow and measured. Next, it
must be made to meet grading specifications by
adding other aggregates as necessary. Finally, the
windrow is built up to the required volume with
implanted material that meets the specifications.
If two or more materials are to be combined on the
road to be surfaced, each should be placed in its
own windrow. These windrows are then mixed
together thoroughly before asphalt is added.
(2) Determining asphalt application rate. Before mixing operations begin, the correct asphalt
application rate and forward speed of the spray
bar equipped mixer or asphalt distributor must be
determined for the quantity of aggregate in the
windrow. Also, when using emulsified asphalt, it
is frequently necessary to moisten the aggregate
before applying the asphalt and the water application rate and forward speed of the water distributor must be determined.
(3) Control of asphalt. Asphalt is added to the
aggregate from an asphalt distributor or by a
travel mixer. Whichever method is used, close
control of quantity and viscosity is required to
ensure a proper mixture. Maintaining the correct
viscosity is critical because the asphaltic material
must be fluid enough to move easily through the
spray nozzles and to coat adequately the aggregate
particles: Cutback asphalts, and occasionally emulsified asphalts, even though already fluid, require
some heating in order to bring them to a viscosity
suitable for spraying. If the proper grade of asphalt has been used, and the mixing is done
correctly, the cutback or emulsified asphalt will
remain fluid until the completion of mixing. As
the actual temperature of the mixture is controlled
by that of the aggregate, care must be taken to see
that mixing is not attempted at aggregate temperatures below 50 degrees F.
5-822-14/AFJMAN
32-1019
(4) Mixing.
(a) Travel plant mixing. Travel-plant mixing
offers the advantage of closer control of the mixing
operation than is possible with blade mixing. With
the windrow-type travel plant, the machine moves
along the windrow, picking up the aggregate,
mixing it with asphalt in the pugmill, and depositing the mixture in a windrow, ready for aerating
or spreading. For this type of plant, the asphalt
application rate must be matched accurately with
the width and thickness of the course, forward
speed of the mixer, and the density of the in-place
aggregate. As the thickness is specified, the density is fixed, and the asphalt application rate is
set; the variable is the forward speed. If the
aggregate windrow is so large that all of the
asphalt cannot be incorporated in one mixing pass,
it should be split into two or more windrows and
the proper amount of asphalt added to each windrow as it is mixed. Sometimes, further mixing of
the windrowed material may be necessary after
the addition of the asphalt. Unless the travel
mixer can be used as a multiple pass mixer, this
addition mixing usually is done with a motor
grader. This ensures that all of the windrowed
material is incorporated into the mix. It also
aerates the mixture for the removal of diluents.
The number of passes with the motor grader
required for this purpose varies with different job
conditions. After the mixing and aeration procedure is completed, the windrow should be moved to
one side of the area to be surfaced in preparation
for spreading. The hopper-type travel plant operates by mixing, in its pugmill, the proper amount
of asphalt with aggregate that is deposited by haul
trucks, directly into the plant’s hopper; then it
spreads the mixture. Except when using opengraded mixtures, care must be taken to ensure
sufficient evaporation of diluents from the mix
prior to compaction.
(b) Rotary mixing. As with windrow travel
plants, rotary mixers equipped with built-in spraying systems require that the asphalt application
rates be matched accurately with the width and
thickness of the course, forward speed of the mixer, and the density of the in-place aggregate. However, when utilizing a rotary mixer not equipped
with spraybars, an asphalt distributor, operating
ahead of the mixer, applies asphalt to the aggregate. Incremental applications of asphalt and
passes of the mixer are usually necessary to
achieve the specified mixture. Most rotary mixers
are now equipped with a spray system. When
using this type of mixer the following steps are
recommended:
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Step 1. Spread the aggregate to uniform
grade and cross section with motor graders.
Step 2. Thoroughly mix the aggregate by
one or more passes of the mixer. When ready for
the asphalt the moisture content of the aggregate
should not exceed 3 percent, unless laboratory
tests indicate that a higher moisture content will
not be harmful when the asphalt is added.
Step 3. Add asphalt in increments of about
0.50 gallons per square yard until the total required amount of asphalt is applied and mixed in.
A total of 0.4 to 0.7 gallons per square yard per
inch of compacted thickness of the course is usually necessary. If the mixer is not equipped with
spraybars the asphalt usually is applied with an
asphalt distributor.
Step 4. Make one or more passes of the
mixer between applications of asphalt, as necessary to thoroughly mix it in.
Step 5. Maintain the surface true to grade
and cross-section by using a motor grader during
the mixing operations.
Step 6. Aerate the mixture by additional
manipulation, if needed.
(c) Blade mixing. With blade mixing, the
imported or in-place material is shaped into a
measured windrow, either through a spreader box
or by running through a windrow shaper. The
windrow is then flattened with the blade to about
the width of the distributor spraybar. The asphalt
is applied by successive passes of the asphalt
distributor over the flattened windrow, each application not exceeding 0.75 gallons per square yard.
After each pass of the distributor the mixture is
worked back and forth across the roadbed with the
blade, sometimes added by auxiliary mixing equipment. Prior to each succeeding application of
asphalt, the mixture is reformed into a flattened
windrow. The material in the windrow is subjected
to as many mixings, spreading, shapings, and
flattenings as are needed to disperse the asphalt
thoroughly throughout the mixture, and to coat
effectively the aggregate particles. During mixing,
the vertical angle of the mold board may require
adjustment from time to time in order to achieve a
complete rolling action of the windrow as it is
worked. As large a roll as possible should be
carried ahead of the blade, since pressure from the
weight of the aggregate facilitates mixing. Additionally, during mixing, care must be taken to see
that neither extra material be taken from the
mixing table and incorporated into the windrow
nor any of the windrow be lost over the edge of the
mixing table or left on the mixing table without
being treated. Sometimes, when cutback asphalt is
used, the formation of “oil balls,” i.e., concentrated
4-24
clusters of fine aggregate saturated and coated
with excessive amounts of asphalt can make a mix
difficult to spread and compact. This condition can
be corrected by windowing the mixture into a tight
windrow and allowing it to cure for a few days.
After mixing and aeration have been completed,
the windrow is moved to one side of the roadbed in
readiness for subsequent spreading. If it is left for
any length of time, periodic breaks in the windrow
should be cut to ensure drainage of rainwater from
the roadbed.
(5) Aeration. Before compaction, most of the
diluents that have made the asphalt cold mix
workable must be allowed to evaporate. In most
cases, this occurs during mixing and spreading
and very little additional aeration is required, but
extra manipulation on the roadbed is needed occasionally to help speed the process and dissipate the
excess diluents. Until the mix is sufficiently aerated, it usually will not support rollers without
excessive pushing under the rolls. Generally, the
mixture is sufficiently aerated when it becomes
tacky and appears to “crawl.” Many factors affect
the rate and the required amount of aeration.
Fine-g-rained and well-graded mixtures will require longer aeration than open-graded and coarsegrained mixtures, all other things being equal.
Also, if an asphalt cold-mix base course is to be
surfaced within a short length of time, aeration
before compaction should be more complete than if
the course is not to be surfaced for some time; the
surface acts as a seal, greatly retarding the removal of diluents.
(a) Emulsified asphalt mixes. Experience
has shown that break-down rolling of emulsified
asphalt mixes should begin immediately before, or
at the same time as, the emulsion starts to break
(indicated by a marked color change from brown to
black). About this time, the moisture content of
the mixture is sufficient to act as a lubricant
between the aggregate particles, but is reduced to
the point where it does not fill the void spaces,
thus allowing their reduction under compactive
forces. Also, by this time, the mixture should be
able to support the roller without undue displacement.
(b) Cutback asphalt mixes. When using cutback asphalt, correct aeration will be achieved
when volatile content is reduced to about 50
percent of that contained in the original asphaltic
material, and the moisture content does not exceed
2 percent by weight of the total mixture.
(6) Spreading and compacting. With mixing
and aeration completed, spreading and compacting
the cold mix follows. Achieving a finished section
and smooth riding surface conforming to the plans
TM
is the objective of these final two construction
steps. The mixture should always be spread to a
uniform thickness (whether in a single pass or in
several thinner layers) so that no thin spots exist
in the final mat. Mixtures that do not require
aeration may be spread to the required thickness
immediately after mixing and then compacted
with pneumatic-tired vibratory or steel-tired rollers. Mixtures that require aeration, however, are
generally deposited upon the roadbed in windrows
and then are spread from these windrows. The
windrow may be placed along the centerline of the
road, or along one side if the mixture is to be
spread by blade. Because there is a tendency to
leave a hump in the road when blade spreading
from a center-line windrow, it is considered better
practice to place the windrow to the side for
spreading. Blade spreading should be accomplished
in successive layers, with no layer thinner than
about 1.5 times the diameter of the maximum
particle size. As each layer is spread, compaction
should follow almost immediately with a pneumatic-tired roller. Because the tires of the motor
grader compact the freshly spread mix, their tracks
will appear as ridges in the finished mat unless
there is adequate rolling between the spreading of
each successive layer. The roller should follow
directly behind the motor grader in order to
eliminate these ridge marks (fig 4-52). If, at any
time during compaction, the asphalt mixture exhibits undue rutting or shoving, rolling should be
stopped. Compaction should not be attempted until
there is a reduction diluent content, occurring
either naturally or by mechanical aeration. After
one course is thoroughly compacted and cured,
other courses may be placed on it. This operation
should be repeated as many times as necessary to
bring the road to proper grade and crown. For a
smooth riding surface the motor grader should be
used to trim and level as the rollers complete
compaction of the upper layer. After the mat has
been shaped to its final required cross section, it
must then be finish rolled, preferably with a
steel-tired roller, until all roller marks are eliminated. Sometimes, a completed course may have to
be opened temporarily to traffic. In this event, to
prevent tire pickup, it may be advisable to seal the
surface by applying a dilution of slow-setting
emulsified asphalt and potable water (in equal
parts) at a rate of approximately 0.10 gallons per
square yard. This should be allowed to cure until
no pickup occurs. For immediate passage of traffic,
sanding may be desirable to avoid pickup.
c. Equipment for Plant Mixing.
(1) Mixing equipment.
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Figure 4-52. Spreading and compacting train.
(a) Stationary plants. Generally, stationary
plant mixing is accomplished at a location away
from the road site, frequently at the aggregate
source. A stationary plant consists of a mixer and
equipment for heating the asphalt (if necessary)
and for feeding the asphalt, aggregate, and additives (if needed) to the mixer. It is similar in many
respects to the hot-mix plant, except that it has no
dryer or screens other than a scalping screen. Like
the bigger hot-mix plant, a stationary cold-mix
plant may be either a batch or continuous type,
although the latter is most prevalently used for
cold-mix construction (figs 4-53 and 4-54). Any
type of plant that can produce an asphalt mixture
conforming to the specifications can be used. But,
as a minimum, it should be equipped with temperature and metering devices to control accurately
the asphalt material being applied to the aggregate and controlled feeders for proportioning aggregates and additives. Although not always a
plant component, a storage silo allows a more
continuous mixing operation, resulting in better
mix uniformity.
(b) Haul trucks. Several types of haul trucks
may be used for cold mix produced in stationary
plants; the type selected depends on the spreading
equipment. The traditional raised-bed end-dump
truck can be used with windrowers or pavers with
hoppers. Bottom dumps produce windrows and are
not used with pavers with hoppers unless a low-lift
loader is used to transfer the mix to the hopper.
Horizontal discharge trucks deposit the mix directly into the paver’s hopper without raising the
bed. These trucks may also be used with windrow
spreader boxes. A sufficient number of haul trucks
with smooth, clean beds should be available to
ensure uniform operation of the mixing plant and
paver.
(2) Spreading equipment.
(a) Paver. If climatic conditions and aggregate gradation permit evaporation of moisture or
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Figure 4-55. Spreading cold mix with conventional paver.
Figure 4-56. Spreading cold mix with full-width cutter-trimmer
modified for paving.
Figure 4-53. Stationary cold-mix plant.
Figure 4-54. Flow diagram of a typical
cold-mix continuous plant.
volatiles without aeration by manipulation, a conventional self-propelled asphalt paver may be used
to place asphalt cold mixture (fig 4-55). A fullwidth paver may be used if the plant can produce
enough mixture to keep the paver moving without
start-stop operation (fig 4-56).
(b) Spreaders. Spreading equipment such as
the Jersey Spreader and towed spreaders are
commonly used. The Jersey Spreader is a hopper,
with front wheels, that is attached to the front end
of a crawler or rubber-tired tractor, into which the
asphalt mixture is dumped. The mixture falls
directly to the road and is struck off and spread to
controlled thickness (fig 4-57). To begin spreading
the mixture at the specified depth, the tractor
should be driven onto blocks or boards of a height
equal to the depth of spread and placed so that the
tractor will ride directly onto the newly-placed
material. Once spreading has begun, a continuous
4-26
flow of mixture from the haul truck to the
spreader must be maintained. Towed-type spreaders are attached to the rear of haul trucks (fig
4-58). The asphalt cold mix is deposited into the
hopper and falls directly to the surface being
paved. As the truck moves forward, the mixture is
struck off by a cutter bar, a blade, or by the screed
and is ironed out by the screed or by rollers. Many
towed-type spreaders have floating screeds. In
order for the spreader to start out spreading to full
depth, blocking should be placed under the screen
before any mixture is dumped into the hopper. The
hopper should be kept full of material during
paving operations to ensure a full, even spread.
The spreader should be towed at a uniform speed
for any given setting of the screed or strike-off
gate. Variations in towing speed will vary spread
thickness.
d. Central Plant Mix Construction.
(1) Preparation of mixture. In batch-type
plants, mixing is usually accomplished by a twinshafted pugmill having a capacity of not less than
2,000 pounds. The correct amounts of asphalt and
aggregate, generally determined by weight, are fed
into the pug-mill. The batch is then mixed and
discharged into a haul truck before another batch
is mixed. In the continuous-mixing plant, the
devices feeding asphalt, aggregate, and water, if
needed, are interlocked to maintain automatically
the correct proportions. Typically, automatic feed-
TM
Figure 4-57. Jersey spreader.
Figure 4-58. Towed-type spreader.
ers measure and govern the flow of aggregates in
relation to the output of a positive displacement
5-822-14/AFJMAN
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asphalt metering pump. A spray nozzle arrangement at the mixer distributes the asphalt over the
aggregate. As the proportioned materials move
through the pugmill, completely mixed material,
ready for spreading, is discharged for subsequent
hauling to the road site.
(2) Aerating plant mix. Mixtures that require
aerating are generally deposited upon the roadbed
in windrows and then are spread from these
windrows. The cold mix is spread with a motor
grader and aerated by blading it back and forth, or
it is aerated by rotary tiller mixing equipment.
(3) Spreading and compacting plant mix. If
aeration is not required-as is generally the case
with plant-mixed emulsified asphalt mixes-the
mixture is most effectively spread with asphalt
pavers having automatic controls. For deep lifts,
however, other equipment such as the Jersey
Spreader type, towed spreaders, large cuttertrimmer-spreaders, or motor graders may be used.
Similar to mixed-in-place, central plant cold mixes
gain stability as the diluents (that have made the
mix workable) evaporate. It is important not to
hinder this process. Therefore, lift thicknesses are
limited by the rate that the mixture loses its
diluents. The most important factors affecting this
loss are the type of asphalt, diluent content,
gradation, and temperature of the aggregate, wind
velocity, ambient temperature, and humidity. Because of these variables, local experience is likely
to be the best guide in determining allowable
placement thicknesses. The mixture should be
spread uniformly on the roadbed, beginning at the
point farthest from the mixing plant. Hauling over
freshly placed material should not be permitted
except when required for completion of the work.
4-27
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CHAPTER 5
QUALITY CONTROL
5-1. General Purpose. Quality control is essential to ensure that the final product will be
adequate for its intended use. It must also ensure
that the contractor has performed in accordance
with the plans and specification, as this is a basis
for payment. This section identifies those control
factors which are most important in soil stabilization construction with cement, lime, lime-fly ash,
and asphalt.
5-2. Cement Stabilization. Those factors which
are most important for a quality control standpoint in cement stabilization are: pulverization,
cement content, moisture content, uniformity of
mixing, time sequence of operations, compaction,
and curing. These are described in detail below.
a. Pulverization. Pulverization is generally not a
problem in cement construction unless clayey or
silty soils are being stabilized. A sieve analysis is
performed on the soil during the pulverization
process with the No. 4 sieve used as a control. The
percent pulverization can then be determined by
calculation. Proper moisture control is also essential in achieving the required pulverization.
b. Cement content. Cement content is normally
expressed on a volume or dry weight basis. Field
personnel should be aware of quantities of cement
required per linear foot or per square yard of
pavement. Spot check can be used to assure that
the proper quantity of cement is being applied, by
using a canvas of known area or, as an overall
check, the area over which a known tonnage has
been spread.
c. Moisture content. The optimum moisture content determined in the laboratory is used as an
initial guide when construction begins. Allowance
must be made for the in situ moisture content of
the soil when construction starts. The optimum
moisture content and maximum density can then
be established for field control purposes. Mixing
water requirements can be determined on the raw
soil or on the soil-cement mix before addition of
the mixing water. Nuclear methods can be used to
determine moisture content at the time construction starts and during processing.
d. Uniformity of mixing. A visual inspection is
made to assure the uniformity of the mixture
throughout the treated depth. Uniformity must be
checked across the width of the pavement and to
the desired depth of treatment. Trenches can be
dug and then visually inspected. A satisfactory
mix will exhibit a uniform color throughout;
whereas, a streaked appearance indicates a nonuniform mix. Special attention should be given to
the edges of the pavement.
e. Compaction. Equipment used for compaction
is the same that would be used if no cement were
present in the soil, and is therefore dependent
upon soil type. Several methods can be used to
determine compacted density: sand-cone, balloon,
oil, and nuclear method. It is important to determine the depth of compaction and special attention
should be given to compaction at the edges.
f. Curing. To assure proper curing a bituminous
membrane is frequently applied over large areas.
The surface of the soil cement should be free of dry
loose material and in a moist condition. It is
important that the soil-cement mixture be kept
continuously moist until the membrane is applied.
The recommended application rate is 0.15 to 0.30
gallons per square yard.
5-3. lime Stabilization. The most important factors to control during soil-lime construction are
pulverization and scarification, lime content, uniformity of mixing, time sequence of operations,
compaction and curing.
a. Pulverization and scarification. Before application of lime, the soil is scarified and pulverized.
To assure the adequacy of this phase of construction, a sieve analysis is performed. Most specifications are based upon a designated amount of
material passing the 1 inch and No. 4 sieves. The
depth of scarification or pulverization is also of
importance as it relates to the specified depth of
lime treatment. For heavy clays, adequate pulverization can best be achieved by pretreatment with
lime, but if this method is used, agglomerated
soil-lime fractions may appear. These fractions can
be easily broken down with a simple kneading
action and are not necessarily indicative of improper pulverization.
b. Lime content. When lime is applied to the
pulverized soil, the rate at which it is being spread
can be determined by placing a canvas of known
area on the ground and, after the lime has been
spread, weighing the lime on the canvas. Charts
can be made available to field personnel to determine if this rate of application is satisfactory for
the lime content specified. To accurately determine
the quantity of lime slurry required to provide the
desired amount of lime solids, it is necessary to
5-1
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know the slurry composition. This can be done by
checking the specific gravity of the slurry, either
by a hydrometer or volumetric-weight procedure.
c. Uniformity of mixing. The major concern is to
obtain a uniform lime content throughout the
depth of treated soil. This presents one of the most
difficult factors to control in the field. It has been
reported that mixed soil and lime has more or less
the same outward appearance as mixed soil without lime. The use of phenolphthalein indicator
solution for control in the field has been recommended. This method, while not sophisticated
enough to provide an exact measure of lime content for depth of treatment, will give an indication
of the presence of the minimum lime content
required for soil treatment. The soil will turn a
reddishpink color when sprayed with the indicator
solution, indicating that free lime is available in
the soil (pH = 12.4).
d. Compaction. Primarily important is the
proper control of moisture-density. Conventional
procedures such as sand cone, rubber balloon, and
nuclear methods have been used for determining
the density of compacted soil lime mixtures. Moisture content can be determined by either oven-dry
methods or nuclear methods. The influence of time
between mixing and compacting has been demonstrated to have a pronounced effect on the properties of treated soil. Compaction should begin as
soon as possible after final mixing has been completed. The National Lime Association recommends an absolute maximum delay of one week.
The use of phenolphthalein indicator solution has
also been recommended for lime content control
testing. The solution can be used to distinguish
between areas that have been properly treated and
those that have received only a slight surface
dusting by the action of wind. This will aid in
identifying areas where density test samples
should be taken.
e. Curing. Curing is essential to assure that the
soil lime mixture will achieve the final properties
desired. Curing is accomplished by one of two
methods: moist curing, involving a light sprinkling
of water and rolling; or membrane curing, which
involves sealing the compacted layer with a bituminous seal coat. Regardless of the method used,
the entire compacted layer must be properly protected to assure that the lime will not become
nonreactive through carbonation. Inadequate
sprinkling which allows the stabilized soil surface
to dry will promote carbonation.
5-4. Lime-Fly Ash (LF) and Lime-Cement-Fly
Ash (LCF). The nature of lime-fly ash and lime-
cement-fly ash stabilization is similar to that for
5-2
lime only. Consequently, the same factors involved
for quality control are suggested.
5-5. Bituminous Stabilization. The factors that
seem most important to control during construction with bituminous stabilization are surface
moisture content, viscosity of the asphalt, asphalt
content, uniformity of mixing, aeration, compaction, and curing.
a. Surface moisture content. The surface moisture of the soil to be stabilized is of concern.
Surface moisture can be determined by conventional methods, such as oven-drying, or by nuclear
methods. The Asphalt Institute recommends a
surface moisture of up to three percent or more for
use with emulsified asphalt and a moisture content of less than three percent for cutback asphalt.
The gradation of the aggregate has proved to be of
significance as regards moisture content. With
densely graded mixes, more water is needed for
mixing than compaction. Generally, a surface
moisture content that is too high will delay compaction of the mixture. Higher plasticity index
soils require higher moisture contents.
b. Viscosity of the asphalt. The Asphalt Institute
recommends that cold-mix construction should not
be performed at temperatures below 50 degrees F.
The asphalt will rapidly reach the temperature of
the aggregate to which it is applied and at lower
temperature difficulty in mixing will be encountered. On occasion, some heating is necessary with
cutback asphalts to assure that the soil aggregate
particles are thoroughly coated.
c. Asphalt content. Information can be provided
to field personnel which will enable them to
determine a satisfactory application rate. The asphalt content should be maintained at optimum or
slightly below for the specified mix. Excessive
quantities of asphalt may cause difficulty in compaction and result in plastic deformation in service
during hot weather.
d. Uniformity of mixing. Visual inspection can
be used to determine the uniformity of the mixture. With emulsified asphalts, a color change
from brown to black indicates that the emulsion
has broken. The Asphalt Institute recommends
control of three variables to assure uniformity for
mixed-in-place construction: travel speed of application equipment; volume of aggregate being
treated; and flow rate (volume per unit time) of
emulsified asphalt being applied. In many cases,
an asphalt content above design is necessary to
assure uniform mixing.
e. Aeration. Prior to compaction, the diluents
that facilitated the cold-mix operation must be
allowed to evaporate. If the mix is not sufficient-
TM
ly aerated, it cannot be compacted to acceptable limits. The Asphalt Institute has determined that the mixture has sufficiently aerated
when it becomes tacky and appears to “crawl.”
Most aerating occurs during the mixing and
spreading stage, but occasionally additional working on the roadbed is necessary. The Asphalt
Institute has reported that overmixing in central
plant mixes can cause emulsified asphalts to break
early, resulting in a mix that is difficult to work
in the field.
f. Compaction. Compaction should begin when
the aeration of the mix is completed. The Asphalt
Institute recommends that rolling begin when an
emulsified asphalt mixture begins to break (color
change from brown to black). Early compaction
can cause undue rutting or shoving of the mixture
due to overstressing under the roller. The density
of emulsion stabilized bases has often been found
to be higher than that obtained on unstabilized
bases for the same compaction effort.
5-822-14/AFJMAN
32-1019
g. Curing. Curing presents the greatest problem
in asphalt soil stabilization. The Asphalt Institute
has determined that the rate of curing is dependent upon many variables: quantity of asphalt
applied, prevailing humidity and wind, the
amount of rain, and the ambient temperature.
Initial curing must be allowed in order to support
compaction equipment. This initial curing, the
evaporation of diluents, occurs during the aeration
stage. If compaction is started too early, the
pavement will be sealed, delaying dehydration,
which lengthens the time before design strength is
reached. The heat of the day may cause the
mixture to soften, which prohibits equipment from
placing successive lifts until the following day.
This emphasizes the need to allow sufficient curing time when lift construction is employed. The
Asphalt Institute recommends a 2- to 5-day curing period under good conditions when emulsified
bases are being constructed. Cement has been used
to accelerate curing.
5-3
TM 5-822-14/AFJMAN 32-1019
APPENDIX A
REFERENCES
Government Publications.
Department of Defense
Unified Soil Classification System for
Roads, Airfields, Embankments, and
Foundations
Test Methods for Bituminous Paving materials
Test Methods for Pavement Subgrade,
Subbase, and Base Course Materials
MIL-STD 619B
MIL-STD 620A
MIL-STD 621A
Departments of the Army and Air Force
TM 5-822-5/
AFM 88-7 Chap.
TM 5-822-8/
AFM 88-6 Chap.
TM 5-825-2/
AFM 88-6 Chap.
TM 5-825-3/
AFM 88-6 Chap.
3
9
Pavement Design for Roads, Streets,
Walks, and Open-Storage Areas
Bituminous Pavements-Standard Practice
Flexible Pavements Design for Airfields
2
Rigid Pavements for Airfields
3
Nongovernment Publications
American Society for Testing and Materials (ASTM): 1961
Race Street, Philadelphia, PA 19103
Soil Stabilization with Admixtures
Terminology Relating to Lime and LimeC 51-90
stone (as Used by the Industry)
Specification for Portland Cement
C 150-89
Fly Ash and Other Pozzolans for Use with
C 593-89
Lime
Specification for Quicklime and Hydrated
C 977-89
Lime for Soil Stabilization
Specification for Calcium Chloride
D 98-87
Particle-Size Analysis of Soils
D 422-63
Test for Liquid Limit of Soils
D 423-66
Test for Plastic Limit and Plasticity Index
D 424-59
of Soils
Test Methods for Moisture-Density RelaD 558-82
tions of Soil-Cement Mixtures
Test Methods for Wetting and Drying
D 559-89
Compacted Soil-Cement Mixtures
Test Methods for Freezing and Thawing
D 560-89
Compacted Soil-Cement Mixtures
Test methods for Moisture-Density RelaD 698-78
tions of Soils and Soil Aggregate Mixtures Using 5.5-lb (2.49-kg) Rammer and
12-in. (305-mm) Drop
Test Method for Cement Content of SoilD 806-89
Cement Mixtures
Test Methods for Water-Soluble Chlorides
D 1411-82
Present as Admixes in Graded Aggregate Road Mixes
A-1
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D 1557-78
D 1632-87
D 1633-84
D 1634-87
D 1635-87
D 1883-84
D 2487-85
D 2901-82 (1986)
D 3155-83
D 3551-83
D 3668-78 (1985)
D 3877-80 (1985)
D 4223-83
D 4318-84
D 4609-86
D 4832-88
A-2
Test Methods for Moisture-Density Relations of Soils and Soil-Aggregate Mixtures Using 10-lb (4.54-kg) Rammer and
18-in. (457-mm) Drop
Practice for Making and Curing SoilCement Compression and Flexure Test
Specimens in the Laboratory
Test Method for Compressive Strength of
Molded Soil-Cement Cylinders
Test Method for Compressive Strength of
Soil-Cement Using Portions of Beams
Broken in Flexure (Modified Cube
Method)
Test Method for Flexural Strength of SoilCement Using Simple Beam with ThirdPoint Loading
Bearing Ratio of Laboratory Compacted
Soils
Test Methods for Classification of Soils for
Engineering Purposes
Test method for Cement Content of
Freshly Mixed Soil-Cement
Test Method for Lime Content of Uncured
Soil-Lime Mixtures
Method for Laboratory Preparation of SoilLime Mixtures Using a Mechanical
Mixer
Test Method for Bearing Ratio of Laboratory Compacted Soil-Lime Mixtures
Test Methods for One-Dimensional Expansion, Shrinkage, and Uplift Pressure of
Soil-Lime Mixtures
Practice for Preparation of Test Specimens
of Asphalt-Stabilized Soils
Test Method for Liquid Limit, Plastic
Limit, and Plasticity Index of Soils
Guide for Screening Chemicals for Soil
Stabilization
Test Method for Preparation and Testing
of Soil-Cement Slurry Test Cylinders
TM
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APPENDIX B
pH TEST ON SOIL-CEMENT MIXTURES
B-1. Materials. Portland cement to be used for soil stabilization.
B-2. Apparatus. Apparatuses used are the pH meter (the pH meter must
be equipped with an electrode having a pH range of 14), 150-millilitre
plastic bottles with screw-top lids, 500-millilitre plastic beakers, distilled
water, balance, oven and moisture cans.
B-3. Procedure.
a. Standardization. Standardize the pH meter with a buffer solution
having a pH of 12.00.
b. Representative samples. Weight to the nearest 0.01 grams, representative samples of air-dried soil, passing the No. 40 sieve and equal to 25.0
grams of oven-dried soil.
c. Soil samples. Pour the soil samples into 150-millilitre plastic bottles
with screw-top lids.
d. Portland cement. Add 2.5 grams of the portland cement.
e. Mixture. Thoroughly mix soil and portland cement.
f. Distilled water. Add sufficient distilled water to make a thick paste.
(Caution: Too much water will reduce the pH and produce an incorrect
result.)
g. Blending. Stir the soil-cement and water until thorough blending is
achieved.
h. Transferal After 15 minutes, transfer part of the paste to a plastic
beaker and measure the pH.
i. Interference. If the pH is 12.1 or greater, the soil organic matter
content should not interfere with the cement stabilizing mechanism.
B-1
TM 5-822-14/AFJMAN 32-1019
APPENDIX C
DETERMINATION OF SULFATE IN SOILS
GRAVIMETRIC METHOD
C-1. Gravimetric Method.
a. Scope. Applicable to all soil types with the possible exception of soils
containing certain organic compounds. This method should permit the
detection of as little as 0.05 percent sulfate as SO,.
b. Reagents. Reagents include barium chloride, 10 percent solution of
BaCl2 l 2H2O (Add 1 milliliter 2 percent HCl to each 100 milliliter of
solution to prevent formation of carbonate.); hydrochloric acid, 2 percent
solution (0.55 N); magnesium chloride, 10 percent solution of MgCl2 l 6H2O;
demineralized water; and silver nitrate, 0.1 N solution.
c. Apparatus. Apparatus used are a beaker, 100 milliliter; burner and
ring stand; filtering flask, 500 milliliter; Buchner funnel, 90 milliliter; filter
paper, Whatman No. 40, 90 millimeter; filter paper, Whatman No. 42, 90
millimeter; Saran Wrap; crucible, ignition, or aluminum foil, heavy grade;
analytical balance; and aspirator or other vacuum source.
d. Procedure.
(1) Select a representative sample of air-dried soil weighing approximately 10 grams. Weigh to the nearest 0.01 gram. (Note: When sulfate
content is anticipated to be less than 0.1 percent, a sample weighing 20
gram or more may be used.) (The moisture content of the air-dried soil must
be known for later determination of dry weight of the soil.)
(2) Boil for 1-1/2 hours in beaker with mixture of 300-milliliter water
and 15-milliliter HCl.
(3) Filter through Whatman No. 40 paper, wash with hot water, dilute
combined filtrate and washings to 50 milliliter.
(4) Take 100 milliliter of this solution and add MgCl2 solution until no
more precipitate is formed.
(5) Filter through Whatman No. 42 paper, wash with hot water, dilute
combined filtrates and washings to 200 milliliter.
(6) Heat 100 milliliter of this solution to boiling and add BaCl2
solution very slowly until no more precipitate is formed. Continue boiling
for about 5 minutes and let stand overnight in warm place, covering beaker
with Saran Wrap.
(7) Filter through Whatman No. 42 paper. Wash with hot water until
free from chlorides (filtrate should show no precipitate when a drop of
AgNO3 solution is added).
(8) Dry filter paper in crucible or on sheet of aluminum foil. Ignite
paper. Weight residue on analytical balance as BaSO4.
e. Calculation.
Percent SO, =
Weight of residue
Oven-dry weight of initial sample
x 411.6
where
Oven-dry weight of initial sample
Note: If precipitated from cold solution, barium sulfate is so finely dispersed that it cannot be
retained when filtering by the above method. Precipitation from a warm, dilute solution will
increase crystal size. Due to the absorption (occlusion) of soluble salts during the precipitation
by BaSO4, a small error is introduced. This error can be minimized by permitting the
precipitate to digest in a warm, dilute solution for a number of hours. This allows the more
soluble small crystals of BaSO4 to dissolve and recrystallize on the larger crystals.
C-1
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5-822-14/AFJMAN
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C-2. Turbidimetric Method
a. Reagents. Reagents include barium chloride crystals (Grind analytical
reagent grade barium chloride to pass a 1-millimeter sieve.); ammonium
acetate solution (0.5 N) (Add dilute hydrochloric acid until the solution has
a pH of 4.2); and distilled water.
b. Apparatus. Apparatus used are a moisture can; oven, 200-milliliter
beaker; burner and ring stand; filtering flask; Buchner funnel, 90 millimeter; filter paper, Whatman No. 40, 90 millimeter; vacuum source; spectrophotometer and standard tubes (Bausch and Lombe Spectronic 20 or
equivalent) and pH meter.
c. Procedure.
(1) Take a representative sample of air-dried soil weighing approximately 10 grams, and weight to the nearest 0.01 grams. (The moisture
content of the air-dried soil must be known for later determination of dry
weight of the soil.)
(2) Add the ammonium acetate solution to the soil. (The ratio of soil to
solution should be approximately 1:5 by weight.)
(3) Boil for about 5 minutes.
(4) Filter through Whatman No. 40 filter paper. If the extracting
solution is not clear, filter again.
(5) Take 10 milliliter of extracting solution (this may vary, depending
on the concentration of sulfate in the solution) and dilute with distilled
water to about 40 milliliter. Add about 0.2 gram of barium chloride crystals
and dilute to make the volume exactly equal to 50 milliliter. Stir for 1
minute.
(6) Immediately after the stirring period has ended, pour a portion of
the solution into the standard tube and insert the tube into the cell of the
spectrophotometer. Measure the turbidity at 30-second intervals for 4
minutes. Maximum turbidity is usually obtained within 2 minutes and the
readings remain constant thereafter for 3-10 minutes. Consider the turbidity
to be the maximum reading obtained in the 4-minute interval.
(7) Compare the turbidity reading with a standard curve and compute
the sulfate concentration (as SO4) in the original extracting solution. (The
standard curve is secured by carrying out the procedure with standard
potassium sulfate solutions.)
(8) Correction should be made for the apparent turbidity of the
samples by running blanks in which no barium chloride is added.
d. Sample calculation.
Weight of air-dried sample = 10.12 grams
Given:
Water content = 9.36 percent
Weight of dry soil = 9.27 grams
Total volume of extracting solution = 39.1 milliliters
10 milliliters of extracting solution was diluted to 50 milliliters after
addition of barium chloride (see step 5). The solution gave a transmission
reading of 81. From the standard curve, a transmission reading of 81
corresponds to 16.0 parts per million. (See fig C-l)
Concentration of original extracting solution = 16.0 x 5 = 80.0 parts per
million.
Percent SO 4 =
80.0 x 39.1 x 100
1,000 x 1,000 x 9.27
= 0.0338 percent
e. Determination of standard curve.
( 1 ) Prepare sulfate solutions of 0, 4, 8, 12, 16, 20, 25, 30, 35, 40, 45,
and 50 parts per million in separate test tubes. The sulfate solution is made
from potassium sulfate salt dissolved in 0.5 N ammonium acetate (with pH
adjusted to 4.2).
C-2
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5-822-14/AFJMAN
32-1019
(2) Continue steps 5 and 6 in the procedure as described in Determination of Sulfate in Soil by Turbidimetric Method.
(3) Draw standard curve as shown in figure C-l by plotting transmission readings for known concentrations of sulfate solutions.
Figure C-1. Example standard curve for spectrophotometer.
C-3
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APPENDIX D
pH TEST TO DETERMINE LIME REQUIREMENTS FOR
LIME STABILIZATION
D-1. Materials. Lime to be used for soil stabilization.
D-2. Apparatus. Apparatus include pH meter (the pH meter must be
equipped with an electrode having a pH range of 14), 150-milliliter (or
larger) plastic bottles with screw-top lids, 50-milliliter plastic beakers,
distilled water that is free of CO,, balance, oven, and moisture cans.
D-3. Procedure.
a. Standardize pH meter. Standardize the pH meter with a buffer
solution having a pH of 12.45.
b. Weight samples. Weigh to the nearest 0.01 gram representative
samples of air-dried soil, passing the No. 40 sieve and equal to 20.0 grams of
oven-dried soil.
c. Pour samples. Pour the soil samples into 150-milliliter plastic bottles
with screw-top lids.
d. Add lime. Add varying percentages of lime, weighed to the nearest
0.01 gram, to the soils. (Lime percentages of 0, 2, 3, 4, 5, 6, 8, and 10, based
on the dry soil weight, may be used.)
e. Mix. Thoroughly mix soil and dry lime.
f. Add distilled water. Add 100 milliliters of distilled water that is
CO,-free to the soil-lime mixtures.
g. Snake soil-lime and water. Shake the soil-lime and water for a
minimum of 30 seconds or until there is no evidence of dry material on the
bottom of the bottle.
h. Shake bottles. Shake the bottles for 30 seconds every 10 minutes.
i. Transfer slurry. After 1 hour transfer part of the slurry to a plastic
beaker and measure the pH.
j. Record pH. Record the pH for each of the soil-lime mixtures. The
lowest percent of lime giving a pH of 12.40 is the percent required to
stabilize the soil. If the pH does not reach 123.40, the minimum lime
content giving the highest pH is required to stabilize the soil.
D-1
TM 5-822-14/AFJMAN 32-1019
The proponent agency of this publication is the office of the
Chief of Engineers, United States Army. Users are invited to
send comments and suggested improvements on DA Form 2028
(Recommended Changes to Publications and Blank Forms) to
HQUSACE (CEMP-ET), WASH DC 20314-1000.
By Order of the Secretaries of the Army and Air Force:
Official:
GORDON R. SULLIVAN
General, United States Army
Chief of Staff
MILTON H. HAMILTON
Administrative Assistant to the
Secretary of the Army
OFFICIAL
JAMES E. MCCARTHY, Maj General, USAF
The Civil Engineer
DISTRIBUTION:
Army: To be distributed in accordance with DA Form 12-34-E, block
0773, requirements for TM 5-822-14.
Air Force: F
*
U.S.
G.P.O.:1994-300-723:58
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