Chapter 13

Soil Stabilization
Topics
1.0.0 Methods of Stabilization
2.0.0 General Requirements for Use of
Stabilizers
3.0.0 Soil-Cement Stabilization
4.0.0 Bituminous Stabilization

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Overview
Broadly defined, soil stabilization is the process of altering or preserving one or more
properties of a soil to improve its engineering characteristics and performance. This
chapter provides a brief overview of soil stabilization in terms of (1) stabilization
methods, (2) the type and selection of various chemical stabilizers used in soil
stabilization, and (3) general guidance and information relative to the designs and tests
of soil-cement and soil-bituminous mixtures.
For a more thorough understanding of soil stabilization, combine the study of this
chapter with the study of the various references cited within the chapter.

Objectives
When you have completed this chapter, you will be able to do the following:
1. Describe the different methods of soil stabilization.
2. Identify the general requirements for use of stabilizers.
3. Describe the materials and testing methods associated with soil to cement
stabilization.
4. Describe types of bitumen utilized in bituminous stabilization.

Prerequisites
None
This course map shows all of the chapters in Engineering Aid Advanced. The suggested
training order begins at the bottom and proceeds up. Skill levels increase as you
advance on the course map.

NAVEDTRA 14336A 13-1

Time Designation and Triangulation E
N
Soil Stabilization G
I
Mix Design: Concrete and Asphalt
N
Soils: Surveying and Exploration/Classification/Field Identification E
E
Materials Testing
R
Specifications/Material Estimating/Advance Base Planning I
N
Project Drawings
G

Horizontal Construction
AID
Construction Methods and Materials: Electrical and Mechanical
Systems
A
Construction Methods and Materials: Heavy Construction D

Electronic Surveying Equipment V

A
Horizontal and Vertical Curves N
C
Engineering and Land Surveys
E
Engineering Division Management D

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NAVEDTRA 14336A 13-2

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NAVEDTRA 14336A 13-3

1.0.0 METHODS OF STABILIZATION
There are two general methods of soil stabilization, mechanical and additive, and the
effectiveness of either method is dependent upon uniformity in blending the various
materials. Mixing materials in a plant (stationary or traveling) is preferable, but other
means of mixing, such as scarifies, plows, disks, graders, and rotary mixers, have also
been satisfactory.
Table 13-1 — Stabilization Methods Most Suitable for Specific Applications
Purpose Soil Type Method

1. Subgrade Stabilization

a. Improved load carrying and stress distribution characteristics Fine granular SA, SC, MB, C

Coarse granular SA, SC, MB, C

Clays of Low PI C, SC, CMS, LMS, SL

Clays of High PI SL, LMS

b. Reduce frost susceptibility Fine granular CMS, SA, SC, LF

Clays of Low PI CMS, SC, SL, LMS

c. Waterproofing and improved runoff Clays of Low PI CMS, SA, LMS, SL

d. Control of shrinkage and swell Clays of Low PI CMS, SC, C, LMS, SL

Clays of High PI SL

e. Reduce resiliency Clays of High PI SL, LMS

Plastic silts or clays SC, CMS

2. Base coarse stabilization

a. Improvements of substandard materials Fine granular SC, SA, LF, MB

Clays of Low PI SC, SL

b. Improved load carrying and stress distribution characteristics Coarse granular SA, SC, MB, LF

Fine granular SC, SA, LF, MB

c. Reduction in pumping Fine granular SC, SA, LF, MB,

membranes

3. Dust palliative (pāl'ē-ā'tĭv) Fine granular CMS, SA, Oil or

bituminous surface
spray, APSB

Plastic soils CMS, SL, LMS, APSB,

DCA 70

KEY: Method of treatments are:

APSB — Asphalt Penetration Soil Binder LF — Lime Fly ash SA — Soil-Asphalt
C — Compaction LMS — Lime Modified Soil SC — Soil-Cement
CMS — Cement Modified Soil MB — Mechanical Blending SL — Soil-Lime
DCA 70 — Polyvinyl acetate emulsion

The amount of stabilization required and a project’s on-site conditions will dictate the
method chosen. Table 13-1 lists the most suitable treatments by objective for various
NAVEDTRA 14336A 13-4
soil types, which will be based on the soil’s soil description and classification. This is
where the skill and ability of a competent EA team is essential to the selection of the
correct materials and procedures.

1.1.0 Mechanical Method

Mechanical stabilization is
accomplished by mixing/
blending soils of two or more
classifications or gradations to
obtain a material meeting
required specifications.
The blending may occur at the
construction site, a central plant,
or a borrow area.
The blended material is then
spread and compacted by
conventional means to meet
requirements. (Figure 13-1)

Figure 13-1 — Typical compaction of mixed

material by conventional method.

1.2.0 Additive Method

The additive method refers to adding a manufactured product to the existing soil that will
improve the properties of the layer.
This chapter will present the use of Portland cement, lime, lime-cement-fly ash, and
bitumen (alone or in combination) as additives to stabilize soils.
Soil classification and the required degree of improvement will determine the method of
improvement and the percentage of additives needed. Typically, it takes a smaller
percentage of additives to alter soil properties, such as gradation, workability, and
plasticity, than it does to improve the strength and durability sufficiently to permit a
reduction in design thickness.
After the additive has been mixed with the soil, spreading and compacting are
accomplished by conventional means

NAVEDTRA 14336A 13-5

1.2.1 Stabilization by Cementing Action

This method involves the

addition of chemical agents to
the soil to produce a hardened
product.
There are three main stabilizing
agents, and the method of each
treatment bears the name of the
agents:
• soil-cement
• soil-lime
• lime-fly ash.

Figure 13-2 — Typical soil-cement additive mix

equipment.
The three methods have much in common and involve somewhat similar construction
practices; they depend upon hydration, pozzolanic (pot-suh-lan-ik) action of lime with
silica and alumina, alteration of the clay material, or a combination of these actions.
The ultimate strength will depend to a great degree on the density achieved during
compaction before the mix cures, but the result when either tested statically or
dynamically is a semi-rigid, fairly brittle material with considerable compressive strength
and moderate flexural strength.

1.2.2 Bituminous Stabilization

In bituminous treatment, the stabilized soil initially behaves differently and is much more
flexible. In addition, its behavior will depend on the nature of the loading (static or
dynamic) and the temperature at the time the load is applied.

1.3.0 Modification Method

This type of modification may use compacting, mechanical blending, the addition of
cementing materials in small amounts, or the addition of chemical modifiers.
Soil stabilization by modification does not usually result in a thoroughly cemented,
hardened, or semi-hardened material. Cement and lime modifiers (cement-modified soil
and lime-modified soil) are used in quantities too small to provide high-strength
cementing action, they reduce the plasticity of clay soils.
Calcium chloride or sodium chloride can be added to the soil to retain moisture and
control dust, to hold fine material for better compaction, and to reduce frost heave by
lowering the freezing point of water in the soil.

NAVEDTRA 14336A 13-6

 Bituminous materials, such as
cutback asphalts or asphaltic
penetrative soil binder (APSB),
and certain chemicals, such as
polyvinyl acetate emulsion
(DCA-70), may be used to
waterproof the soil surface and
to control dust.

Figure 13-3 — Typical bituminous modification.

2.0.0 GENERAL REQUIREMENTS FOR USE OF STABILIZERS

Before addressing the need for, or selecting an appropriate stabilizer, a soil analysis
must be done with corresponding sieve analysis and Atterberg limits test results. Both
are discussed in the EA Basic NRTC and in Materials Testing, NAVFAC MO-330.

2.1.0 Lime
Lime reacts with many medium, moderately fine, and fine-grained soils. The resultant
soil exhibits decreased plasticity, increased workability, reduced swell, and increased
strength.
Using the Unified Soil Classification System (USCS), consider the following soils as
potentially capable of being stabilized with lime:
CH, CL, GC, GM, MH, ML, OH, OL, SC, SM
GM-GC, GP-GC, GW-GC, ML-CL, SM-SC, SP-SC, SW-SC

2.2.0 Cement
Cement is an effective stabilizer for a wide range of materials. However, the soil should
have a PI less than 30, and for coarse-grained soils, the amount passing the No. 4
sieve should be greater than 45 percent.
You can use fly ash, mixed with lime, to stabilize most coarse- and medium-grained
soils. However, the PI should not be greater than 25.
Using the Unified Soil Classification System (USCS), consider the following soils as
potentially capable of being stabilized with fly-ash:
NAVEDTRA 14336A 13-7
 GP, GW, SP, SW
GC-GM, GP-GC, GP-GM, GW-GC, GW-GM, SC-SM, SP-SC, SW-SC, SW-SM

2.3.0 Bituminous
Most bituminous soil stabilization is performed with asphalt cement, cutback asphalt,
and asphalt emulsions. Soils for this method of stabilization need to contain less than 30
percent passing the No. 200 sieve and have a PI less than 10.
Using the Unified Soil Classification System (USCS), consider the following soils as
potentially capable of being stabilized with bituminous materials:
GC, GM, GP, GW, SC, SM, SP, SW
GM-GC, GP-GC, SM-SC, SP-GM, SP-SC, SP-SM, SW-GC, SW-GM, SW-SC, SW-SM
Combination stabilization is specifically defined as:
• lime-cement
• lime-asphalt
• lime-cement-fly ash (LCF)
Combinations of lime and cement often are acceptable expedient stabilizers. Lime can
be added to increase workability and mixing characteristics as well as reduce plasticity
then cement can be mixed into the soil to provide rapid strength gain.
Combinations of lime and asphalt are acceptable stabilizers as well. The lime addition
may prevent stripping at the asphalt-aggregate interface and increase the stability of the
mixture.

2.4.0 Selection of a Stabilizer

Selecting a stabilizer additive involves a number of factors for consideration:
• type of soil to be stabilized
• purpose for which the stabilized layer will be used
• type of soil quality improvement desired
• required strength and durability of the stabilized layer
• environmental conditions
• cost
The selection of candidate/stabilizers is made using Figure 13-4 and Table 13-2. The
soil gradation triangle in Figure 13-4 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 13-2, which indicates for each area
shown in Figure 13-4, candidate stabilizers and restrictions based on grain size and/or
plasticity index (PI). Also provided in the second column of Table 13-2 is a listing of soil
classification symbols applicable to the area determined from Figure 13-4. 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.

NAVEDTRA 14336A 13-8

 Figure 13-4 — Gradation triangle for aid in selecting a commercial stabilizing
agent.
Data required to enter Figure 13-4 are:
• percent material passing the No. 200 sieve
• 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 13-4 is then found in the first column of Table 13-2
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.

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 Table 13-2 — Guide for Selecting a Stabilizing Additive
Restriction
Type of stabilizing
Soils Restriction on LL on Percent
Area additive Remarks
Class¹ and PI of soil passing No.
recommended
200 sieve¹
1A SW or SP (1) Bituminous
(2) Portland Cement
(3) Lime-cement-fly ash PI not to exceed 25
1B SW-SH or (1) Bituminous PI not to exceed 10
SP-SH or (2) Portland Cement PI not to exceed 30
SW-SC or (3) Lime PI not to exceed 12
SP-SC (4) Lime-cement-fly ash PI not to exceed 25
1C SM or (1) Bituminous PI not to exceed 10 Not to exceed
SC or 30% by weight
SM-SC (2) Portland Cement See footnote 2
(3) Lime PI not to exceed 12
(4) Lime-cement-fly ash PI not to exceed 25
2A GW or GP (1) Bituminous Well-graded material
(2) Portland Cement only.
(3) Lime-cement-fly ash PI not to exceed 25 Material should contain
at least 45% by weight
of material passing No.
4 sieve.
2B GW-GH or (1) Bituminous PI not to exceed 10 Well-graded material
GP-GH or (2) Portland Cement PI not to exceed 30 only.
GW-GC or (3) Lime PI not to exceed 12 Material should contain
at least 45% by weight
GP-GC (4) Lime-cement-fly ash PI not to exceed 25
of material passing No.
4 sieve.
2C GM or (1) Bituminous PI not to exceed 10 Not to exceed Well-graded material
GC or 30% by weight only.
GM-GC (2) Portland Cement See footnote 2 Material should contain
at least 45% by weight
(3) Lime PI not to exceed 12
of material passing No.
(4) Lime-cement-fly ash PI not to exceed 25 4 sieve.
3 CH or CL or (1) Portland Cement LL less than 40 and Organic and strongly
MH, or ML PI less than 20 acid soils falling within
or OH or OL this area are not
susceptible to
or ML-CL (2) Lime PI not less than 12
stabilization means.
¹ Soil classification corresponds to MIL-STD-619B. Restriction on liquid limit (LL) and plasticity index (PI) is in accordance with
Method 103 in MIL-STD-621A
50 − passing No. 200 sieve
² PI ≤ 20 +
4
For example, assume a soil is classified as an SC with:
• 93 percent passing the No. 4
• 25 percent passing the No. 200
• a liquid limit of 20
• a 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 13-4 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 13-2, 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.
NAVEDTRA 14336A 13-10
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 than the
equation indicated in footnote 2. 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 stabilization 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

3.0.0 SOIL-CEMENT STABILIZATION

In general, there are three types of soil-and-cement mixtures as follows:
• Plastic soil-cement — a hardened mixture of soil and cement that contains, at the
time of placing, enough water to produce a consistency similar to plastering
mortar. Used to line or pave ditches, slopes, and other areas subject to erosion, it
may also be used for emergency road repair by mixing high-early-strength
cement into the natural material in mud holes.
• Cement-modified soil — an unhardened or semi-hardened mixture of soil and
cement. When relatively small quantities of Portland cement are added to
granular soil or silt-clay soil, it changes the chemical and physical properties of
that soil. Cement reduces the plasticity and water-holding capacity of the soil and
increases its bearing value.
The degree of improvement depends upon the quantity of the cement used and
the type of soil. In cement-modified soil, only enough cement is used to change
the physical properties of the soil to the degree desired. Cement-modified soils
may be used for base courses, subbases, treated subgrades, highway fills, and
as trench backfill material.
• Compacted soil-cement — often referred to as simply soil-cement, this is a
mixture of pulverized soil and calculated amounts of Portland cement and water,
compacted to a high density. The result is a rigid slab having moderate
compressive strength and resistance to the disintegrating effects of
wetting/drying and freezing/thawing.
The remainder of this discussion of soil-cement mixture is directed towards this type,
compacted soil-cement. (Figure 13-5)

NAVEDTRA 14336A 13-11

 Figure 13-5 — Seabees operating typical soil-cement stabilization equipment.

3.1.0 Materials for Soil-Cement

The three basic materials needed to produce soil-cement are soil, Portland cement, and
water. Users usually achieve low cost by using inexpensive local materials, soil (the
bulk of material) is either in place or nearby, and water is usually hauled only short
distances.
Soil used in the context of soil-cement, means almost any combination of gravel, sand,
silt, and clay, and includes such materials as cinder, caliche (kuh-lee-chee), shale,
laterite (lat-uh-rahyt), and many waste materials including dirty and poorly-graded
sands from gravel pits.
Tests need to be performed to determine 1) the quantities of Portland cement and water
to be added, and 2) the density to which the mixture must be compacted. The water
serves two purposes: it helps to obtain maximum compaction (density) by lubricating the
soil grains and it is necessary for hydration of the cement that hardens and binds the
soil into a solid mass. Properly produced soil-cement contains enough water for both
purposes.
Types I (normal) and IA (air entrained) Portland cements are the most commonly used
cements, but almost any type of Portland cement can be used that complies with the
requirements of the latest ASTM (American Safety for testing and Materials), AASHTO
(American Association of State Highway and Transportation Officials), or federal
specifications.

NAVEDTRA 14336A 13-12

The water should be relatively clean and free from harmful amounts of alkalis, acid, or
organic matter. Potable water is satisfactory and sometimes seawater has been used
satisfactorily when fresh water was unobtainable.
Portland cement can harden practically all soils and soil combinations. The soils do not
need to be well-graded aggregates since hydration of the cement, not cohesion and
internal friction of the materials, provides the stability.
Before testing, gradation and a soil’s position in the soil profile can determine the
general suitability of a soil for soil-cement mixture. Based on gradation, soils for soil-
cement construction can be divided into three broad groups as follows:
1. Sandy and gravelly soils with about 10- to 35-percent silt and clay combined
have the most favorable characteristics and generally require the least amount of
cement for adequate hardening.
o Glacial-and water-deposited sands and gravels, crusher-run limestone,
caliche, lime rock and almost all granular materials work well if they
contain 55 percent or more material passing the No. 4 sieve and 37
percent passing the No. 10 sieve.
o Stones over an inch or two in diameter are undesirable.
o Exceptionally well-graded materials may contain up to 65-percent gravel
retained on the No. 4 sieve and have sufficient fine material for adequate
binding. These soils are readily pulverized, easily mixed and can be used
under a wide range of weather conditions.
2. Sandy soils deficient in fines, such as some beach sands, glacial sands, and
windblown sands, make good soil-cement although the amount of cement
needed for adequate hardening is usually slightly greater than with the soil in
Group 1.
o Because of poor gradation and absence of fines in these sands,
construction equipment may have difficulty in obtaining traction. Traction
can be vastly improved by keeping the sand wet and by using track-type
equipment. These soils are likely to be “tender” and require care during
final packing and finishing to obtain a smooth, dense surface.
3. Silty and clayey soils make satisfactory soil-cement but soils containing high clay
contents are harder to pulverize.
o Generally the more clayey the soil, the greater the cement required to
harden it adequately. Construction with silty and clayey soils is more
dependent on weather conditions, but if the soil can be pulverized, it is not
too heavy textured for use in soil-cement.

3.2.0 Soil-Cement Tests

Laboratory tests determine three fundamental control factors for soil-cement as follows:
1. Proper cement content
2. Proper moisture content
3. Proper density
The first requirement for a quality soil-cement mixture is sufficient cement content.
Before construction, a soil survey of the construction area should be made. The soils
should be identified, with the limits of each soil defined, and a representative sample of
NAVEDTRA 14336A 13-13
each type forwarded to the laboratory to determine the quantity of cement required to
harden it.
Proper soil surveying, identification, and sampling are very important. For instance, if
one soil type was sampled and tested while actual construction involved a different soil
type, the tests would be worthless and, in fact, detrimental since they would mislead the
engineers. This can significantly increase project delays and costs, so obviously, it is
important to sample and test the soils that will actually be used in the soil-cement
construction. A 75-pound sample of each type of soil is adequate for laboratory testing.
EA Basic NRTC and Materials Testing, NAVFAC MO-330, provide instructions on
sampling methods and procedures. Take soil samples from a graded roadway by
digging a trench from the centerline to the edge of the proposed pavement and to the
depth of processing. For proposed roadways not yet graded, take soil samples with an
auger from the various soil horizons of each soil type from the “dressed-down” face of
exposed cuts or from the surface.
Take samples so that only one horizon of each soil type is represented by each sample.
It is not good practice to take a composite sample from various locations. Data obtained
from a composite sample does not apply to soil in any single location and may be
misleading.
There are exceptions, however, but be sure you provide a complete identification with
each sample.
• If you are sampling pit material that will be loaded by a shovel operating over the
vertical face of the pit, take the sample from the bottom to the top of the vertical
face after the overburden is removed.
• If you are on a small project, it is practical to sample only the poorest soil on the
job, and determine the cement content for this sample for use throughout the job.
Laboratory testing has a twofold purpose:
1. Determine the optimum moisture content (OMC) and density values to be used
for construction — identified by a moisture-density test.
2. Determine the minimum cement content needed to harden the material
adequately — identified by a wet-dry test for pavements located in nonfrost
areas, or a freeze-thaw test for pavements located in frost areas.
The following provides a brief description of each test:
• Moisture-Density Test — This test determines the OMC and the maximum
density for molding laboratory specimens, which translates in the field to
determine the quantity of water to be added and the density to which the soil-
cement mixture should be compacted.

NAVEDTRA 14336A 13-14

Before you start this test, select the Table 13-3 — Basic Range of Cement
cement contents that will be used in the Requirements
wet-dry or freeze-thaw test. The cement Cement Required
Soil Classification
(% by weight)
contents are usually selected in 2-percent
increments to encompass values given in GW, GP, SW, SP, GM, or SM 3-5

Table 13-3. SP, GM, SM, or GP 5-8

Since maximum density varies only slightly SM, SC, some GM, or GC 5-9
with variations in the cement content, only SP 7-11
the median value is used in preparing
specimens for the test. CL or ML 7-12

ML, MH, or OH 8-13

You can find additional information on
selecting the cement content in Chapter 5 CL or CH 9-15
of Materials Testing, NAVFAC MO-330. OH, MH, or some CH 10-16

Procedures for determining the OMC are similar to those described in Chapter 16 of EA
Basic, with the following exceptions:
o Perform compaction on five layers of approximately equal thickness to
result in a total compacted depth of 5 inches.
o Compact each layer by 25 uniformly spaced blows using a 10-pound
tamper dropped from a height of 18 inches.

• Wet-Dry Test (ASTM D 559) — This test determines the cement content for soil-
cement mixtures used in nonfrost areas. The objective is to determine the
minimum amount of cement that will enable the soil-cement mixture to pass the
test.
For the test, mold specimens using the OMC and the cement contents described
in Table 13-3 for the different soil classifications. Use the appropriate procedure
for OMC determination to mold the specimens, and take a 750-gram sample from
the second layer for a moisture determination.
Cure the specimens for 7 days in high humidity. After curing, weigh the
specimens, submerge them in tap water at room temperature for 5 hours, then
oven-dry them for 42 hours at 160°F.
Using two firm strokes of a wire brush, remove material loosened by wetting and
drying, then reweigh the specimens and subtract the new weight from the old
weight to determine the amount of disintegration (soil-cement loss) occurring
during the cycle.
Repeat the process for 12 cycles; a passing grade ranges from 14-percent loss
for sandy or gravelly soils, down to 7-percent loss for clayey soil.
Materials Testing, NAVFAC MO-330 provides additional information about the wet-dry
test and an example of determining soil-cement loss.

NAVEDTRA 14336A 13-15

 • Freeze-Thaw Test (ASTM D 560) — This test determines the cement content for
soil-cement mixtures used in areas subject to frost action due to repeated
freezing and thawing. As in the wet-dry test, the objective of the freeze-thaw test
is to determine the minimum amount of cement that enables the mixture to pass
the test.
For the test, mold and cure specimens in the same manner as the wet-dry test.
Following the 7 days of curing in high humidity, weigh the specimens, place them
on moist blotters to refrigerate for 24 hours at -10°F, then thaw them in a moist
atmosphere at 70°F for 23 hours.
Brush the specimens as described in the wet-dry test, and, if necessary, remove
any half-loose scales using a sharp-pointed instrument.
After 12 cycles, oven-dry and reweigh the specimens to determine the soil-
cement loss in the same manner as in the wet-dry test. Again, passing grades
range from 14-percent loss for sandy or gravelly soils, down to 7-percent loss for
clayey soil.
Materials Testing, NAVFAC MO-330 also provides additional information regarding the
freeze-thaw test.
A hardened soil-cement mixture’s principal requirement is to withstand exposure to the
elements. Strength is also a requirement, but most soil-cement mixtures with adequate
resistance to the elements have adequate strength as well.
Consistent with the characteristics of cement itself, soil-cement specimens tested in
compression at various ages should increase in strength with age and with increases in
cement. For example, you can consider a sample as adequately stabilized, which
attains an unconfined compressive strength of approximately 300 pounds per square
inch (psi) after curing 7 days, and shows increasing strength with age.
Materials Testing, NAVFAC MO-330 provides the procedures you should follow when
performing unconfined compression tests. In addition, ASTM D 2166 provides guidance
for the Standard Test Method for Unconfined Compressive Strength of Cohesive Soil.
For a discussion of modified mix design for sandy soils and for approximate and rapid
test procedures you can use when complete testing is impracticable, refer again to
Materials Testing, NAVFAC MO-330
For additional guidance, you can find information on construction methods using soil-
cement in Military Soils Engineering, FM 5-410, in commercial publications, such as
Moving the Earth, by Herbert L. Nichols, Jr., and in various publications from the
Portland Cement Association.

4.0.0 BITUMINOUS STABILIZATION

Bituminous soil stabilization is a process that mixes a controlled amount of bituminous
material with an existing soil or aggregate material to form a stable base or wearing
surface. Bitumen increases the soil’s cohesion and load-bearing capacity and makes it
resistant to water action.

NAVEDTRA 14336A 13-16

4.1.0 Soil Gradation
Table 13-4 — Recommended
The recommended soil gradations for subgrade and Gradations for Bituminous-
base or subbase course materials are shown in Stabilized Subgrade Materials
Tables 13-4 and 13-5, respectively. Mechanical
Sieve Size % passing
stabilization may be required to bring the soil to
3 inch 100
proper gradation. No. 4 50-100
No. 30 38-100
No. 200 2-30

Table 13-5 — Recommended Gradations for Bituminous-Stabilized Subbase

Materials
Sieve Size 1 ½-in. Maximum 1-in. Maximum ¾-in. Maximum ½-in. Maximum

1 ½ in. 100 ------ ------ ------

1 in. 84 + 9 100 ------ ------
¾ in. 76 + 9 83 + 9 100 ------
½ in. 66 + 9 73 + 9 82 + 9 100
3/8 in. 59 + 9 64 + 9 72 + 9 83 + 9
No. 4 45 + 9 48 + 9 54 + 9 62 + 9
No. 8 35 + 9 37 + 9 41 + 9 47 + 9
No. 16 27 + 9 28 + 9 32 + 9 36 + 9
No. 30 20 + 9 21+ 9 24 + 9 28 + 9
No.50 14 + 7 16 + 7 17 + 7 20 + 7
No.100 9+5 11 + 5 12 + 5 14 + 5
No.200 5+2 5+2 5+2 5+2

4.2.0 Types of Bitumen

Bituminous stabilization typically uses asphalt cement, cutback asphalt, or asphalt
emulsion, but the type of bitumen used will depend on the type of soil to be stabilized,
the method of construction, and weather conditions. In frost areas, avoid using tar as a
binder because of its high-temperature susceptibility.
Asphalts are affected less by temperature changes, but the prevailing climate should
dictate the suitable grade of asphalt. Generally, using the most viscous liquid asphalt
that can be readily mixed into the soil will obtain the most satisfactory results.
If a central plant is used for higher quality mixes, it should use viscosity-grade asphalt
cements. However, most bituminous stabilization is performed in place.
The bitumen is applied directly on the soil or soil-aggregate system, and the mixing and
compaction operations are conducted immediately thereafter. For this type of
construction, liquid asphalts, such as cutbacks and emulsions, are used. Emulsions are
preferred over cutbacks because of energy constraints and pollution control efforts.
(Figure 13-6)

NAVEDTRA 14336A 13-17

Figure 13-6 — Seabees preparing crushed rock road for typical asphalt emulsion
application.

The specific type and grade of bitumen will depend on the aggregate’s characteristics,
the type of construction equipment, and climate conditions. Table 13-6 indicates the
types of bituminous materials that will typically be used for soil gradation.
Table 13-6 — Bituminous Requirements
Open-graded aggregate
• Rapid- and medium-curing liquid asphalts RC-250, RC-800, and MC-3000
• Medium-setting asphalt emulsion MS-2 and CMS-2
Well-graded aggregate with little or no material passing No. 200 sieve
• Rapid- and medium-curing liquid asphalts RC-250, RC-800, MC-250, and MC-800
• Slow-curing liquid asphalts SC-250 and SC-800
• Medium-setting and slow-setting asphalt emulsions MS-2, CMS-2, SS-1, and CSS-1
Aggregate with a considerable percentage of fine aggregate and material passing No. 200 sieve
• Medium-curing liquid asphalts MC-250 and MC-800
• Slow-curing liquid asphalts SC-250 and SC-800
• Slow-setting asphalt emulsions SS-1, SS-1h, CSS-1, and CSS-1h
• Medium-setting asphalt emulsions MS-2 and CMS-2
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.
NAVEDTRA 14336A 13-18
4.3.0 Mix Design and Methods of Testing Mixtures
For guidance on the design of bituminous-stabilized base and subbase courses, refer to
Standard Practice Manual for Flexible Pavements, UFC 3-250-03, and to Materials
Testing NAVFAC MO-330.

For more information on soil stabilization, refer to Soil Stabilization for Pavements, UFC
3-250-11.

To find information on recycling pavement, refer to Standard Practice for Pavement

Recycling, UFC 3-250-07.

In addition, the American Society for Testing and Materials (ASTM) provides the
following guidance:
• ASTM D5 - 06e1 Standard Test Method for Penetration of Bituminous Materials
• ASTM D95 - 05e1 Standard Test Method for Water in Petroleum Products and
Bituminous Materials by Distillation
• ASTM D140 / D140M - 09 Standard Practice for Sampling Bituminous Materials
• ASTM D244 - 09 Standard Test Methods and Practices for Emulsified Asphalts
• ASTM D 5361 Standard Practice for Sampling Compacted Bituminous Mixtures
for Laboratory Testing

Summary
Soil stabilization is an important element in the scope of a battalion’s capabilities to
execute construction in both peaceful and hostile environments. In the multitude of
possible taskings, from roads to revetments, from airfields to building foundations, the
soil must be stable to support the designated project. Your contribution as an EA, with
your ability to test and identify soil characteristics and types, is at the very foundation,
figuratively and literally, of a project. Your technical knowledge and input provides the
Engineering Officer with the data necessary to design a course of steps for achieving
soil stabilization through either the mechanical or the additive process.

NAVEDTRA 14336A 13-19

Review Questions (Select the Correct Response)
1. Which of the following tests must be performed before a stabilizer can be
selected?

A. Moisture content
B. Sieve analysis
C. Specific gravity
D. Bearing tests

2. Cement can be used with coarse-grained soils that meet at least _____?

A. 45% retained on a No. 4 sieve

B. 45% passing a No. 4 sieve
C. 45% retained on a No. 40 sieve
D. 45% passing a No. 40 sieve

3. What plasticity index criteria should you meet when you use a bituminous
material for soil stabilization?

A. Greater than 30
B. Less than 30 but greater than 10
C. Equal to 25
D. Less than 10

4. When you choose a stabilizer additive, which of the following factors must be
considered?

A. Environmental conditions
B. Cost
C. Type of soil quality improvement desired
D. Each of the above

5. For which of the following purposes is plastic soil-cement used?

A. Emergency road repairs

B. Erosion prevention
C. Paving ditches
D. Each of the above

6. Which of the following properties increases when you add cement to the soil?

A. Bearing capacity
B. Plasticity
C. Water-holding capacity
D. All properties

NAVEDTRA 14336A 13-20

7. For what purpose is water used in soil-cement?

A. For hydration of the cement

B. To obtain maximum compaction
C. Both 1 and 2 above
D. To increase the weight

8. (True or False) Soils used for soil-cement must be well graded to provide proper
aggregate cohesion.

A. True
B. False

9. Which of the following soils is the most desirable for soil-cement construction?

A. Silty and clayey soil that contains a relatively high percentage of clay
B. Sandy and gravelly soil with more than 55% passing a No. 4 sieve
C. Sandy and gravelly soil that contains 10% to 35% silt and clay
D. Sandy soil that is deficient in fines

10. What is the first requirement for quality soil-cement?

A. Proper moisture content

B. Adequate cement content
C. Density of the soil
D. Proper compacting equipment

11. (True or False) When you perform laboratory tests, composite samples should
not be used because they could provide misleading and inaccurate results.

A. True
B. False

12. Which of the following tests determines the required cement content for nonfrost
areas?

A. Moisture-density
B. Freeze-thaw
C. Wet-dry
D. Both 2 and 3 above

13. Approximately, how long does it take to complete the wet-dry test?

A. 1 day
B. 2 days
C. 24 days
D. 108 days

NAVEDTRA 14336A 13-21

14. Your sample is classified as a gravelly soil. What is the passing criteria for this
type of soil when the freeze-thaw test has been performed on the sample?

A. At least 7% weight loss

B. Not more than 7% weight loss
C. At least 14% weight loss
D. Not more than 14% weight loss

15. The principle requirement of a soil-cement mixture is to withstand exposure to

the weather. By meeting this requirement, another requirement is also met. What
is that other requirement?

A. Strength
B. Moisture content
C. Plasticity
D. Coarseness

16. Which of the following effects does the use of bitumen have on the soil?

A. Decreases the load-bearing capacity

B. Decreases cohesion
C. Increases the resistant to water action
D. Each of the above

17. (True or False) In frost areas, tar is the recommended bituminous binder.

A. True
B. False

18. When pollution control concerns exist, what type of bituminous product is
recommended?

A. Tar
B. Cutback asphalt
C. Asphalt cement
D. Asphalt emulsion

19. For a well-graded aggregate with little to no mineral filler, which of the following
bituminous materials should you use?

A. MC-3000
B. MC-250
C. SS-1h
D. SC-70

NAVEDTRA 14336A 13-22

Trade Terms Introduced in this Chapter
Palliative Relieving or soothing the symptoms of a disorder
without effecting a cure.
Of or similar to a siliceous volcanic ash used to produce
Pozzolanic
hydraulic cement.

NAVEDTRA 14336A 13-23

Additional Resources and References
This chapter is intended to present thorough resources for task training. The following
reference works are suggested for further study. This is optional material for continued
education rather than for task training.
Nichols, Herbert L., Jr., Moving the Earth, 3d ed., North-Castle Books, Greenick, Conn.,
1976.
Materials Testing, NAVFAC MO-330/FM 5-472, NAVFAC/U.S. Army Engineers School,
Fort Belvoir, Va., 1987
Soil Stabilization for Pavements, UFC 3-250-11, U.S. Army Corps of Engineers/
NAVFAC, January 2004
Military Soils Engineering, FM 5-410, Headquarters, Department of the Army,
Washington, DC, June 1997

NAVEDTRA 14336A 13-24

CSFE Nonresident Training Course – User Update
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NAVEDTRA 14336A 13-25