TM
5-822-14/AFJMAN
32-1019
Table 3-3. Gradation requirements for lime stabilized base
treated material should also be determined as indi-
and subbase courses
cated in appropriate pavement design manuals.
(5) Step 5. Compare the results of the uncon-
Sieve Size
Percent Passing
Type Course
fined compressive strength and durability tests
100
1 in.
Base
with the requirements shown in tables 2-2 and
70-100
in.
2-3. The lowest cement content which meets the
45-70
No. 4
No. 40
10-40
required unconfined compressive strength require-
No. 200
0-20
ment and demonstrates the required durability is
the design cement content. If the mixture should
1
in.
100
Subbase
No.
4
45-100
meet the durability requirements but not the
No.
40
10-50
strength requirements, the mixture is considered
No.
200
0-20
to be a modified soil. If the results of the speci-
mens tested do not meet both the strength and
pared at different lime treatment levels such as 2,
durability requirements, then a higher cement
4, 6, and 8 percent lime and the pH of each slurry
content may be selected and steps 1 through 4
is determined. The lowest lime content at which a
above repeated.
pH of about 12.4 (the pH of free lime) is obtained
is the initial design lime content. Procedures for
3-2. Stabilization with lime. In general, all
conducting the pH test are indicated in appendix
lime treated finegrained soils exhibit decreased
D. An alternate method of determining an initial
plasticity, improved workability and reduced vol-
design lime content is by the use of figure 3-1.
ume change characteristics. However, not all soils
exhibit improved strength characteristics. It
Specific values required to use figure 3-1 are the
should be emphasized that the properties of soil-
PI and the percent of material passing the No. 40
lime mixtures are dependent on many variables.
sieve.
(2) Step 2. Using the initial design lime con-
Soil type, lime type, lime percentage and curing
tent conduct moisture-density tests to determine
conditions (time, temperature, moisture) are the
most important.
the maximum dry density and optimum water
a. Types of lime. Various forms of lime have
content of the soil lime mixture. The procedures
contained in ASTM D 3551 will be used to prepare
been successfully used as soil stabilizing agents for
the soil-lime mixture. The moisture density test
many years. However, the most commonly used
products are hydrated high-calcium lime, monohy-
will be conducted following procedures in
drated dolomitic lime, calcitic quicklime, and dolo-
MIL-STD 621 Method 100 (CE 55 effort) or ASTM
D 1557.
mitic quicklime. Hydrated lime is used most often
(3) Step 3. Prepare triplicate samples of the
because it is much less caustic than quicklime,
however, the use of quicklime for soil stabilization
soil lime mixture for unconfined compression and
durability tests at the initial design lime content
has increased in recent years mainly with slurry-
type applications. The design lime contents deter-
and at lime contents 2 and 4 percent above design
if based on the preferred method or 2 percent
mined from the criteria presented herein are for
above at 2 percent below design if based on the
hydrated lime. If quicklime is used the design lime
alternate method. The mixture should he prepared
contents determined herein for hydrated lime
as indicated in ASTM D 3551. If less than 35
should be reduced by 25 percent. Specifications for
percent of the soil is retained on the No. 4 sieve,
quicklime and hydrated lime may be found in
the sample should be approximately 2 inches in
ASTM C 977.
diameter and 4 inches high. If more than 35
percent is retained on the No. 4 sieve, samples
ments for lime stabilized base and subbase courses
should be 4 inches in diameter and 8 inches
are presented in table 3-3.
c. Lime content for lime-modified soils. The
high. The samples should be prepared at the
density and water content expected in field con-
amount of lime required to improve the quality of
struction. For example, if the design density is
a soil is determined through the same trial-and-
95 percent of the laboratory maximum density,
error process used for cement-modified soils.
d. Lime content for lime-stabilized soils. The
the sample should be prepared at 95 percent
density. Specimens should be cured in a sealed
following procedures are recommended for deter-
container to prevent moisture loss and lime car-
mining the lime content of lime stabilized soils.
(1) Step 1. The preferred method for determin-
bonation. Sealed metal cans, plastic bags, and so
forth are satisfactory. The preferred method of
ing an initial design lime content is the pH test.
curing is 73 degrees F for 28 days. Accelerated
In this method several lime-soil slurries are pre-
3-3
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