TM 5-822-14/AFJMAN 32-1019
3-3. Stabilization with Lime-Fly Ash (LF) and
characteristics such as strength and durability are
Lime-Cement-Fly Ash (LCF). Stabilization of
directly related to the quality of the matrix mate-
coarse-grained soils having little or no tines can
rial. The matrix material is that part consisting of
often be accomplished by the use of LF or LCF
fly ash, lime, and minus No. 4 aggregate fines.
Basically, higher strength and improved durability
combinations. Fly ash, also termed coal ash, is a
are achievable when the matrix material is able to
mineral residual from the combustion of pulver-
"float" the coarse aggregate particles. In effect,
ized coal. It contains silicon and aluminum com-
pounds that, when mixed with lime and water,
the fine size particles overfill the void spaces
forms a hardened cementitious mass capable of
between the coarse aggregate particles. For each
obtaining high compressive strengths. Lime and
coarse aggregate material, there is a quantity of
fly ash in combination can often be used success-
matrix required to effectively fill the available
fully in stabilizing granular materials since the fly
void spaces and to "float" the coarse aggregate
ash provides an agent, with which the lime can
particles. The quantity of matrix required for
react. Thus LF or LCF stabilization is often appro-
maximum dry density of the total mixture is
priate for base and subbase course materials.
referred to as the optimum fines content. In LF
a. Types of fly ash. Fly ash is classified accord-
mixtures it is recommended that the quantity of
ing to the type of coal from which the ash was
matrix be approximately 2 percent above the
derived. Class C fly ash is derived from the
optimum fines content. At the recommended fines
burning of lignite or subbituminous coal and is
content, the strength development is also influ-
often referred to as "high lime" ash because it
enced by the ratio of lime to fly ash. Adjustment of
contains a high percentage of lime. Class C fly ash
the lime-fly ash ratio will yield different values of
is self-reactive or cementitious in the presence of
strength and durability properties.
water, in addition to being pozzolanic. Class F fly
(1) Step 1. The first step is to determine the
ash is derived from the burning of anthracite or
optimum fines content that will give the maxi-
bituminous coal and is sometimes referred to as
mum density. This is done by conducting a series
"low lime" ash. It requires the addition of lime to
of moisture-density tests using different percent-
form a pozzolanic reaction.
ages of fly ash and determining the mix level that
b. Evaluation of fly-ash. To be acceptable quality
yields maximum density. The initial fly ash con-
fly ash used for stabilization must meet the re-
tent should be about 10 percent based on dry
quirements indicated in ASTM C 593.
weight of the mix. It is recommended that mate-
ments for LF and LCF stabilized base and subbase
rial larger than in. be removed and the test
course are indicated in table 3-4.
conducted on the minus in. fraction. Tests are
run at increasing increments of fly ash, e.g. 2
Table 3-4. Gradation requirements for fly ash
percent, up to a total of about 20 percent. Moisture
stabilized base and subbase courses
density tests should be conducted following proce-
dures indicated in MIL-STD 621, Method 100 (CE
Sieve Size
Percent Passing
Type Course
55 effort) and ASTM D 1557. The design fly ash
2 in.
100
Base
content is then selected at 2 percent above that
in.
70-100
yielding maximum density. An alternate method
3/8 in.
50-80
is to estimate optimum water content and conduct
No. 4
35-70
No. 8
25-55
single point compaction tests at fly ash contents of
No. 16
10-45
10-20 percent, make a plot of dry density versus
No. 200
0-15
fly ash content and determine the fly ash content
1 in.
100
Subbase
that yields maximum density. The design fly ash
No. 4
45-100
content is 2 percent above this value. A moisture
No. 40
10-50
density test is then conducted to determine the
No. 200
0-15
optimum water content and maximum dry density.
(2) Step 2. Determine the ratio of lime to fly
d. Selection of lime-fly ash content for LF and
LCF mixtures. Design with LF is somewhat differ-
ash that will yield highest strength and durability.
Using the design fly ash content and the optimum
ent from stabilization with lime or cement. For a
water content determined in step 1, prepare tripli-
given combination of materials (aggregate, fly ash,
cate specimens at three different lime-fly ash
and lime), a number of factors can be varied in the
ratios following procedures indicated in MIL-STD
mix design process such as percentage of lime-fly
621 Method 100 (less effort) or ASTM D 1557. Use
ash, the moisture content, and the ratio of lime to
LF ratios of 1:3, 1:4, and 1:5. If desired about 1
fly ash. It is generally recognized that engineering
3-5
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