TM
5-822-14/AFJMAN
32-1019
Not practical for use with very wet
The fast drying action of the dry lime
soils.
requires an excess amount of water
(3) Pulverization and mixing. To obtain satis-
during the dry, hot seasons.
(h) Some of the advantages and disadvan-
factory soil-lime mixtures adequate pulverization
and mixing must be achieved. For heavy clay soils
tages of dry quicklime are as follows:
1. Advantages:
two-stage pulverization and mixing may be re-
quired, but for other soils one-stage mixing and
More economical as it contains approxi-
pulverization may be satisfactory. This difference
mately 25 percent more available
is primarily due to the fact that the heavy clays
lime.
are more difficult to break down.
Greater bulk density for smaller-sizes
(a) Two-stage mixing. Construction steps in
silos.
two-stage mixing consist of preliminary mixing,
Faster drying action in wet soils.
moist curing for 24 to 48 hours (or more), and final
Faster reaction with soils.
mixing or remixing. The first mixing step distrib-
Construction season can be extended, in
utes the lime throughout the soil, thereby facilitat-
both spring and fall, because of faster
ing the mellowing action. For maximum chemical
drying.
action during the mellowing period, the clay clods
2. Disadvantages:
should be less than 2 inches in diameter. Before
Field hydration less effective than com-
mellowing the soil should be sprinkled liberally to
m e r c i a l hydrators, producing a
bring it up to at least two percentage points above
coarser material with poorer distribu-
optimum moisture in order to aid the disintegra-
tion in soil mass.
tion of clay clods The exception to excess watering
Quicklime requires more water than
would be in cool, damp weather when evaporation
hydrate for stabilization, which may
is at a minimum. In hot weather, however, it may
present a problem in dry areas.
be difficult to add too much water. After prelimi-
Greater susceptibility to skin and eye
nary mixing, the roadway should be sealed lightly
burns.
with a pneumatic roller as a precaution against
(i) Some of the advantages and disadvan-
heavy rain, because the compacted subgrade will
tages of slurry lime are as follows:
shed water, thereby preventing moisture increases
1. Advantages:
that might delay construction. Generally, in 24 to
Dust-free application is more desirable
48 hours the clay becomes friable enough so that
from an environmental standpoint.
desired pulverization can be easily attained during
Better distribution is achieved with the
final mixing. Additional sprinkling may be neces-
slurry.
sary during final mixing to bring the soils to
In the lime slurry method, the lime
optimum moisture or slightly above (fig 4-35). In
hot weather more than optimum moisture is
spreading and sprinkling operations
needed to compensate for the loss through evapora-
are combined, thereby reducing job
tion. Although disc harrows (fig 4-36) and grader
costs.
scarifiers are suitable for preliminary mixing,
During summer months slurry applica-
high-speed rotary mixers (fig 4-37 to fig 4-39) or
tion prewets the soil and minimizes
one-pass travel plant mixers (fig 4-15) are re-
drying action.
quired for final mixing. Motor graders are gener-
The added heat when slurry is made
ally unsatisfactory for mixing lime with heavy
from quicklime speeds drying action,
clays.
which is especially desirable in cooler
(b) One-stage mixing. Both blade and rotary
weather.
mixing, or a combination, have been used success-
2. Disadvantages:
fully in projects involving granular base materials.
Application rates are slower. High ca-
However, rotary mixers are preferred for more
pacity pumps are required to achieve
uniform mixing, finer pulverization, and faster
acceptable application rates.
operation. They are generally required for highly
Extra equipment is required, therefore,
plastic soils that do not pulverize readily and for
costs are higher.
reconstructing worn-out roads in order to pulverize
Extra manipulation may be required for
the old asphalt.
drying purposes during cool, wet, hu-
(c) Blade mixing. When blade mixing is
mid weather, which could occur dur-
used in conjunction with dry lime, the material is
ing the fall, winter, and spring con-
generally bladed into two windrows, one on each
struction season.
4-17
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