TM
5-822-14/AFJMAN
32-1019
the water has already been added, however, can be
placed immediately ahead of the bituminous appli-
serious. Generally, the best procedure is to obtain
cation.
(6) Construction joints. After each day's con-
rapid compaction by using every available piece of
equipment so that the section will be compacted
struction, a transverse vertical construction joint
and shaped before too much damage results. In
must be formed by cutting back into the completed
such instances it may be necessary to complete
soil-cement to the proper crown and grade. This is
final blading later; any material bladed from the
usually done the last thing at night or the first
thing the following morning, using the toe of the
surface is wasted. After the mixture has been
compacted and finished, rain will not harm it.
motor-grader blade or mixer. The joint must be
(2) Wet soils. Excessively wet material is diffi-
vertical and perpendicular to the centerline. After
the next day's mixing has been completed at the
cult to mix and pulverize. Experience has shown
joint, it must be cleaned of all dry and unmixed
that cement can be mixed with sandy materials
material and retrimmed if necessary. Mixed moist
when the moisture content is as high as 2 percent
material is then bladed into the area and com-
above optimum. For clayey soils, the moisture
pacted thoroughly. The joint is left slightly high
content should be below optimum for efficient
until final rolling when it is trimmed to grade
mixing. It may be necessary to dry out the soil
with the motor grader and rerolled. Joint construc-
material by aeration. This can be done by using
tion requires special attention to make sure the
single-shaft traveling mixers with the hood in a
joints are vertical and the material in the joint
raised position, or by cutting out the material with
area is adequately mixed and thoroughly com-
the tip of a motor grader blade and working and
pacted. When bituminous material is used as a
aerating with a disc. The maintenance of good
curing agent, it should be applied right up to the
crown and surface grade to permit rapid runoff of
joint and sanded to prevent pickup.
surface water before soil-cement processing is the
(7) Multiple-layer construction. When the spec-
best insurance against excessive amounts of wet
ified thickness of soil-cement base course exceeds
material.
the depth (usually 8 or 9 inches compacted) that
(3) Cold weather. Soil-cement, like other
can be compacted in one layer, it must be con-
cement-using products, hardens as the cement
structed in multiple layers. No layer should be less
hydrates. Since cement hydration practically
than 4 inches thick. The lower layer does not have
ceases when temperatures are near or below freez-
to be finished to exact crown and grade, nor do
ing, soil-cement should not be placed when the
surface compaction planes have to be removed
temperature is 40 degrees F or below. Moreover, it
since they are too far from the final surface to be
should be protected to prevent its freezing for a
harmful. The lower layer can be cured with the
period of 7 days after placement, and until it has
moist soil that will subsequently be used to build
hardened, by a suitable covering of hay, straw, or
the top layer-which can be built immediately, the
other protective material.
following day, or some time later. With mixed-in-
4-2. Construction with lime.
place construction, care must be taken to elimi-
a. Lime stabilization methods. Basically, there
nate any raw-soil seams between the layers.
are three recognized lime stabilization methods;
e. Special construction problems.
(1) Rainfall. Attention to a few simple precau-
in-place mixing, plant mixing, and pressure injec-
tion.
tions before processing will greatly reduce the
(1) In-place mixing.
possibility of serious damage from wet weather.
(a) In-place mixing may be subdivided into
For example, any loose or pulverized soil should be
three methods: mixing lime with the existing
crowned so it will shed water, and low places in
materials already a part of the construction site or
the grade where water can accumulate should be
pavement (fig 4-15); off-site mixing in which lime
trenched so the water will drain off freely. As
is mixed with borrow and the mixture is then
shown by the construction of millions of square
transported to the construction site for final ma-
yards of soil-cement in all climates, it is unlikely
nipulation and compaction (fig 4-16); and mixing
that rainfall during actual construction will be a
in which the borrow source soil is hauled to the
serious problem to the experienced engineer or
construction site and processed as in the first
contractor. Usually construction requires the addi-
method.
tion of water equivalent to 1 to 1 inches of rain.
(b) The following procedures are for in-place
If rain falls during cement-spreading operations,
mixing:
spreading should be stopped and the cement al-
One increment of lime is added to clays or
ready spread should be quickly mixed into the soil
granular base materials that are easy to pulverize.
mass. A heavy rainfall that occurs after most of
4-10
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