TM 5-822-14/AFJMAN 32-1019
rollers are used for initial compaction, the mixed
readily; there is less water evaporation; and daily
material must be in a loose condition at the start
production is increased.
(4) Finishing. There are several acceptable
of compaction so that the feet will pack the bottom
material and gradually walk out on each succeed-
methods for finishing soil-cement. The exact proce-
ing pass. If penetration is not being obtained, the
dure depends on equipment, job conditions, and
scarifier on a motor grader or a traveling mixer
soil characteristics. Regardless of method, the fun-
can be used to loosen the mix during start of
damental requirements of adequate compaction,
compaction, thus allowing the feet to penetrate.
close to optimum moisture, and removal of all
Vibratory-steel-wheeled rollers and grid and seg-
surface compaction planes must be met to produce
mented rollers can be used to satisfactorily com-
a high quality surface. The surface should be
pact soil-cement made of granular soil materials.
smooth, dense, and free of ruts, ridges, or cracks.
Vibratory-plate compactors are used on nonplastic
When shaping is done during finishing, all smooth
granular materials. Pneumatic-tired rollers can be
surfaces, such as tire imprints and blade marks,
used to compact coarse sand and gravel soil-
should be lightly scratched with a weeder, nail
cement mixtures with very little plasticity and
drag, coil spring, or spiketooth harrow to remove
very sandy mixtures with little or no binder
cleavage or compaction planes from the surface.
material, such as dune, beach, or blow sand. Some
Scratching should be done on all soil-cement mix-
permit rapid inflation and deflation of the tires
tures except those containing appreciable quanti-
while compacting to increase their versatility.
ties of gravel. The surface should be kept damp
Pneumatic-tired rollers pulled by track-type trac-
during finishing operations. Steel-wheeled rollers
tors equipped with street plates can be used to
can be used to smooth out ridges left by the initial
compact cohesionless sand mixtures. The weight
pneumatic-tired rolling. Steel-wheeled rollers are
and vibration of the tractor aid in compaction.
particularly advantageous when rock is present in
Heavy three-wheeled steel rollers can be used to
the surface. A broom drag can sometimes be used
compact coarse granular materials containing lit-
advantageously to pull binder material in and
tle or no binder material. Gravelly soils that
around pieces of gravel that have been set by the
contain up to about 20 percent passing the No. 200
steel-wheeled roller. Instead of using a steel roller,
sieve and have low plasticity are best suited for
surfaces can be shaved with the motor grader and
compaction with these rollers. Tandem-steel-
then rerolled with a pneumatic-tired roller to seal
wheeled rollers are often used during final rolling
the surface. Shaving consists of lightly cutting off
to press down or set rock particles and to smooth
any small ridges left by the finishing equipment.
out ridges. There are two general types of road
Only a very thin depth is cut and all material
cross section: trench and featheredge. Both can be
removed is bladed to the edge of the road and
built satisfactorily with soil-cement. In trench-type
wasted. The final operation usually consists of a
construction, the shoulder material gives lateral
light application of water and rolling with a
support to the soil-cement mixture during compac-
pneumatic-tired roller to seal the surface. The
tion. In the featheredge type of construction, the
finished soil-cement is then cured.
(5) Curing. Compacted and finished soil-
edges are compacted first to provide some edge
stability while the remaining portion is being
cement contains sufficient moisture for adequate
compacted. The edge slope should not be steeper
cement hydration. A moisture-retaining cover is
than 2:1 to facilitate shaping and compacting.
placed over the soil-cement soon after completion
Shoulder material is placed after the soil-cement
to retain this moisture and permit the cement to
hydrate. Most soil-cement is cured with bitumi-
has been finished. Occasionally, during compaction
and finishing, a localized area may yield under the
nous material, but other materials such as water-
compaction equipment. This may be due to one or
proof paper of plastic sheets, wet straw or sand,
more causes: the soil-cement mix is much wetter
fog-type water spray, and wet burlap or cotton
than optimum moisture; the subsoil may be wet
mats are entirely satisfactory. The types of bitumi-
and unstable; or the roller may be too heavy for
nous materials most commonly used are RC-250,
MC-250, RT-5, and emulsified asphalt SS-1. Rate
the soil. If the soil-cement mix is too damp, it
of application varies from 0.15 to 0.30 US gallons
should be aerated with a cultivator, traveling
per square yard. At the time of application, the
mixer, or motor grader. After it has dried to near
soil-cement surface should be free of all dry, loose
optimum moisture, it can be compacted. For best
and extraneous material. The surface should also
results, compaction should start immediately after
be moist when the bituminous materials are ap-
the soil material, cement, and water have been
mixed. Required densities are then obtained more
plied. In most cases a light application of water is
4-9
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