Abstract :
Soil cement is a construction material, a mix of
pulverized natural soil with small amount of portland cement and water, usually
processed in a tumble, compacted to high density. Hard, semi-rigid durable
material is formed by hydration of the cement particles.
Soil cement is frequently used as a construction
material for pipe bedding, slope protection, and road construction as a sub
base layer reinforcing and protecting the sub grade. It has good compressive
and shear strength, but is brittle and has low tensile strength, so it is prone
to forming cracks.
Soil cement mixtures differ from Portland cement
concrete in the amount of paste (cement-water mixture). While in Portland
cement concretes the paste coats all aggregate particles and binds them together,
in soil cements the amount of cement is lower and therefore there are voids
left and the result is a cement matrix with nodules of uncemented material.
Use Soil-Cement?
Failing granular-base pavements, with or without
their old bituminous mats, can be salvaged, strengthened, and reclaimed as
soil-cement pavements. This is an efficient, economical way of rebuilding
pavements. Since approximately 90 percent percent of the material used is
already in place, handling and hauling costs are cut to a minimum. Many
granular and waste materials from quarries and gravel pits can also be used to
make soil-cement; thus high-grade materials are conserved for other purposes.
Highway and city engineers praise soil-cement’s
performance, its low first cost, long life, and high strength. Soil-cement is
constructed quickly and easily – a fact appreciated by owners and users alike.
How is Soil-Cement Built?
Before construction begins, simple laboratory tests
establish the cement content, compaction, and water requirements of the soil
material to be used. During construction, tests are made to see that the
requirements are being met. Testing ensures that the mixture will have strength
and long-term durability. No guesswork is involved.
Soil-cement can be mixed in place or in a central
mixing plant. Central mixing plants can be used where borrow material is
involved. Friable granular materials are selected for their low cement
requirements and ease of handling and mixing. Normally pugmill-type mixers are
used. The mixed soil-cement is then hauled to the jobsite and spread on the
prepared subgrade.
Compaction and curing procedures are the same for
central-plant and mixed-in-place procedures. There are four steps in
mixed-in-place soil-cement construction; spreading cement, mixing, compaction,
and curing. The proper quantity of cement is spread on the in-place soil
material.
Then the cement, the soil material, and the
necessary amount of water are mixed thoroughly by any of several types of
mixing machines. Next, the mixture is tightly compacted to obtain maximum
benefit form the cement. No special compaction equipment is needed; rollers of
various kinds, depending on soil type, can be used. The mixture is cemented
permanently at a high density and the hardened soil-cement will not deform or
consolidate further under traffic.
Curing, the final step, prevents evaporation of
water to ensure maximum strength development through cement hydration. A light
coat of bituminous material is commonly used to prevent moisture loss; it also
forms part of the bituminous surface. A common type of wearing surface for
light traffic is a surface treatment of bituminous material and chips .5- to
.75-inch thick. For heavy-duty use and in severe climates a 1.5-inch asphalt
mat is used.
Contractors bidding on soil-cement jobs know that
construction will be relatively easy and problem-free; weather delays rare; and
reworking of completed sections unnecessary.
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