Soil-Cement Basics (SCB)
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Soil-Cement > Cement-Treated Base (CTB)
What is Soil-Cement?
 Soil-cement
is a highly compacted mixture of soil/aggregate, cement, and water.
It is widely used as a low-cost pavement base for roads, residential
streets, parking areas, airports, shoulders, and materials-handling
and storage areas. Its advantages of great strength and durability
combine with low first cost to make it the outstanding value in
its field. A thin bituminous surface is usually placed on the soil-cement
to complete the pavement.
What Type of Soil is Used?
The soil material in soil-cement can be almost any combination
of sand, silt, clay, gravel, or crushed stone. Local granular materials,
such as slag, caliche, limerock, and scoria, plus a wide variety
of waste materials including cinders, fly ash, foundry sands, and
screenings from quarries and gravel pits, can all be utilized as
soil material. Old granular-base roads, with or without bituminous
surfaces, can also be reclaimed to make great soil-cement.
Soil-cement is sometimes called cement-stabilized base, or cement-treated
aggregate base. Regardless of the name, the principles governing
its composition and construction are the same.
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 ½ to ¾-inch (13 to 19 mm) thick. For heavy-duty
use and in severe climates a 1-1/2-inch (38 mm) 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.
Why 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% 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,
it’s low first cost, long life, and high strength. Soil-cement
is constructed quickly and easily – a fact appreciated by
owners and users alike.
How Does Soil-Cement Perform?
Soil-cement thicknesses are less than those required for granular
bases carrying the same traffic over the same subgrade. This is
because soil-cement is a cemented, rigid material that distributes
loads over broad areas. Its slab-like characteristics and beam strength
are unmatched by granular bases. Hard, rigid soil-cement resists
cyclic cold, rain, and spring-thaw damage.
Old soil-cement pavements in all parts of the continent are still
giving good service at low maintenance costs. Soil-cement has been
used in every state in the Untied States and in all Canadian provinces.
Specimens taken from roads show that the strength of soil-cement
actually increases with age; some specimens were four times as strong
as test specimens made when the roads were first opened to traffic.
This reserve strength accounts in part for soil-cement’s good
long-term performance.
Is Soil-Cement Economical?
The cost of soil-cement compares favorably with that of granular-base
pavement. When built for equal load-carrying capacity, soil-cement
is almost always less expensive than other low-cost pavements. Economy
is achieved through the use or reuse of in-place or nearby borrow
materials. No costly hauling of expensive, granular-base materials
is required; thus both energy and materials are conserved.
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