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Frequently Asked Soil-Cement Questions
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FAQs > CTB vs GAB
What are the different types of soil-cement materials?
Soil-cement is an engineered material designed and constructed
for various pavement applications or material characteristics. The
best soil-cement product is the one best suited to the specific
application. Each of these cement-based pavement materials are engineered
specifically for their intended purpose as follows:
Cement-Modified Soil (CMS) – Many problems
can occur during construction when silt and clay soils are encountered,
particularly when they are wet. These soils can be soft, plastic,
and difficult to compact. CMS is used to improve the engineering
properties and construction characteristics of silt and clay soils
by reducing the plasticity and enhancing the compaction and strength
of the material. With 3 – 5% (by dry weight) of cement used
to modify the soil, the final product is an improved construction
material.
Cement-Treated Base (CTB) – CTB a general
term that applies to all hardened soil-cement that meets the project
specified minimum durability and strength requirements. The soil-cement
can be mixed-in-place (like CMS) using on-site soils or mixed in
a central plant using selected aggregate. However, CTB uses more
cement than CMS resulting in a strong, durable, frost resistant
layer for the pavement structure. Typical cement contents range
from 3 – 10% cement, resulting in 7-day unconfined compressive
strengths from 300 – 800 psi (2.1 - 5.5 MPa).
Full-Depth Reclamation (FDR) – A special
case of cement-stabilization is FDR, where aggregate for the cement-stabilized
base is obtained by pulverizing and recycling the old asphalt surface
and base material. This construction procedure is very similar to
mixed-in-place construction, except that there is an aggregate specification
for the blend of the pulverized asphalt and old base material. FDR
commonly uses 4 – 6% cement and results in 300 – 400
psi (2.1 – 2.8 MPa) unconfined compressive strengths in 7
days.
The four major variables that control the properties and characteristics
of soil-cement are (1) the nature of the soil material; (2) the
proportion of cement in the mix; (3) moisture conditions; and (4)
the degree of compaction. It is possible, simply by varying the
cement content, to produce mixes ranging from those which result
in only modification of the compacted soil to those which result
in hard soil-cement that will meet durability and strength requirements.
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