Cement-Modified Soils (CMS)
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 A
cement-modified soil (CMS) is a soil material that has been treated
with a relatively small proportion of portland cement – less
cement than is required to produce hardened soil-cement. The objective
of the treatment is to amend undesirable properties of problem soils
or substandard materials so that they are suitable for use in construction.
With the small quantities of cement generally used, CMS becomes
caked or slightly hardened. However, it still functions essentially
as a soil, although an improved one. The degree of improvement depends
on the quantity of cement used and the type of soil. Therefore,
by the addition of varying amounts of cement, it is possible to
produce cement-modified soils with a wide range of engineering properties.
The improvement in engineering properties of a soil due
to the addition of small quantities of cement can be measured in
several; ways including:
- Reduction in plasticity characteristics as measured by Plasticity
Index (PI)
- Reduction in the amount of silt and clay size particles
- Increase in the California Bearing Ratio (CBR)
- Increase in shearing strength
- Decrease in volume-change properties
Cement-modified soils are usually classified into two groups according
to the predominant grain size as follows:
- Cement-modified silt-clay soils are soils that
contain more than 35% silt and clay (defined as material passing
a No. 200 (75 µm) sieve in accordance with ASTM D4318).
The general objective is to improve soils that are otherwise unsuitable
for use in subgrades or subbase layers. Specific objectives may
be to decrease plasticity and volume change characteristics, to
increase the bearing strength, or to provide a stable working
platform on which pavement layers may be constructed.
- Cement-modified granular soils are soils that
contain less than 35% silt and clay (defined as material passing
a No. 200 (75 µm) sieve in accordance with ASTM D4318).
The usual objective is to alter substandard materials so that
they will meet requirements specified for pavement base or subbase
layers.
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