Cement-modified soil (CMS) is a term used to describe native soils and/or
manufactured aggregates that have been treated with a relatively small proportion of
portland cement. Cement application rates for CMS typically vary from 2 to 6 percent
by dry weight of the soil/aggregate being modified with the majority of cases being
between 3 and 5 percent. The objective of the treatment is to amend the undesirable
properties of problem soils/aggregates so that they are suitable for use in construction.
The amount of cement added to produce CMS is typically less than that required to
produce a strong, frost-resistant cement-treated base (CTB) but is enough to improve
their engineering properties. The degree of modification increases with greater
amounts of cement. Therefore, for a given soil/aggregate, a cement content can be
selected that will provide a material meeting the specified level of modification,
expressed in terms of plasticity, bearing capacity, or other criteria.
Laboratory and field work on CMS indicate that the relatively small quantities of cement
bind some of the soil/aggregate particles together to form small conglomerate masses
of new soil/aggregate. In addition to this slight cementing reaction, the surface
chemistry of clay particles, either in clay soils or the clay fraction of granular soils, is
improved by cation exchange phenomenon. As a result, the modified soils/aggregates
have lower plasticity (cohesiveness), lower volume change characteristics, and greater
strength than untreated soils/aggregates.
Field and laboratory tests show that changes in the physical characteristics of a
soil/aggregate by cement modification are permanent. The soil/aggregate does not
revert back to its original state, even after many cycles or years of weathering and
service. This paper will look at the types of CMS available, their modification
mechanisms, material properties, proper construction techniques, and longevity.
Menu
