Cement-Modified Soil for Long Lasting Pavements

摘要

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 two to six percent by dry weight of the soil/aggregate being modified with the majority of cases being between three and five percent. The objective of the treatment is to permanently 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 long lasting and sustainable 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), making CMS a very sustainable pavement material. This paper will look at the types of CMS available, their modification mechanisms, material properties, proper construction techniques, and longevity.