The quality and life of pavement is greatly affected by the type of sub-grade, sub base
and base course materials. The most important of these are the type and quality of sub-grade soil.
But in Kenya most of the flexible pavements are need to be constructed over weak and
problematic sub-grade. The California bearing ratio (CBR) of these sub-grades are very low and
therefore more thickness of pavement. Decrease in the availability of suitable sub base and base
materials for pavement construction have leads to a search for economic methods of
improvement of locally available problematic soil to suitable construction materials. The
improvement of soil properties is one of the main branches of geotechnical science that has been
considered by researchers in different countries. In developing country like Kenya due to the
remarkable development in road infrastructure, soil stabilization has become the major issue in
construction activity. Stabilization is an unavoidable for the purpose of highway and runway
construction, stabilization denotes improvement in both strength and durability which are related
to performance. Stabilization is a method of processing available materials for the production of

low-cost road design and construction. Fine clayey soils properties due to high swelling
necessitate the need to improve its geotechnical properties. Black cotton soils when used as a
subgrade for pavements has risks of substantial settlements, heave and low bearing capacity.
This project is an investigation carried out to study the effect of cement on engineering
and strength properties of the Black Cotton Soils. The properties of stabilized soil such as
compaction characteristics, consistency limits, California bearing ratio and swell potential were
evaluated and their variations with cement content evaluated. Ways of curbing the cyclic swell
shrinkage behavior of black cotton soil were looked in to by provision of fly ash cushion.
Available literature on the subject of soil stabilization is surveyed. Various types of
cement are looked into with a view of establishing their viability of use in soil stabilization.
Laboratory test to examine the engineering properties of black cotton soil and soil-cement
mixtures are presented based on existing procedures for testing materials.
The interpretation of test results leading to various conclusion and recommendation on
the use of cement in soil stabilization to counter the difficulty posed by black cotton soil for
subgrade material is discussed.


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