Investigation of the effects of Rice Husk Ash (RHA) on the engineering properties of red coffee soil for sub-grade

Traditionally, rice husk has been considered a waste material and has generally been disposed off
by damping or burning, although some has been used as low grade fuel. However, when burned,
the resulting Rice Husk Ash (RHA) is a pozzolanic material that could be potentially used in
stabilization of clayey soils for road construction. This study investigates the effects of RHA on
the engineering properties of one of the common road construction material in Kenya, the red
coffee soil. The investigation includes laboratory tests and analysis of the results of the tested
samples. The properties that were evaluated includes the California Bearing Ratio (CBR),
plasticity index (PI), and linear shrinkage with Rice Husk Ash content of 3%, 5%, 7%, 9% and
11% by weight of the dry soil.
From analyzing the laboratory results, it was found that addition of RHA to the natural soil
generally reduced the liquid limit and the linear shrinkage, with a maximum reduction of 13%
and 44% respectively after treatment with RHA content of 11%. In addition, the soaked CBR
and plastic limit increased by approximately 500% and 31% respectively after addition of 11%
RHA. It was also found that the plasticity index of the stabilized red coffee soil also reduced by
48% after treatment with 11% Rice Husk Ash.


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