An assessment of cement-PFA and lime-PFA used to stabilize clay-size materials

Difficulties in construction operations are often associated with clay soils. However, the engineering behaviour of such soils can be improved by stabilizing them with the addition of small amounts of cementitious materials. Nonetheless because clay soils possess a range of mineralogical compositions some are more easy to estabilize than others. In order to investigate this problem, three of the principal components found in clays, namely, kaolinite, montmorillonite and quartz, were chosen. These three components were treated with varying amounts of cement plus PFA. and lime plus PFA. PFA was used as an extender with cement and with lime to evaluate how effective such mixtures are when used to stabilize clay soils. The addition of PFA reduces the cost of the stabilizing agent. Because stabilization of clay soils most frequently has been used in connection with road construction, kaolinite, montmorillonite and quartz were subjected to the types of test used in the design procedure for roadways, that is, consistency limit tests, compaction tests, California bearing ratio tests, unconfined compressive tests, and tests to determine Young's modulus. Except for those samples used for assessment of consistency limits, the others were prepared with optimum values of moisture content and maximum dry density. Those samples used for unconfined compression and modulus of elasticity measurements were cured for different periods of time. The results of the various tests were examined to see if there was an optimum amount for a particular addition which would bring about maximum enhancement of engineering performance of the components concerned. Generally mixtures of cement and PFA or lime and PFA did not give as good results as when cement and lime were used on their own. Also those mixtures with the highest proportions of cement and of lime usually gave the better improvement in values. Nevertheless it may be worth making some sacrifice in soil improvement to obtain the saving in cost that the use of PFA brings.