Influence of fly ash and lime on plasticity characteristics of residual lateritic soil

Residual lateritic soils, developed in tropical and similar other climates associated with high temperature and abundant rainfall, are widely used as fill material for various construction activities. The effective use of these soils is often hindered by difficulty in handling them, particularly under moist and wet conditions typical of tropical regions. An attempt has been made to study the plasticity behaviour of a residually derived lateritic soil mixed with a low-calcium fly ash and lime. Three proportions of soil and fly ash were used, with the maximum amount of soil replaced with fly ash limited to 50%. Lime was added in quantities varying from 1% to 8% of the dry weight of soil or soil-fly ash mix. Atterberg limits were determined for the mixes after different curing periods up to 56 days. Owing to the presence of sesquioxides in the residual lateritic soil, unlike other soils, the addition of the low-calcium fly ash caused a decrease in the plastic limit. It was only when lime was also added that the plastic limit of the soil-fly ash mixes was noted to increase, leading to an improvement in workability.