Evaluating the effect of agro-based admixture on lime-treated expansive soil for subgrade material

Abstract

ABSTRACT An experimental study was carried out on an expansive black cotton soil (BCS) treated with lime and bamboo ash (BA) to determine its suitability as subgrade material. Preliminary tests conducted on the natural BCS indicated that the soil cannot serve as subgrade in the design of flexible pavement as the values obtained failed to meet the recommendations of the Nigeria general specification. Tests were carried out to determine the compaction and strength characteristics of the stabilised soil using an optimal 4% lime content selected based on plasticity index value, with various percentages of BA (4%, 8%, 12%, 16% and 20%). After stabilisation, an optimal value of 4% lime and 12% BA, added by weight of the air-dried soil showed that the compaction and strength characteristics of the soil improved significantly due to chemical actions experienced between the admixtures and the soil. Furthermore, whilst the resilient modulus (MR ) of the natural soil decreased with increasing deviatoric and bulk stresses, the MR of the stabilised soil improved significantly with increase in deviatoric and bulk stresses. The scanning electron microscope analysis of the specimen admixed with the optimal value and subjected to 28 days curing clearly showed that cementitious compounds were formed.