Abstract: The swelling, swelling pressure and moisture dependent shear strength of expansive soils pose serious problems to civil engineers. Disposal of large quantities of fly ash, which is an industrial waste, poses a major ecological problem. This paper studies the efficiency of fly ash without lime as an additive in improving the engineering characteristics of expansive soils. An experimental program has evaluated the effect of fly ash content on the particle size distribution, atterberg limits, specific gravity, plasticity, compaction, free swell index, swell indices under non-compression and with an axial compression of 50 kPa, swelling pressure and axial shrinkage percent characteristics of expansive soil. The plasticity index, activity, the optimum water content, the maximum dry unit weight, free swell index, swell potential, swelling pressure and axial shrinkage percent decreased with an increase in fly ash content. It is found that with the increase in the curing time, the swell potential and swelling pressure reduced. The unconfined compressive strength test results show that there is no remarkable change in the unconfined compressive strength of the soils immediately treated with fly ash alone. However, 7 days curing brings a remarkable increase in the unconfined compressive strength.

Key words: expansive soil, fly ash, physical properties, swell potential, swelling pressure, unconfined compressive strength