This paper presents a series of laboratory tests and evaluates the effect of fly ash as an additive in improving the physical and engineering characteristics of an expansive soil. An experimental program has evaluated the effect of fly ash on the Atterberg limits, grain size distribution, specific grativity, activity, free swell index, swell potential, swelling pressure, axial shrinkage, compaction and unconfined compressive strength characteristics of expansive soil. The test results show that the plasticity index, activity, free swell index, swell potential, swelling pressure and axial shrinkage percent decreased with an increase in fly ash content. With the increase in the curing time, the swell potential and swelling pressure decreased. It is found that there is no remarkable change in the unconfined compressive strength of the soils immediately treated with fly ash. However, after 7 days curing of the fly ash treated soils, the unconfined compressive strength increased significantly.
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