Effect of cement and fly-ash on the geotechnical properties of expansive clay soils

The study analyses the effects of two chemical agents - cement and fly ash - in changing the swelling potential and the strength parameters of an expansive clay soil collected from Currila area in the city of Durrës, Albania. The results obtained show a significant reduction of the plasticity index, with the addition of 3% cement and the combination of 3.5% cement with 8% fly-ash for a curing period for 1, 24 and 48 hours. The agglomerations formed after the reaction with the additives, changed the particle size and plastic behaviour of the soil from clay to silt of high plasticity, and the compaction curve shifted from a bell-shaped one into a flat shape. The swelling potential decreased to zero, as observed for curing periods of 7 and 28 days, reducing the swelling pressure from 70, to 30, to 0 kPa and the change in volume due to settlement to a mere 0.15mm for a 20mm initial height. The unconfined compressive strength increased by a factor of 1.52 and 2.22 with the addition of 3.5C-8FA for a 7-day and 28-day curing period, respectively.