Effect of desiccation on the geotechnical properties of lime-fly ash stabilized collapsible residual sand

Berea Red Sands underlying most of the Kwazulu Natal midlands and coastal plain is a very recent unconsolidated, weakly cemented red to brown, collapsible sands. The effect of wetting and drying cycles on the Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) of compacted and cured samples of stabilized Berea Sands was investigated. Different sample mix were prepared with 4% and 8% Lime and 0%, 6% 12% and 18% Fly Ash, and tested after 4, 8 and 12 cycles of wetting and drying. Changes in mass of the stabilized sands were measured to facilitate the interpretation of changes in strength properties. The results showed reduction in UCS and CBR with increase in the number of wetting and drying cycles that is dependent on the amount of Lime and Fly Ash and the ratio of Lime to Fly Ash. For given amount of Fly Ash, samples stabilized with 8% Lime are more durable than samples stabilized with 4% Lime. For samples stabilized with 8% Lime, increase in Fly Ash quantities results in an increase in durability for up to 18% Fly Ash used in this research. The process of wetting and drying results in general reduction in the mass of the test samples, and the percentage reduction in mass decreases with increase in quantities of Fly Ash. In the long term, defined by 12 cycles of wetting and drying, only the 8% lime and 18% fly ash material have adequate CBR under the operative drainage conditions to sustain the stresses applied by traffic loadings.