Compaction and strength of Lime - Fly ash stabilized collapsible residual sand

Berea Red Sands are weakly bonded residual collapsible sands underlying significant portions of the west coastal plain of South Africa. Freshly quartered samples of Berea Sand mixed with 4% and 8% Lime as stabilizers and 0%, 6%, 12% and 18% Fly Ash as additive by weight of the dry soil, were compacted and cured for 7 days, 28 days and 56 days. At different stages of curing, some samples were tested to determine their Unconfined Compression Strength (UCS) and California Bearing Ratio (CBR). Similar but limited number of tests were conducted on visually identical, commercially used reconstituted road fill materials. The stabilization of Berea Sand with Lime and Fly Ash results in significant improvement on the strength and bearing properties. Marginal difference in the magnitude of UCS and CBR of the 4% Lime and 8% Lime mixes for percent Fly Ash up to 12% for the 7 days curing period was indicated. Further addition of Fly ash result in lower strength of 4% Lime mixes and marginal increase in the strength of 8% Lime mixes over the extended curing period. The max UCS of Lime stabilized Berea Sand is however significantly lower than the UCS of Lime stabilized reconstituted road fill materials due to different particle and mineralogical constitution and thus may only be suitable for recompacted subgrades and sub base of low level municipal road projects.