The long-term performance of two fly ash stabilized fine-grained soil subbases

An experimental study was conducted to investigate the long-term performance of fly ash stabilized two fine-grained soil subbases. One low plasticity clay soil and one high plasticity expansive clay soil were stabilized with a Class C fly ash with fly ash contents of 0%, 5%, 10%, and 20%, and compacted statically at the maximum dry density (standard Proctor) and at the optimum moisture content of the corresponding soil to prepare ten sets of replicates from each of the combinations. After curing all specimens for 7 days, the first set was subjected to plasticity index tests, unconfined compression tests, and vertical swell tests to estimate the improvement due to stabilization. Similar tests were also conducted on another nine sets of replicates in which six sets were subjected to 12 wet–dry cycles (three sets with tap water and the other three sets with saline water), and the other three sets were subjected to 12 freeze–thaw cycles in a laboratory controlled environment to simulate the weathering action. The effect of wet–dry cycles on stabilized soils was essentially insignificant; however, the fly ash stabilized soils lost up to 40% of the strength due to freeze–thaw cycles. Even after losing the strength significantly, the strength of stabilized soils was at least three times higher than that of the unstabilized soils. The swell potential of stabilized expansive soils also increased due to freeze–thaw cycles. The vertical swell increases rapidly for first four to five cycles and then increases very slowly.