| Summary: | This paper aims to compare the strength behaviour of demolished concrete material (DCM) and ordinary Portland cement (OPC) in addition to coal ash for stabilizing marine clay, thus determining the optimum mix. Coal ash with different ratio of bottom ash (BA) and fly ash (FA) were prepared at various percentages (i.e. 3%, 6% and 8%). In addition, limited amount of DCM and OPC of 2% was added at different curing periods of 0, 7 and 28 days respectively. Thus, the percentage of admixture added to the marine clay were 5%, 8% and 10% respectively. Unconfined compressive strength (UCS) test was done and the results revealed that the strength of treated marine clay soil increased significantly with increment percentage of coal ash and also for both DCM and OPC. For admixture with OPC, treated marine clay with 5% admixture shows the highest strength gained, while the effective combination between bottom ash and fly ash is 50:50. At the first 7 days the strength gain was very high but from 7 days to 28 days the gain of strength was reduced. While for DCM, 5% of additive at 30BA:70FA shows the highest strength. In addition, both OPC and DCM provide significant strength gained between 0-7 days and decrease for 7-28 days. In conclusion, when comparing both stabilizer, OPC is a much more efficient secondary stabilizer when reacted with coal ash. As it provide early gain in strength with a much higher strength.
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