EFFECT OF CEMENT REPLACEMENT BY FLY ASH AND FGD GYPSUM ON STRENGTH OF SUBBASE
Keywords:Fly ash, FGD gypsum, Soil improvement, Compressive strength, Subbase
The using of Portland cement as an admixture to improve the strength of poor subbase induce
a high cost for road construction. The replacement of cement with by-product materials from Mae Moh power
plant in the admixture is a good alternative to reduce the amount of cement and cost for subbase improvement.
Therefore, this study focused on fly ash and FGD gypsum replaced cement in the admixture. The soil samples
mixed with the admixture at 3% were conducted on unconfined compressive strength test to determine the
strength of soil improvement. The results demonstrated that the replacement of cement by fly ash at 1.5% and
FGD gypsum at 0.5% is the optimum content to replace cement in the admixture. This mixture can develop the
strength more than the requirements recommended by the Thailand Department of Highways. Moreover, soil
mixed with cement at 2% and FGD gypsum at 1% can develop the strength near the soil mixed with cement at
3%. Soil mixed with cement at 2% and fly ash at 1% can increase the strength 29% from soil mixed with
cement at 3%. The results illustrated that the strength of soil improvement tended to increase with the increase
of fly ash. However, the strength of soil improvement decreased with the increase of FGD gypsum in the
admixture. In conclusion, the partial replacement of cement by fly ash and FGD gypsum can develop the
strength of soils and reduce the amount of cement in the admixture.