Abstract
The present study focuses on evaluating influence of calcium sulfate dihydrate (CaSO4.2H2O) as a chemical activator on compressive strength of hardened pastes containing fly ash and cement as cementitious materials. A high amount of Class-F fly ash used to replace Portland cement ranged from 85 to 93% by mass of cementitious materials. For all the pastes, a low water-to-cementitious materials ratio of 0.20 was prepared. The amounts of CaSO4.2H2O added to the mixtures were 0.0, 1.5, 2.0, and 2.5% by mass of cementitious materials. Experimental results showed that at the age of 3 days, the compressive strength of hardened paste specimens using CaSO4.2H2O was higher 1.21–2.15 times than that of the control paste specimen without CaSO4.2H2O. At the age of 7 days, the compressive strength of hardened paste specimens using CaSO4.2H2O still continued to be higher 1.03–2.06 times than that of the control paste specimen without CaSO4.2H2O. At the ages of 14 and 28 days, the compressive strength of hardened paste specimens using CaSO4.2H2O was approximately equal to that of the control paste specimen without CaSO4.2H2O. Consequently, the addition of CaSO4.2H2O improved the early-age compressive strengths of the fly ash-cement pastes, and the CaSO4.2H2O content of 2.0% by mass of the cementitious materials was effective in increasing the compressive strength of such pastes.
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