Effect of temperature on the strength development of mortar mixes with GGBS and fly ash

The concrete mixes used in this study had 28 d mean strengths of 50 and 30 MPa and also had Portland cement (PC) partially replaced with ground granulated blastQ-furnace slag (GGBS) and fly ash (FA). These mixes were the same as those used in a UKQ-based project that involved casting of blocks, walls and slabs. The strength development of 'equivalent' mortar mixes was determined in the laboratory for curing temperatures of 10, 20, 30, 40 and 50 degrees C. High curing temperatures were found to have a beneficial effect on the earlyQ-age strength, but a detrimental effect on the longQ-term strength. GGBS was found to be more sensitive to high curing temperatures than PC and FA, as reflected in its higher 'apparent' activation energy. The accuracy of strength estimates obtained from maturity functions was examined. The temperature dependence of the NurseQ-Saul function (i.e. concrete strength gain rate varies linearly with temperature) was not sufficient to account for the improvement in earlyQ-age strengths resulting from high curing temperatures. The ArrheniusQ-based function, on the other hand, overestimated them because of the detrimental effect of high curing temperature on strength starting from a very early age. Both functions overestimated the longQ-term strengths, as neither function accounts for the detrimental effect of high curing temperatures on the ultimate compressive strength.