Accuracy of maturity functions’ strength estimates for fly ash concretes cured at elevated temperatures

The effect of elevated curing temperature on the strength development of concrete mixes with fly ash (FA) has been investigated for strength grades C32/40 and C55/67. Percentages of fly ash in the total binder were 15, 30 and 45 per cent. High curing temperatures have a beneficial effect on the early age strength but a detrimental effect on the long-term strength development. Fly ash concrete mixes have been shown to be less sensitive to curing at high temperatures than Portland cement (PC) concretes and this was reflected in their lower “apparent” activation energies. The accuracy of strength estimates obtained from maturity functions was examined. The temperature dependence of the Nurse-Saul function, i.e. the concrete strength gain rate varies linearly with temperature, was not sufficient to account for the improvement in early age strengths resulting from high curing temperatures. The Arrhenius 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 overestimate long term strengths as neither accounts for the detrimental effect of high curing temperatures on the ultimate compressive strength.