Effects of Accelerated Curing on Hydration Products of Cement and Cement-Fly Ash Pastes

Accelerated curing procedures are being used more and more frequently to obtain an estimate of concrete strength by testing accelerated specimens at ages ranging from 24 hr plus or minus 15 min, 28-1/2 hr plus or minus 15 min, or 48 to 96 hr, depending on whether the warm water, the boiling water, or the autogenous curing procedure standardized in ASTM C 684 is followed. Modifications of these procedures also exist. Good correlations between strength of early accelerated specimens and that of 28-day specimens offer the advantage of evaluating the strength level of the concrete within 1 to 4 days from the time of placement which provides economies in construction by giving early warning of unsatisfactory strength. We believe that in the future design strengths will be specified as accelerated strengths.