Effects of Silica Fume on Heat Generation of Curing Concrete

Abstract

During the curing of concrete heat is generated from the chemical reactions in the concrete mixture. As heat accumulates within the concrete mass a substantial rise in temperature occurs. The heat dissipation through the concrete surface causes nonuniform temperature distribution leading to an uneven thermal expansion and contraction of the concrete mass. Internal restraint due to temperature difference within the concrete mass and external restraint due to rigid connections to movement restraints often induce tensile strains that are large enough to cause early thermal cracking. Currently, silica fume (SF) is quite commonly used for the production of high-performance concrete. The effects of SF on heat generation of curing concrete, however—especially in the presence of other pozzolanic materials such as fly ash (FA) and at different water-cementitious material ratios (w/cm)—are still not clearly known. To study the combined effects of SF and FA at different w/cm, concrete mixtures with SF replacement up to 10% are presented, FA replacement up to 20%, and w/cm ranging from 0.24 to 0.40 were produced for semi-adiabatic curing tests. Heat loss compensation was applied to determine the adiabatic temperature rises of the concrete mixtures. The test results revealed that (1) the heat generation per weight of cementitious materials is generally smaller at a lower w/cm; (2) within the range of parameters studied, SF replacement would reduce the amount of heat generation but increase the rate of heat generation; and (3) compared on an equal strength basis, 5 and 10% SF replacement would reduce the amount of heat generation by approximately 10% and 20%, respectively.