Effect of Limestone Powder and Fine Gypsum on the Cracking Tendency of Blast-Furnace Slag Cement Concrete Subjected to Accelerated Curing

Thermal stresses are generated in concrete during the accelerated curing process in precast concrete. These stresses may cause concrete to crack, which would have a negative effect on the general concrete performance. This paper provides the results of the thermal stress analysis of concrete containing 25% replacement of ordinary Portland cement (OPC) by ground granulated blast-furnace slag cement (GGBFS) with 3000 cm²/g fineness. A total of 2.5% of limestone powder and 1.75% of fine gypsum by mass of OPC were incorporated in the other concrete mix proportion to check their effect on the cracking tendency of concrete. The concrete was subjected to heat curing. JCMAC, a 3D finite element analysis software developed in Japan, was used in this study for the thermal stress analysis. The heat curing period of one day, similar to generally used in the precast concrete industry for civil engineering products consisting of 3 h preheating period, heating to a peak temperature of 65 °C and this temperature was kept for 3 h, and lastly cooling was used in the study. A standard precast box culvert model member together with some experimental results obtained in the laboratory were used in the analysis. Lower cracking resistance at 1 day was observed in both mix proportions that would lead to cracking at demolding time. Curing sheets were then introduced in the analysis to cover the precast mold during accelerated curing and this showed improvement in cracking resistance of concrete containing limestone powder and fine gypsum.

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