Abstract
In this study, the effect of high temperature history arising from the hydration heat on mechanical properties of concrete with low water-to-binder ratio was experimentally investigated. Cement paste and mortar specimens using Ordinary Portland cement, slag cement and fly ash cement were exposed to constant temperatures（20℃ and 80℃）and fictitious temperature rise at early age due to the hydration reaction under sealing conditions soon after casting. At an age of 28 days, mercury intrusion porosimetry test and compressive strength test were carried out for each specimen to compare different temperature histories and cement types. The compressive strength of cement paste with mineral admixture at 28 days of age was increased when it was exposed high temperature. It is attributed to the promotions of latent hydraulic reactions of slag and pozzolanic reaction of fly ash under high temperature. The mercury intrusion porosimetry test revealed denser porosity of cement paste exposed to high temperature than that of cement paste cured at 20℃. The compressive strength of mortar cured at 80℃ was reduced in all cement cases. It is speculated that the continuous high temperature exposure may make interfacial transition zone between cement paste and aggregate damaged due to the self-desiccation under high temperature. In addition, the compressive strength of mortar with high temperature rise at an early age was reduced at an age of 91 ages comparing to the strength at an age of 28 days in all cases. It is suggested that the strength of mortar with low water-to-binder ratio may be gradually decreased when it has a high temperature history at an early age.
