Abstract
The objective of this study is to estimate the mechanisms of strength development in cement pastes cured first at high temperatures and then in water at a room temperature of 20℃. In this study, pastes of ordinary Portland cement (OPC) and blended cement (containing 40% ground granulated blast furnace slag; BB) were used, and changes in microstructure were examined using backscattered electron images, while hydration
products forming around cement grains were determined by EDX. Large voids called "hollow shells" were formed in the OPC pastes during the heat curing, and hydration products precipitated within the hollow shells during the subsequent curing in water. These voids partly remained unfilled; which was likely to be the cause of lower strength of cement pastes cured at high temperatures than that of those cured at 20℃. The formation of rims observed around cement grains in the OPC pastes was suppressed in the BB pastes during the heat curing. This resulted in less formation of hollow shells, and the voids were further reduced during the subsequent curing in water at 20℃ because the continued reaction of slag contained in the BB pastes allowed the hydrates to fill them. Consequently, higher strength gain was achieved in BB pastes cured first at high temperatures and then in water as compared to the OPC pastes.
