Influence of curing temperature on hydration and microstructural development of ordinary Portland cement

The influence of curing temperature on hydration kinetics, phase assemblage, and strength development on ordinary Portland cement is investigated. Apart from three isothermal curing conditions, 10 °C, 27 °C and 50 °C, specimens were also exposed to a different temperature regimes by exposing them from lower temperature to higher temperature at later ages. While the hydration of belite appears to be significantly influenced by temperature in the long term, alite and ferrite are less affected. It was also observed that the degree of hydration of belite increases with a delay in high-temperature exposure at the initial days of hydration. The long-term degrees of hydration of the clinkers were seen to be similar irrespective of the curing temperature. However, a reduction in compressive strength was observed after curing at 50 °C which could be due to the formation of a high density of C-S-H on unhydrated clinker grains. The influence of sulphate content on this temperature effect was also investigated. It is found that the presence of additional gypsum can reduce the adverse effect of high-temperature exposure, possibly due to the formation of additional ettringite and subsequent reduction in ettringite conversion.