Development of microstructures in plain cement pastes hydrated at different temperatures

Various methods have shown indirectly that insufficient time for diffusion of the hydration products and the large pores that form as a result are responsible for the reduction in strength of concretes cured at elevated temperatures. backscattered electron imaging provides a direct means of examining the uniformity of diffusion. This paper describes an examination of the developing microstructure of cement pastes hydrated at 5–50°C. In accordance with the indirect evidence developed previously, the investigation shows that low curing temperatures result in a uniform distribution of hydration products, while elevated temperatures result in a coarsened pore structure. Specimens cured under variable-temperature regimes show some features typical of both initial and final curing temperatures. Compressive strengths of companion mortar specimens are consistent with the observed pore structure of the pastes.