Abstract 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.
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