Impact of elevated curing temperature on mechanical properties and microstructure of MgO‐based expansive additive cement mortars.

MgO‐based expansive additive (MEA) is uniquely used in China to compensate for the thermal shrinkage. For mass concrete, its inner temperature can soar up to 60°C due to the accumulation of hydration heat, which will strongly impact the mechanical properties and microstructures. In this paper, the impacts of elevated curing temperatures on the compressive strength developments, the tensile strengths as well as the pore structures of MEA cement mortars are investigated by means of X‐ray diffraction, scanning electron microscope, and mercury intrusion porosimetry. The results show that the external addition of MEA weakens, not eliminates, the crossover effect found in the temperature‐affected strength developments, which is mainly attributed to the accelerated expansion of MEA. For the tensile strength, the weakness of the crossover effect is found more obvious. The ratio of tensile to compressive strength is also positively correlated to the MEA content and the curing temperature. A scattered prestress effect is proposed to explain this phenomenon. The microcosmic evidence proves that the elevated temperature promotes the hydration of MEA and cement, and thereby improves the early‐age microstructures but impairs the late‐age one, which is generally consistent with the mechanical results. [ABSTRACT FROM AUTHOR]