Synergetic effects of curing temperature and hydration reactivity of MgO expansive agents on their hydration and expansion behaviours in cement pastes

Effects of curing temperature on the hydration and expansion behaviours of MgO expansive agents with different reactivities in cement pastes were investigated via quantitative examination on the hydration degree of MgO, expansion, and microstructure of the cement pastes cured under various temperatures. Results reveal that reactive MgO with a reactivity value of 65 s (represented as MEA-R) produces more rapid and greater expansions than the less reactive MgO with a reactivity value of 145 s (MEA-M) at early age (within 28 d) and less expansions at late age under 20 degrees C. However, under higher temperatures (20 degrees C-80 degrees C) or at late age, the MEA-M produces larger expansions. The curing temperature has a synergetic influence on the hydration and expansion of cement pastes containing MgO expansive agents. MEA-M is more sensitive to the curing temperature as more considerable differences are caused among the expansions of cement pastes cured under different temperatures. (C) 2019 Elsevier Ltd. All rights reserved.