Heat damage of concrete surfaces under steam curing and improvement measures

•The heat damage effect of steam curing for concrete was explained.•It provides a concrete and feasible way to alleviate heat damage.•The sorptivity coefficient was used to quantitatively characterize the heat damage. Steam curing is commonly used in the production of prefabricated elements in China. However, this curing regime has proven to have an adverse effect on the long-term performance of concrete due to heat damage effects. Steam curing (60 ℃) were compared with standard curing (20 ℃ and 90% RH), and the temperature field inside the cement pastes under two curing regimes was tested by a temperature sensor. The effects of the precuring time, water-binder ratio, surface treatment methods, mineral admixtures, forming process, and subsequent curing conditions on heat damage of steam-cured concrete were examined by capillary water absorption, pore structure and microstructure. The results indicate that there are obvious pore gradients and microstructure differences of hydration products in the surface and interior of steam-cured concrete, and the sorptivity coefficient of the surface is also higher than the internal. Prolonging the precuring time can achieve high early resistance, and surface treatment can reduce the interconnected porosity of the exposed surface. Moreover, concrete mixed with mineral admixtures can delay the hydration process of the cementitious component, which is also beneficial to reduce heat damage. The higher stiffness of the steel mold can offset part of the internal stress, which reduces the sorptivity coefficient of the steam-cured concrete. In addition, appropriate subsequent curing conditions are necessary for steam-cured concrete.