Effects of secondary water curing on the long-term strengthand durability of concrete after steam-autoclave curing

To study the effects of secondary water(SW)curing of 20 ℃ for 7 d on concrete long-term strength and durability after steam-autoclave curing, concrete specimens were fabricated and subjected to standard, steam-autoclave or steam-autoclave + SW curing. The compressive strength, accelerated carbonation depth, and Coulomb electric charges of the specimens were tested at the ages of 28, 90, 180, and 360 d. Furthermore, mercury intrusion porosimetry experiments on the specimens were conducted at the age of 180 d. Results indicate that compared with standard curing, steam-autoclave curing can enhance the early-age strength of concrete; however, it is detrimental to the development of later-age strength, and reduces chloride and carbonation resistance. Due to the replenishment of water into concrete, SW curing can refine the micro-pore size and decrease the ratio of harmful and more harmful pores in concrete. As a result, SW curing is effective in improving the long-term strength and durability of steam-autoclaved concrete, and makes it approach that under standard curing. The improvement amplitudes of SW curing on the concrete compressive strength, chloride and carbonation resistance at 360 d can reach 20.3%, 48.6%, and 80.9%, respectively.