Evaluation on later-age performance of concrete subjected to early-age freeze–thaw damage

This research studies the influences of pre-curing time, the number and environment of early-age freeze–thaw damage (E-FTD) and later-age curing methods on later-age performance of concrete subjected to E-FTD. The concrete specimens with pre-curing time of 18 h, 24 h, 48 h and 72 h were subjected to four different E-FTD systems. Subsequently, three later-age curing methods were performed to the time of 28 days respectively and finally the later-age compressive strength, resistance to chloride penetration and freeze–thaw of concrete were evaluated. The results show that all three later-age performance indexes improve gradually as the pre-curing time prolongs. The damage of the salt freeze–thaw environment to early-age concrete is severer than that of the water freeze–thaw environment, resulting in the unsatisfactory later-age performance even with restorative curing. Among all later-age curing methods, the restoration effect of water curing on later-age performance is the best. Compared to the standard curing, the restoration effect of natural air curing on later-age compressive strength and resistance to chloride penetration of concrete is better, but that on resistance to freeze–thaw is worse. For the concrete with shorter pre-curing time, the recovery percentage of durability indexes, especially the resistance to freeze–thaw, is always lower than that of compressive strength. The pre-curing time should be prolonged appropriately for the early-age freeze–thaw damaged concrete with the requirement of durability.