Early-age shrinkage development of ultra-high-performance concrete under heat curing treatment

Abstract

The effects of a novel heat curing regime and longitudinal reinforcement ratio on early-age shrinkage of ultra-high performance concrete (UHPC) were experimentally investigated in this study. The microstructure, porosity and calcium hydroxide (CH) content of UHPC after different heat curing durations were characterized with scanning electron microscopy, mercury intrusion porosimetry and thermal analysis. The results indicate that slight shrinkage was observed when the heat curing duration was less than 60min and curing temperature reached 48°C. However, when the heat curing duration approached 70min and curing temperature was around 55°C, the early-age shrinkage increased dramatically. It was found that the early-age shrinkage is approximately 450με after 48h of heat curing. The results also show that the early-age shrinkage of UHPC significantly decreased by percentage of 33–60% with the increase of longitudinal steel reinforcement ratio from 2.0 to 4.52%. Meantime, after 10h of heat curing, the cement hydration and secondary hydration in UHPC tend to finish, which consequently leads to dense microstructure and low CH content in UHPC.