Influence of Early-Age Curing Regimes on Late-Age Hydration of UHPC

Abstract

Abstract This paper investigates the influence of metakaolin (MK) as well as various early-age curing regimes on late-age hydration of ultrahigh-performance concrete (UHPC) immersed in hot water. To reduce the consumption of cement, we partially substitute cement by limestone (LS) in the UHPC mixture. After 24 h of hardening, UHPC specimens are demolded and exposed to different curing regimes, including standard water curing at 20°C for up to 28 days as well as steam curing at 55°C or 90°C for 24 or 48 h followed by standard water curing for up to 28 days. Afterward, the UHPC mortar and paste specimens are transferred into the water at 80°C and left for predesigned testing ages (7, 14, 21, and 28 d). We evaluate the compressive strength of UHPC mortar as well as hydration and microstructural properties of UHPC paste with the analysis of chemically bound water, differential thermal analysis, and mercury intrusion porosimetry. The results indicate that the compressive strength of the UHPC has an increasing tendency from 28 to 42 days and then a decreasing tendency. The addition of MK alleviates the late-age strength development tendency of the steam-cured UHPC specimens compared with the control mixtures without MK. The hydration results verify this strength development tendency of UHPC from 28–56 days. The ternary MK- and LS-blended UHPC exhibits similar strength development tendency and microstructure with binary paste incorporated with MK at later ages.