Effects of ambient temperature and relative humidity on early-age shrinkage of UHPC with high-volume mineral admixtures

This study focuses on the early-age shrinkage of ultra-high performance concrete (UHPC) with high-volume mineral admixtures. Two low cement UHPC mixtures, which have similar compressive strength with control mixture, were obtained with high-volume ground granulated blast furnace slag (GGBFS) or fly ash (FA) replacements. The effects of exposure temperature on autogenous shrinkage of sealed specimens and drying shrinkage were studied at early-age (<24 h). Moreover, effect of relative humidity (RH) on early-age drying shrinkage was investigated at a constant temperature. As a result, the following five major conclusions can be drawn: (1) producing eco-friendly UHPCs, which have compressive strength of 150 MPa, with 50% GGBFS or 30% FA replacements is possible, (2) GGBFS replacement can lead to remarkable increase in both autogenous and drying shrinkage at early-age, (3) the use of high volume mineral admixtures may increase the sensitivity of UHPC to external RH, but can reduce temperature sensitivity in terms of shrinkage strain (4) an increase in superplasticizer demand due to FA replacement may trigger the formation of elephant skin under drying conditions, (5) elephant skin can reduce evaporation from the young UHPC, thus, reduce its sensitivity to arid conditions in terms of drying shrinkage.