Prediction model for internal relative humidity in early-age concrete under different curing humidity conditions

•The IRH in early-age HPC under different curing humidity conditions was investigated.•The moisture diffusion of early-age HPC under different curing humidity conditions was investigated.•A prediction model for IRH in early-age HPC considering the effect of curing humidity was proposed. The decrease of internal relative humidity (IRH) in early-age high performance concrete (HPC) may increase the autogenous shrinkage under the combined effects of self-desiccation and moisture diffusion. Correspondingly, the tensile stress induced by restrained shrinkage may cause premature cracking of HPC. Evaluating the cracking potential of concrete needs to know the development of autogenous shrinkage. The prediction of autogenous shrinkage requires quantitative analysis of the variations of IRH in HPC. Although the variations of IRH and prediction models for IRH in concrete have been studied, a prediction model for the IRH in HPC at early age based on experimental results considering the effect of curing humidity remains lacking. Thus, the critical time of IRH, IRH, IRH decrease rate, and the moisture diffusion coefficient of HPC under different curing humidity conditions were studied in this research. Experimental results and corresponding analysis demonstrated that: (1) the critical time of IRH in sealed HPC was longer than that in unsealed HPC under different curing humidity conditions, and the critical time of IRH in unsealed HPC increased as the curing humidity increased; (2) the IRH in unsealed HPC increased as the curing humidity increased at the same curing age; (3) the IRH decrease rate of sealed or unsealed HPC gradually decreased with the growth of age, and the IRH decrease rate of unsealed HPC decreased as the curing humidity increased at the same curing age; (4) the moisture diffusion coefficient of unsealed HPC was calculated, and the prediction model for IRH in HPC at early age under the combined effects of self-desiccation and moisture diffusion considering the effect of curing humidity was proposed.