Prediction model for relative humidity of early-age internally cured concrete with pre-wetted lightweight aggregates

The decrease of internal relative humidity (IRH) in high-performance concrete (HPC) induces autogenous shrinkage, which is fundamental to evaluate the cracking resistance. Internal curing (IC) with pre-wetted lightweight aggregates (LWAs) is used to mitigate the shrinkage of HPC, and prediction of shrinkage of HPC requires knowledge of the IRH variations. Although investigations on IRH in concrete have been conducted, the prediction model for IRH in internally cured concrete with LWAs considering IC remains lacking. Experimental research and analysis on IRH in early-age concrete with pre-wetted LWAs were conducted. Test results show that: (1) the average value of IRH decrease rate in internally cured concrete with pre-wetted LWAs decreased nonlinearly with the increase of IC water-to-cement (w/c) ratio; (2) the prediction models for critical time and working w/c ratio were proposed; (3) a prediction model for the IRH in early-age internally cured concrete was proposed considering the working w/c ratio, critical time, and age. These models showed the good accuracy of the experimental results.