Relationship between internal relative humidity and autogenous shrinkage of early‐age concrete containing prewetted lightweight aggregates

Abstract Internal curing (IC) agents such as prewetted lightweight aggregates (LWAs) have been proved to be advantageous in reducing the autogenous shrinkage and early‐age cracking of concrete by introducing additional water. Quantitative analyses of internal relative humidity (IRH) of concrete are essential to better estimate the autogenous shrinkage of early‐age concrete. Existing studies investigate the IRH or autogenous shrinkage of early‐age concrete, respectively; however, the relevance between them of concrete containing prewetted LWAs remain lacking. Accordingly, the IRH, autogenous shrinkage, and the correlation between them for early‐age concrete with various LWAs replacement ratios were investigated. A noncontact device was utilized to measure the IRH and autogenous shrinkage of concrete simultaneously. Test results suggested that: (1) the absolute value of the maximum expansion increased from 0 με to 20, 50, and 96 με when the proportion of prewetted LWAs increased from 0% to 10%, 30%, and 50%, respectively; (2) compared with Mixture LWA00, the autogenous shrinkage at 28 days decreased by 14.7%, 36.3%, and 62.6% for Mixture LWA10, LWA30, and LWA50, respectively; (3) the IRH at 28 days or the critical time of IRH was 88.7%, 90.1%, 93.2%, and 95.9% RH or 5, 6, 8, and 10 days for Mixture LWA00, LWA10, LWA30, and LWA50, respectively; (4) a prediction model for the evaluation of the autogenous shrinkage was constructed based on IRH of early‐age concrete considering the quantity of IC water introduced by various replacement ratios of LWAs.