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

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 mu epsilon to 20, 50, and 96 mu epsilon 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.