Experimental study and prediction model for autogenous shrinkage of recycled aggregate concrete with recycled coarse aggregate

This study intends to propose a new model for estimating the autogenous shrinkage of recycled aggregate concrete (RAC) with recycled coarse aggregate (RCA). To this end, two groups of RCAs were selected to prepare RAC samples with different RCA substitution levels and water-to-cement (w/c) ratios. The autogenous shrinkage was monitored on 22 specimens for 8 months. Results indicate that the final autogenous shrinkage was influenced both by the internal curing effects induced by the absorbed water of RCA and by the RCA stiffness loss caused by the adhered residual mortar. Compared with the autogenous shrinkage of natural aggregate concrete (NAC), RAC with 100% RCA under saturated surface-dry condition exhibited 46.3%–65.8% smaller autogenous shrinkage for w/c ratios of 0.30–0.60; while a 26.8% increment was obtained from the literature for the autogenous shrinkage of RAC with 100% oven-dried RAC. Larger autogenous shrinkage development at earlier days was observed in RAC compared with NAC, as RAC had larger total w/c ratios. Based on available test data, a prediction model was theoretically developed for RAC, considering the influences of RCA content, residual mortar content, and moisture state. The model is capable of predicting well the autogenous shrinkage of RAC, which will bring new meaningful findings and strong adaptability.