Experimental study and prediction model for non-uniform shrinkage of recycled aggregate concrete in composite slabs

Abstract

This paper investigates the influence of coarse recycled aggregate (CRA) on the non-uniform shrinkage of concrete with a single surface exposed to the air. A 210 d experiment was conducted on 17 slabs made with recycled aggregate concrete (RAC), measuring the shrinkage strain distribution through the slab depth. The parameters considered included the replacement ratios of CRA, slab depths, and the moisture-transferring boundary conditions (MTBC). The internal relative humidity distribution through the slab depth was monitored to verify the reasonableness of the occurrence of the non-uniform shrinkage. Based on the test results, a prediction model for the non-uniform shrinkage of RAC with a single surface exposed to the air was established and validated. Based on the age-adjusted modulus method, a cross-sectional analysis was conducted on the long-term strains of composite slabs using the proposed model. The investigation results indicated that (1) the incorporation of recycled aggregate significantly increased the shrinkage gradient by 84%−102%; (2) the influence of recycled aggregate on the shrinkage distribution of single-surface exposed concrete increased with a decrease in slab depth; and (3) the proposed equations can accurately predict the non-uniform shrinkage of single-surface exposed RAC.