Coupled effects of the freeze-thaw cycles and salt erosion on the performance of recycled aggregate concrete

This study investigates the deterioration of RAC subjected to the combined action of chloride penetration and freeze-thaw cycles (SFT cycles). The effects of replacement rates (0 %, 50 %, and 100 % by mass, namely R0, R50, and R100) of recycled coarse aggregate (RCA) and the number of freeze-thaw cycles on the compressive strength and frost resistance of RAC were explored. Based on Isaac Newton's law of material cooling and the RDEM degradation model, the damage model of RAC under freeze-thaw cycles was proposed. The microstructural evolution in RAC after freeze-thaw cycles were characterized by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results indicate that after 75 cycles of water freeze-thaw (WFT) and SFT actions, the compressive strength of R100 was decreased by 41.98 % and by 77.35 %, while that of R0 was reduced by 16.26 % and 36.51 %, respectively. As the SFT cycles continues, both the number and width of cracks as well as the proportion of harmful pores significantly increase, compared to WFT cycles. The correlation degree of the freeze-thaw damage evolution model exceeded 0.9, confirming the rationality and accuracy of this developed model. These testing results could provide several theoretical supports for the broader application of RAC in harsh environments.