Performance and deterioration mechanism of concrete incorporated with corrosion-inhibiting admixtures under the coupling effect of composite salt and freeze-thaw cycles

The purpose of this study is to provide multi-functional, green, low-carbon and environmental-friendly corrosion-inhibiting admixtures (CIA) to alleviate the deterioration of reinforced concrete under the coupling effect of composite salt and freeze-thaw cycles (FTCs). The effects of different contents of CIA on the performance of C30 concrete, including mechanical behavior (mass loss rate (MLR), compressive strength loss rate (CSLR) and relative dynamic elastic modulus (RDEM)), chloride ion penetration of concrete, and the electrochemical performance of rebars in concrete, were investigated. Furthermore, the deterioration mechanism of reinforced concrete was probed in detail by evaluating the pore structure parameters of concrete and the microscopic morphology of concrete and rebars via low-field nuclear magnetic resonance (NMR) and scanning electron microscope (SEM), respectively. The results showed that the mechanical behavior of concrete with CIA was prominently superior to that of concrete without CIA, with MLR decreased by 51.13–78.60%, CSLR decreased by 40.11–84.93%, and RDEM increased by 29.89–56.27% after 100 FTCs. The average content of free chloride ion in the concrete containing CIA was decreased by 12.14–55.65% under 100 FTCs due to the addition of CIA reducing the transmission path and the percentage of much detrimental pores (decreased by 39.03–85.99% after 100 FTCs). The correlation between free chloride ion content and diffusion depth conformed to Fick's second law, showing that there was a linear positive correlation between chloride diffusion coefficient (D) and FTCs. In addition, the electrochemical performance of rebars in concrete with CIA was improved owing to the good protection of CIA to rebars. This study is of great significance for improving the durability of reinforced concrete in harsh environment.