Mechanism of chloride binding in alkali-activated materials exposed to combined chloride, sulfate and carbonation environment

Considering that concrete structures located in marine tidal and splash zones often suffer the most severe attack, the deterioration of cement (OPC) and alkali-activated materials (AAMs) under single chloride and combined attack of chloride, sulfate and carbonation was comparatively investigated. The results indicated that while OPC exhibits superior chloride binding compared to AAMs under single chloride exposure, narrowing significantly when subjected to combined attacks. Moreover, alkali-activated fly ash/slag (AAFS) demonstrated the highest chloride binding capacity. This performance was primarily attributed to the superior stability of the C-(N)-A-S-H gels, which exhibited better stability in adsorbing chloride. Additionally, the combined attack of carbonation and sulfate appeared to mitigate each other's detrimental impact on the gel structure. After 18 cycles of exposure in this study, the chloride binding coefficient of AAFS approached that of OPC, suggesting that the chloride binding capacity and stability of AAFS may be more superior in the long term.