RS-AAT with distributed permeable pipes and alkaline water: Enhancing concrete durability through chloride reduction, pH optimization, and pore structure improvement

Reverse-seepage and Saturation based Active Anti-corrosion Technology (RS-AAT) is a novel and environmentally-friendly approach that enhances the ability of unsaturated concrete in marine alternating wetdry areas to resist chloride ion intrusion. Comprehending its influence on ions transport and the pore structure within the concrete is vital for assessing the rationality of the technique and further predicting its service life. In this study, cross-section specimens of cast in situ concrete piles with RS-AAT were exposed to a chloride wet-dry cycling environment for 150 days. Spatiotemporal variation patterns of chloride ion content, pore fluid pH, and pore structure in the concrete cover were investigated by free chloride titration, pH determination, and mercury intrusion porosimetry (MIP). The findings indicate that RS-AAT can effectively inhibit chloride ion intrusion into the protective layer of concrete. Moreover, implementing alkaline water in RS-AAT elevates the pore fluid pH and improves the compactness of the pore structure, especially diminishing the harmful pore ratio. Besides, increasing the number of distributed permeable pipes reinforces these effects and reduces the technology's dependence on water pressure. This insight demonstrates the viability of using alkaline water and distributed permeable pipes in RS-AAT to bolster the resistance of concrete structures to chloride ion erosion in an environmentally sustainable manner.