Durability of porous concrete incorporating recycled aggregates in coastal areas: Attack of chloride salt and oxalic acid

Porous concrete incorporating recycled aggregates (PCRA) is a promising material for sustainable coastal buffer strips. However, its long-term durability under tidal saline conditions and oxalate-rich environments remains insufficiently explored. This study evaluated the physico-chemical behavior of PCRA exposed to prolonged wetting–drying cycles in deionized water and chloride solutions for 360 days, and examined its strength and microstructural evolution during a 90-day immersion in oxalic acid. The results showed that, compared with specimens cured under identical conditions without exposure, PCRA subjected to wetting–drying cycles in chloride solution exhibited greater strength loss than those in deionized water. The deterioration was possibly related to the dissolution of portlandite and decalcification of the C-S-H phase caused by chloride, weakening the cementitious matrix. PCRA immersed in oxalic acid initially gained strength due to the precipitation of calcium oxalate but experienced gradual strength loss with prolonged exposure as hydration products were progressively consumed. These findings emphasize the importance of monitoring the concentration of oxalic acid and the duration of exposure in oxalate-rich environments to preserve material durability. Overall, this study provides critical insights into the deterioration mechanisms of PCRA and offers guidance for developing durable and sustainable materials for coastal protection applications.