Long-term corrosion behavior of reinforced recycled aggregate concrete under acid rain condition

The corrosion resistance of reinforced concrete (RC) is critical for long-term durability, particularly in recycled aggregate concrete (RAC) exposed to sulfate attacks. To enhance knowledge about anti-corrosion measures in concrete structures and optimize RAC mix proportions, this study evaluates the corrosion resistance of RAC at early age, mid-term, and long-term stages (28, 90, 180, 365, and 730 days) with varying percentages of coarse recycled concrete aggregate (RCA) replacement (0%, 50%, and 100%) and different dosages of nano-silica (NS). The RAC specimens were subjected to acid rain simulation and immersion in acidic solution. The results indicated that Half-cell potential decreased by ~300–400 mV in RAC under acid rain simulation, exceeding reductions in submerged acidic solutions. This disparity was linked to higher oxygen exposure during acid rain’s drying-wetting cycles. NS mitigated corrosion, preserving half-cell potentials closer to neutral conditions. Additionally, compressive strength (CS) of RAC declined by 28 to 49% at pH 2.5 to 5.5 after 730 days, with pH 2.5 causing the most severe degradation. Conversely, neutral conditions (pH 7) increased strength by ~15%, attributed to curing effects. NS enhanced strength retention, particularly in specimens with 50% RCA. Prolonged exposure to acidic conditions led to increased porosity in all RAC specimens, which consequently caused a decline in electrical resistivity (ER) by 30–50%, and increase in sorptivity coefficient (SC) by 40–60%. Scanning electron microscopy (SEM) analysis revealed that the addition of NS significantly improved the corrosion resistance of RAC.