Synergistic corrosion inhibition of steel reinforcement in concrete using calcined clay pozzolan and Acacia leaf extract

Chloride-induced corrosion of steel reinforcement is a major durability concern for reinforced concrete structures exposed to marine and de-icing environments This study evaluated the synergistic corrosion inhibition of calcined clay pozzolan cement (CPC) combined with acacia leaf extract in reinforced concrete. Specimens with partial OPC replacement by CPC and varying extract dosages were exposed to 3% and 5% NaCl for 28 days. Corrosion was assessed using potentiodynamic polarization, supported by XRD and FTIR. The combined CPC and extract significantly reduced corrosion current density versus OPC controls and mixes with individual additives. The most consistent 28-day accelerated performance occurred with 20% CPC and 2% extract, yielding rates of 1.0±0.1 mpy in 3% NaCl and 3.0±0.3 mpy in 5% NaCl, corresponding to 97.1% and 95.4% inhibition efficiencies, respectively. Higher extract dosages did not consistently improve performance and exhibited instability under 5% NaCl exposure. Hence, 2% extract is recommended as the most reliable dosage under the tested conditions. These findings demonstrate that coupling supplementary cementitious materials with plant-based inhibitors offers a promising, environmentally benign strategy for mitigating steel corrosion in reinforced concrete.