Rajiv K N, Ramalinga Reddy Y

Abstract: The corrosion of steel reinforcement in concrete, often caused by carbonation and chloride ingress, poses a significant threat to the durability of reinforced concrete structures. The use of secondary treated wastewater (STW) in concrete has emerged as a sustainable alternative to potable water, though its residual contaminants—such as chlorides and dissolved solids—raise concerns about increased corrosion risk. This study investigates the corrosion behavior of M30-grade concrete made with STW, incorporating 10% fly ash as a partial cement replacement and sodium nitrite at 1%, 2%, and 3% (by cement weight) as a corrosion inhibitor. Using the half-cell potentiometer method in accordance with ASTM C876-15, corrosion activity was monitored over 14 months. Concrete specimens with 50 mm and 100 mm cover depths were prepared using STW from three Bangalore treatment plants: Bellandur, Jakkur, and Nagasandra. Results revealed that sodium nitrite, particularly at 1% and 2%, significantly reduced corrosion risk, with half-cell potentials remaining above -200 mV—indicating a low probability of corrosion. A 100 mm cover depth provided better protection than 50 mm. Despite initial corrosion susceptibility due to STW contaminants, the use of fly ash and inhibitors effectively mitigated the risk. By the end of the study, corrosion performance was comparable to concrete made with potable water, supporting STW’s feasibility in sustainable construction

Keywords: Secondary treated wastewater, Sodium nitrite, Fly ash, Durability, Half-cell potentiometer, reinforced concrete corrosion.

Date Published: November 25, 2025
DOI: 10.11159/ijci.2025.018

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