Influence of modified montmorillonite on the passive state stability of reinforcing steel in chloride-containing concrete pore solution

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Abstract
Environmentally friendly anticorrosion additive based on the natural mineral montmorillonite enriched with calcium cations were obtained by liquid-phase ion exchange. It was established that the degree of enrichment of the mineral with calcium cations exceeded 3 wt% and depended on the concentration of the calcium acetate solution. Electrochemical methods established that the addition of the modified mineral (2 g/l) into a model chloride-containing porous concrete solution (pH=12) provided an inhibitory efficiency of steel protection used in almost 95% production of reinforcement. The protection mechanism is based on the controlled release of calcium cations, which maintains high alkalinity of the surface layer and promotes the formation of a dense passive film on the steel surface. According to SEM/EDX analysis, the presence of the additive reduces the chloride content on the steel surface from 3.5 to 0.07 wt%, preventing pitting. The results obtained confirm the prospects of calcium-enriched montmorillonite as an additive to the concrete mix to prolong the service life of reinforced concrete structures in aggressive conditions.

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