Experimental investigation on inhibiting compounds against steel corrosion in concrete admixed with different chloride salts.

This experimental study reports the effect of internally admixed chloride salts and their associated cations on corrosion performance of sodium nitrite (NaNO₂) and di-sodium hydrogen phosphate (Na₂HPO₄) in concrete. The performance of corrosion inhibitors in chloride contaminated concrete was monitored by conducting corrosion tests on reinforced cylindrical members at regular intervals up to 854 days. Chloride analysis and microstructure analysis were performed on powder concrete samples collected from adjacent to the rebar surface of cylindrical members. Results indicated that NaNO₂ and Na₂HPO₄ increased the chloride binding of concrete thereby reducing the free chloride near rebar level. NaNO₂ was more capable in protecting the steel passivity than Na₂HPO₄. In most of the cases, chloride salt plus Na₂HPO₄ showed more corrosion activity than that in the concrete with only chloride salt. Further, NaCl showed higher corrosion activity than MgCl₂ and CaCl₂. Between MgCl₂ and CaCl₂, initially MgCl₂ exhibited higher corrosion activity than CaCl₂. However, at later ages, CaCl₂ showed more corrosion activity as compared to MgCl₂. The ordinary Portland cement (OPC) mixes showed better performance against steel reinforcement corrosion than Portland pozzolana cement (PPC) mixes. The XRD and FESEM analyses confirmed the formation of more amount of calcium chloroaluminate in the concrete admixed with corrosion inhibitor plus chloride salt than that admixed with only chloride salt. The XRD analysis indicated more formation of calcium oxychloride in the concrete added with MgCl₂ in comparison to CaCl₂, whereas the formation of calcium chloroaluminate was higher in CaCl₂ than MgCl₂. [ABSTRACT FROM AUTHOR]