Evaluation of electrochemical behavior of steel in pore solution of geopolymer concrete and microstructural characteristics under aggressive environment, and correlating with geopolymerization process

This research investigation focused on evaluating corrosion behavior of steel in pore solution of geopolymer concrete (GeC) subjected to aggressive environment and correlating the variations in microstructure of GeC with geopolymerization process, and that in the microstructure of corrosion products of steel with corrosion behavior. The GeC mixtures were produced with fly ash and ground granulated blast furnace slag (GBS) at different molarity of NaOH solution. Electrochemical behavior of steel in electrolytic pore solution of GeC was evaluated by conducting linear polarisation resistance, and potentiodynamic polarisation measurements. Microstructural characteristics of GeC, and corrosion products formed on steel were also investigated. The obtained results of corrosion current density (i_corr) and passivity range of steel indicated higher extent of corrosion in GeC subjected to chloride exposure than those subjected to chloride plus sulphate exposure. Microstructural investigations showed comparatively compact microstructure in GeC subjected to chloride plus sulphate exposure than chloride exposure. The GeC subjected to 5 % NaCl + 5 % Na₂SO₄ solution showed more formation of binding gels i.e., N-A-S-H and C-S-H gels than 5 % NaCl + 5 % MgSO₄ solution as indicated by XRD analysis, which is supported by variation in compressive strength of GeC. Microstructural analysis of corrosion products of steel showed that formation of akaganeite was higher in GeC subjected to chloride exposure. The XPS analysis of corrosion products revealed that Fe^2 +/Fe³⁺ atomic (%) increased with GBS content and NaOH solution concentration. Furthermore, this ratio was lower in GeC subjected to chloride exposure than chloride plus sulphate exposure.