Evaluation of durability and microstructure evolution of chloride added fly ash and fly ash-GGBS based geopolymer concrete

Abstract

The evaluation of corrosion behaviour of rebar and changes in microstructure evolution in geopolymer concrete (GPC) in the presence of chloride ions form an important aspect of durability investigation. For this purpose, an experimental investigation was undertaken to examine the corrosion of reinforcing steel and changes in microstructure development of fly ash based geopolymer concrete (FGC) and fly ash-GGBS based geopolymer concrete (FSGC) containing chloride ions. Corrosion behaviour was evaluated through corrosion potential (Ecor) and corrosion current density (Icor) and microstructural changes of GPC were examined at various ages and that at rebar level by XRD, EDS, FTIR, and FESEM analyses. Test results revealed that chloride ions had significant influence on consistency, strength, and microstructure of GPC. NaCl improved the consistency of GPC mixes. FSGC mixes showed 38.1% to 114.2% higher strength than FGC mixes at all ages irrespective of NaCl concentration. Further, GPC mixes exhibited lower strength with increase in NaCl concentration at all ages. Rebar embedded in FSGC specimens exhibited mostly less negative Ecor and lower Icor compared to FGC specimens. Results of chloride analysis revealed lack of chloride binding in GPC mixes. Higher peak intensity of aluminosilicate gels and presence of C-S-H gel in FSGC mixes as identified from XRD analysis and higher atomic Ca/Si ratio in FSGC mixes obtained from EDS analysis confirmed the improved performance of FSGC mixes in terms of higher strength, lower corrosion activity and lower chloride content over FGC mixes.