Role of slag in strength, microstructure, and rebar corrosion in chloride-rich geopolymer concrete

This study investigates the role of slag substitution (0%, 30%, and 60%), and chloride concentration (1.5% and 3.5% NaCl) on microstructural changes during strength development between 28 and 360 days, rebar corrosion up to 600 days, and chloride binding behaviour in chloride-rich geopolymer concrete (GC). The microstructural changes of GC were evaluated through field-emission-scanning-electron-microscopy (FESEM), energy-dispersive-X-ray-spectroscopy (EDS), X-ray-diffraction (XRD), and Fourier-transform-infrared-spectroscopy (FTIR) analyses. The obtained results indicated that strength enhancement was higher for fly ash-GC (F-GC) mixes. The presence of chloride in GC mixes caused strength reduction at all ages, however, fly ash/slag-GC (F/S-GC) mixes made with higher slag mostly showed lower strength reduction than other mixes. Further, F/S-GC mixes made with higher slag exhibited less negative corrosion potential (Ecor) and lower corrosion current density (Icor) than other mixes, indicating better resistance against rebar corrosion. Chloride binding capacity was mostly higher for GC mixes made with higher slag content. Higher amount of Ca-bearing gels and higher atomic Ca/Si ratio in F/S-GC mixes were responsible for reducing the influence of chloride in strength reduction and rebar corrosion, when compared with F-GC mix. The shifting of Si-O-Si(Al) bond to lower wavenumber indicated more binding gel formation, thereby denser microstructure in F/S-GC mixes.