Evaluation of Different Mix Parameters Related to Alkaline Activator on Microstructure and Rebar Corrosion Behavior of Chloride-Added Fly Ash–Based Geopolymer Concrete

This study delves into the effects of different mix parameters pertaining to the alkaline activator on the corrosion behavior of rebars and the microstructure evolution of fly ash–based geopolymer concrete (Fa-GpeC) when exposed to chloride ions, which play a crucial role in evaluating durability. The corrosion behavior of rebars was assessed by measuring the corrosion potential (Cpo) and corrosion current density (Icorr). In addition, microstructural changes were examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM) techniques. The findings reveal that in the presence of chloride ions, at different ages, although the variations in Cpo (corrosion potential) and Icorr of rebars in GpeC were mostly unsystematic with changes in NaOH molarity, there was a noticeable increase in the extent of corrosion at higher-alkaline solution and at higher sodium silicate–sodium hydroxide (SS/SH) ratios. The GpeC made with lower-molarity NaOH solution exhibited higher free chloride content (Cf) content near the rebar at 600 days when compared with higher-molarity NaOH solutions. The GpeC mixes made with lower-alkaline solution exhibited higher free chloride (Cf), total chloride (Ct), and bound chloride (Cb) content than those made with higher-alkaline solution content. The Fa-GpeC made with lower-alkaline solution and having a lower SS/SH ratio mostly showed higher peak intensity for geopolymeric compounds in the XRD patterns. The variations in the formation of microstructure as observed from the FESEM images of GpeC near rebar level in prismatic specimens with alkaline solution, SS/SH ratio, and admixed NaCl concentration align with the changes in peak intensity of geopolymer gel–related compounds in the XRD patterns of the GpeC mixes.