A comparative study of the performance of delithiated beta spodumene, fly ash and ground granulated blast furnace slag on the chloride and corrosion resistance of steam-cured concrete for precast culverts in saline environments

The performance of steam-cured concrete in high-chloride environments is influenced by several interacting material and exposure factors. The performance of newer supplementary cementitious materials (SCMs) such as Delithiated Beta Spodumene (DBS), under such conditions has not been widely researched. This study compared the chloride resistance and corrosion behaviour of reinforcing steel in steam-cured concrete incorporating commercial SCMs, such as Ground Granulated Blast Furnace Slag (GGBFS) and fly ash combined with DBS, an emerging SCM at a partial cement replacement level of 20%. Rapid chloride penetration tests (RCPT) were performed at 28, 90, and 180 days, and bulk diffusion tests were conducted under standard conditions of 165 g/L and 350 g/L NaCl exposure designed to accelerate the chloride concentration found in site soil and water samples. Accelerated corrosion tests using the impressed voltage method were analysed to evaluate the corrosion rate and electrical resistivity of the concrete specimens. X-ray diffraction (XRD) was performed on the concrete surrounding the reinforcement to identify chloride binding phases. The incorporation of SCMs was found to significantly reduce the ionic transport through concrete. The total charge passed at 180 days decreased by 18%, 39%, and 39% for GGBFS, FA, and DBS incorporated mix, respectively, while the apparent chloride diffusion coefficient decreased by 6–28% under standard and 6–40% under high salinity exposure after using the SCMs. The fly ash and DBS mixed concretes exhibited the lowest diffusivity across both conditions. Corrosion cracking was delayed in fly ash and DBS mixed concretes, initiating at weeks 14 (3.5% NaCl) and 6 and 5 (13.8% NaCl), compared with weeks 10 and 3 for the control and GGBFS mixes, respectively. Analysis of the test data showed substantially lower anodic current and higher electrical resistivity in the concretes using fly ash and DBS. Silver nitrate mapping confirmed lower free chloride in the fly ash and DBS mixed concretes, which was supported by the XRD peak intensity. The findings demonstrated that DBS provides chloride resistance comparable to fly ash and superior to GGBFS, indicating its suitability as a sustainable SCM for precast concrete.