Assessing structural integrity of fly ash-based geopolymers with different modifiers under microbial-induced corrosion in real-world environments

This study examines the use of geopolymers as repair materials resistant to microbial-induced corrosion (MIC) in real-world wastewater infrastructure conditions, addressing the gap in field data despite an abundance of laboratory tests completed. The research explores how various additives, including ground granulated blast furnace slag (GGBS), xanthan gum (XG), PVA fibres, and heavy metals, influence the durability of geopolymers. Carbonation was observed within 6–12 months of exposure, which facilitated microbial colonization and initiated MIC. This process led to significant mechanical degradation in certain mixtures after 26 months of exposure. Mixtures with higher GGBS content showed delayed onset of corrosion due to finer pore structures, but once MIC began, deterioration accelerated, likely due to the increased calcium availability in reaction gels, which dissolved rapidly under acid attack. Heavy metals such as zinc oxide (ZnO) were more prone to carbonation without notably improving MIC resistance, whereas copper proved more effective in inhibiting MIC. Mixtures containing fibers or XG performed poorly, likely due to higher porosity, which facilitated mass transfer through the matrix and accelerated degradation. The chemical and mechanical properties of the geopolymer mixtures, evaluated after 24 months of exposure through residual strength testing, XRD analysis, and FTIR spectroscopy, indicated that replacing 10% of fly ash with GGBS yielded the most effective MIC-resistant formulation. This study provides important insights into the application of geopolymers for repair in environments with high levels of hydrogen sulfide gas exposure.