Mitigating Strength Loss in Geopolymers in Low-Temperature Environments by Sodium Nitrite Addition

Geopolymer binders are a promising low-carbon substitute for Portland cement, but their behavior in cold climates remains underexplored. This study investigates the influence of sodium nitrite (NaNO₂) on geopolymer properties cured at -10 °C for 28 days. The binders were formulated from bauxite residue, fly ash, and waste glass, and NaNO₂ was added in various dosages as a chemical admixture. The geopolymer was tested for its setting time, compressive strength, and chemical and morphological characterizations. The addition of the 3 wt% NaNO₂ significantly improved the strength retention in the cold environment, with a compressive strength of 40.7 MPa, compared to a geopolymer without an admixture (26.1 MPa). The X-ray diffraction (XRD) analysis confirmed the presence of gismondine, quartz, and FeSiO₃, with NaNO₂ remaining largely unreacted within the matrix. Fourier Transform Infrared Spectroscopy (FTIR) indicated the presence of Si-O-T bonds in the NaNO₂-modified samples, which showed continued geopolymerization at low temperatures. Scanning electron microscopy (SEM) revealed reduced cracking and a denser microstructure with increasing concentrations of NaNO₂. The results indicate that NaNO₂ not only mitigates the adverse effects of subzero curing but also promotes structure development, and hence it is a viable admixture for enhancing the cold weather durability of geopolymer materials.