Physico-Mechanical Characterization of Kazakhstan Diatomite–Opacifier Geopolymers under Electrothermal and Conventional Curing

Focusing on sustainable construction materials, this study investigates the development of Geopolymer Composites (GCs) using Kazakhstan's abundant industrial by-products, including Fly Ash (FA), Slag (S), Diatomite (D), and Opacifier waste (OP). All precursors were sieved to below 90 µm to improve homogeneity and reactivity, and a 2:1 mass fraction binary alkali activator comprising 12M NaOH and Na2SiO3 was used at an Activator/Binder (A/B) ratio of 0.7, resulting in an Ms value of 3.29 and an estimated value for the water/binder ratio of about 0.28. Seven different GCs, ranging from single-phase mixtures containing only D and opaque to ternary combinations, were prepared and subjected to three curing regimes: ambient (23 ± 2 °C, 95% RH), thermal (80 °C for 24 h), and electrical curing (30-50V for 1-24 h). Compressive and flexural strength, capillarity, water absorption, and microstructural properties were evaluated. Electrical curing at 40 V in the 50S25FA25D series did not improve compressive strength compared with thermal curing at 80 °C; however, it improved flexural strength by approximately 13.5%, outperforming thermal curing and indicating enhanced tensile stress distribution and internal gel continuity. Although apparent porosity slightly increased by 2-3% and water absorption was 5-12% higher under electrical curing, these values remained within acceptable ranges. They were compensated by more uniform heat distribution and reduced the risk of thermal gradient cracking. The energy consumption required for electrical curing was more than 60% lower than thermal curing, making it significantly more sustainable and operationally more efficient.