Impact of water-to-binder ratio on the physical, mechanical and durability-related performance of industrial waste-based one-part geopolymer concrete

The development of just-add-water geopolymer technology offers a sustainable alternative to conventional alkali-activated systems by eliminating the handling risks associated with corrosive alkaline solutions. This study investigates the effect of the water-to-binder (W/B) ratio on the fresh, mechanical, durability, and microstructural properties of a one-part geopolymer concrete (OPGC) produced using a binary blend of industrial by-products, namely Magnesium Slag (MS) and Ground Granulated Blast Furnace Slag (GGBS). Five mixtures with W/B ratios ranging from 0.42 to 0.60 were prepared using a binder composition of 30% MS and 70% GGBS activated by solid sodium metasilicate. The results show that increasing the W/B ratio significantly improves workability but leads to reductions in density and compressive strength beyond an optimum W/B ratio of 0.47, which achieved the highest 28-day compressive strength of 54 MPa. Durability results indicated that water absorption decreased as the W/B ratio approached the optimum level of 0.47, which promoted better matrix continuity and reduced pore connectivity. However, further increases in the W/B ratio led to higher capillary porosity and increased water absorption. High-temperature exposure at 600 °C and 900 °C revealed that mixtures with lower W/B ratios experienced greater relative strength degradation, while higher W/B mixtures retained comparatively higher residual strength. SEM observations confirmed the transition from a compact gel matrix at low W/B ratios to a more porous and heterogeneous structure at higher W/B ratios.