Study on basic performance and drying shrinkage of binary solid waste geopolymer prepared with recycled powders and slag

The growth of construction industry has escalated demands on building material supplies, leading to the accumulation of construction waste. Addressing these issues, our study proposes a novel approach that utilizes alkali activation and slag solid waste to prepare binary geopolymer. This technique notably enhances the utilization of low-activity recycled powders, which are typically underutilized from construction waste. To validate its engineering applicability, we comprehensively examine how recycled powder content influences the properties of recycled powder-slag based geopolymers (RPSG), employing the critical factor of alkali equivalent for property regulation. Our research primarily focuses on investigating drying shrinkage behavior RPSG and elucidating the microstructure through XRD, TG, MIP, and SEM analyses. The experimental results indicate that the incorporation of RP, due to its higher water absorption and rougher particles, leads to a decrease in the workability of geopolymers. The presence of inert quartz and calcite in the RP also slows down the hydration reaction rate, resulting in a looser microstructure and increased porosity. This diminishes the mechanical properties of RPSG, and exacerbates drying shrinkage and mass loss. These effects become more pronounced with a mix proportion exceeding 30%. At a 40% mix proportion, the flowability of RPSG decreases by 15.5%, the 28-day compressive strength is reduced by 21.0%, and the drying shrinkage increases by 39.26%. Although raising the alkali equivalent can improve workability and mechanical properties, it also intensifies drying shrinkage and mass loss. An alkali equivalent of 5% yields the best overall performance. The study underscores the importance of maintaining RP content below 30% and selecting a suitable alkali equivalent to optimize RPSG's overall performance.