Abstract: To address the challenges of solid waste disposal and utilization, this study employed solid sodium silicate to activate a binary precursor system (comprising slag and fly ash) for synthesizing geopolymers. These geopolymers were then used to stabilize sludge with an 80% moisture content, transforming it into recycled fine aggregate for geotechnical engineering applications, such as railways and roads. The research initially examined the effects of precursor proportions, precursor content, sodium silicate molar ratio, and sodium silicate concentration on the unconfined compressive strength, splitting tensile strength, and electrical resistivity of the stabilized sludge (aggregate matrix). Subsequently, confined compression tests were conducted to evaluate the compressive properties of the recycled fine aggregate, considering the influence of these factors. Afterwards the relationship between the physical and mechanical properties of the aggregate matrix and the compressive characteristics of fine aggregates was established. The results demonstrate that precursor proportions, content, molar ratio, and concentration significantly affect both the physical and mechanical properties of the matrix and the compressive performance of the aggregate. There is an optimal range for these parameters: when the precursor consists of 90% slag and 10% fly ash, the precursor content is 30%, the sodium silicate molar ratio is 0.8, and the concentration is 1.8 mol/L, the matrix achieves its maximum unconfined compressive strength, splitting tensile strength, and electrical resistivity. Under these conditions, the fine aggregate exhibits the lowest initial strain rate under confined compression, the smallest final strain, and the highest yield strength. Furthermore, the physical and mechanical properties of the matrix are positively correlated in a nonlinear manner with the yield strength of the aggregate. This suggests that the aggregate not only inherits the physical and mechanical characteristics of the matrix but also retains the matrix’s pore structure. This study demonstrates how controlling the properties of the aggregate matrix can improve the geotechnical properties of the aggregates, thereby enhancing the resource utilization potential of solid waste in geotechnical engineering. It also offers new approaches for achieving sludge reduction, stabilization, harmlessness, and resource recycling.

Key words: geopolymer, sludge, aggregate matrix, physical and mechanical properties, recycled fine aggregate, compression properties