Study on mechanical properties and mix ratio optimization of granulated blast furnace slag based composite materials for solidifying inorganic softened sludge from power plants

This study addresses the challenges of solidifying high-moisture, high-alkalinity inorganic softening sludge (ISS) by utilizing alkali-activated slag-based cementitious materials. The research investigated strength evolution via unconfined compressive strength tests, while X-ray diffraction and scanning electron microscopy were employed to analyze phase composition and microstructural changes. Furthermore, response surface methodology was utilized to optimize mix proportions and explore interaction mechanisms. Results indicate that granulated blast furnace slag is the primary strength contributor, whereas fly ash and sodium silicate exhibit nonlinear effects. Microscopic analysis reveals that changes in raw material ratios influence strength development by regulating the formation of products such as calcium aluminosilicate hydrate (C-A-S-H) and sodium aluminosilicate hydrate (N-A-S-H). Optimization results from response surface methodology show that, when sodium hydroxide dosage is fixed at 2.5%, the optimal dosages for granulated blast furnace slag, fly ash, and sodium silicate are 30.65%, 29.98%, and 6.96%, respectively, achieving a 7-day unconfined compressive strength of 5.38 MPa. Furthermore, significant interactions exist between granulated blast furnace slag and fly ash, as well as between fly ash and sodium silicate. This study provides a theoretical basis for the resource utilization of ISS in road base materials.