Bing Bai

With continued urbanization and industrialization, contamination by heavy metals (HMs) and metalloids has become an increasingly prominent environmental concern. These pollutants persist in the env...

While standard desulfurization gypsum is widely utilized, the application of long-term stockpiled inferior desulfurization gypsum remains limited due to its inherent compositional instability. To bridge this research gap, this study investigated the feasibility of utilizing inferior desulfurization gypsum combined with fly ash to form a geopolymer as a factory foundation fill material. Through a comprehensive approach incorporating microstructural analysis, shear strength testing, water stability evaluation, and in-situ field validation, the study evaluated the material’s macroscopic performance and discussed the hypothesized underlying reaction mechanisms. Microstructural and calorimetric analyses suggest that a polymeric network serves as the primary structural framework, which appears to be reinforced by ettringite interlocking and micro-aggregate filling and encapsulation by desulfurization gypsum and fly ash. When mixed at a mass ratio of DG:FA = 50:50 and incorporating 3% sodium hydroxide by mass, the resulting geopolymer exhibits favourable load-bearing capacity, excellent water stability, and negligible expansion effects. The plate load test results revealed a bearing capacity of 150–200 kPa and a deformation modulus of 52.7–56.5 MPa, satisfying the load-bearing and deformation requirements of the investigated project conditions.

The disposal of red mud (RM), a hazardous industrial residue, has become a global environmental challenge. This study aims to develop a well-performing, high-strength RM-based geopolymer (RG) using RM, fly ash, and granulated blast furnace slag. RM was calcined to maximize its reactivity. Taguchi orthogonal method was employed to systematically investigate the effects of solid ratio, calcination temperature, water-solid (W/S) ratio, alkaline activator modulus, and dosage on the workability, mechanical properties, and bulk density of RG. ANOVA was performed to determine the optimal mix for the mechanical performance of RG. The results indicated that after calcining RM at 800 °C, the 28-day compressive strength of RG increased by 35.99%, reaching 51.11 MPa. The W/S ratio is the primary factor affecting the mechanical properties of RG. Excessive water suppresses the generation of N-A-S-H and C-A-S-H gels, weakening the RG performance.