Study on the pozzolanic reactivity and mechanical properties of coal gasification slag in cement-alkaline environment

Coal gasification slag（GS） is rich in pozzolanic amorphous aluminosilicate minerals, making it a potential cement-based material. To deeply understand and quantify the pozzolanic activity of GS and enhance its utilization in construction materials, a simplified GS-Ca（OH）₂-H₂O system is constructed to simulate the reactions in a cementitious alkaline environment. The study employs acid dissolution methods to quantitatively analyze the chemical insoluble content and reaction rates of GS powder, thereby establishing a kinetic model for pozzolanic reactions and examining the relationship between the degree of GS reaction and system strength. The results indicates that GS itself lacks self-cementitious properties but demonstrates pozzolanic activity when CaO is involved in the reaction. In a cementitious alkaline environment, the early dissolution rate of active components in GS is low, resulting in slow pozzolanic reactions within the first 7 days; however, the activity significantly increases after 7 days, and the reaction rate stabilizes after 28 days. By employing decarbonization and de-ironing pretreatments and extending effective grinding time, the pozzolanic activity of GS can be effectively enhanced. CaO significantly stimulates GS activity, and under different C/GS conditions, the pozzolanic reactions of GS conform to a first-order kinetic model. When the C/GS ratio is 0.25, the system exhibits optimal reaction degree, mechanical strength, and hydration product structure. Although further increases in CaO content can promote the dissolution of active silicon-aluminum components, excessive Ca²⁺ may hinder later-stage surface reactions and Ca²⁺ diffusion and penetration, affecting structural stability and long-term mechanical strength. The relationship between the degree of GS reaction and system strength shows a good exponential correlation; when the reaction rate exceeds approximately 10%, the paste strength increases significantly. Enhancing the pozzolanic activity and mechanical strength of gasification slag provides greater potential for its application in cement-based materials.