Mechanical model and strength development evolution of high content fly ash–cement grouting material

Mine adopts grouting process for stope stability filling treatment, and the difference in grouting materials affects the overall treatment effect. This study used high content fly ash to replace part of cement as grouting material, and its feasibility and economic analysis were carried out. The study emphasizes the control of variables such as fly ash particle size (Ⅰ-fly ash, II-fly ash, III-fly ash), fly ash content (80%, 70%, 60%, 50%), and slurry concentration (45%, 50%, 55%, 60%). Experimental analyses were assessed the initial and final setting time, porosity, and unconfined compressive strength of the grouting material. The grey relational analysis method was employed to determine the optimal mix of grouting material for on-site mining filling. The research findings indicate that increasing the fly ash content led to exponential growth in both the initial and final setting time, while the strength of the consolidated material exhibited a linear decrease. Similarly, reducing the slurry concentration resulted in exponential growth in the initial and final setting time and an exponential decrease in strength. The relationship between fly ash content, slurry concentration, and the strength of the consolidated body can be described by the function UCS = a − bx − cy + dx2 + ey2 − fxy, with fly ash content showing higher sensitivity to strength variations. A constitutive damage model was constructed by incorporating the initial porosity of the consolidated body and separately considering the solid skeleton and pores. Additionally, considering the curing age, a three-dimensional surface for predicting the strength of the consolidated body was constructed. The prediction indicates that the strength of the consolidated body gradually increases with a decrease in the particle size of fly ash, and the curing age also increases. The final setting time of the consolidated body gradually increases with an increase in the fly ash content. Finally, the optimal grouting material mix determined consisted of Type I fly ash with a content of 50% and a slurry concentration of 60%, providing a scientific reference for achieving the optimal grouting material mix in on-site mining filling.