Exploring a fly ash-based grouting material for toughening through in situ polymerization of acrylamide

Efficiently controlling the water inflow (loss) of burnt rocks in the roof of coal mining faces requires grouting reinforcement materials with excellent compressive toughness. Silicate cement-based grouting materials, characterized by low costs, have been extensively applied to grouting reinforcement in coal mines. However, their hardened grout is susceptible to deformation, exhibiting poor toughness. By employing the in-situ polymerization of acrylamide (AM) for toughening, this study investigated the effects of AM, cross-linking agent, initiator, and water-cement ratio on the setting time, swelling capacity, compressive strength, and toughness index of the fly ash-based grouting materials. Furthermore, the microstructures of the hardened grout were observed using a scanning electron microscope (SEM). Key findings are as follows: (1) AM can polymerize in-situ in the fly ash grout to form polyacrylamide (PAM) gel. (2) With AM content of 25%, cross-linking agent content of 0.75%, initiator content of 2.25%, and the water-cement ratio of 0.575, the fly ash-based grouting material exhibits a compressive deformation rate of above 60%, a swelling ratio of 113.43, and a toughness index of 257.92%. (3) Observations of SEM images reveal that the hardened grout of the grouting material forms an inorganic-organic mosaic network structure, with fly ash particles and PAM gel constituting its rigid framework and flexible network, respectively. The deformation rates derived from the compressive stress-strain curves of the hardened grout generally exceed 40%, suggesting significant plastic deformation characteristics. (4) Engineering experimental results show a maximum flexural toughness deformation rate of up to 25.86%. Overall, the grouting material developed in this study, with excellent toughness and fluidity, as well as favorable swelling properties in water, can be applied to water seepage and leakage control for coal mine roofs.