Optimization of the Injection and Physical Properties of Sulfoaluminate Cement via the In Situ Polymerization of Acrylamide

Deep coal mining requires grouting to reinforce the coal rock walls. The conventional polymer-modified cement-based grouting materials have improved toughness but poor fluidity. The purpose of this paper was to improve the injectability of grout. The preconditions were that the physical properties of the stones are not obviously damaged and the mechanical properties are optimized. The acrylamide monomer was incorporated into the sulfoaluminate cement-based grouting material system. The effects of the in situ polymerization modification of the acrylamide on the paste properties and stone body strength were investigated. The results showed that the acrylamide mixed with the sulfoaluminate cement could increase the fluidity of the grouting material, prolong the paste setting time, and improve the flexural strength of the stone body. Compared with the blank group, the 500 mL efflux time of the 1006 mud viscometer in the 35% AM (acrylamide) dosing group decreased from 51 s to 41 s, the initial setting time increased from 15 min to 98 min, and the flexural strength at three days increased by 202.8%. The compressive stress–strain of the stone body gradually changed from brittle to ductile damage as the acrylamide dosing increased. Based on the microscopic analysis, a composite structure model of the inorganic skeleton of the flexible polyacrylamide network of toughened AFt (ettringite) was built in this paper. A mechanical study of the compressive stress–strain characteristics of the stone body was performed. It was concluded that the acrylamide in situ polymerization-modified sulfoaluminate cement-based grouting material is suitable for coal rock wall grouting reinforcement.