A novel CO2 foaming agent for the preparation of foamed sulfoaluminate cement material: Application to coal mine filling

Abstract

High-risk areas in coal mines have become an increasingly serious issue in recent years. However, the chemical foaming agents used in coal mine filling management are mostly hydrogen peroxide which produces combustible O2 and aluminum or zinc powder which is explosive H2. All of the above chemical foaming agents do not have safe filling conditions. In this paper, we propose a new inorganic foaming material that generates inert gas CO2. Foamed sulfoaluminate cement-based grouting material (FSCGM) was prepared by chemical foaming. The expansion capacity of CO2 foaming agent was studied. The effects of W/C, foaming agent admixture, and Lime/Anhydrite (L/A) on expansion times, foaming time and setting time were studied and the optimum proportion of FSCGM was determined. The mechanical properties, durability, and fire prevention performance of the FSCGM with the optimal proportion were studied and simulated filling tests were conducted. The results showed that the CO2 foaming agent with 30% dosing expands 8.8 times after 10 min of foaming. The best proportion of W/C was 2.2, CO2 foaming dosing was 25%, L/A was 3:5, 6 h compressive strength was 0.52 MPa, 7 d water absorption rate was 46.2%, softening coefficient was 0.75. With the increase of foam admixture and W/C, the CO2 concentration gradually increased, and the fire prevention effect became more apparent. After simulated filling, the slurry did not collapse the mold, the expansion times was 1.74 times, and the dry density of the sampled specimens was about 0.3 g/cm3. It is observed that the bubbles were evenly distributed, and the hole structure was small and dense. Therefore, we prepared FSCGM with ultra-low density, high early compressive strength, and good fire prevention performance by using novel CO2 foaming agent. In addition, the feasibility results indicate that the FSCGM has great potential for engineering applications.