Study on characteristics of new modified cement mortar spraying material

Air leakage in goaf is an important factor affecting coal spontaneous combustion.In order to improve the efficiency of plugging air in goaf, characteristics of modified cement materials are analyzed in this paper.Materials (rubber powder, water reducer and quick setting agent with cement) are used to test the influence on drying shrinkage, flow velocity and initial setting time of modified cement materials.A new type air blocking material is set.Mercury intrusion test and on-site application are proceeded to measure the effect of air blockage.Experimental results show that the shrinkage rate is smaller and the fluidity is better when the mass ratio of rubber powder and water reducer is 0.030 and 0.003.With dosage of quick-setting agent decreasing to 0.003-0.006, the initial setting time of mortar can be controlled within 5-10 min.The porosity of mortar material is 24.76% tested by mercury intrusion, with compact structure and superior wind insulation performance.After on-site application, the average air leakage per 100 meters in tunnel decreased from 6.5 m³/min to 0.7 m³/min in 15 days; the average oxygen concentration in the mined-out area decreases from 12.6% to 3.6%, and eventually stabilizes at about 4%.Remarkable plugging air effect is shown.