Study On The Preparation And Related Properties Of Self-Repairing Spray Material For Plugging Leakage In Coal Mine

Cement-based materials are used as coal mines plugging materials.The biggest disadvantage is that during the material preparation process and during service,micro-cracks are prone to occur due to load and external factors.If these micro-cracks are not repaired in time,they will form a leak path,which in turn causes a mine fire.Therefore,self-heal of cracks in cement-based materials can be important to prevent spontaneous combustion of coal.This paper focuses on the central problem of using the mineralization ability of microorganisms to plug the cracks of air leak blocking spraying materials in coal mines.A carbonate mineralization strain was screened,and the effects of different external environments on the growth and enzyme activities of the bacteria were studied,and the bacterial growth conditions were optimized.On this basis,in order to avoid the negative impact of high alkali and high calcium environment on bacterial activity in cement-based materials,an inorganic cementitious material was selected and prepared as a coating material for bacteria,and a kind of cementitious material was used to prepare a kind of material.The effect of the biocapsules on the properties of cement-based materials and the effect of crack healing were studied.It lays a foundation for improving the application effect of air leakage blocking spraying materials in coal mines.In terms of the selection and cultivation of carbonate mineralization bacteria,bacteria were isolated from calcium carbide slag with high alkali and calcium content.The results showed that Bacillus cereus had good alkaline resistance,good growth at pH 10 and high enzyme activity.The bacteria also have a certain tolerance to urea and calcium ions.The concentrations of urea and calcium ions that do not affect the growth of the bacteria but maintain certain enzyme activities are 0.9 mol/L and 0.75 mol/L respectively.At the same time,the study found at low temperature(10?)can inhibit the growth of bacteria,at high temperatures(40?)can promote the growth of bacteria,and to make up for the growth of bacteria at low temperature and low enzyme activity can join excess nutrients yeast extract.In the preparation process and performance of biocapsules,the original environmental calcium carbide slag of Bacillus cereus was selected as the wall material,and the activity of the fly ash and blast furnace slag was used to prepare the cement material with certain strength.The orthogonal test was carried out,and the best ratio of raw materials was determined by range analysis and variance analysis.The biocapsules were prepared by pressing cake.extruding,pelletizing and forming four steps,and then the performance of biocapsules was studied.The test results show that when the content of calcium carbide slag,fly ash,blast furnace slag and desulfurization gypsum in biocapsule wall materials is 12.18%,62.82%,16.03%and 8.97%,respectively,the mechanical properties of the wall material are the best;The capsule has good water repellency,storage stability and mineralization activity,and the bacterial spore survival rate after encapsulation is as high as 80.61%.In terms of plugging effect of self-healing spraying material for air leakage in coal mine,the self-healing spraying material was prepared by using biocapsules and cement mortar at first.The effects of different biocapsules on the setting time,consistency,mechanical properties and capillary water absorption of cement-based materials were studied,and the optimal dosage of biocapsules was determined.The effect of self-healing spraying material for blocking air leakage was studied by the index of crack healing area and permeability of cement-based materials.The test results show that the optimal dosage of biocapsules is 5%.At this time,biocapsules have little effect on the setting time and consistency of cement mortar,and at the same time can improve the mechanical properties of cement-based materials.When the dosage of biocapsules is 5%,the specimen is maintained in the solution containing mineralized substrates for 21 d,which can achieve complete healing of cracks,and the best effect of dry-wet cycling maintenance is achieved.The results of permeability test show that the self-healing material for coal mines has a good effect of air leakage prevention.