Study On The Influence Of Mineral Admixture On The Performance Of Coal Gangue Permeable Brick

Permeable bricks have the advantages of good water permeability,sound absorption and noise reduction,anti-skid road surface and have certain regulation ability for urban ecological environment.Traditionally,permeable bricks often use cement as the cementing material and natural sand and gravel as the aggregate.However,in recent years,there is a shortage of natural sand and gravel,and the ecological environment is damaged by over-exploitation.In response to the above problems,combined with a large number of stockpiles of coal gangue and fly ash in Ningxia region.In this paper,using coal gangue as a substitute for natural gravel,the effect of fly ash and mineral powder as mineral admixture instead of cement on the compressive strength,permeability coefficient,porosity,water retention and frost resistance of coal gangue permeable bricks was investigated.The aim is to apply fly ash,mineral powder and coal gangue to permeable bricks to achieve the purpose of pollution reduction and solid waste resource utilization.The main research contents and conclusions of the paper are as follows.(1)A combination of theoretical analysis and experiment is adopted to determine the permeable brick preparation process in this paper,including the design method of permeable brick ratio,mixing process,molding process and maintenance process.On this basis,the three factors of water-cement ratio,aggregate particle size gradation and target porosity are considered.The compressive strength and permeability coefficient of permeable bricks were used as evaluation indexes to determine the optimal mix ratio of the base group of permeable bricks.The results show that the volumetric method is used as the design method of permeable brick ratio,cement-coated stone method of mixing,and static compression molding with molding pressure of 5MPa and holding time of 60s The standard curing conditions as the preparation process in this paper are beneficial to the performance of permeable bricks.The best ratio is:water-cement ratio 0.3,aggregate particle size gradation 2.36～4.75mm:50%each of 4.75～9.5mm.The target porosity is 15%,at this time the benchmark group 28dcompressive strength is 61.5MPa,and the permeability coefficient is 3.44×10-2cm/s.(2)To investigate the effect of coal gangue substitution rate(0%,25%,50%,75%and 100%)on the compressive strength,permeability coefficient,porosity,water retention and frost resistance of permeable bricks.The results show that with the increase of gangue replacement rate,the performance of permeable brick is decreasing trend.When the replacement rate of coal gangue is 75%,the compressive strength of 28d permeable brick is 35.6MPa,and the permeability coefficient is 1.85×10-2cm/s,which can be used for parking lot and community road.Coal gangue replacement rate of 100%coal gangue permeable bricks,28d compressive strength of 26.7MPa,permeability coefficient of 1.24×10-2cm/s,still can be used for sidewalks and pedestrian streets and other sites.(3)On the basis of 100%coal gangue permeable bricks,the effect of fly ash(Class Ⅲ fly ash,ClassⅡ fly ash)and mineral admixture on the performance of permeable bricks was investigated,considering different substitution rates(0%,10%,20%,30%and 40%).The results show that the appropriate amount of mineral admixture alone replaces cement and helps to improve the overall performance of coal gangue permeable bricks,but if the amount is too much it makes the performance worse.The gradeⅢ fly ash mixed with 10%will improve the water permeability,porosity and water retention of coal gangue permeable bricks,but will cause the decrease of compressive strength and frost resistance.The overall performance of the permeable brick was optimal when the amount of Class Ⅱ fly ash was 10%.The comprehensive performance of permeable brick reaches the optimum when mineral powder is mixed at 10%.(4)On the basis of 100%coal gangue permeable bricks,the effect of compounding fly ash(GradeⅢ fly ash and Grade Ⅱ fly ash)and mineral powder on the performance of permeable bricks was investigated,in which the compounding substitution rate was 30%,and the ratio between fly ash and mineral powder was 2:1,1:1 and 1:2.The results show that the optimal integrated performance of fly ash and mineral powder is 1:1,But to combine the performance of 30%of mineral powder;The optimal comprehensive performance of fly ash and mineral powder occurs when the mixing ratio is 2:1,And at this time,the performance of coal gangue permeable brick is greater than 30%of grade powder ash,Also better than the 30%single mixing performance of mineral powder,indicating that the synergistic effect of Grade Ⅱ fly ash and mineral powder at a suitable compounding ratio(2:1)helped to improve the performance of coal gangue permeable bricks.The performance meets the requirements of the specification and can meet the demand for sidewalks and pedestrian streets.