Study On Mechanical Properties And Structural Deterioration Characteristics Of Basalt Fiber Coal Gangue Concrete Under The Influence Of Temperature

China is a large country of coal consumption.During the mining process of coal mines,the coal gangue produced is regarded as solid waste and dumped,which not only seriously waste land resources,but also laid hidden dangers for mines.At the same time,with the rapid development of the construction industry,high-rise buildings between cities,the market demand for natural aggregates is huge.If the coal gangue becomes "waste" into treasure,it can not only alleviate the pressure on the natural environment caused by the shortage of natural aggregates,but also promote the green and sustainable development process of the construction industry and the coal mining industry.If the high-temperature resistance of high-rise buildings can be enhanced at the same time,reduce the cost of post-disaster repair,extend the service life of buildings,and ensure the safety of people’s lives and property.It can be said that "three birds with one stone" will bring huge scientific research value and socioeconomic benefits.In this paper,the no-spontaneous combustion gangue from a mine in Pingxiang City,Jiangxi Province was taken as an example,and its physical and chemical properties and thermal activation properties were studied.The coal gangue was used as crude aggregate instead of 50% natural stone,and basalt fibers were added to prepare environmental protection high temperature resistant concrete.The effects of the content and length of basalt fibers and the activation degree of coal gangue coarse aggregate on the mechanical properties of concrete at room temperature were investigated,and the optimum orthogonal combination was determined.Designed a high temperature test scheme suitable for the actual situation,through macroscopic and microscopic observation and mechanical test,the concrete properties under different temperature and cooling conditions were studied,and the damage degree after fire was qualitatively evaluated.The main conclusions were as follows:(1)Pingxiang no-spontaneous combustion gangue has low activity,high content of carbon and impurities,its strength is lower than natural stone,and its activity is the highest after calcination at 800℃.The coal gangue aggregate without thermal activation(no activated coal gangue aggregate)is loosely cemented with the matrix and is easy to be broken and stripped during the stress process.The gangue aggregates activated by 800℃(activated gangue aggregates(800℃))are closely cemented with the matrix and are not easy to be peeled off during the stress process.Adding coal gangue improves the toughness of concrete.(2)Basalt fibers have a small improvement in the compressive performance of concrete.When the fibers content are appropriate(0.1%～0.2%),the fibers and matrix cooperate to form a three-dimensional network structure to bear the load and enhance the compressive strength of concrete,but when the content is too low or too high,the strength will be reduced.Basalt fibers can improve the splitting tensile performance of concrete greatly.When the content of fibers are appropriate,they can give full play to their high elasticity,inhibit the development of cracks,and increase the tensile strength of concrete,but when the content is too high,its strength will be reduced.When the strength of concrete is constant,the longer the basalt fibers are,and the optimal content of basalt fibers are smaller.Different length fibers have different strength improvement ability and stability of concrete.12 mm and18mm fibers can stably enhance the compressive strength of concrete,and 6mm and 18 mm fibers can stably enhance the splitting tensile strength of concrete.When 0.1% 18 mm fibers are added,the concrete has high strength,stable performance and low production cost.(3)Under high temperature,activated coal gangue aggregate and basalt fibers do not decompose and expand,which reduces the number of cracks,crack development and deformation of concrete test blocks.In the case of natural cooling,the mechanical strength of concrete increases first and then decreases with the rise of temperature.Before 200℃,it belongs to the high temperature curing section,and the strength of concrete gradually increases and reaches the peak value at 200℃.After 200℃,the strength of concrete gradually deteriorates.At the same temperature,the strength of basalt fiber coal gangue concrete(BFCGC)is always higher than that of OC.At 800℃,the axial compressive strength of naturally cooled BFCGC and OC is 17.89% and 22.97% respectively at room temperature,while that of watered BFCGC is only 14.82% at room temperature.(4)The fire damage degree of concrete is mainly affected by temperature.The addition of basalt fibers and activated coal gangue aggregate can alleviate the high temperature damage of concrete,but they are not enough to resist temperature deterioration.Watering cooling aggravate the damage of concrete,the higher the temperature,the more serious the damage,even affect the rating results.At the same temperature,the degree of fire damage from low to high is naturally cooled BFCGC,naturally cooled OC,water cooled BFCGC.