Experimental Study On Mechanical Properties Of Coal Gangue Concrete After Freeze-thaw In Northern Shaanxi Mining Area

Replacing natural aggregates with coal gangue to prepare concrete can effectively solve the problem of massive accumulation of coal gangue in northern Shaanxi,while also saving natural sand and stone resources,which has significant environmental value.The various properties of coal gangue concrete are closely related to the origin of coal gangue,and the northern Shaanxi region is prone to natural freeze-thaw cycles.Therefore,studying the durability of coal gangue concrete in the northern Shaanxi mining area under freeze-thaw action has important scientific research significance and practical application value.The main research content and results of this article are as follows:(1)A scanning electron microscope test was carried out to compare the change of the interface transition zone of coal gangue concrete before and after freezing and thawing.It was found that there were more cracks in coal gangue concrete than in ordinary concrete,and the cracks developed faster after freezing and thawing than in ordinary concrete.Small pieces of concrete were taken before and after freezing and thawing and ground into powder samples for X-ray diffraction test and X-ray fluorescence spectrum analysis.It was found that the main chemical composition of coal gangue concrete did not change significantly before and after freezing and thawing,and it was concluded that the freezethawing effect was mainly frost heave The physical effect of force has little effect on the chemical composition of concrete and the mineral composition of coal gangue.Mercury intrusion tests were used to compare and analyze the characteristic parameters of coal gangue pore structure before and after freezing and thawing.It was found that freezing and thawing reduced the connectivity of coal gangue pore structure in coal gangue concrete,and the porosity increased after 60 freeze-thaw cycles.(2)Taking coal gangue substitution rate and freeze-thaw times as variables,the mass loss rate,relative dynamic elastic modulus loss rate and basic mechanical properties of coal gangue concrete were studied after freeze-thaw.The test results show that under the same freeze-thaw times,the mechanical properties of coal gangue concrete decrease with the increase of coal gangue replacement rate,which shows that the freeze-thaw damage of coal gangue concrete is more severe than that of ordinary concrete.And established the calculation formulas of cube compressive strength,flexural strength and splitting tensile strength with respect to freeze-thaw times and coal gangue replacement rate.(3)The uniaxial compression test of gangue concrete after freeze-thaw was carried out,and the full curve of uniaxial compressive stress-strain was obtained.After comparative analysis of the failure patterns of each group,it was found that the singleaxis compression failure mode of gangue concrete after freeze-thaw was close to that of natural aggregate concrete,but the freeze-thaw action destroyed the aggregate bite force and mechanical friction in the test block,resulting in certain brittle characteristics in the failure stage of the specimen,which in turn led to the incomplete descending section of the stress-strain curve.According to the experimental data,on the basis of the Zhenhai model,the uniaxial compressive stress-strain curve of coal gangue concrete after freezethaw is fitted,the uniaxial compressive stress-strain equation after freeze-thaw of coal gangue concrete is established,and the calculation formula of segmentation coefficient with the number of freeze-thaw times as the variable is given.(4)A binary surface regression model of mass loss rate,compressive strength loss rate,freeze-thaw number and gangue substitution rate of gangue concrete under freezethaw action was established.Comparing the accuracy of the two models,the mass loss rate model was used to predict the freeze-thaw durability life of gangue concrete in northern Shaanxi environment.