Deterioration Evolution And Mechanism Of Cemented Gangue Backfill Material In Acid Mine Water Environment

During the service period,the filling body will not only be subject to the complex and variable stress of the overlying rock formations,but also to the erosion of the mine water rich in corrosive ions.A hydration reaction occurs,which causes the strength of the filling material to deteriorate,affects long-term stable performance,reduces the carrying capacity of the filling body,shortens the service life,and even causes safety accidents.Therefore,it is necessary to study the changing law of the properties of filling materials in the acid mine water environment.In this paper,the cemented gangue backfill material（CGBM）is taken as the research object.Preparation of test specimens with different mass concentrations,simulating acid mine water with sulfuric acid solutions of different p H values.Using a combination of experiments and theoretical analysis,the uniaxial compressive strength,ultrasonic wave velocity,mass evolution law and mechanism of CGBM in an acid-corrosive environment were studied.The diffusion law and the incorporation of barium hydroxide reagent in the CGBM to improve the acid corrosion resistance,XRD and SEM analysis of microstructure and composition change of filling materials after corrosion.The main research contents and conclusions are as follows:（1）The uniaxial compressive strength,ultrasonic wave velocity,and mass evolution law of test specimens with different mass concentrations in a solution of p H=4 and a mass concentration of 80%in different p H solutions（p H=3、4、5、6）were experimentally studied.The damage degree was evaluated by using the compressive strength,and the relational expressions with mass concentration,p H value and corrosion age were established.The results show that the lower the mass concentration of the test piece and the smaller the p H value of the immersion solution,the more obvious the change of the test piece’s mass,compressive strength,and ultrasonic wave velocity.with the increase of the age of corrosion,the mass of the specimen decreases first and then increases and then decreases,the compressive strength and ultrasonic wave speed of the specimen increase first and then decrease,and the damage degree gradually increases.XRD and SEM tests showed that the main hydration products in the early corrosion stage were ettringite and calcium silicate gel to fill the internal pores of the specimen.In the late stage of corrosion,ettringite was decomposed,and accompanied by the formation of dihydrate gypsum,the dihydrate gypsum absorbed water and swelled,destroying the internal structure of the specimen,and causing the crystal structure inside the material to be damaged.（2）The creep characteristics of specimens with different mass concentrations in a solution of p H=4 and a mass concentration of 80%in different p H values（p H=3、4、5、6）under loading were studied.Based on the experimental data,the B3 creep model was revised.The model was verified with the data in the literature.The B3 creep model was used to calculate the predicted creep value of the CGBM under different mass concentrations and different p H values.The creep of the specimen under the load in the corrosive solution tends to increase rapidly and then slowly increase with the extension of the corrosion age.The smaller the solution p H value,the lower the mass concentration of the specimen,the faster the creep increase.The corrosion age is 0～3000 days.The creep of the specimen under load is linearly increasing with the extension of the corrosion age.In the solution of p H=3,the specimen increases rapidly after 2000 days.（3）The diffusion rules of sulfate ions in the specimens with different mass concentrations in the p H=4 solution and 80%mass concentration in the different p H solutions（p H=3、4、5、6）were experimentally studied.And prediction model of sulfate ion diffusion was established.The results show that the content of sulfate ions in CGBM increases rapidly and then increases slowly with the increase of the age of corrosion.The smaller the p H value of the solution,the lower the mass concentration of the sample,and the more the sulfate ion concentration in the test specimen,The sulfate ion concentration in the specimen gradually decreased with the increase of corrosion depth,and the sulfate ion diffusion coefficient showed a trend of rapid decrease and then slow decrease with the extension of the corrosion age.When the age of corrosion exceeds 3 months,the predicted value agrees well with the experimental value,and can effectively predict the sulfate ion concentration in the CGBM at any time.（4）The effects of Ba（OH）₂ doped on the mass,uniaxial compressive strength,ultrasonic wave velocity,and the diffusion of sulfate ions of CGBM under simulated acid mine water environment were studied through experiments.SEM and XRD tests were used to analyze the micromorphology and composition changes of the CGBM,and to explore the performance law and mechanism of Ba（OH）₂ to improve the CGBM.The results show that the corrosion reaction rate of the specimens doped with Ba（OH）₂ is slowed down,and the changes in the mass,strength and wave velocity of the specimens caused by corrosion are reduced.The content of sulfate ions in the specimens gradually became smaller than that of the undoped specimens as the corrosion age prolonged,and the improvement effect is the most significant after immersion in the test specimen with the dosage of 2 kg/m³.The content of corrosion products such as ettringite and gypsum in the specimens are reduced,and the internal structure is more complete.As the amount of barium sulfate precipitation gradually increases,it will inhibit the formation of ettringite and further delay the corrosion reaction.