Research On The Coupling Effect Of Acid Rain And Freeze-thaw On The Performance Of Coal Gangue Pervious Concrete

"Sponge city"is a trend in the construction and development of cities in the new era.Permeable concrete is an essential material for building"sponge cities."Promoting the reuse of solid waste such as coal gangue is not only a requirement for achieving carbon peaking and carbon neutrality,but also a necessary requirement for green development.Moreover,if coal gangue permeable concrete is used instead of impermeable materials to pave the soil,it can meet the basic requirements of road surface use.However,in harsh natural environments,such as acid rain and severe cold regions,the material is bound to be subject to the combined effects of multiple erosion factors.Based on this,this study uses solid waste coal gangue as coarse aggregate to prepare permeable concrete and investigates the variations of its properties under acid rain,freeze-thaw,and their coupling effects.The main research and achievements obtained are as follows:The changes in the appearance,mass,compressive strength,and permeability coefficient of coal gangue permeable concrete were studied under simulated acid rain erosion environments with different p H values（p H=3,p H=4）.The results show that with the continuous acid rain erosion,the surface of coal gangue pervious concrete with brown substances and corrosion pits increased.The mass and compressive strength increased first and then decreased,and the permeability coefficient decreased first and then increased.As the p H value of the simulated acid rain solution decreased,the deterioration degree of the specimen became more serious.The mechanism of acid rain erosion of coal gangue pervious concrete is analyzed by microcosmic test method.The study found that the main erosion includes H⁺corrosive erosion and SO₄^2-expansive erosion,and the main erosion products are Ca SO₄·2H₂O,Si O₂·n H₂O gels and Al₂O₃·n H₂O gels.The study investigated the changes in appearance,mass,compressive strength,relative dynamic modulus of elasticity,and permeability coefficient of coal gangue permeable concrete under different freeze-thaw cycling media（pure water,3.5wt%Na Cl solution）freeze-thaw cycling.The results show that with the increase of the number of freeze-thaw cycles,the cement slurry and aggregate on the surface of the specimen constantly fall off,and finally the weak parts appear fracture failure.The loss of compressive strength and relative dynamic elastic modulus was slow in the early stage,and gradually became faster in the late stage,showing a parabolic downward trend.The permeability coefficient increases gradually;When freezing-thawing failure occurs,the mass of the specimen decreases precipitously.The freeze-thaw failure of coal gangue pervious concrete is more likely to occur in 3.5wt%Na Cl solution,and the freeze-thaw failure times of specimens with different design porosity are 25 times earlier than that of clear water solution.The quadratic polynomial was used to fit the relationship between the permeability coefficient and the number of freeze-thaw cycles.The R² was more than 0.93.On this basis,the nonlinear surface fitting of the relationship between the permeability coefficient,the number of freeze-thaw cycles and the design porosity is carried out.The R² is more than 0.90.The changes of apparent mass,compressive strength,relative dynamic elastic modulus and permeability coefficient of coal gangue permeable concrete under the coupling effect of acid rain and freeze-thaw（successively and alternately）are studied.The results show that under the action of acid rain freezing and thawing,the cement slurry and aggregate on the surface of the specimen fall off continuously until fracture occurs.The mass,compressive strength and relative dynamic elastic modulus of the specimen decreased gradually,while the permeability coefficient increased continuously.When acid rain eroded for 30 days,the frost resistance of coal gangue pervious concrete did not deteriorate significantly,and even some specimens showed increased frost resistance.With the increase of acid rain erosion time,the frost resistance of coal gangue pervious concrete decreases gradually.Under the alternating action of acid rain and freeze-thaw,the mass,compressive strength and relative dynamic elastic modulus of the specimen decreased in a step manner,while the permeability coefficient increased in a step manner.Under the same erosion period,the deterioration degree of coal gangue pervious concrete under the alternating action of acid rain freeze-thaw is higher than that under the action of acid rain freeze-thaw successively.In the coupling process of acid rain and freeze-thaw,freeze-thaw cycle plays an important role.Based on the grey system theory,a mean GM（1,1）model was established to predict the compressive strength of 15 groups of coal gangue perpermeable concrete after freezing and thawing,and the residual qualified model was used to test the GM（1,1）model.The test results showed that the average relative error was less than 10%,indicating that the prediction model had good accuracy.This thesis contains 65 figures,56 tables and 126 references.