Research On Durability Damage And Deterioration Mechanism Of Aeolian Sand Concrete In Freeze-thaw And Salt Corrosion Environment Of Wind Erosion Area

In this study,with aeolian sand and natural pumice from Inner Mongolia as the main raw materials,ordinary aeolian sand concrete and aeolian sand pumice concrete are developed,while considering the coupling influences of multiple factors such as wind-sand erosion,freeze-thaw cycle and chlorine salt corrosion.Based on the macroscopic deteriorating law,3D surface morphology,internal microstructure,chemical composition,pore structure evolution and other aspects,the durability damage and deterioration mechanism of aeolian sand concrete in the wind-sand environment of the cold saline area are explored,which is of important theoretical foundation and application value of concrete durability design in such harsh environments.The main research contents and results of the study are shown as follows:1.The destruction processes of the two types of aeolian sand concrete under wind-sand erosion are simulated by means of a self-made concrete wind-sand erosion test device.Three factors,i.e.wind speed,sand carrying capacity and angle of attack,are selected for the orthogonal experiment of wind parameters.The angle of attack has the maximum significance and variance contribution.When the attack angle is 90°,the wind-sand is dominated by vertical impact to produce “deflation pit” destruction with greater damage.When the attack angle is 15°,the wind-sand is dominated by horizontal cutting to produce “deflation trench” destruction with smaller damage.The destruction process of wind-sand erosion is divided into three stages,i.e.accelerated development,attenuation and stabilization,of which the accelerated development stage inflicts greater damage on the concrete surface.The larger the sand grain size is,the larger the energy from the impacting concrete surface will be,and in turn the greater the resulting damage will be.2.Wind-sand erosion exhibits “catalytic” effects on the freeze-thaw cycles of the two types of aeolian sand concrete.Under accelerated freezing and thawing,the internal concrete cracks are formed and developed.With the coupling between wind-sand erosion and freezethaw cycle,the concrete damage is greater than that of a pure freeze-thaw cycle.The frost resistance of the aeolian sand pumice concrete is better than that of ordinary aeolian sand concrete.This is mainly due to the fact that it is difficult for the pores of pumice aggregate inside the aeolian sand pumice concrete to be completely filled by water in the freezing and thawing process.A pore structure which is rich in pumice can satisfy the free expansion of water-ice phase change,making it able to “unload” for water migration in the process of freezing,thus presenting good frost resistance.3.Under long-term natural soaking,the macro performances of the two types of aeolian sand concrete are relatively stable.The chloride-ion erosion depth is increased over immersion time,and abundant pore structures inside the aeolian sand pumice concrete lead to the maximum chloride-ion erosion depth being greater than that of ordinary aeolian sand concrete.After long-term natural immersion,the total porosities of the two types of aeolian sand concrete are increased,of which the proportion of pores < 0.1 ?m is decreased,that of pores 0.1~10 ?m are fluctuated,and that of pores > 10 ?m is increased.4.Representative Friedel's salt is generated inside the two types of aeolian sand concrete after the wet-dry circulation of chlorine salt.Under the coupling between windsand erosion and chlorine salt dry-wet circulation for concrete,the damages from wind-sand erosion and chlorine salt dry-wet circulation account for approximately 7.5~8.8% and 91.2~92.5%,respectively.Wind-sand erosion causes a “deflation pit” to occur on the concrete surface,providing “channels” for salt to enter the concrete,and the wind-sand erosion effect can increase the chloride ion erosion depth of aeolian sand concrete,and deteriorate salt corrosion damage.5.Under the multi-factor coupling effect of freeze-thaw,chlorine-salt dry-wet and wind-sand erosion,the damage degrees of the two types of aeolian sand concrete are greater than that of dual-factor coupling,i.e.freeze-thaw and chlorine salt dry-wet.Wind-sand erosion destroys the surface protection layer of concrete,thereby accelerating the influences of internal concrete structure from the freeze-thaw water-ice phase change,chlorine-salt chemical corrosion,crystallization pressure corrosion,and other damages.6.Based on the grey system theory,correlation analysis is carried out on the concrete pore distribution and damage degree.The influence of pore distribution on the damage degree is sequenced as follows from large to small: for ordinary aeolian sand concrete: 0.01~0.1 ?m > 0.1~1 ?m > 1~10 ?m > greater than 10 ?m > less than 0.01 ?m;and for aeolian sand pumice concrete: less than 0.1 ?m > 0.1~1 ?m > 1~10 ?m > greater than 10 ?m.