Research On Mechanism And Application Of Freeze-thaw Damage And Deterioration Of Dune Sand Concrete

The rapid development of infrastructure and urbanization construction in the western region of China in recent years,the rapid consumption of concrete makes the contradiction between supply and demand of engineering sand increasingly prominent.Reasonable development of alternative materials according to local conditions,in the construction project with dune sand instead of engineering sand as basic engineering materials,not only can effectively alleviate the contradiction between supply and demand of coarse and medium sand,but also provides a new idea for the sustainable development of dune and surrounding areas.The natural environment of different regions in China is obviously different,which directly affects the durability of concrete,especially in cold regions.The phenomenon of freeze-thaw damage of concrete projects due to freeze-thaw action occurs from time to time.The regional climate of Xinjiang is different from that of the plain area.The amount of snowfall in winter is very large.The positive and negative temperatures alternate frequently in winter and spring.After the snow melts,thin ice is formed on the building.The building is in a state of freeze-thaw for a long time,which can easily induce the freeze-thaw damage of concrete materials and the later frost resistance durability.In order to speed up the application and promotion of dune sand concrete in Xinjiang construction engineering,it is necessary to carry out research on the mechanism and application of freeze-thaw damage degradation of desert sand concrete.In this thesis,Xinjiang Gurbantungt desert sand is used as fine aggregate raw material to gradually replace river sand to make dune sand concrete.The following main research results are obtained through rapid freeze-thaw test:The freeze-thaw damage deterioration of dune sand concrete is similar to that of ordinary concrete,which increases with the increase of freeze-thaw cycles.The macroscopic damage deterioration is gradually accumulated from light to heavy,from the surface to the inside,and the microstructure is gradually loosened.The frost resistance performance indexes such as mass,relative dynamic elastic modulus,compressive strength and splitting tensile strength gradually decrease and the decreasing speed gradually accelerates.Under the same freeze-thaw cycle,the frost resistance of concrete with different dune sand substitution rates is significantly different from that of ordinary concrete.With the increase of dune sand content,the frost resistance shows a trend of decreasing first,then increasing and then decreasing.The loss of frost resistance index of concrete with dune sand substitution rate of 10-20%is greater than that of ordinary concrete.The loss of frost resistance index of concrete with dune sand substitution rate of30-100%is less than that of ordinary concrete.The frost resistance is optimal when the dune sand substitution rate is 40%.The freeze-thaw damage model of dune sand concrete was obtained by linear regression analysis of the experimental data of damage variables.The failure characteristics of dune sand concrete under axial compression after freeze-thaw damage are similar to those of ordinary concrete.The more serious the damage deterioration is,the smaller the stiffness is,the lower the maximum axial compression strength is,the larger the displacement during loading is,and the stress-strain curve is flat to the right.By studying the variation of characteristic values of peak stress,peak strain,ultimate strain and elastic modulus,it is found that the characteristic value index of concrete with dune sand replacement rate of 30-60%is generally better than that of ordinary concrete,and the effect is most obvious when the dune sand replacement rate reaches 40%.The freeze-thaw damage constitutive model of dune sand concrete is established,which can express the ductility,residual strength and plastic deformation ability of dune sand concrete under different freeze-thaw cycles.The correlation coefficient R~2is above 0.99.The randomness of freeze-thaw damage degradation of dune sand concrete conforms to the two-parameter Weibull distribution.The establishment of probability density function and reliability function can effectively describe the damage degradation and failure process of dune sand concrete.Under the same freeze-thaw cycle,the reliability of concrete with desert sand replacement rate of 10-20%is lower than that of ordinary concrete,and the reliability of concrete with desert sand replacement rate of30-100%is higher than that of ordinary concrete.Among them,the reliability is the highest when the dune sand replacement rate is 40%.Based on the reliability level of 0.6,the freeze-thaw damage life of dune sand concrete was predicted and analyzed.