Study On Freeze-Thaw Cycles With Salt Of Fly Ash Concrete Under Bending Load

Concrete is the most important building material in civil engineering construction,and the durability and service life of its structure are the active concerns of the domestic and foreign engineering circles.Among them,the salt freezing cycle will increase the amount of erosion of the concrete surface,and the freezing and thawing medium is more likely to invade the inside of the structure.The corrosion of chloride ions will cause corrosion of the steel bar,resulting in a decrease in the bearing capacity of the concrete structure and shortening its service life.So far,experts and scholars at home and abroad have obtained more results through various theoretical and experimental studies on the effects of freeze-thaw damage and chloride ion corrosion on concrete durability respectively.However,there are relatively few studies on the durability of concrete under the action of freeze-thaw cycles and chloride ions,and most of them take plain concrete as the research object.Most studies do not limit the free deformation of concrete specimens,which is different from the actual concrete in service.Structural durability damage laws are very different,so the test results obtained can not truly reflect the damage of concrete structures in actual service.Based on this,in this paper,through the self-developed bending loading device,the reinforced concrete specimens with different amounts of fly ash are used as the research object to discuss the salt freezing resistance of reinforced concrete under different bending loads,which is the durability problem of actual concrete engineering provide a reasonable reference.Through the rapid freeze-thaw test of reinforced concrete members under bending load,the effects of fly ash content,bending load level,and chloride ion corrosion on the frost resistance of reinforced concrete were discussed;the ultrasonic non-destructive testing technology was used to propose concrete specimens under different bending loads;the ultrasonic wave velocity and the thickness of the damaged layer at the level;the damage degree of reinforced concrete under the combined action of bending load and salt freezing cycle is proposed,and the relationship between the damage degree and the elastic modulus is established;on the basis of the damage degree,the consideration is established the freeze-thaw cycle,chloride salt erosion and bending load and other factors of the reinforced concrete salt freeze damage prediction model provide a theoretical reference for the prediction and evaluation of the durability of the fly ash concrete structure in actual projects.The research results show that:(1)The presence of reinforcing steel slows down the internal damage of the concrete,and chloride salt corrosion accelerates the quality loss of the concrete;(2)The addition of fly ash will improve the frost resistance of the concrete to a certain extent,fly ash The content of 20%is the best content;(3)The bending load accelerates the salt freeze damage of reinforced concrete.With the increase of the load level,the dynamic elastic modulus and mass loss rate of the member gradually decrease;(4)The use of ultrasonic non-destructive the detection technology obtains the ultrasonic wave velocity of the concrete and the thickness of the surface damage layer.Through regression analysis,it can be found that the ultrasonic wave velocity has a binary relationship between the number of salt freezing cycles and the bending load level;the thickness of the surface damage layer and the fly ash content and bending,there is also a binary relationship between the load levels(5)According to the principle of strain equivalence,the damage degree D=1-Edn/Ed0 is established.Through regression analysis,it can be known that the damage degree D and the ultrasonic wave rate when the fly ash content is constant It is a proportional function relationship,and the damage degree D and the thickness of the damaged layer have a logarithmic relationship;(6)Based on the damage degree D,the salt freeze damage model of fly ash concrete under bending load is established.