Study On Damage Rules Of Concrete Under Corrosion Of Freeze-Thaw And Saline Solution

The concrete durability damage of bridge structure in our country is usually serious because of the salt water environment in the western salt lake basin and the cold area of the north coast,and the salt is mainly chloride and sulfate.This paper takes C50 concrete as the research object and designs the three factors corrosion orthogonal test for concrete specimens of different specifications.The freeze-thaw cycles in corrosion factors are divided into 100,200and 300 times,the chloride ion concentration is divided into 2%,3.5%and 5%,and the sulfate ion concentration is divided into 3%,5%and 7%.After corrosion test on concrete prismatic and cube specimens,range analysis,variance analysis and regression analysis were used to study the orthogonal test results,the change characteristics and damage rules of concrete durability related indexes were obtained.It is found that sulfate ion has the most serious effect on concrete when relative dynamic elastic modulus is used as damage index of concrete prism after corrosion test.In the mixed solution of 2%NaCl and 3%Na₂SO₄,freeze-thaw for 100 times,the relative dynamic elastic modulus of concrete was the smallest.When the change rate of mass is used as the concrete damage index,sulfate ion also has the most serious effect on concrete.In the mixed solution of3.5%NaCl and 5%Na₂SO₄,the mass of the concrete specimen increased the most when it was freeze-thawed for 100 times.The mass loss of the concrete specimen was the greatest when it was freeze-thawed for 300 times in a mixed salt solution of 2%NaCl and 7%Na₂SO₄.The ultrasonic velocity of concrete increases with the increase of concrete density.After the corrosion test,the thickness of damaged layer of each group did not reach the minimum concrete protective layer of reinforced concrete of 30mm.When the mixed salt solution of2%NaCl and 5%Na₂SO₄ was freeze-thawed for 200 times,the concrete damage layer was the largest,27.29mm.Chloride ion has the most serious effect on ultrasonic wave velocity and damage layer thickness of concrete.Freeze-thaw has the most serious effect on the flexural strength of concrete.The ultrasonic wave velocity of concrete is positively correlated with its flexural strength and negatively correlated with the thickness of the damaged layer.High concentration of salt solution and high freeze-thaw cycle times seriously damage the compressive strength of concrete.The order of influence of corrosion factors on compressive strength of concrete cube is freeze-thaw,chloride ion and sulfate ion.When the compressive strength of the cube specimen are taken as the concrete damage index,the compressive strength of concrete decreases the most when freeze-thaw for 300 times in the mixed solution of 5%NaCl and 5%Na₂SO₄,and increases the most when freeze-thaw for 100 times in the mixed solution of 2%NaCl and 3%Na₂SO₄.In variance analysis,freeze-thaw and chloride ion have a significant effect on the change rate of compressive strength of concrete cube,and the degree of freeze-thaw is greater than that of chloride ion.Only in the freeze-thaw environment,when the axial compressive strength of concrete prism is taken as the damage index the damage is most serious;The second is the salt freezing corrosion of 3.5%sodium chloride solution,but the corrosion damage degree of concrete is less than that of freeze-thaw and chloride freezing when the sulfate and chloride exist at the same time or the ion concentration in the salt solution exceeds a certain limit,the damage is not aggravated with the increase of ion concentration.At the same time,the damage evolution equation of compressive strength of concrete cube and other indexes changing with the level of corrosion factors is established on the basis of the test data.Based on the damage theory,the damage degree of concrete is defined through the specific corrosion test of prism,and the damage constitutive model of concrete under different corrosion environments is established by combining the stress-strain curve of the specimen.The research results can provide reference for engineering practice,testing and maintenance.