Analysis Of Corrosion-induced Cover Cracking Of Reinforced Concrete Under The Environment Of Freezing And Thawing

Cracking of concrete protective layer caused by corrosion of steel bar will have a great influence on the function of structure use,even endanger the safety of the structure.The concrete structure in the cold area is often subjected to freezing and thawing cycle,which causes the concrete to produce freezing and thawing damage,peel off and produce micro-cracks,which will aggravate the erosion of the harmful medium to the concrete interior,thus accelerating the corrosion of steel bars in the concrete.Therefore,the establishment of rust and swelling cracking conditions of concrete protective layer under freezing and thawing environment is of great significance to the durability and life prediction of concrete structures.There are many researches on concrete rust and swelling cracking under the general atmospheric environment,chlorine salt erosion environment.There is still a lack of research on the rust and swelling cracking of concrete in freezing and thawing environment.In this paper,the problem of rust and swelling cracking of concrete in frozen and thawing environment is studied by means of theoretical analysis and experiment,the main work is as follows:(1)A theoretical model of rust and swelling cracking of reinforced concrete protective layer is established based on fracture theory.Using double-layer thick wall cylinder model,the concrete is divided into cracking layer and non-cracking layer.Based on fracture theory and elasticity theory,the whole process of concrete rust expansion cracking is analyzed,and the displacement of the whole field stress and reinforced concrete interface is obtained.This paper presents a theoretical calculation model of the corrosion rate of reinforced steel with compressive strength of concrete,the ratio of the thickness of concrete protective layer to the diameter of steel bar and the volume expansion rate of the rust product as the main parameters,The proposed model is verified by using the experimental data at home and abroad.The parameter analysis is carried out by using the proposed theoretical model,and a simplified calculation model of rust expansion cracking condition characterized by critical mass loss rate of steel bar and a formula for calculating the position of concrete cracking point and the length of critical crack are given.(2)The acceleration test of steel bar corrosion of reinforced concrete specimens with freeze-thaw damage was carried out.The rapid freezing and thawing tests of cubes,prism concrete test blocks and reinforced concrete specimens were carried out,and the mechanical properties of concrete under different freezing and thawing cycles(50,100,150,200,250)were tested.The rapid freeze-thaw test of 5 kinds of reinforced concrete with different thickness of protective layer and the diameter of steel bar was designed,and the additional current accelerated corrosion test was carried out for reinforced concrete specimens after different freezing and thawing cycles.The corrosion rate of reinforced concrete specimens after rust heave and cracking is obtained by the crack of concrete rust swelling and cracking time with different freeze-thaw cycles.Using DIC(Digital Image Correlation)technology to monitor the surface strain of the protective layer in the process of accelerating the corrosion test of steel bar,the strain of the concrete surface above the steel bar at the time of concrete cracking is analyzed,and the shape of the rust heave cracking of the freeze-thaw damaged concrete is studied.(3)The calculation model of reinforced concrete rust heave cracking condition under freezing and thawing environment is establishedThe freeze-thaw damaged concrete is divided into freeze-thaw damage layer and undamaged layer,and the calculation method of splitting tensile strength of damaged layer and undamaged layer concrete is put forward.Based on the theoretical model of corrosion rate of reinforced steel and the calculation method of concrete strength of damaged layer at the time of concrete rust and swelling cracking,the calculation model of rust heave cracking condition of frozen and thawing environment with the number of freeze-thaw cycles and the compressive strength of concrete as the main parameters is established,and the model is modified by using the test results.