Corrosion And Cracking Process Of Reinforced Steel Bar Under Chloride Salt-fatigue Loading

The most important factor affecting the durability of reinforced concrete structure is the corrosion of steel bars inside the structure.With the increase of corrosion time,the corrosion of steel bars becomes more serious,which causes greater harm to concrete structure.The corrosion product not only reduces the effective area of steel bar,but also weakens the cohesive force between concrete and steel bar,resulting in the failure of reinforced concrete structure.With the increase of corrosion products of steel bars,the volume of corrosion products expands rapidly,which results in cracks in concrete,promotes chloride ion penetration and accelerates corrosion of steel bars.At present,reinforced concrete is often in the service environment of fatigue load,so it is of great practical significance to study the rust cracking process of reinforced concrete under the coupling action of chloride salt and fatigue load.In this paper,experimental research and detection analysis are combined to explore and study the corrosion process of reinforced concrete from macro,meso and micro scales.Based on the growth characteristics of corrosion products,a corrosion structure model of reinforced concrete is concluded.The main contents are as follows:(1)The loading device of specimens under chloride-fatigue load coupling was designed.Constant current-dry-wet cycle accelerated corrosion method was used to rust specimens at different stress levels for different time.The composition of corrosion products and cracking of concrete were analyzed from macro,micro and micro scales.(2)The cracking conditions of specimens under different stress levels/corrosion time were found out.The half-potential test and mass loss test of specimens under different stress levels/corrosion time were carried out.The surface cracks of concrete specimens and the interface cracks between steel and concrete at different locations were analyzed.The results show that under the same corrosion time,the cracking of concrete and the corrosion degree of steel bar are more serious with the increase of stress level.The cracking of concrete at the edge of the specimen is more serious than that at the middle span.Because of the fatigue load,the corrosion cracking also occurs on the side far from the protective layer.At the beginning,the steel bar first corrodes at the edge and then increases with the corrosion time,and the corrosion of steel bar in the middle span is more serious than that in the middle span.The situation is getting worse and worse than that at the edge of the reinforcing bar.This is because the effect of translation is higher than that of bending at the beginning of corrosion,and the effect of bending is more obvious than that of translation with the increase of corrosion time.(3)The spatial distribution of the corrosion layer and the morphology of the corrosion products at the steel/concrete interface were revealed.X-ray diffraction was used to detect the phase of corrosion products,optical microscopy was used to analyze the spatial distribution of the corrosion layer on the steel/concrete interface,three-dimensional scanning was used to establish the solid model of the corroded steel bar,and scanning electron microscopy and energy spectrum analysis were used to analyze the morphology of the corrosion products and the elements of the corrosion layer.The results show that the stress level does not affect the types of corrosion products.The corrosion products of steel bars under fatigue load mainly concentrate on the side far from the protective layer.This is because the specimen is subjected to fatigue load.Under capillary action,chloride ions concentrate on the side far from the protective layer.The earlier the stress level is,the more the corrosion products are,and the more the corrosion layer is.Thickness;corrosion products first occur at the edge,and then the corrosion of the steel bar in the middle of the span becomes more serious.(4)A model of steel bar rust cracking under chloride salt-fatigue load coupling is established.Based on the experimental research and test results,the model of steel bar corrosion under chloride-fatigue load coupling is established on the basis of the analysis results of steel bar corrosion at different scales.Through the structural model,the distribution of steel corrosion and corrosion products under the coupling action of chloride salt and fatigue load can be obtained,and the cracking of concrete under fatigue load can be defined.