Study On Corrosion Law Of HRB400E Steel Bars Caused By Stress And Defects

At present,the most widely used building structure in bridge construction is reinforced concrete structure.As the main stress component of the structure,the corrosion of inner reinforcement not only affects its mechanical properties,but also reduces the mechanical properties of the whole structure,thus affecting the safety and durability of the bridge.In order to study the corrosion rule of HRB400 E steel bar,the research method combining experiment and simulation is adopted in this paper.Respectively apply different experimental variables of stress,defect and stress-defect coupling to reinforcing bar,explore the corrosion process of reinforcing bar under different conditions,and study the electrochemical impedance,mechanical properties and structural changes of reinforcing bar by means of electrochemical and macro-and micro-characterization.Based on the above research,establish the corrosion process model and explore the development process and corrosion mechanism of reinforcing bar defects under stress conditions.The main achievements are as follows:(1)Experiments on accelerated corrosion of steel barsThe influence of tensile stress on corrosion and mechanical properties of steel bar is studied.The accelerated corrosion test is carried out on the flawless HBRB400 E steel bar specimens under 33 MPa,67 MPa,100 MPa and 150 MPa tensile stress respectively.The electrochemical test shows that the corrosion rate increases obviously when the tensile stress is greater than 67 MPa,and the corrosion rate is0.722 mm/a at 150 MPa.The elongation of reinforcement decreases by about 7.55%.Metallographic structure is loose and transgranular corrosion occurs.To study the influence of surface defects on corrosion,accelerated corrosion test was carried out on steel bar with micro-cracks and scarring defects.Metallographic structure in defective area has different structures and contains a lot of harmful elements such as nitrogen,phosphorus and sulfur,which leads to accelerated local corrosion in defective area,and the corrosion rate of steel bar with crack defect increases by about 179%.To investigate the effect of defects and stresses on corrosion,67 MPa tensile force was applied to accelerate corrosion test after pre-cracking defects on the surface of reinforcement in order to investigate the corrosion at critical points.The tensile stress causes micro-cracks and increases the original cracks,which accelerates the rust under the coupling effect,and the defective surface is not easy to produce oxide film.(2)Simulation prediction of reinforcement defect corrosion under tensile stressBased on Nernst-Planck equation and COMSOL software platform,the corrosion process of cracks,scars and pits under tensile stress is simulated according to experimental conditions.From the internal stress distribution of different defects,change of electrolyte potential,concentration of various substances and ion migration,the change process of micro-corrosion morphology and local corrosion of reinforcement defects are analyzed and studied.The main reason for the different corrosion conditions of different defects is the efficiency of material exchange between inside and outside.Among them,the depth of corrosion in scarring defects is the highest,reaching 0.226 μm on the 15 th day.Comprehensive analysis of test and simulation shows that tensile stress and different defective structures can significantly increase the corrosion rate of steel bars.Under the coupling action of tensile stress and defect,the corrosion rate of steel bars surface increases 35.93% compared with that of only existing defect and 194.37% compared with that of only existing tensile stress,especially the stress concentration at defect leads to the increase of local corrosion.(3)Corrosion mechanism of steel bar under coupling action of tensile stress and defectsThe electrochemical experiment results show that the coupling effect of tensile stress and defect accelerates the corrosion process of steel bar and prevents the formation of stable oxidation film on the surface.The effect of surface defect on corrosion is much greater than that of tensile stress.Based on comprehensive experiment and characterization analysis,a new corrosion mechanism model of steel bar in bridge with "tear cavity circulation expansion" mode is put forward innovatively,which provides theoretical reference for grasping the actual condition of bridge and maintaining it timely and scientifically.