Study On Corrosion Behavior Of Reinforced Concrete Specimens Based On Different Cementitious Materials

As a widely used structural form of buildings,most reinforced concrete structures can be damaged under the environmental erosion,especially the corrosion of steel bars can cause cracks in the concrete.To analyze the causes of the steel corrosion cracking and propose corresponding improvement measures,this thesis studies the corrosion behavior of ordinary Portland cement concrete,magnesium phosphate cement concrete,and magnesium oxysulfate cement concrete based on the corrosion behavior of reinforced concrete specimens of different cementitious materials under the electrochemical corrosion and seawater corrosion.The specific research contents are as follows:(1)The electrochemical corrosion tests are conducted to analyze the cracking time and maximum crack width of ordinary Portland cement concrete,magnesium phosphate cement concrete,and magnesium oxysulfate cement concrete specimens,and the fitting curves and equations of the crack width and cracking time of the three cementitious materials are obtained.The results show that the protective effect of the magnesium phosphate cement concrete on steel bars is better than the ordinary Portland cement concrete,and the ordinary Portland cement concrete is better than the magnesium oxysulfate cement concrete.(2)Analysis of the cracks on the surface of the reinforced concrete specimen after electrochemical corrosion shows that the cracks are distributed along the direction of the steel bar.Analyzing the cracks in the reinforced concrete section,it is found that the coarse aggregate increases the cracking degree of the crack and leads to different bending degrees of cracks for the cracks with a single development trend.(3)The macroscopic morphology of reinforced concrete specimens before and after corrosion is compared after electrochemical corrosion and seawater corrosion.The inner and outer rust layers of steel bars are analyzed by environmental scanning electron microscopy and energy dispersive spectrometer,and the composition distribution of corrosion products of steel bars under different microstructure of cementitious materials is obtained.By using XRD diffractometer,the rust layer composition of reinforced concrete with different cementitious materials is measured,and the crystal composition of corrosion products of steel bars under different cementitious materials is obtained.The corrosion resistance of steel bars after seawater corrosion is analyzed by three-electrode system.It is found that the corrosion resistance of magnesium phosphate cementitious material steel bar samples is better than the silicate cementitious material steel bar samples,and the corrosion resistance of silicate cementitious material steel bar samples is better than the magnesium oxysulfate cementitious material steel bar samples.(4)The finite element software ABAQUS is used to simulate the cracking form of concrete under the action of steel rust expansion in the plane element simulation of the reinforced concrete structure.The results of the macro and mesoscopic simulations are in good agreement with the experimental data,which verify the effectiveness of the model.The parametric analysis of concrete strength,different steel bar diameters and steel bar positions is conducted.The research results of this thesis provide a certain reference for the service life evaluation and residual life prediction of reinforced concrete.