Establishment And Experimental Analysis Ofcorrosion Force Model For Reinforced Concrete Under Chloride Salt Erosion

Reinforced concrete structures such as port engineering in coastal areas,offshore structures,and buildings in wet environments are susceptible to erosion by environmentally erosive substances(especially chloride ions).The steel bars in the reinforced concrete structure begin to rust,and the volume of the rust products is often 2 to 4 times the volume of the original steel bars.Corrosion products are squeezed by concrete and steel bars,producing rust expansion forces that cause the concrete to be pulled circumferentially.With the increase of rust products,the rust expansion force of steel bars increases continuously.When the tensile strength limit of concrete exceeds the limit,cracks begin to appear in reinforced concrete structures.The bearing capacity,safety and durability of the reinforced concrete structure after cracking have been reduced,which seriously threatens the personal safety of the user.Measuring the magnitude of rust expansion force is of great significance for the quality evaluation and maintenance of reinforced concrete structures,durability design,structural reinforcement,structural service life and residual life prediction.In this paper,the reinforced concrete structure under the corrosion of chloride salt is taken as the research subject.By establishing the uniform corrosion model and the non-uniform corrosion model,and conducting the electric accelerated corrosion test,the concrete surface strain and the steel rust expansion of the reinforced concrete specimen under uniform and non-uniform corrosion are analyzed.The relationship between forces,discuss the size of the rust expansion force at the time of cracking.With this theme,the following aspects have been studied:(1)Review the relevant literatures at home and abroad to introduce the research status of rust and rust expansion of reinforced concrete structures.(2)Based on the elastic mechanics,the relationship model between the surface strain of the reinforced concrete specimen and the rust expansion force of the steel is established under the condition of uniform corrosion.Using this model,it is possible to obtain the rust expansion force at any time before the crack occurs in the specimen by directly measuring the surface strain of the concrete.Matlab and Origin software are used to carry out the programming calculation of the model and the drawing of related graphics and charts.(3)Produce a rectangular parallelepiped reinforced concrete specimen with a square cross section,and conduct an electric accelerated corrosion test to simulate the process from uniform service to cracking of the reinforced concrete structure under uniform corrosion.According to the test results,the model of the relationship between surface strain and steel rust expansion force of reinforced concrete specimens is verified and corrected,and the validity of the model is proved.From the test data,the relationship between the rust expansion force of the steel bar and the surface strain of the concrete,the corrosion rate of the steel bar at the time of cracking,the variation of the rust expansion force of the steel bar with time and the distribution law of the depth of the steel bar are further explored.(4)Based on the theory of elastic mechanics,a non-uniform rust model with a steel bar in the middle of the regular cube is established.In the model,the distribution of rust products is in the form of a sinusoidal function,which is consistent with the actual corrosion of the steel bars under the concrete protection layer.According to the corrosion rate at the cracking time and the expansion rate of the rust product,the magnitude of the rust expansion force at the time of cracking is calculated.The model analyzes the influence of the diameter of the steel bar,the expansion rate of the corrosion product and the thickness of the concrete protective layer on the rust expansion force,and proposes a method for prolonging the service life of the reinforced concrete structure.(5)Conduct electric accelerated corrosion test to simulate the process of reinforced concrete structure from service to cracking under non-uniform rust condition,and record the whole test process with CCD camera.At the same time,use relevant software to process the data and analyze the change law of concrete surface strain.