Anti-Corrosion Law And Mechanism Of Steel Reinforcement In Self-Healing Concrete

Reinforced concrete is the most used civil engineering material worldwide.However,the concrete material itself has shortcomings such as high brittleness,low tensile strength,and easy shrinkage and deformation in the early stage.During service,the interior or surface of the concrete is prone to produce many micro-cracks and defects.These cracks become the channels for harmful substances to enter the interior of the concrete,resulting in corrosion and expansion damage of steel bars,which are also one of the key factors that reduce the service life of concrete.Traditional steel anti-corrosion technologies such as surface coating,electrochemical protection,migration-type rust inhibitor,etc.have shortcomings such as reduced concrete performance,limited application environment and poor economy,which do not meet the development strategy of sustainable development and carbon emission reduction.In order to realize the integrated design of self-healing of cracks and anti-corrosion of steel bars in reinforced concrete,this paper proposes a method of corrosion prevention of steel bars based on microbial mineralization technology（MICI）.The type III and type IV microbial repairing agents independently developed by our research group were applied to concrete,and the self-healing performance of concrete cracks and the anti-corrosion performance of steel bars under the curing conditions of ordinary aqueous solution and simulated marine environment solution were explored respectively.The anti-corrosion mechanism of steel bars in concrete was discussed in detail in two aspects:Biofilm formation and concrete crack repairing to prevent the erosion of external harmful media.The main research conclusions and innovations obtained are as followed:（1）Under the condition of ordinary solution curing,the repair ratio of the crack area of the concrete specimens with type III and type IV microbial repairing agent was higher than 95%at the curing time of 28 days;the repair ratio of resistance to chloride ion penetration reached 78.1%and85.5%respectively;ultrasonic pulse speed were significantly improved reaching 3.35 km/s and 3.30km/s respectively;the relative water permeability coefficients were 2.46%and 1.34%respectively,all of which had good resistance to water penetration.The electrochemical impedance results show that the concrete specimens of type III and type IV microbial repairing agents have a larger capacitive reactance radius,and the impedance modulus and phase angle in the low frequency region are significantly improved compared with the control group,showing better corrosion resistance.The weight loss test results are consistent with the electrochemical test,and the calculated corrosion rate of microbial groups is between 0.008 mm·y^-1 and 0.009 mm·y^-1;Under the curing condition of simulated marine solution,for type III and type IV microbial group,the area repair ratio of the concrete specimens were 93%and 95%after curing for 28 days,the resistance to chloride ion penetration repair ratio were 73%and 75%,respectively,and the ultrasonic pulse speeds were 3.13km/s and 3.27 km/s,respectively.Compared with the specimens cured in ordinary solution,the corrosion performance of steel bars,the impedance value and weight loss results show that the corrosion performance is reduced.The secondary repairing performance and steel corrosion resistance performance of the specimens in the ordinary solution and the simulated marine solution were lower than the primary repair.（2）The anticorrosion mechanism of the protective film on the surface of the steel bar was explored in the simulated mineralization solution.In order to facilitate the microscopic detection of the protective biofilm,an experimental study was carried out on the steel sheet,and it was concluded that the steel sheet was soaked in the simulated mineralization solution for 9 days.After that,the corrosion performance test of steel sheet was carried out.The electrochemical test results show that the impedance modulus value and phase angle in the low-frequency region of the microorganism test group are significantly improved,and the i_corr was about 5 times lower than that of the control group.The R_ct value of the microorganism group was calculated by the fitting circuit reaches 3461Ω·cm²,the Q_f value increased significantly,showing a better anti-corrosion effect.The weight loss test showed that the corrosion rate of the steel sheet obtained in the solution containing the bacterial solution was 0.01 mm·y^-1,which was 3 times lower than that of the control group.The morphology,composition and particle size of the protective film on the surface of the steel sheet were analyzed by microscopic characterization technology,and the anti-corrosion effect and related mechanism of the protective film was revealed from the aspects of the compactness of the protective film,the compatibility with the steel sheet substrate and the inhibitory effect on the corrosion reaction.（3）The anti-corrosion mechanism of the repairing of concrete cracks was explored.From the perspective of microbial mineralization-induced deposition of calcium carbonate on crack repairing,through the repair performance of crack area repair rate,ultrasonic pulse speed,rapairing ratio of the resistance to water and chloride ionpenetration,the concrete density is greatly improved while closing the transmission channels of Cl^-,O₂ and other corrosive media,which significantly improved the protective effect of steel bars in concrete.The synergistic mechanism model of"outside and inside"dual protection of crack repair and steel biofilm formation were revealed.