Corrosion Behavior Of Reinfored Bar In Concrete And Chloride Ion Transport

There are high concentrations of chloride and sulfate ions in seawater and coastal saline soil. In addition to the degradation of the performance of the concrete, the composite ion can also cause reinforcement corrosion in concrete by osmosis. This makes the durability of reinforced concrete structures in marine environment more prominent. At the same time, there are a huge economic losses and security risks. Correctly grasp the corrosion of reinforcing steel bar under the effect of compound ion mechanism, and seawater dry-wet circulation under the action of chloride ion transport in the reinforced concrete and steel bar corrosion behavior, the service life of structure can be predicted more accurately, provide the basis for the timely diagnosis and repair of structural corrosion problems. Therefore, the corrosion process and corrosion behavior of steel in different simulated salt solutions and different types of concrete are studied systematically in this paper, and uses the method of combining the macroscopic observation and microscopic analysis, reveals the mechanism of corrosion. This paper’s mainly studies are as follows:(1) The corrosion behavior of reinforcing steel in different kinds of sulfate corrosion solutions and different concentrations of sulfate solution was studied by electrochemical impedance spectroscopy. The following conclusions are obtained by experiment: Steel lack of basic environmental protection, produced corrosion in a short time. In neutral environment, the higher the concentration of sodium sulfate, the higher the corrosion degree of steel bar. Saturated Ca(OH)2 and Na2SO4 solution composite, powder cement composite resulted ettringite and gypsum formation on the surface of steel, delaying the corrosion rate of reinforcing steel. Compared with the passive film of the steel electrode, the corrosion time of the passive film is shorter than that of the passive film, comparison of corrosion of seawater, 1%NaCl+0.5%MgSO4,1%NaCl+ saturated Ca(OH)2 three corrosion solutions, sea water is more than 1% NaCl+0.5% MgSO4, 1%NaCl+0.5% MgSO4 is greater than 1% NaCl+ saturated Ca(OH)2.(2) The chloride ion penetration in concrete was accelerated by the laboratory and dry wet cycle, according to the second law of Fick, the variation law of chloride ion diffusion coefficient is studied. The conclusions are as follows: With the increase of corrosion time, the chloride ion content in concrete increases gradually, and with the increase of the depth of chloride ion content is gradually reduced, and finally tends to be stable. In the concrete mixed with fly ash and slag can improve the resistance of concrete to chloride ion permeability, and can significantly reduce the chloride ion diffusion coefficient and surface chloride concentration. Under the same corrosion conditions, for C30 series of concrete, the content of fly ash is 15%, which is the best dosage, which can effectively reduce the chloride ion permeability of concrete, effectively prevent the intrusion of the outside world chloride ion. Concrete admixture quantity in 30% effect is the best. Surface chloride ion concentration is the lowest, slag in more than 20% when the resistance to chloride ion erosion performance improvement is not obvious.(3) By alternating current impedance spectroscopy method, study the influence of reinforcement corrosion in concrete corrosion solution, the microstructure of reinforced concrete was analyzed by SEM, and the following conclusions were obtained: The influence of corrosion solution on the corrosion of steel bar is the size of the order: sea water is more than 3.5%NaCl is greater than 3.5%NaCl+5% Na2SO4,Concrete internal temperature in the dry wet cycle process has a cumulative process and response lag law. With the increase of the number of dry wet cycles, the internal temperature of the accumulation gradually increased, will gradually accelerate the corrosion of steel bars in concrete. Reinforced concrete in chloride environment corrosion product is density, the presence of sulfate ions in the composite salt causes the corrosion products loose, corrosion stress reducs, and sulfate ion in the early dense concrete structure can delay chloride ion penetration rate, so as to delay the corrosion cracking of reinforced concrete. Concrete mixed with fly ash and slag concrete can be made of rebar depassivation time delay, and can make the steel bar when the concentration of chloride ion concentration increases, and also can improve the capacity of reinforced concrete.