Study On Critical Value Of Steel Bar Depassivation In Marine Environment

With the development of our infrastructure, a lot of marine projects are under construction or have been completed. Taking the combines effects of various marine environmental factors on durability into account, this paper has studied the critical value problems of the corrosion of steel bars which are in simulated pore solution or buried in concrete specimens; also then, the chloride ion penetration resistance and the salt-frost resistance of the marine concrete are researched by using electric flux test and CDF method.The results of the evaluation of the marine concretes shows that in a simulation system of Ca(OH)₂ and Cl^--based pore solution, under normal temperature and pressure, if the pH value is ranged from 12.5 to 13.4, the critical value of [Cl^-]/[OH^-] inducing steel bar depassivation is 0.1; if the pH value is lower than 11.7, the critical value is uncertained. And then a new critical value, which can be used to check that whether steel bar is depassivated or not, is proposed——the polarization resistance of steel bar Rp is supposed to be 3×10⁵Ω·cm^-2.For the steel bars which have the same thickness of concrete, during the acceleration of chloride ion permeability, under the same acceleration voltage, the higher the water-cement ratio is, the shorter the time used to accelerating chloride ion is; if the water-cement is 0.35 and the acceleration voltage is 8V, compared with the reference concrete, the specimens mixed with 30% FA are as well, and the specimens mixed with 12% FA and 18% SL are better, and the specimens mixed 25% FA and 5% SF are the best and the steel bars in which costs the longest time to be depasivated.For marine concrete which is not mixed with admixtrues, the higher the water-cement ratio is, the lower its chloride ion penetration resistance is, and also the worse the salt-frost resistance is. For the marine concrete having the same water-cement ratio (0.35), the greater the mixed content of FA and SL is, the lower the chloride ion penetration resistance is, and the lower the salt-frost resistance is; Compared with reference concrete, if the content is within a certain range, the content of blending FA and SL will help improve chloride ion permeability resistance and salt-frost resistance of marine concrete. For the marine concrete having the same water-cement ratio (0.35), the greater the mixed content of SF and SL is, the higher the chloride ion penetration resistance is, and also the better the salt-frost resistance is; Compared with reference concrete, blending SF and SL can significantly improve the chloride ion penetration resistance and the salt-frost resistance of marine concrete.