| The durability of concrete structures is the major issue which engineering circles especially pays attention now, and chloride ion corrosion is the main factor of influencing durability of concrete. Invaded chloride ions in interior concrete will cause passivation and corrosion of reinforce steel bar. Along with the aggravating corrosion, the volume expanding of bar corrosion product in concrete will lead cracking or spalling of concrete protective layer, and then durability failure of the concrete structure will happen with corrosion developing.In this paper, study background is the natural climate and chlorine salt environment, according to the mix proportion of concrete estimated by the existing concretes sample which had been adopted in the scene, and considering influencing factors including environment, curing periods, water-cement ratios and fly ash, the corrosion rule of chloride ion in concrete and major effect factors are studied under the test condition, and the variation rule of chloride ion diffusion coefficients of the concrete along with time are also analyzed in detail. The effect of anti-chlorine erosion of fly ash concrete in different fly ash content is tested and analyzed under under chloride environment.Influencing factors of the diffusibility of concrete are studied under different test conditions in this paper, the main results are below:1. According to measued results by the alternating current baridge method and the NEL method, thare is a good correlation among diffusion coefficients with water-cement ratios and porosity and compressive strength of test concrete. It is evident that diffusion coefficients using alternating current baridge method are bigger than those diffusion coefficients using the NEL method. There is also a good correlation among diffusion coefficients using the NEL method with porosity and compressive strength of test concrete, in which correlation coefficients are 0.98 and 0.99, respectively. The result shows that the NEL method is a better measurement method to reflect the true performance of anti-chlorine erosion of concrete.2. Under the artificial corrosible environment, there are two region of chloride ion with convective and stable proliferative in the concrete sample. The free chloride ion concentration reduces in the stable proliferative with increase of erosion depths, and the distribution of the chloride ion concentration increases with water-cement ratios in the same penetration depth, generally. The free chloride ion concentration in the stable diffusion area increases with increase of the erosion test time, but reduces with the increment of curing time under the same water-cement ratios, eg. the free chloride ion concentration in concret of curing 56d is the 70%～90% of the 28d'in the same erosion depths.3. Diffusion coefficients of test concrete reduce with length of curing or erosion time, eg. The diffusion coefficient of curing 200d A15 is only 37.9% of the curing 40d A11's. When the erosion time is same, diffusion coefficients of test concrete increase with increase of water-cement ratios, eg. The diffusion coefficient of water-cement ratio 0.45 A51 is only 65.5% of the 0.61 water-cement ratio A11's。4. A model of diffusion coefficient with time has been established to simulate the diffusibility of existing concrete after 27 and 37 years under the standard curing and artificial corrosible environment. The result show that the simulation method of artificial corrosible environment is a more accurate method than NEL method under standard curing condition,in which more influencing factors are considered and the results are more closed to that under the natural environment.5. The free chloride ion concentration and chloride ion diffusibility in the stable diffusion area are all reduced with the increment of fly ash content and length of curing periods under artificial corrosible environment.
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