Experiment Research Of Transport Model Of Chloride In Concrete Under Cycles Of Wetting And Drying Conditions

Reinforced Concrete structures have been widely used in which both concrete and steel bars can be made the best use of. But still a great deal of concrete structures have been invalidated ahead for lack of durability.Especially in marine environment, chloride ion penetrates into concrete through the cracks which leads to the corrosion of steel bars.Then the durability of the structures declines and the security of the structures are changed. So the problem of durability of concrete structures caused by chloride ions corrosion is very important and needed to solve exigently.In this paper, it was mainly studied the penetration capacity of chloride ions in concrete with different concentration of NaCl and different water cement ratio under the cycles of wetting and drying conditions. Considering the effect of pores' adsorption affinity, it discloses the transport mechanism of chloride in concrete under the cycles of wetting and drying conditions roundly.The degeneration mechanism of concrete under both wetting and drying cycle and salt attack is expatiated. And based on Darcy's law, the model theory of unidirectional transport of chloride ions is described.Chloride ions' contents in each layer of different concretes are mensurated by experiment. Comparatively analyzing the experiment data in two conditions of the entire state of immersion and wetting and drying cycle, a nonlinear fitting is made to obtain the empirical formula of chloride concentration changing with invading depth and corrosion time, which considers concentration diffusion and pore adsorption separately. Experiment data are in good agreement with data calculated by the formula for different water cement ratio and concrete adulterated with fly ash. Leading in the effect of pore adsorption based on traditional diffusion model, the formula can better accord with the engineering practical situation being acted by several factors. Test results show that the invading depth of chloride ions in concrete under wetting and drying cycle is larger than that under immersion. With accretion of environment chloride concentration, the effect of chloride penetration in concrete is larger under both conditions. Based on the formula, the effect of pore adsorption is further considered. The difference between the state of wetting and drying cycle and immersion is considered to be brought on by the effect of pore adsorption mainly and it is found that the connection of chloride ions' contents caused by the effect of pore adsorption and concentration diffusion is a kind of linear compages.