Experimental Research On Chloride Threshold Level Using Seepage Pressure Method

It is a key issue in structure durability research to determine the chloride threshold level in concrete under chloride contained environment. In order to explore a quick experimental method measuring the chloride threshold level in concrete, an experimental research and theoretical analysis on the distribution of chloride concentration in concrete under stressed solution is introduced. The main researches and achievements are as followings:(1) The theoretical research on the chloride transport in concrete under stressed solution has been investigated. According to the transport mechanism, the chloride transport model in concrete is developed. The factors that influence the accumulation of the chloride in concrete have been studied, including the binding capacity of the concrete and the capillarity.(2) Through improving the apparatus which determines the permeability of the concrete, the instrument measuring the chloride threshold level in concrete under stressed solution is developed. The permeability coefficient of concrete with 0.65 water to cement ratio (w/c) under 1.0Mpa pressure and the distribution of chloride concentration during different pressuring time are measured. The results show that we can ignore the binding capacity of the concrete during quite a short time less than 20 days. Also the conclusion can be used in numerical simulation.(3) The distributions of the chloride concentration along the depth of concrete are obtained. The results show that, with pressing time increasing, the free chloride concentration increases at the same depth in concrete. The conclusions from numerical simulation agree well with experimental results. Comparing with the distribution of chloride after chloride diffusion only, using seepage pressure method abviously accelerates the chloride transport progress.(4)Comparing the results under the same water to cement ratio (w/c) but different pore saturation degree of the concrete, the capillary accelerates the chloride ingress into the concrete when the concrete pores are unsaturationc. Also comparing the results under the same pore saturation but different water to cement ratio (w/c), the higher water to cement ratio accelerates the chloride ingress into the concrete. The present paper provides good experimental and theoretical bases for the quick method measuring the chloride threshold level in concrete.