Evaluation of Chloride Penetration into Cementitious Materials Using Short-Term Ponding Test

Abstract

Many concrete structures have recently been constructed on the seashore. In structures exposed to seawater, chloride ion is transported through concrete by various mechanisms such as diffusion, and results in the corrosion of embedded steel in concrete structures. So, the chloride transport rate in concrete needs to be predicted, to prevent degradation of the durability of concrete structures in service life. The chloride ion diffusion coefficient is a crucial factor in evaluating the chloride transport rate in concrete. A number of test methods have been developed to measure the chloride ion diffusion coefficient of concrete. Most of these test methods require excessive test duration, or else represent a chloride ion penetration mechanism that does not adequately reflect chloride ion transport in real concrete structures. This thesis proposes a new test method to determine the chloride ion diffusion coefficient, while avoiding these deficiencies. The proposed method incorporates a new analytical approach that determines the diffusion coefficient from the change of chloride ion concentration in a source solution. The proposed method can be called a short-term ponding test, in comparison with traditional long-term immersion tests. Validation tests were performed to verify the developed test method and mathematical model. It was found that the proposed test method and analytical solution could estimate the chloride ion diffusion coefficient within two weeks. The short-term ponding test was validated by comparison with a long-term immersion test, and an electrical migration-diffusion test (CTH test). Both the long-term immersion test and the short-term ponding test produced similar results, but the CTH test results differed significantly. This indicates that the short-term ponding test is a time-efficient and realistic method that reflects the actual marine environment. Numerical analysis was performed to verify assumptions in the mathematical model of the short-term ponding test. Pdepe function, one of the Matlab functions, was used to calculate the chloride concentration with time in the source solution, solving the governing equation of the mathematical model. The effects of concrete age and concentration change in the source solution on the diffusion coefficient in the short-term ponding test were verified. From numerical analysis, it can be concluded that in the short-term ponding test, the effect of concrete age and concentration change in the source solution can be neglected. The chloride binding isotherm of the short-term ponding test was also verified. Inverse analysis was adopted to estimate the effective diffusion coefficient, and Freundlich binding isotherm coefficients. It was found that the linear binding isotherm could be assumed in the short-term ponding test.