The Research Of Chloride Diffusion In Concrete Structure Using Close-Form Solution

The durability problem of the concrete structure has occurred due to different corrosion factors of the environment. The problem has been affecting the use of the concrete stucture and led to huge economic lose. The chloride diffusion is the most evident factor of the durability problem. At present, the Close-Form Solution(CFS) for the diffusion is based on Fick’s Second Law and mainly considering the one-dimension or orthogonal two-dimension model, less for the nonorthogonal model. The time-dependency of surface chloride concentration and chloride diffusion coefficient is the consensus of academia, but less CFS research is carried out with the two time-dependent parameters. To solve the problems above, the paper carries on the research work on the following areas:1. The chloride distribution rule in concrete is established by CFS for the nonorthogonal two-dimension diffusion. The CFS for sector is achieved by the polar coordinate. The example analysis shows that the nonorthogonal two-dimension diffusion rule is different from the one-dimension or orthogonal two-dimension diffusion. The impact of two-dimension diffusion has a negative correlation with the angle of sector.2. The time-dependency of the surface chloride concentration and the diffusion coeffient is analyzed in the paper. By using the Integral Transformation Method(ITM) twice, the derived CFS can take the time-dependency of the two parameters into account. The surface chloride concentration can vary as a power function or a logarithm function and the diffusion coefficient decreases as a continuous power function. A CFS with much better applicability can be derived by using the ITM three times. The CFS is proved by the FEM and the in-situ data. The function of surface chloride concentration could be power, logarithm, exponential or piecewise. The diffusion coefficient can be a continuous decreasing power function or piecewise function. Through the example analysis, the impact of the time-dependency proves valued and the piecewise time-dependency shows the influence on the durability design.3. The theory of the diffusion control zone for the time-dependent diffusion is studied by CFS. The CFS for the two-dimension diffusion has been derived with the consideration of the time-independent or time-dependent surface chloride concentration and diffusion coefficient, which is used for the diffusion control zone at the orthogonal area. Through the example analysis, the two-dimension diffusion leads to the chloride enrichment at the corner. It could not be ignored in the service life prediction.