TIME-DEPENDENT CHLORIDE DIFFUSION MODEL BASED ON LUMPED CONCENTRATION MATRIX AND PRECISE TIME-INTEGRATION METHOD

Abstract

In order to overcome the disadvantages of traditional models which cannot balance the computational accuracy, efficiency and numerical stability by adopting the coordinated concentration matrix and the Taylor series expansion technology, a time-dependent chloride diffusion model was proposed based on the lumped concentration matrix and the precise time-integration method: The governing equation of time-varying chloride diffusion was transformed into that of equivalent constant chloride diffusion by introducing the equivalent diffusion time. a finite element model for time-varying chloride diffusion was established based on the lumped concentration matrix and the Galerkin weighted residual method. a time-dependent chloride diffusion model which is based on the lumped concentration matrix and the precise time-integration method was proposed by adopting the Pade series expansion technology. The applicability of the proposed model was verified through a comparison among the traditional finite element model, analytical model and natural exposure field data. The analysis shows that: it is more accurate to adopt the lumped concentration matrix than to adopt the traditional coordinated concentration matrix since the former can solve the numerical stability problems such as oscillations and negative values. The computational accuracy and efficiency can be improved obviously by adopting the Pade series expansion technology which requires only a small scale factor to guarantee the computational accuracy, compared with the traditional Taylor series expansion technology. The proposed model can not only balance the computational accuracy, efficiency and numerical stability, but also be insensitive to the meshed sizes of spatial grids and time steps.