Abstract: Numerical simulation is an effective means to study the contact dissolution of cement-based materials; but the problem regarding its 3D finite element modeling has not been effectively solved. In view of this, attempts were made to build a 3D calcium dissolution model. First of all, the governing equation of calcium ion transmission was deduced in line with the mass conservation law, and on this basis a 3D mathematical model of calcium ion transportation was built based on the solid-liquid equilibrium curve, the porosity evolvement model and the effective diffusion coefficient evolvement model. The ion exchange boundary condition is incorporated to reflect the change of calcium ion concentration at the contact boundary, which provides the basis for calculating the quantity of calcium dissolution. Furthermore, according to the Galerkin finite element method, the finite element computing scheme is derived for numerical solution of the proposed model. The proposed model and FEM program is validated with two examples. Result demonstrates that the proposed model is applicable to simulating the multidimensional contact dissolution of cement-based materials. The spatial distribution and temporal distribution of characteristic variables are obtained by the numerical test of three-dimensional contact dissolution of a cylinder specimen. In 3D state, the contact dissolution develops from the surface to the inside, the dissolution rate varies from fast to slow in the same position, and the radial dissolution rate is larger than axial dissolution rate. The research achievements offer theoretical basis and approach for analyzing the impact of dissolution of cement-based material.

Key words: cement-based material, calcium ion transmission, contact dissolution, characteristic dissolution, three-dimensional finite element model