Computational 3D simulation of calcium leaching in cement matrices

Abstract

Calcium leaching is a degradation process consisting in the progressive dissolution of the paste by the migration of calcium atoms to the aggressive solution. It is therefore, a complex phenomenon involving simultaneously several crystalline phases and dissolution and diffusion processes. During this work a new program for the simulation of the degradation process in three dimensions was developed. The program decouples the transport and chemical reaction equations and solves them separately. Transport equations are solved by the Finite Element Method using an algorithm that enables the description of multi-ionic solutions on arbitrary domains. The chemical algorithm accounts for the degradation of portlandite and the CSH gel which are the main constituents of ordinary Portland cement matrices. The program was used to simulate accelerated calcium leaching by a 6M ammonium nitrate solution, in order to test it. The obtained output was a three dimensional representation of the matrix and the values calcium concentration of each particular pixel of the structure at different time steps. This not only makes possible to study the calcium to silicon ratio, porosity and elastic properties of each particular phase as a function of time but also as a function of the position within the matrix.