Modelling the durability of novel cementitious materials exposed to the drying and carbonation

The behaviour of novel cementitious materials (low clinker cement CEM II/C and CEM VI) exposed to CO2 is simulated and investigated with a simplified model in this paper. Based on studies of the evolution of the phase assemblage obtained from GEMS, the carbonation process is simplified into the dissolution of one combined Cacontaining phase and the precipitation of calcite phase. The purpose is to quantify some physical variables representative of the reactive transport properties: saturation degree for drying, porosity, calcite and Ca-containing phase content for carbonation. The dissolution rate of the Ca-containing phase and corresponding precipitation of calcite are assumed to be determined by the saturation degree, the partial pressure of CO2, and the concentration of calcium in solid phases. The carbonation process is assumed to be ruled by two phenomena: the water migration through the connected porosity and the diffusion of carbon dioxide in the gaseous phase, which are governed by two mass conservation equations. This model is solved by the finite element code Cast3M, and is verified using experimental data from carbonation depth measurements using a pH indicator, portlandite and carbonate profiles from thermogravimetric analysis and drying experiments on mortar and concrete.