We propose and analyse a unified reactive transport model for leaching of cement paste in brines, with and without CO2. We investigate the impact of the boundary conditions on the rate of propagation of the reaction. In agreement with experiments, we observe distinct mechanisms as a function of the pH and the CO2 concentration of the leaching brine. In particular, clogging is observed at intermediate concentration of CO2 while higher concentration accelerates the reaction. In addition, we leverage the flexibility of the simulator to explore the impact of different models on the simulations. In particular, aqueous species, phase assemblage and diffusion coefficient model are varied. We demonstrate that in order to be able to obtain quantitative predictions, it is important to accurately capture the feedback between chemical reactions, microstructure and macroscopic transport parameters.