Modelling and simulation of concrete carbonation: competition of several carbonation reactions

Concrete carbonation, i.e. the reaction of alkaline species (inside the concrete) with atmospheric carbon dioxide, is one of the major physicochemical processes compromising the service life of concrete structures. While the main carbonation reaction is that of calcium hydroxide, other constituents such as calcium silicates or calcium-silcate hydrates in the concrete can also carbonate. Many authors neglect the carbonation of these additional constituents competing with calcium hydroxide for carbon dioxide when formulating prediction models. This paper is concerned with the theoretical and numerical investigation of this competition. In particular, the effect on the simulated carbonation depth, i.e. the depth how far the carbonation layer has advanced into the concrete at any given time, is investigated. For this purpose, the concrete-carbonation process is modelled by a semi-linear coupled system of reaction-diffusion equations. For this system, a dimensional analysis is carried out and it is solved by numerical techniques. Experimental data is used for reference.