Modelling and simulation of concrete carbonation with internal layers

Transport and reaction of carbon dioxide with alkaline species in concrete is modelled by a closed system of ordinary and partial differential equations. Varying porosity and varying external exposure as well as nonlinear reaction rates are taken into account. Proper nondimensionalisation is introduced to pay attention to the different characteristic time and length scales. We emphasise the effects of the size of the Thiele modulus on the penetration curves. It is shown that an internal reaction layer is formed whose properties are related to the Thiele modulus. The model is tested for accelerated and natural carbonation settings and is found reliable. A discussion of the effects of different sizes of several model parameters yields information about their relevance. Special attention is paid to the effects of moisture on the whole process. For the accelerated setting, a water-production layer is observed.