Oxygen permeability of concrete and its relation to carbonation

• A relationship between permeability and carbonation is established.
• A performance-based carbonation prediction model is presented.
• Relationship between RH and carbonation is modelled.
• Carbonation coefficients are linked to diffusion coefficients.

The corrosion of steel reinforcement due to carbonation of concrete presents one of the major deterioration mechanisms in reinforced concrete structures. The South African concrete durability design method for reinforced concrete structures incorporates a performance based approach to evaluate the penetrability and quality of the concrete cover. With respect to carbonation, the method relies on measurement of an index of the oxygen permeability of concrete, which is used as an input parameter to a carbonation model. This paper presents a revised model for concrete carbonation, which expands common carbonation models by accounting for the effect of relative humidity on both diffusion and chemical reactions. Using experimental data, oxygen permeability results are correlated with the carbonation coefficient as well as the carbon dioxide diffusion coefficient of concrete. This correlation enables prediction of time-dependent carbonation depths of concretes based on the environmental exposure, mix design and oxygen permeability of the concrete.