In the present study, 20% concentration of CO2 is a dividing
point for defining the influence of CO2 concentration on the carbonation
depth of concrete. For low CO2 concentration (less than
20%), the increase of CO2 concentration can lead to an increase of
carbonation depth remarkably. For high CO2 concentration (more
than 20%), the increase of CO2 concentration has almost no influence
on the carbonation depth. This is largely due to the change
of the porosity and capillary pore structure caused by concrete carbonation
at higher CO2 concentrations.
For low surface CO2 concentrations, the penetration of CO2 into
concrete can be estimated using the diffusion model given by Eq.