Extraction of Carbonation Rate from Depth Profile of Concrete Carbonation by using Pseudo-analytical Solution of Two-component Reaction-diffusion Equation

The accurate numerical solution of a one-dimensional two-component reaction-diffusion equation including a second-order chemical reaction between concrete constituents and carbon dioxide to generate carbonated products was approximated by a simple analytical function which was given as a function of the effective diffusion coefficient of CO₂, the rate constant of CO₂ absorption, and parameters determined by the initial and the boundary conditions of the system. The pseudo-analytical solution thus obtained showed that the depth profile of carbonation shifts in parallel with square-root of time, and the rate constant of carbonation is determined from the location where the amount of the carbonated product is a half of the maximum amount. Comparison of the pseudo-analytical solution with an observed depth profile of concrete carbonation makes it possible to directly extract the rate constant of concrete carbonation that is necessary for predicting the future progress of the carbonation.