The presence of lime dissolving carbonic acid in water can attack concretes. After initial carbonization of the uppermost layer of concrete the dissolved carbon dioxide reacts with the calcium carbonate that is hardly soluble, forming easily soluble calcium hydrogen carbonate.

Upon further attack, the calcium is separated from the cement matrix, leaving a softened gel layer. This gel layer serves as a diffusion barrier for both the lime-dissolving carbonic acid and for the reaction products.
In the eighties Grube and Rechenberg developed an equation based on Fick's laws. The equation estimates the thickness of the softened gel layer. The diffusion coefficient of the gel layer is considered in this equation. However, this factor is only known for a few concretes.

There are plans to develop a database, which can help to calculate the thickness of the gel layer of various concretes depending on the duration of the attack.