A methodology to study carbonation of cement paste and its effect on permeability

Carbonation is mainly known as a deterioration phenomenon for reinforced concrete structures. However, it has also a beneficial effect when we consider transport of aggressive species. This study aims at developing an optimized technique, in terms of quantification of carbon dioxide uptake, to control the carbonation of cement-based materials and to examine the permeability of the carbonated specimens. Samples were embedded in a special cell and subjected to an elevated CO2 pressure at the upstream side. The CO2 uptake was measured in the up-and downstream part by precise mass flow controllers. The experiments were performed on hardened cement. Post-analysis techniques like TGA, XRD and pH measurents were used to determine the phase changes, hence the carbonation front, while MIP and nitrogen adsorption were used to characterize the microstructure changes The effect of carbonation on the general transport behaviour was studied by measuring changes in the water permeability. Results show that the carbonation of fully saturated sample was very slow. Even this limited carbonation leaded to a decrease in permeability by one order of magnitude.