Effect of carbonation
Carbonation often reduces the capillary porosity of the cement paste matrix in cover concrete [4.69-4.74]. However, where
large amounts of calcium silicate hydrate are formed (by replacing large amounts of Portland cement with fly ash or slag),
carbonation can increase the capil-lary porosity [4.73]. The permeability of cover concrete would be expected to change withcarbonation in parallel to the changes of capillary porosity. Kropp [4.71] reported a reduced rate of water vapour diffusion in
carbonated mortar. For an OPC mortar with w/c=0.5, results are given in Fig. 4.51.