An investigation of the carbonation of cement paste using trimethylsilylation

Ground samples of hydrated cement paste were exposed to atmospheric carbon dioxide and the progress of reaction was monitored by trimethylsilylation of the silicate phases and differential thermal gravimetry (DTG) for calcium hydroxide. The data indicate that carbonation for calcium silicate hydrate (CSH) proceeds via high molecular weight intermediates to give an amorphous hydrous silica material. The carbonation of CSH and calcium hydroxide occurs simultaneously, but a residue of calcium hydroxide carbonates more slowly. This is consistent with a rate-determining stage controlled by the rate of diffusion of carbon dioxide through calcium hydroxide crystals coated with calcium carbonate, and hence also by crystal size.