ABSTRACT
Lime-based composite materials gain, strength through atmospheric carbonation but the process is normally very slow. Using supercritical carbon dioxide to carbonate lime-based composites rapidly could potentially produce strong, chemically stable materials. Investigations were therefore carried out to assess the effectiveness of supercritical carbon dioxide treatment, applied to samples of a particular type of lime-based material (Casamic), produced by autoclaving compacted mixtures of soda-lime glass, hydrated lime and water. Increased bending strength and reduced reversible shrinkage were observed after supercritical carbonation, but the strength increase was not sustained when samples were exposed to. water. Micro structural changes induced by supercritical carbonation were examined by SEM and 29Si MAS-NMR and it was found that formation of crystalline sodium bicarbonate was a factor associated with the increase in bending strength. The high water solubility of this substance appeared to account for the observed reversion of strength on wetting of supercritically carbonated Casamic. Work in progress is aimed at evaluating effects of replacing soda-lime glass powder with flyash and preliminary results have been promising.
