ABSTRACT
This proj ect is aimed at investigating the potential for using a supercritical carbonation process in combination with other novel processing techniques to fabricate a new class of ceramic composites from a variety of calcium-based precursor materials, including lime and cement. The process has the potential to help mitigate the CO2 impact of the manufacture of cements by re-combining some of the CO2 emitted. Compression moulding techniques, as used for mass-produced polymer components, are used to fabricate green forms, which are then treated with supercritical CO2. Considerable development of the moulding process and mix design was required to produce viable green forms. The effect of the treatment on the microstructure and engineering properties of specimens was investigated using XRD and 4-point bending tests. XRD tests confirmed that complete depletion of calcium hydroxide and anhydrous species was achieved during the carbonation process in most samples, with consequent formation of calcite. Mechanical testing indicated that considerable improvement in flexural strength could be achieved by carbonation, well over and above that which would be expected during conventional water curing. Results also indicated that ‘full carbonation' as indicated by calcium hydroxide depletion is not a reliable indicator for achieving high strength; the mix design plays a critically important role.
