Advanced calcareous ceramics via novel green processing and super-critical carbonation

The work presented in this thesis is aimed at evaluating the potential for using supercritical carbonation (SCC) in conjunction with novel processing techniques, to fabricate new blended calcareous matrix composites with superior engineering properties and lower environmental impacts than conventional cement-based materials. Taking combinations of waste materials such as steel slag (SS) and fuel ash (PFA), binders such as hydrated and cement and various aggregate types to manufacture green forms and exposing them to supercritical carbon dioxide has produced a number of promising ceramic materials. The project looked at novel ways to process the ‘green forms’ from these composites, such as dry- and wet-compression moulding, 3-D printing and hand lay up technique that was adapted from the fibre-reinforced polymer industry. Work concentrated on optimising mix designs, green processing and SCC conditions to produce the highest strength materials. Three main avenues were explored. The effects of mix design, different curing regimes and SCC treatment, on the microstructure and chemistry of the composites was investigated using SEM, TSP, DTA, XRD, helium pycnometry and other techniques. Investigation showed that SCC process significantly enhances the mechanical and microstructural properties of carbonated products. It was shown that SCC treatment activates materials such as steel slag, that in the unground state are not activated by high temperature curing, to form useful composites. It was revealed that the relationship between the ‘degree of carbonation’ and strength is not straightforward and the order in which the various phases in the concrete react is important. Microstructural investigations hinted that the bond between carbonate limestone aggregate and the carbonated matrix was much stronger and more intimate (less porous) than for other aggregates. Chemical analysis also determined how much carbon dioxide could be ‘locked-up’ in the samples and this data was then used in the life-cycle assessment (LCA) of potential products. LCA was used to assess the green credentials of the SCC process and results were encouraging; a net reduction in CO2 emission of around 50% can potentially be achieved. Overall, the project has made many significant advances both in the practical application of SCC to ceramic composite manufacture and in the science of the reaction between sc-CO2 and cementitious phases. The technology could now be exploited by the manufacturing industry as a lowtemperature, rapid, low raw material cost and a sustainable route for manufacture of a wide range of ceramics.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Council (Great Britain) (EPSRC) (GR/T01518/01)GBUnited Kingdo