Decreasing amounts of available ideal materials, as well as environmental and economic considerations, lead the cement industry to investigate new products to be used as supplementary cement materials. Dolomite, ideally CaMg(CO3)2, is a carbonate that is already used by the concrete industry as an aggregate but which can be thermally activated to form a mixture of MgO and CaCO3 that is often referred to as “half-burnt dolomite”. The production of this thermally activated dolomite and its use as an addition to Portland cement were investigated in this study. Half-burnt dolomite was successfully obtained under experimental conditions (i.e. temperature and atmosphere composition) which appear compatible with industrial production. The decomposition product consists of nanometric platelets of MgO within a porous calcite matrix. The reactivity of half-burnt dolomite, in aqueous solutions and cement paste, depends on the size of the MgO crystallites and on their accessibility to water (e.g. the surface area of the half-burnt dolomite), both parameters being influenced by the decomposition conditions and the properties of the dolomite. Sintering during partial decomposition seems to control, at least partially, the reactivity of half-burnt dolomite. The reactivity during early hydration stages (i.e. typically < 72 h), which needs to be high while cement is still plastic, is however incomplete. The addition of half-burnt dolomite to Portland cement is not found to influence significantly the properties of cement pastes and even induces an improvement of the compressive strength at 28 days at ~ 10 mass% replacement of cement by half-burnt dolomite. This study suggests that half-burnt dolomite is an interesting potential addition to Portland cement and so more work is recommended (e.g. tests and pilot scale production) with the objective of industrial application.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:558659 |
| Date | January 2012 |
| Creators | Jauffret, Guillaume |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=186092 |
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