摘要：Coal fly ashes and metallurgical slags are currently widely used as supplementary cementitious materials in production of Portland cement-based concretes. However, this application makes very poor use of the intrinsic reactivity of the glassy phases present in the waste materials, and can hardly therefore be considered ‘valorisation’ in the true sense of the word. Addition of these materials to Portland cements can also cause difficulties in early strength development, limiting their use to certain applications. Geopolymerisation, on the other hand, makes full use of the glassy ash and slag materials by using them as the key reactants in synthesis of aluminosilicate gel binders for waste-based concrete production. The activation of the glassy phases by alkaline solutions provides the opportunity to greatly reduce the Portland cement content of a concrete, but requires a sound understanding of the ash chemistry and its effects on workability, water demand and setting time if it is to be implemented successfully on a commercial scale. In this paper, various aspects of fly ash valorisation via geopolymerisation are discussed, including in particular the determination of ash reactivity by a recently-developed technique utilising dilatometric data. The correlations between ash reactivity as measured by dilatometry and geopolymer mechanical strength are discussed in detail, and comparisons with other measures of ash reactivity presented. Some commercial examples of geopolymer concrete in-place are also discussed to highlight these differences in real world usage.
