Title : CALCINED CLAYS IN MODERN BUILDING MATERIALS: POTENTIAL APPLICATIONS IN CONCRETE AND COMPOSITE CEMENTS
Authors : Eugen Kleen
Publication : 23 - 26 October 2013
Volume :
Pages :
Price : 250
Abstract : The use of calcined clays as additives in mortars and concretes dates back to antiquity. In light of the current focus on sustainability and due to the increased demands on the technical performance of modern construction materials, calcined clays are back in use in advanced civil engineering applications. The application areas being explored for calcined clays include: use as a concrete additive; use as a main ingredient in composite cements (OPC-Pozzolan Blends); and use as alumina siliceous components in geopolymer systems / geopolymer concrete. While the use of geopolymers in construction has limited applications, the first two fields open up a vast application potential for the use of calcined clays. Non-calcined clays exhibit no pozzolanic reactivity whatsoever, and are largely unsuitable for use, even as purely inert filler in cementitious systems. This is due to their special crystalline structure and the associated negative effects on concrete properties such as decreased frost resistance, decreased resistance to freeze-thaw, shrinkage/swelling, etc. When calcined clays are used as additions to concrete, it is mostly burnt kaolin, or so-called metakaolins. With them, special specific concrete properties can be achieved, aside from an improved eco-balance. Metakaolin can be used in high-strength and ultra-high-strength concretes as an alternative to microsilica. Metakaolin can furthermore considerably increase the durability of concretes (increased resistance to ASR, increased chemical resistance, etc.). This is achieved by the optimal combination of physical, chemical and mineralogical mechanisms of the individual components in the mix. Ultrafine / nanoscale pozzolanic materials, such as calcined kaolin, facilitate better particle packing at similar corresponding water-binder ratios. This enhances the chemical resistance of the binder, even in case of slightly higher permeability in the matrix. This paper reviews the latest applications / joint studies between Bauhaus University, Weimar, MC-Bauchemie Mueller GmbH and Co. KG and other industry partners incorporating these materials in the development of ceramiclike UHPCs and also their use in new generation composite cements.