Development of Nanostructured Cementitious Binders Incorporating Calcined Clays

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Construction of concrete infrastructure relies primarily on the application of Portland cement and its hydrated phases as a binding material. This requires the annual production of about 4,000 million tonnes of cement worldwide which accounts for 5-8% of global CO2 emissions. Improvements in cement technology and development of new cementitious binders are, therefore, necessary to reduce the emissions. Calcined clays are among the most promising sources of supplementary cementitious materials which can be used as partial substitutions for Portland cement. Their application, in addition to the environmental advantages, can benefit the concrete performance. Metakaolin, the most reactive calcined clay, is currently used in projects where high strength and improved durability are required. Typical replacement levels of metakaolin are currently about 10-20% by mass of Portland cement. Innovative approaches to promote wider applications of metakaolin, and permit higher replacement levels can significantly reduce the emissions. In addition, the use of locally available and less expensive calcined clays is needed. This research program is aimed at developing a new class of calcined clay-based cementitious binders using a nanotechnology approach. A more in-depth understanding of the nanostructure of cement pastes incorporating calcined clays at the early ages and long-term as well as in exposure to potentially aggressive environmental conditions will first be provided. A seeding method will then be used to modify the nanostructure of calcium-alumino-silicate-hydrates (C-A-S-H), the principal binding phases in concrete incorporating calcined clays. The seeding method enables control of the stoichiometry and structural composition of the C-A-S-H phases permitting nanostructural tailoring of cement systems for various applications. Three types of calcined clays will be studied. They include a high purity and a cement grade metakaolin as well as calcined oil sands fine tailings. Management of tailings is an important environmental challenge for the oil sands mining sector in the Province of Alberta. This program will provide a practical solution for the tailing management. The proposed program will have a significant impact on promoting the application of novel and sustainable binders incorporating calcined clays in the construction industry. It can be extended for the use of other industrial by-products such as fly ash and slag. In addition, it will develop the basis for modifying the current standards to include specifications for production of high-volume calcined clay-based cements in the long-term. A diverse group of highly qualified personnel will be trained to become leaders in designing and implementing sustainable infrastructure materials in Canada and worldwide.