Metakaolin in the formulation of UHPC

Silica fumes have characteristics that make them exceptional in cement matrices and, in particular, in UHPC. Nevertheless, they have important disadvantages: lack of availability, cost and color. The search for substitute products thus appears important if the use of UHPC is to become more widespread in the concrete industry, e.g. in the fields of mechanical engineering (machine parts, tools, molds, etc.) and civil engineering (pipes for water or waste water conveyance for example). The substitute product used in this study was metakaolin obtained by fixed-bed calcination. It proved to be almost equivalent to silica fume in terms of mechanical properties and durability. Kaolinite, the clay from which metakaolin is produced, readily available in most countries, so the price of this ultra fine is acceptable. Moreover, its white color gives it an esthetic advantage. (C) 2008 Elsevier Ltd. All rights reserved.