Supplementary Cementitious Materials for Concrete: Characterization Needs

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Supplementary Cementitious Materials for Concrete: Characterization Needs Maria Juenger1, John L. Provis2, Jan Elsen3, Winnie Matthes4, R. Doug Hooton5, Josée Duchesne6, Luc Courard7, Huan He7, Frédéric Michel7, Ruben Snellings8 and Nele De Belie9 1

University of Texas at Austin, U.S.A. University of Sheffield, United Kingdom 3 Katholieke Universiteit Leuven, Belgium 4 Holcim Group Support Ltd., Switzerland 5 University of Toronto, Canada 6  Université Laval, Canada 7 Université de Liège, Belgium 8 École Polytechnique Fédérale de Lausanne, Switzerland 9 Universiteit Gent, Belgium 2

ABSTRACT A wide variety of materials are currently used as supplementary cementitious materials (SCMs) for concrete, including natural materials and byproducts from various industries. Historically, natural SCMs, mostly derived from volcanic deposits, were common in concrete. In recent years, the dominant SCMs have been industrial by-products such as fly ash, ground granulated blast furnace slag (GGBFS), and silica fume. There is currently a resurgence of research into historic and natural SCMs, as well as other alternative SCMs for many reasons. The primary benefits of SCM use in improvement of long-term mechanical performance, durability, and sustainability are widely accepted, so local demand for these materials can exceed supply. This paper describes some of the SCMs that are attracting attention in the global research community and the properties and characteristics of these materials that affect their performance. Special attention is paid to the importance and demands of material characterization. Many SCMs do not necessarily lend themselves to characterization methods used in standardized test methods, which sometimes fail to describe the properties that are most important in predicting reactivity. INTRODUCTION SCMs are used to substitute either portland cement clinker in the production of composite cements or cement in the production of concrete. The use of SCMs is widespread in the concrete industry because of the economic and performance benefits they provide. Recently, SCMs have been receiving increasing attention for the role they play in reducing the carbon footprint of concrete, since the energy use and CO2 emissions from portland cement clinker manufacturing significantly outweigh those of other concrete components, and SCMs have a smaller environmental impact than portland cement clinker [1]. The demand for high quality SCMs is large, as exemplified by the fact that the world average clinker factor (percentage of clinker in cement) decreased from 0.85 in 2003 to 0.77 in 2010, and long-term predictions are that this number will continue to decrease as far as 0.71 [2]. Blended cements represented 75% of Holcim’s cement production in 2009, compared to 39% in 1995 [2]. In the U.S., where SCMs are

added to concrete rather than to cement, over 60% of ready-mixed concrete uses SCMs as a substitute for a portion of the portland cement [3]. In some regions, demand for SCMs is outpacing supply, particularly in developing countr

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