Title: Potential of Calcined Mixed-Layer Clays as Pozzolans in Concrete
Author(s): Nancy Beuntner, Ricarda Sposito, and Karl-Christian Thienel
Publication: Materials Journal
Appears on pages(s): 19-29
Keywords: activity index; calcination; calcined clays; durability; fresh concrete properties; pozzolanic reaction; specific surface area; supplementary cementitious material; water demand
Calcined clays have become increasingly attractive as supplementary cementitious materials (SCMs). This paper begins with describing the mineralogical diversity of clays and presents the advantages of naturally occurring mixed-layer clays. It illustrates the necessity of optimal calcination temperatures depending on type of clay, and first steps are discussed toward industrial production. The following chapter gives an overview of selected physical and chemical-mineralogical properties and the essential reaction mechanisms of calcined clays as SCMs. The latest findings on their influence on early hydration and their special role in fresh concrete are presented. The potential of calcined clays in concrete is highlighted exemplary for selected mechanical properties and durability aspects. Lastly, the potential and limits of calcined clays as a future part of blended cements or concrete additive are evaluated, considering ecological aspects, as well.