Properties and occurrence of clay resources for use as supplementary cementitious materials: a paper of RILEM TC 282-CCL

Abstract

The use of clays as resource of supplementary cementitious materials (SCMs) for a new generation of low-carbon cements and concretes is currently the subject of intense research efforts. To this purpose, a large number of clay resources have been explored, characterized and evaluated. This paper introduces the basic knowledge and concepts on clay occurrence and clay mineralogy, before presenting up-to-date knowledge on properties and occurrence of clay resources suitable for use as SCMs. Occurrence, distribution and chemical and mineralogical selection criteria are discussed for kaolinitic clays, which often show superior reactivity and performance. 2:1 clay mineral resources have received somewhat less attention as SCMs resources, however recent developments indicate significant potential for calcined impure common clays, and are reviewed. An overview of ubiquitous clay mineral-bearing waste materials also identifies important opportunities for alternative clay sourcing in mining or extraction residues, and dredged or excavated sediments.

Thermodynamics of calcined clays used in cementitious binders: origin to service life considerations

“…55 Therefore, kaolinite is oen deposited in tropical soils where the climate (e.g., rainfall and high heat) coupled with organic matter causes extensive leaching of alkali and earth-alkali metals; there are numerous weathering pathways that can lead to the formation of kaolinite. 56,57 In contrast, kaolinite is much less abundant in cooler and dry regions. In such climates, other clay minerals such as illite and chlorite are more dominant as weathering products in soils.…”

Practical experiences in the use of a combination of calcined clay and limestone as clinker substitute in cement

“…The kaolinite content is the overwhelming parameter determining the reactivity of kaolinitic clays. [9,10]. Figure 1 presents the international benchmark database developed at EPFL with clay candidates from all over the world.…”

1:1 or 2:1 ‐ Does it matter for calcined clay as supplementary cementitious material?

“…2:1 clay minerals like illite, smectite and montmorillonite as well as 2:1:1 chlorite are rather formed in cold regions as in the northern or southern hemisphere [8,9]. Alujas Diaz et al [10] provide a comprehensive overview on the global occurrence of clay minerals. Maier et al [11] highlight the domination of 2:1 clay minerals in Germany in their view on local availability of the different clay types.…”

“…At the same time they transform into inert high temperature phases at lower temperatures than kaolinite [15]. As a result, their temperature window for thermal activation is narrower and pozzolanic reactivity is lower [10]. Figure 2 summarizes some practical production temperatures (upper x-axis) and the corresponding CO2 emission originating from the raw material and the fuel used for production [16] with data from [14].…”