Paper of RILEM TC 282-CCL: mineralogical characterization methods for clay resources intended for use as supplementary cementitious material

Abstract

To respond to the rapid introduction and development of calcined clays as supplementary cementitious material (SCM), the toolbox of characterization methods for cementitious materials requires extension to raw clay characterization. Borrowing concepts and methods developed in the field of clay mineralogy, this paper outlines the merits and limits of widely accessible characterization techniques for raw clays intended for use as SCM, when calcined. The paper focuses mainly on the identification and quantification of the raw clay mineral components, as these characteristics have important implications for further material processing and performance. General notes are provided on clay sampling and pre-treatment as well as bulk chemical analysis. The main techniques considered are X-ray diffraction, thermal analysis and infrared spectroscopy. Their application on raw clays is introduced, highlighting clay-specific aspects of sample preparation, data acquisition, and processing. Guidelines and interpretation tables are provided to aid in the analysis of the acquired data, while limitations and potential interferences are identified. Options for remote prospection by infrared spectroscopy are included as well. To illustrate the type of information to be gained and the complementarity of the techniques, two representative raw clays are fully characterised. This paper aims to highlight that mineralogical characterization is a feasible and often necessary step in the study and assessment of raw clays that can deliver a wealth of informative data if carried out appropriately.

Characterisation, Activation, and Reactivity of Heterogenous Natural Clays

“…Therefore, the dehydroxylation peak here could be brought about by either kaolinite alone or collectively by 1:1 and 2:1 minerals present in the clays. Some other phases like calcite as shown in the FTIR for SC, could also start to decompose at this temperature range [43]. SC has another dehydroxylating peak at 760 • C that could be attributable to montmorillonite or illite.…”

“…From the TGA curves in Fig. 3, the mass losses at a temperature range of 300-800 • C relate to dehydroxylations of clay phyllosilicates [43]. It is known that the mass losses of these minerals commonly overlap in specific temperature intervals [37].…”

Reactivity of Calcined Clays as SCM—A Review

“…The most influencing characteristic of the reactivity potential of clays is the mineral phase composition of the raw material. Concerning an appropriate mineralogical phase characterization, it is referred to [60]. Firstly, the material must contain sufficient content of activatable phases.…”

Supplementary Cementitious Material Based on Calcined Montmorillonite Standards

“…1b) are exceptionally broad. The amount of clay mineral in each standard was calculated based on its dehydroxylation reaction, as proposed in [48], and is 88 % and 90 % for SWy-3 and SAu-1, respectively. Finally, a small S-shaped endothermic/exothermic set of reactions, without associated mass loss, due to the structural decomposition of montmorillonite and crystallisation of spinel [45,49], at ~910 and ~870ºC, is observed in Fig.…”