Mineralogical characteristics influence the structure and pozzolanic reactivity of thermally and mechano-chemically activated meta-kaolinites

Alastair T. M. Marsh, Andy P. Brown, Helen M. Freeman, Anke Neumann, Brant Walkley, Helen Pendlowski, Susan A. Bernal

Research output: Contribution to journalArticlepeer-review

Abstract

Increasing early age reactivity of cement replacements is a barrier to reducing the embodied carbon of blended Portland cements. Mechano-chemical activation is an emerging alternative to conventional thermal activation for clays, which can accelerate early age reactivity. Knowledge gaps on the structure and reactivity of mechano-chemically activated kaolinitic clays include the influence of Fe-bearing phases and the mineralogical characteristics of kaolinites from different sources. This study evaluated the effectiveness of mechano-chemical vs. thermal activation for an Fe-rich clay containing disordered kaolinite and 24 wt% goethite, and a low-Fe clay containing highly ordered kaolinite. In the Fe-rich clay, mechano-chemical activation simultaneously caused dehydroxylation of kaolinite to form meta-kaolinite, and dehydration of goethite to form hematite. Agglomerates of intermixed meta-kaolinite and goethite/hematite nanoparticles were shown to have similar Al and Si environments after thermal or mechano-chemical activation (as determined by STEM-EDX, 27Al and 29Si MAS nuclear magnetic resonance and electron energy loss spectroscopy). Mechano-chemical activation enhanced early age (<12 hours) reactivity for both clays. Evaluating early age reactivity by unit mass of anhydrous meta-kaolinite explains how surface-adsorbed moisture results in underperformance of mechano-chemical activation at later ageing times. External surface area alone does not predict reactivity acceleration well – edge : basal surface area of meta-kaolinite is proposed as a more relevant factor that governs early age performance of mechano-chemically activated clays. The structure–property–performance relations of mechano-chemically activated meta-kaolinites are explained through interactions of kaolinites' intrinsic mineralogical characteristics (i.e. initial particle size, aspect ratio, structural order) and extrinsic processing effects (i.e. intensive milling on structural order and physical characteristics).
Original languageEnglish
Pages (from-to)24260–24277
JournalJournal of Materials Chemistry A
Volume12
Early online date19 Aug 2024
DOIs
Publication statusPublished - 19 Aug 2024

Data Availability Statement

All data associated with this paper are openly available from the University of Leeds Data Repository https://doi.org/10.5518/1563.

Acknowledgements

Thanks are given to Vicky Leadley and Dan Geddes for assistance with 27Al MAS NMR measurements, to Sreejith Krishnan for advice on XRD analysis, and to Maggie White for assistance with the Mössbauer spectroscopy measurements. Thanks are also given to Mark Hodson, Rob Mills and Amy Wright for helpful discussions around clay characterisation.

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