Title: Activation of Na- and Ca- Bentonites: Comparison of Thermal and Mechanical Treatments

Author(s): Alastair Marsh

Publication: Web Session

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Date: 10/17/2021

Abstract:
To help realize the global potential of calcined clays as supplementary cementitious materials, there is a move towards valorizing a wider range of common clays exhibiting lower purities and non-kaolinitic clay minerals. 2:1 clay minerals are less favorable for calcination, as their layer structure largely retains its ordering after dihydroxylation. For this reason, mechanical treatment is advocated as an alternative to calcination for increasing the pozzolanic reactivity of 2:1 clays. However, there is still a relatively poor understanding of the comparative effects of thermal and mechanical treatments on the structural ordering of 2:1 clay minerals and their reactivity. In this study, high purity smectites were used as relatively simple systems to help understand processing-structure-properties relations. A Ca-bentonite and a Na-bentonite were subjected to thermal treatment by soak calcination in a furnace, and mechanical treatment by intensive milling in a planetary ball mill. A variety of techniques were used to characterize the changes in hydroxyl and water group distribution (TG-MS, FTIR), structural disorder (XRD, 27Al MAS-NMR) and physical characteristics (laser particle diffraction, SEM) for the different treatments. This information was then used to explain differences in reactivity observed through calorimetry (R3 cumulative heat release test).