Structural features of thermally or mechano-chemically treated montmorillonite clays as precursors for alkali-activated cements production
Alastair Marsh, Sreejith Krishnan, Susan A. Bernal
Abstract
In this study it was determined the impact of calcination or mechano-chemical activation (MCA) on the physico-chemical properties and reactivity of Ca-montmorillonite and Na-montmorillonite clays, and its subsequent effect on phase assemblage evolution of sodium hydroxide activated cements. MCA enabled colour control, enhanced early age reactivity of montmorillonite clays, associated with dehydroxylation and amorphization of the treated clay, while inducing spheroidal particle morphologies and reduced external surface area. These factors led to an accelerated onset of the polycondensation reaction, as well as an enhanced workability of alkali-activated pastes produced with them, compared with pastes produced with calcined clays. Independent of the clay treatment, a sodium aluminosilicate hydrate (N-A-S-H) alongside zeolitic reaction products were identified. This study demonstrates that MCA is an effective route to enhance reactivity of montmorillonites, resolving some challenges when using calcined clays for producing alkali-activated cements.