Krishnan, Sreejith

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.

The pozzolanic reaction degree of supplementary cementitious materials (SCMs) is a crucial parameter influencing the performance of SCM-blended concrete. Although several methods, such as partial-or-no-known-crystal-structure (PONKCS) analysis with X-ray diffraction (XRD) testing and image analysis, have been developed to estimate the pozzolanic reaction degree of SCMs, they have their own challenges in achieving reliable estimation. Ethylenediaminetetraacetic acid (EDTA) with NaOH is an efficient and reliable agent for selectively dissolving calcium-rich phases (e.g., cement clinkers and hydration products) without dissolving low-calcium SCMs. In this study, the ionic selective dissolution method (ISDM) that combines the use of an EDTA–NaOH dissolving agent and inductively coupled plasma–optical emission spectroscopy is developed to efficiently and reliably determine the pozzolanic reaction degree of low-calcium SCMs. Furthermore, the chemical compositions of aluminium-incorporated calcium–silicate–hydrate gel are determined via the ISDM coupled with the Rietveld analysis of XRD data, according to mass conservation principles.