Title: Characterization of Calcined Clay Reactivity For Use as Additive in a Blended Cement
Author(s): Victor Poussardin, Michael Paris, Dimitri Deneele, and Arezki Tagnit-Hamou
Publication: Symposium Paper
Appears on pages(s): 563-574
Keywords: belite, blended cement, calcination, clay, dehydroxylation, palygorskite, pozzolanic activity
Although normal portland cement is made from natural and recyclable materials its manufacture causes significant pollution, especially because of clinkerization which leads to important CO2 releases into the atmosphere. The use of supplementary cementitious materials (SCMs) to partially replace clinker in normal portland cement and reduce its environmental cost is now well known (e.g., fly ash, metakaolin, glass powder or blast-furnace slag). This study investigates the potential for calcination and reactivity of a carbonate sample containing phyllosilicates. Samples were calcined at different temperatures and investigated using X-ray diffraction (XRD) with Solid State Nuclear Magnetic Resonance (NMR). The results show that the calcination of the sample leads to a dehydroxlation phenomenon of the clay fraction resulting in a change in the coordination of the aluminium atoms. Furthermore, the reaction between the Dolomite and the Palygorskite present in the sample leads to the formation of poorly-crysallized Belite during calcination. Hydration tests on the red-clay sample have demonstrated the hydraulic reactivity of the Belite and the pozzolanic reactivity of the calcined Palygorskite that lead to the formation of hydrates phases (C-S-H ; C-(A)-S-H). The multi-technique analysis applied in this study allows to highlight a direct correlation between the structural modification induced by calcination and the reactivity of the calcined sample.