Potential for calcination of a palygorskite-bearing argillaceous carbonate

Abstract

The intensive use of cement as a building material causes significant pollution. The majority of CO2 emissions come from the manufacturing process and not from the product itself. Indeed, the decarbonation of limestone and the use of fuels during clinkerisation are very polluting. One of the main solutions to reduce the environmental footprint of the cement industry is the use of Supplementary Cementitious Materials (SCMs) in substitution of clinker. Among them are glass powders, fly ashes, blast-furnace slags or calcined clays. This article focuses on the thermal reactivity of an argillaceous‑carbonate sample containing palygorskite, smectite and dolomite. The sample was calcined at different temperatures and investigated using Solid State Nuclear Magnetic Resonance (NMR), X-ray diffraction (XRD), and Scanning Electron Microscope (SEM). The increase in calcination temperature leads to an amorphisation of the clay fraction of the sample, resulting in a change in the coordination of the octahedral aluminium atoms. The progressive transformation of 6-fold aluminium atoms to 5-fold and 4-fold was quantified as a function of the calcination temperature. Furthermore, calcium issued from the decarbonation of dolomite reacts with silicon from the amorphisation of clay phases to form poorly-crystallized belite (C2S). This dual system (pozzolanic and hydraulic) makes this sample a promising candidate as SCM in blended cements. The multi-technique analysis applied in this study allows to highlight a direct correlation between the calcination temperature and the induced structural modification.