Abstract
Raman spectroscopy and Raman mapping analysis, combined with density functional theory calculations were applied to the problem of differentiating similar clinker materials such as alite and belite. The Portland cement clinker 217 (further: clinker) was analysed using colocalised Raman mapping and atomic force microscopy mapping, which provided both spatial and chemical information simultaneously. The main constituents found in the clinker were alite, belite, portlandite, amorphous calcium carbonate, and gypsum. Since phonon bands of alite and belite greatly overlap, and their distinction is important for the hydration process during cement setting, we provided the calculated phonon density of states for alite Ca3SiO5 (<M>Pc structure) and belite Ca2SiO4 (β P21/n structure) here for the first time. Both calculated phonon densities have similar distribution of phonon modes, with a gap between 560 and 810 cm−1. A comparison of the calculated phonon frequencies for Ca3SiO5 and Ca2SiO4 shows that the lowest calculated phonon frequency of β-Ca2SiO4 lies at 102 cm−1, while for <M>Pc alite the lowest phonon frequency is predicted at 27 cm−1. Low frequency Raman spectroscopy could therefore be used for a clearer distinction of these two species in a clinker material.
Highlights
In order to correctly attribute the observed bands in the clinker, a calculation of phonons for charges of +1.41e (Ca)(OH)2 using LDA for exchange and VWN correlation pseudopotentials as implemented in the CRYSTAL09 program [53] was performed
Raman spectroscopy has been used in the study of dry clinker, ordinary Portland cement, and calcium sulfoaluminate cement and the spectra interpreted by comparison with previous results from the literature and our own calculations of the vibrational density of states performed for crystalline β-Ca2 SiO4 and monoclinic Pc Ca3 SiO5
The predicted phonon density of states, both for C2S and C3S, displays no vibrational bands in the 560–810 cm−1 interval; tricalcium aluminate or tetracalcium aluminoferrite can be confidently assigned in that interval
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Superposition of the image obtained by backscattered electrons and the images obtained using an energy dispersive X-ray analyser for each selected element (e.g., S, K, Al, Mg, Fe, Na...), using appropriate software, allows one to obtain a segmentation image showing regions of spatial distribution of chosen elements This contemporary golden standard procedure is a sequel to the light microscopy of the Portland cement clinker of Henry de Chatelier (1887), which is still very useful in distinguishing alite and belite microcrystals [19]. We shall present the results on dry clinker material coming from three different sources—the first was granular, consisting mainly of alite in the M3 phase; the second was a Portland cement powder of the CEM I type; and the third, a polished calcium sulfoaluminate clinker. The calculation of alite’s and belite’s VDOS is, as far authors are aware, published for the first time
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