Applications of clinker microscopy for approaching a special case study in cement production

Within this article the importance of the optical light microscopy for the investigation of cement clinker is illustrated by three examples: (a) Ono's method plays an important role in the case of the production of oil well clinker where the reactivity of alite and additionally the melting phase influences strongly the properties of the later cement; (b) the use of secondary fuels can lead to unexpected phenomena in the clinker matrix accompanied by strange changes in colour; (c) for the interpretation of CSA clinkers, the combination of light and scanning electron microscopy can give important information about the formation of clinker phases depending on the burning conditions which can hardly be detected by other methods. However, in case of CSA clinker, there is still little knowledge about the relationship between production and hydraulic properties of the clinker and therefore no systematic documentation is available.

Use of Design of Experiments (DoE) to Model the Sulphate Agent Amount of (Ultra)Finely Ground and Fast Hardening Portland Cement Clinker

This paper presents a model to calculate the sulphate agent amount and sulphate agent ratio for fine grounded and fast hardening Portland cement clinker. Despite sufficient knowledge about the influence of calcium sulphate on the hydration process of cement, the sulphate agent amount is mostly adjusted empirically. As a result, often a wide and unfeasible experimental matrix has to be tested. In this work, Design of Experiments (DoE) was used in combination with in-situ X-ray diffraction (XRD) tests to accurately adjust the sulphate agent of different finely ground cement by calculation. With only 42 tests, it was possible to analyse in total the influence of the sulphate agent, the grinding fineness and the use of C-S-H-seeds for the use in fast-hardening Portland cement-based systems. In addition, it was found that a hemihydrate to anhydrite content of 25/75 leads to a stabilisation of the hydrated system in the first 24 h of hydration. A model for the optimisation of the sulphate agent composition in dependency of the cement fineness could be determined. Furthermore, it was shown that the DoE also provides optimal results in material sciences in a resource-saving way.

Combining Raman Spectroscopy, DFT Calculations, and Atomic Force Microscopy in the Study of Clinker Materials

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 (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 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.