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2010-09-07 - Colloque/Présentation - poster - Anglais - 1 page(s)

Sciamanna Valérie, de Haan André, Gonon Maurice , "Effect of Fe, Cr and Mn impurities on the color of White Cement" in Twelfth European Inter-Regional Conference on Ceramics (CIEC 12), Mons, Belgique, 2010

  • Codes CREF : Matériaux céramiques et poudres (DI2744)
  • Unités de recherche UMONS : Science des Matériaux (F502)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux)

Abstract(s) :

(Anglais) White Portland cement is made by grinding 95% of clinker with small amounts of gypsum and limestone. The clinker is obtained by heating limestone and clays at about 1450°C. At this temperature, the main phases of white clinker are formed : tricalcium silicate (C3S), dicalcium silicate (C2S) and tricalcium aluminate (C3A). The properties of Portland cements are defined by the fineness of grinding and by the composition of clinker. In the case of white Portland cements, the white quality is evaluated with three parameters : - The purity (%) which corresponds to the difference between the clinker sample and a white reference - The dominant wavelength (nm) which characterizes clinker coloration - The brilliance (%) which is the power to reflect incident light For white cements, the purity should be lower than 4-5% and the brilliance values between 84% to 88%. Some parameters affect the coloration of the clinker : purity of raw materials, burning and cooling conditions, … Very pure raw materials are selected for white clinker production : their content in iron and other coloring impurities (chromium, manganese …) is as low as possible. Another particularity of white clinker manufacture is the local reducing atmosphere in the kiln, in order to minimize the coloring effect of iron. This atmosphere is generated after the clinkerisation, during the cooling between 1450°C to 1250°C, just before rapid quenching. In this study, we reproduced typical industrial conditions in terms of burning, reduction step and cooling. A kiln was modified in order to work in reducing atmosphere (3% CO - 27% CO2 - 70% N2) and to allow rapid quenching of the clinker. The first step was to work with industrial raw materials in order to compare laboratory and industrial clinkers. Chemical analysis and colorimetric measurements were performed on each sample. XRD spectra were also recorded in order to reveal clinker main minerals. The second step was to examine the distribution of iron, chromium and manganese between the major phases of clinker. SAM and KOSH extractions were used to isolate aluminate from silicate phases. Finally, brilliance and purity values were related with clinker content in iron, manganese and chromium.