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A total of six washed French and Algerian kaolins were studied. Kaolinite, halloysite, muscovite, feldspars, anatase, rutile, gibbsite, goethite, and todorokite were present. The thermal behavior of the samples was studied and the transformation heats were determined and quantified by differential thermal analysis. Calcined samples from 900°C to 1400°C are studied by X‐ray diffraction, the results show that the crystallite sizes of mullite rises as the temperature rises. The calcined samples showed an inverse correlation of L* and the crystallite sizes of mullite due to the incorporation of chromophore elements (Fe3+, Ti4+, and Mn2+) in its structure. Muscovite and rutile phases decreased lightness and increased chromaticity. The reduction state of Fe3+/Fe2+ and Mn4+/Mn2+ at 1400°C enhanced lightness leading to the diminution of the b* parameter. The CIELAB color parameters were significantly affected with mineralogy and chemical compositions of the samples. Lightness of the natural kaolins is decreased (L* < 59) when organic matters beside manganese and iron oxides are present. L* was not affected when only iron (Fe2+) is present in the kaolin; however, the chromaticity is increased (b* > 22). Whiteness and tint indices (W10, Tw,10) revealed that only one kaolin could be considered white (limits of CIE Colorimetry, 1986), though upon calcination, this number is enhanced to two. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 499–505, 2014

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Cement industry is a large energy consumer and a major CO 2 producer. In cement manufacture, most of the CO 2 footprint is due to the decarbonation of limestone. The designing of new clinkers that require less limestone and less energy for their production is a means to significantly reduce the environmental impact of this binder, the most widely used in construction worldwide. The present study focuses on the elaboration and characterization of environmentally friendly cements of very low lime saturation factor, obtained at low burning temperatures with hydraulic properties similar to those of alite cement. Four types of complete belite cements of high hydraulic reactivity were obtained thanks to the stabilization of the most reactive phases of the belite using quick cooling associated to four different mineralizations. The obtained cements have been characterized for their burnability on the basis of the free lime content. Their chemical and mineralogical compositions were studied using Xray fluorescence, X-ray diffraction and optical microscopy. The composition and morphology of the belite were studied using scanning electron microscope coupled with EDAX. The compressive strength and hydration heat were determined according to French standards. The results show that the sintering temperature can be reduced to 1,100 • C which is 50 • C less than reported in similar researches and 350 • C less than alite cement, with an improvement of the chemical, mineralogical and structural properties of the belite. This results in a hydraulic reactivity comparable to that of ordinary alite cements, with 28-day compressive strength of 38 MPa.

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