Volume 5, Issue 9 (October 2008)
XRF, XRD, and Thermal Analysis Techniques for Quantitative Determination of Portland Cement and Slag Cement Constituents
Two rapid test methods to determine and quantify sulfate forms in cement are presented—DSC and XRD. The DSC method is applicable to hydrated calcium sulfates: gypsum and bassanite. Its description includes preparation of standards, calibration curves, and calculation of hydrated sulfates in an unknown cement sample. The XRD method is used qualitatively and quantitatively for both hydrated and nonhydrated sulfate forms. The qualitative approach is used to identify the presence of sulfates in cement samples. The quantitative approach describes the Rietveld analysis applied to a cement sample containing gypsum, bassanite, anhydrite, and arcanite. The calculated total SO3 content is compared with another direct analytical technique (Sulfur Analyzer). The other two methods used to determine the amount of granulated blast furnace slag added to cement are discussed—DTA and XRD. With the DTA method, the exothermic peak that accompanies slag devitrification at high temperatures is measured and converted in slag percentages. The method’s description includes preparation of standards, calibration curve, and calculation of slag content of an unknown cement sample. The XRD method works as a qualitative tool to show the effect of amorphous slag to a cement diffractogram as well as a quantitative tool (Rietveld analysis using an internal standard). Rietveld analysis on cement containing slag samples is used with XRF oxide analysis to correct the Bogue formula calculation for C3S. Three different calculations/corrections are discussed showing reasonably good approximate results.