Development of an Astm Standard Test Method on X-ray Powder Diffraction Analysis of Hydraulic Cements

X-ray powder diffraction provides a direct analysis of phase abundance of portland cement clinkers and cements. The ASTM C01 (Cement) Committee formed a task group to investigate quantitative X-ray powder diffraction analysis that resulted in the ASTM C 1365 standard test for X-ray powder diffraction of portland cement clinker and portland cement. Estimates of test precision and bias are required in ASTM test methods with round robin testing used to generate these data. Seven laboratories participated in a clinker round robin using the NIST Standard Reference Material (SRM) clinkers and Rietveld analysis. The results were used to estimate interand intra-laboratory precision and bias. The application of the Rietveld method for analysis of complex powder diffraction patterns of clinker and cements provides an improved means to measure individual phase pattern intensities by accommodating the intrinsic variability of parameters affected by chemical substitution. Results indicate an improvement over round robins conducted prior to use of Rietveld method in cements analysis. The standard test method is being modified to include this approach. INTRODUCTION Hydraulic cement composition and fineness, along with other concrete constituents, influences fresh concrete properties such as rheology, heat evolution, setting, rates of strength development, ultimate strength, and color. For hardened concretes, the hydration products (and on occasion, residual cement phases) affect concrete durability. Phase composition and texture of clinker result from complex interactions of raw feed particle size, feed homogenization, and the plant heating and cooling regime. Mill grinding affects the cement microstructure through fracturing of the calcium silicates and interstitial phase crystals and, depending upon conditions, it may alter the form of calcium sulfate added at this stage to control cement setting. These features in turn influence the cement’s hydration characteristics, the process of conversion of the anhydrous cement and water to hardened hydration products that ultimately affect the development of strength and durability of a structure. Recognizing these variables, classification of cements in ASTM C 150 is made on the basis of bulk chemistry, fineness, and, for some cements, limits on phase abundance [1]. Estimates of phase abundance are derived from the bulk chemistry using formulas referred to as the Bogue calculation. Errors in these estimates derive, in part, from the variability of clinker phase chemistry relative to the assumed compositions, and not accounting for minor constituents [2,3]. An alternative approach for quantitative phase analysis is X-ray powder diffraction (XRD). Copyright ©JCPDS International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume 47. 206