XRD analysis of clinker has been used in cement studies for the past 60 years, and applied in phase abundance analysis over the past 40 years. ASTM 1365 [4] details a standard test method for quantitative phase abundance analysis using XRD (QXRD). X-ray powder diffraction patterns provide phase, chemical, and crystal structure information data that may afford greater understanding of cement property/performance relationships. However, XRD analysis of clinker has proven difficult as the multiple phases result in substantial peak overlap. There is also difficulty in securing suitable pure phase reference standards. These concerns may be addressed using the Rietveld method for X-ray powder diffraction [5]. Public domain code General Structure Analysis System (GSAS) can be used to refine the powder diffraction data [6].
The Rietveld method allows standardization of powder diffraction analysis through use of calculated reference diffraction patterns based upon crystal structure models (Fig. 4). The result is a set of refined crystal structure models for each phase in the clinker. From these data one can obtain pattern intensity information that may be related to phase abundance. Additional data on the chemical and structural properties of each phase may also be explored relative to selected performance properties. This can be used in research, and for quality control in cement production, and is used here to analyze the NIST Reference Clinkers. This method is acceptable under ASTM C1365, where users are required to qualify their instruments and procedures. Initial crystal structure models were taken from the literature [7-11, 14] and are provided in Appendix A.