Strategies for XRD quantitative phase analysis of ordinary and blended Portland cements

The PONKCS (Partial Or No Known Crystal Structure) approach has become popular in quantitative phase analysis (QPA) of Portland cements blended with amorphous supplementary cementitious materials (SCMs). However, little information on the PONKCS models creation is available. Besides, the small contents and preferred orientation (PO) of calcium sulfate sources (e.g., gypsum and bassanite) can make their accurate quantification difficult in ordinary and blended Portland cements. Our paper brings light to important aspects of XRD QPA that are often neglected/not reported. This was assessed by the production of ordinary and blended Portland cements with clinker, gypsum/hemihydrate, limestone, fly ash, slag, and calcined clay at different proportions. Results showed that backloading preparation was ineffective in preventing PO of alite, gypsum, and bassanite. The March-Dollase function was preferred for PO correction. The space group and background fit used for PONKCS models creation directly affected the method's accuracy. PONKCS yielded good QPA results for binary/ternary blends, except for the simultaneous presence of fly ash and calcined clay.