Polymorph and minor phase quantification in Portland clinker by X-ray powder diffraction analysis: Addressing challenges and foreign ion effects

Abstract

A comprehensive investigation of the phase composition of eight commercial clinkers was conducted through state-of-the-art synchrotron (SXRD) and laboratory (LXRD) X-ray diffraction, and supporting techniques. Challenges involved in polymorph and minor phase quantification, and the effects of foreign ions on the clinker chemistry were addressed. SXRD yielded higher C₃S and lower C₂S contents than LXRD, besides higher C₃S M₃. Visual identification of C₃S predominant polymorphs did not always match the Rietveld results for LXRD. Using orthorhombic-C₃A in the refinement of samples that did not have this polymorph led to an underestimation of C₄AF and α′_H-C₂S. Axial divergence made the quantification of β-C₂S inaccurate for non-monochromatic LXRD. C₃S formation was governed by the sulfate/magnesium ratio and Na₂O_eq content rather than LSF, while C₃S polymorphism was governed by the sulfate/magnesium + alkali ratio. Optimal chemistry ranges were proposed for maximizing C₃S formation. C₃A polymorphism was generally controlled by the sulfate/alkali ratio.