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

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 C4AF and alpha ' H-C2S. Axial divergence made the quantification of beta-C2S inaccurate for non-monochromatic LXRD. C3S formation was governed by the sulfate/magnesium ratio and Na2Oeq 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.