Phase quantification of anhydrous CSA cements: a combined X-ray diffraction and Raman imaging approach

Abstract

Calcium sulfoaluminate (CSA) cements are known for their special properties, such as shrinkage compensation and high early-age strength. These properties are dependent on the hydrated phase assemblage, which in turn is governed by the phases present in the initial anhydrous cement. However, the anhydrous CSA phase quantification by X-ray diffraction (XRD) Rietveld can be challenging due to the presence of overlapping peaks, polymorphs and preferred orientation. To overcome this problem, an approach involving high-resolution large-area Raman imaging (5 mm × 5 mm, 250 000 pixels, with 10 μm/pixel resolution) complemented by XRD analysis is introduced. This integrated approach of combined XRD and Raman imaging is found to be crucial in the initial identification of phases that are present in a CSA system. Most importantly, quantitative analysis shows a strong correlation (R2 > 0.99) and agreement (variation <5 wt%) between the two independent methods, adding confidence and reliability to the phase assemblage obtained by this dual-technique approach.