Determination of the amount of reacted metakaolin in calcined clay blends

This paper presents a comparative study of three methods to determine the amount of reacted metakaolin in calcined clay blends: mass balance, thermodynamic modelling, and the Partial or not Known Crystalline Structure method (PONKCS) based on Rietveld analysis of X-ray diffraction. The methods are applied to Limestone calcined clay cements (LC3-50) in this study. Mass balance and thermodynamic modelling results show good agreement, especially at early age. PONKCS method shows globally comparable results, even if it has higher variability. The precision of PONKCS becomes poor for blends with <60% of metakaolin in calcined clay.