Impact of hydration stoppage on quantification of the GGBS content in ternary limestone cements using the PONKCS method

Abstract

Most supplementary cementitious materials (SCMs) are predominantly poorly-crystalline or amorphous. Their reactivity is routinely evaluated through SEM image analysis (SEM/IA), which is a laborious and resource intensive technique. Quantitative X-ray diffraction (QXRD) provides an alternative, facilitating simultaneous evaluation of reaction kinetics and phase assemblages. However, QXRD requires relevant model structures, which are lacking for amorphous phases. In this study, we use the Phases of No Known Crystal Structures (PONKCS) method to model and calibrate ground granulated blast furnace slag (GGBS) and assess robustness in quantifying the GGBS content in synthetic and hydrated ternary blended CEM I-GGBS-limestone cements. Implications of sample preparation, in particular hydration stopping methods on the quantification was measured via the external standard method. Subsequently, the results are compared with SEM/IA calculations, based on backscattered images and magnesium maps. Robustness of the calibrated PONKCS phase is demonstrate with and without hydration stopping. However, X-ray absorption by the cements must be accounted in the attenuation co-efficient calculation. Freeze-drying destroyed water-rich phase assemblages and led to overestimation of the calibrated GGBS phase contents.