Quantification of hydration phases in supersulfated cements: review and new approaches

Quantification of the progress of hydration of supersulfated cements (SSC) may be approached in two ways: (a) from recording the increasing dissolution of the slag particles directly, and (b) indirectly from quantifying the formation of the hydration phases. Image analysis based on backscattered electron imaging in a scanning electron microscope (SEM), the dissolution of hydrates (EDTA), differential thermal analysis (DTA) and sulfide concentration (SP) were used to quantify the dissolution of the slag particles; selective extraction of hydrates by sodium carbonate (SE), X-ray diffraction (XRD) with Rietveld analysis and thermogravimetric (TGA) refinement methods were used to quantify the amount of hydration products formed. SEM-based image analysis was found to be a direct and promising way for the quantification of slag particles. With the help of selective extraction by sodium carbonate (SE), it was possible to quantify the amorphous C–S–H phase in SSC. Mass balance calculations constrained by thermodynamic stability were used to calculate the amount of reacted slag in the system. XRD Rietveld and TGA methods were used to assess the amounts of specific hydration products formed in SSC but did not allow an absolute quantification of the amount of slag reacted. Other methods such as the dissolution of the hydrates by EDTA and DTA were not found to be reliable due to intrinsic problems.