C-(N)-S-H and N-A-S-H gels: Compositions and solubility data at 25°C and 50°C

Calcium silicate hydrates containing sodium [C-(N)-S-H], and sodium aluminosilicate hydrates [N-A-S-H] are the dominant reaction products that are formed following reaction between a solid aluminosilicate precursor (eg, slags, fly ash, metakaolin) and an alkaline activation agent (eg NaOH) in the presence of water. To gain insights into the thermochemical properties of such compounds, C-(N)-S-H and N-A-S-H gels were synthesized with compositions: 0.8Ca/Si1.2 for the former, and 0.25Al/Si0.50 (atomic units) for the latter. The gels were characterized using thermogravimetric analysis (TGA), scanning electron microscopy with energy-dispersive X-ray microanalysis (SEM-EDS), and X-ray diffraction (XRD). The solubility products (K-S0) of the gels were established at 25 degrees C and 50 degrees C. Self-consistent solubility data of this nature are key inputs required for calculation of mass and volume balances in alkali-activated binders (AABs), and to determine the impacts of the precursor chemistry on the hydrated phase distributions; in which, C-(N)-S-H and N-A-S-H compounds dominate the hydrated phase assemblages.