FTIR study of the sol–gel synthesis of cementitious gels: C–S–H and N–A–S–H

The study explored the compatibility between the main product of Portland cement hydration and the main product of the alkali activation of fly ash: C–S–H and N–A–S–H gels, respectively. Both gels were synthesized with laboratory reagents at different pH values. Blends of the two were synthesized as well, using the sol–gel procedure. All the gels were characterized with Fourier transform IR spectroscopy (FTIR). The gels synthesized with this procedure were shown to precipitate together with a silica-rich gel. In addition, the pH level was found to play a determinant role in both C–S–H and N–A–S–H gel synthesis. The C–S–H gel is the major phase formed at pH > 11 and N–A–S–H gel for pH > 12. The results relating to the joint synthesis of the two (C–S–H and N–A–S–H) gels were not conclusive. Technique used for the characterization failed to differentiate between them in the blended material.