X-rays diffraction spectra of hardened geopolymeric materials (resins and cements) do not supply accurate information (amorphous structure). High-resolution MAS-NMR (Nuclear Magnetic Resonance) spectroscopy of 29Si and 27Al is a very powerful tool that provides useful structural data.
For more updated information, see in Davidovits’ book, Geopolymer Chemistry & Applications, the Chapter 4. You may also download previous scientific papers #12 J. Thermal Analysis, #3 NASTS award or #8 Alkaline Cements and Concretes. Other scientific means of investigation, including DTA, XRF, ANOVA, liquid NMR, FTIR spectroscopy, SEM, TEM, mechanical resistance, fatigue under stress and cycles, load-deflection, thermal resistance, leaching behavior, hydraulic conductivity, microbial stability, are discussed in the various papers presented at the Geopolymer World Congress and published in the Proceedings of Geopolymer 2005.
Evidence of oligomer units by NMR
Low molecular elements (monomer, dimer, trimer, tetramer, pentamer) are called oligomers. Oligo-sialate designates the monomer ortho-sialate, the dimer is disialate, etc.; same for oligo(sialate-siloxo) and oligo(sialate-disiloxo). At the beginning of geopolymer research, Joseph Davidovits in 1976 and afterwards for at least 25 years, assumed that the geo-chemical syntheses occurred through hypothetical oligomers (dimer, trimer). Further polycondensation of these hypothetical building units provided the actual structures of the three dimensional macromolecular edifice as displayed in the Figure below. Review papers published at the First Geopolymer Conference in 1988, and at the second, 11 years later, in 1999, could not present scientific details describing the actual reaction mechanism.
Reaction mechanism for sialate and sialate-siloxo species, described as hypothetical by Davidovits in 1988.