The pozzolanic reaction of a natural zeolite-rich tuff and portlandite was investigated by means of IR spectroscopy. The zeolite tuff consisted mainly of Ca-rich clinoptilolite. A detailed analysis of the changes in the bonding environment during reaction presented by the IR spectra showed that the vibrations assigned to the reactant phases were progressively consumed and implied that Si-rich environments were preferentially depleted. The contemporaneous appearance and rise of vibration bands characteristic for calcium-silicate-hydrates and calcium-aluminate-hydrates demonstrated the formation of reaction products.
Changes in bonding environment were spatially visualized by means of synchrotron-IR microspectroscopy. Promising results showed the distribution of reactants and reaction products and allowed to analyze spatial trends in IR-vibration frequencies. A shift in calcium-silicate-hydrate mean peak position from 972 to 968 cm−1 indicated a decrease in silicate chain length with increasing distance from the clinoptilolite-matrix interface.