Effect of source materials on geopolymerization

Few attempts have been made to understand the effect of the structural and surface properties of source materials on geopolymerization. In the present work, kaolinite, albite, and fly ash have been chosen for a case study to answer this question. X-ray diffraction, X-ray fluoresence, X-ray photoelectron spectroscopy, Al-27 and Si-29 magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and scanning electron microscopy (SEM) have been used to characterize the source materials and geopolymers. The fly ash that has an amorphous structure and possesses the lowest binding energies in its structure shows the highest reactivity during geopolymerization. Apart from the reactivity, the desired Si/Al molar ratio in the gel phases and the leaching of the source materials are observed to significantly affect the geopolymerization. The geopolymerization of mixtures of two or three source materials demonstrates the benefits derived from the interaction between the source materials. Such interactions could optimize the gel phase composition and result in high strength geopolymers. It is expected that the geopolymers containing Ca and K and having Si/Al molar ratios of about 2 in the gel phase could have a high compressive strength.