Acid based geopolymerization kinetics: Effect of clay particle size

The kinetic of acid-based geopolymer synthesis was studied for different granulometric classes (125 μm, 100 μm, 80 μm and 63 μm) of calcined illito-kaolinitic clay. X-ray diffraction (XRD), infrared spectroscopy (IR), Nuclear Magnetic Resonance (MAS NMR), scanning electron microscopy (SEM) and mechanical measurements were used to investigate geopolymerization kinetic. These techniques have shown that the fineness of the precursor has a significant effect on geopolymerization kinetic and on the mechanical properties of the product. A geopolymerization mechanism including three steps has been proposed: dealumination of metakaolinite, reaction between phosphoric acid PO4 tetrahedral units with SiO layer, on one hand, to form an amorphous (SiOPO) structure, and with leached aluminum, on the other hand, to give crystalline AlPO4 and finally polycondensation in the amorphous phase. The final product is a geopolymeric composite composed by crystalline AlPO4 and amorphous (SiOPO) structure.