Role of water in the synthesis of calcined kaolin-based geopolymer

Water plays an important role in the whole process of geopolymer synthesis. X-ray diffraction (XRD) and thermogravimetry (TG) showed that residual water depressed the activity development of calcined kaolin before stable crystalline phases formed as confirmed by the compressive strength. Reaction heat evolution measurement revealed that high liquid/solid ratio could accelerate the dissolution of raw materials and the hydrolysis of Si4+ and Al3+ compounds but hinder the polycondensation when OH− concentration is high enough as 12 mol/L. The effect of nonevaporable water on the strength variation of geopolymers was firstly analyzed. The results indicated that nonevaporable water was necessary to keep the strength stable and the optimum content was about 7.4%.