Characterization of the properties of perlite geopolymer pastes

This paper deals with the characterization of perlite-based geopolymer pastes, using fine perlite as raw material. The present study examined the effects of the main synthesis parameters such as perlite to activator ratio, NaOH concentration, the addition of soluble silica to the activator, and curing temperatureon the setting time, the stability in an aquatic environment, the viscosity of the paste, and the compressive strength of the solidified geopolymers. The results showed that these inorganic polymer pastes are non-Newtonian shear thinning fluids that achieve low viscosities at high shear stresses. The optimum synthesis conditions for the geopolymer pastes proved to be a) a low initial NaOH concentration in the alkaline phase (2–5 M) and b) a solid to liquid ratio of 1.2–1.4 g/mL. If very fast setting is necessary, the pastes should be prepared with a soluble silica-doped alkaline activating phase and cured at high temperatures around 90 °C.