Role of Soluble Aluminum Species in Activating Solution of Phosphate-based Geopolymer

A new chemical activation mode which is phosphate-based is studied, by which the aluminosilicate source can transfer to a novel type of phosphate-based geopolymer. The activiation occurs in an acidic or low alkaline medium, where the phosphate instead of the alkai-silica activates the aluminosilicate species to yield a compact geopolymer matrix with a condensed poly (alumino-silico-phosphate). The newly-formed Al-O-P linkage could compensate the charge caused by the shift of chemical environment of aluminum. Thus, a charge balance within the molecular structure is achieved without the involvement of monovalent cations. These features enable the phosphate-based geopolymer to inhibit efflorescence and dielectric loss problems which are often encountered in alkali-based geopolymer. In some previous investigations, high temperature curing (e.g., 60°C or 80°C curing for a period of time) was usually employed for the phosphate-based geopolymer in order to achieve fast setting and high strength. In the present study, a soluble aluminum source is introduced into the activator solution to induce a room-temperature hardening mechanism, and to improve the setting time and rheology of the fresh geopolymer pastes.