Mechanism and Chemical Reaction of Fly Ash Geopolymer Cement- A Review

This paper presents the work carried out on the chemical reaction, mechanism, role of materials, applications and microstructure of fly ash geopolymer cement. Geopolymer is a type of amorphous alumino-silicate cementitious material. Geopolymer can be synthesized by polycondensation reaction of geopolymeric precursor, and alkali polysilicates. Literature demonstrates that the exact geopolymerization mechanism is not well understood because the geopolymerization process involves a substantially fast chemical reaction. However, the most proposed mechanism includes three stages: (1) dissolution of Si and Al atoms from the source material through the action of hydroxide ions, (2) transportation or orientation or condensation of precursor ions into monomers, (3) setting or polycondensation/polymerisation of monomers into polymeric structures. Every materials used in geopolymer cement have their own function and role to create a chemical reaction and mechanism. The atomic ratio Si:Al in the polysialate structure determines the application fields. A low ratio Si:Al (1,2,3) initiates a 3D-Network that is very rigid. A high ratio Si:Al, higher than 15, provides polymeric character to the geopolymeric material.