Synthesis of rice husk ash based alkaline activators for geopolymer binder systems: A review

At present, geopolymer binders have been considered to be one of the most promising low-carbon building materials. Apart from low carbon emissions, the production of geopolymer materials also helps in mitigating several industrial solid waste management problems. The geopolymer binder can be produced using any aluminosilicate waste material followed by mixing with an alkaline activator. However, the major limitation associated with geopolymers is their production cost which is slightly higher than traditional cement-based binders. Out of all the ingredients, sodium silicate is found to be the most expensive and least environment friendly material. Several researchers have therefore utilized many silica-rich waste products such as rice husk ash (RHA) based silicate solution as a low-cost alternative to commercial sodium silicate solution. In this regard, this paper provides an in-depth review of the past literature to understand the properties of geopolymer binders produced using RHA-derived alkaline activator. The production process, and the factors affecting dissolution of RHA have been elaborated. Further, the properties such as compressive strength, and microstructure have been detailed. Lastly, the sustainability and lifecycle assessment of geopolymers synthesized using RHA-based sodium silicate solution are presented. The information provided in this study shall encourage the scientific community to adopt RHA-based sodium silicate as a cost-effective, and environment friendly activator to produce geopolymers.