High-performance geopolymer binders using rice husk ash-based alkali activators: a sustainable approach

Conventional geopolymers are eco-friendly compared to cementitious composites, but their sustainability is limited due to high carbon emissions and costs associated with commercial sodium silicate solution. The study presents a sustainable method for producing an alkali activator solution (AAS) as an alternative of commercial sodium silicate solution. The AAS is formulated by combining sodium hydroxide (NaOH) with rice husk ash (RHA) through an alkaline thermal extraction process. The NaOH solution efficiently dissolves the silica content in the RHA, resulting in the formation of the AAS. This AAS is then employed in two different forms: First is the filtered solution obtained after removing residual silica in the form of RHA, and the other is where the residual silica remains within the AAS. The morphological characteristics and evolution of hydration products in geopolymer mixes made with different forms of AAS were analysed using various characterisation techniques. A higher heat release was observed for the geopolymer mix prepared using AAS incorporating RHA sludge compared to the AAS mix without RHA sludge. The compressive strength of the geopolymer mortar exhibited a significant increase, ranging from 58 to 83 MPa (28 days). These findings were further validated through FE-SEM and the ITZ during the early stages of geopolymer mortar development.