Biomass ash in alkali-activated materials technology - a scoping review

As the construction industry moves toward decarbonization, there is a growing focus on developing alternative binders with a lower carbon footprint to replace Portland cement. Alkali-activated materials (AAMs) have emerged as one of the promising solutions because of the lower CO₂ emissions from their production and comparable performance. The main components of AAMs are amorphous aluminosilicate-rich precursors that react with alkali activators to form a solid binding matrix. Raw materials generally used as precursors in AAMs are industrial by-products such as slag, coal combustion fly ash, or metakaolin. The most commonly used activators to reach the desired performance of the binder are alkali hydroxides and alkali silicates. However, conventional alkali activators are chemicals characterized by a negative environmental impact and high cost, which limits the wide-scale application of AAMs in the construction sector. Replacing conventional chemical activators with alternative ones derived from waste materials is a promising solution to enhance the sustainability of AAMs while promoting their broader application. This paper presents a targeted scoping review on the use of different biomass ashes instead of chemical activators in the AAMs technology. The results showed that different biomass ashes can be used not only as a source of alkalis and silicates but also as a partial replacement for commonly used precursors.