Waste-derived activators for alkali-activated materials: A review

Alkali-activated materials (AAMs) are increasingly attracting attention as a promising sustainable alternative to Portland cement-based materials. This study presents the key advancements in the synthesis of alternative sodium silicate activators using silica-rich waste resources, such as rice husk ash, waste glass, nanosilica and microsilica. Different silicate extraction methods, including fusion, hydrothermal, and thermochemical processes were compared, and the roles of various parameters on the silica dissolution rate were deliberated. In addition, the efficiency controlling factors of the synthesized activators were rigorously reviewed using the compressive strength, setting time, and microstructural characteristics of the resulting AAMs. The extraction of silica was shown to be effective using hydrothermal and thermochemical processes. Moreover, the recent studies showed that the proper selection of the raw materials and the extraction conditions allow for maximizing the yield of silica from the silica-rich wastes. Such proper selection provides mechanical and microstructural properties of AAMs activated by the synthesized activators comparable to those from the commercially available activators.

Automated summary

This study presents advancements in synthesizing alternative sodium silicate activators using silica-rich waste resources. Different silicate extraction methods were compared and their effects on silica dissolution rate discussed. The synthesized activators were rigorously evaluated for efficiency control factors, showing that hydrothermal and thermochemical processes are effective in silica extraction. Proper selection of raw materials and extraction conditions can maximize silica yield from waste, providing mechanical and microstructural properties of AAMs comparable to commercially available activators.