Leaching characteristics of alkali-activated materials incorporated with different by-products

Abstract

Alkali-activated materials (AAMs) are sustainable alternatives to ordinary Portland cement, offering lower carbon emissions. Whereas AAMs exhibit superior mechanical properties, their environmental impact, particularly the potential leaching of heavy elements, is a critical concern. In this paper, the leaching attributes of AAMs synthesized from different industrial by-products, including ground granulated blast furnace slag (GGBS), fly ash (FA), and red mud (RM), are reviewed, highlighting the primary leaching mechanisms and the influence of pH, activator type, precursor composition, and environmental exposure on the release of hazardous elements. GGBS-incorporated AAMs can efficiently trap heavy metals through the production of dense C-A-S-H gel, especially when activated with sodium silicate. FA-based AAMs exhibit varying leaching attributes, influenced by the activator, with higher immobilization for cationic metals; however, oxyanions, such as As and Cr(VI), are difficult to immobilize, particularly at high pH levels. RM-based AAMs demonstrate complex leaching properties due to their high alkalinity and metallic ion content, with elements like V and Cr(VI) showing elevated mobility. Therefore, blending with GGBS or FA is preferred because it significantly enhances immobilization. The findings emphasize the critical role of precursor selection, activator chemistry, and curing conditions in optimizing AAMs to improve their environmental safety and long-term performance in construction applications.