Fly ash plastering mortar: heavy metal leaching rule, coupling mechanism and life cycle carbon reduction

The application range of fly ash in mortar products is gradually expanding, and the harm of heavy metals and environmental damage are also deepening. This study centers around the plastering mortar prepared from fly ash from three provinces in southwestern China (FA1 in Sichuan, FA2 in Chongqing, and FA3 in Guizhou), and systematically studies its basic properties, heavy metal leaching rule and coupling mechanism, life cycle assessment. The research results indicate that there is a certain regularity between the performance of fly ash plastering mortar and the content of fly ash added, but there is no obvious regularity of different origins in the performance. The experimental results showed that the heavy metal content in fly ash plastering mortar showed a significant trend of gradually decreasing over time. The leaching kinetics fitting results showed that the Parabolic equation model was suitable for the leaching of Cr, the Elovich leaching model was suitable for the leaching of Hg, and the Elovich and Second-order kinetics equations were suitable for the leaching of Cd. In fly ash plastering mortar products, Cr, Cd, and Hg elements exist in the forms of Cr3+, Cr6+, Cd2+, and Hg2+. The relative atomic mass of Cr in these two forms is influenced by factors such as the origin, content, and strength grade of fly ash. The occurrence and coupling mechanism of heavy metals in cementitious materials and hydration products were also explored. The results of the life cycle assessment showed that fly ash plastering mortar provides better environmental benefits compared to conventional ones and has a greenhouse effect carbon emissions of about 983 kgCO2eq, which can be reduced by approximately 30% compared to conventional plastering mortar.