Red mud as geotechnical composite

Red mud (RM), a by-product of the Bayer process, is produced in large quantities worldwide. It is mainly disposed of in settling ponds or through dry stacking, both of which pose environmental risks due to instability, alkaline emissions, and leaching of potentially toxic elements (PTEs). Several efforts have been made to utilize RM as an additive in soil remediation or in the production of construction materials. However, due to its fine-grained texture, poor mechanical properties, and tendency to leach harmful substances, RM alone is unsuitable for direct use in construction. Nevertheless, its mechanical properties and workability can be significantly improved by mixing it with hydraulic or pozzolanic binders, such as calcareous ashes. In the present study the use of calcareous paper mill ash (PA) as an additive to RM, for production of geotechnical RM/PA composite was studied. The results demonstrate that mixing RM slurry with PA produces a soil-like geotechnical composite with suitable workability and mechanical properties for use in earthworks, comparable tonatural soils. Moreover, the RM/PA composite exhibits lower leaching of PTEs, in comparison to the RM, improvingthe environmental acceptability of RM for its use in construction. This study confirms that RM composites, with addition of alternative binders, can be a viable construction material, which not only meet the geotechnical performance requirements for earthworks but also comply with Slovenian environmental standards. This approach offers a dual benefit: it reduces the environmental and economical burden associated with RM disposal while simultaneously decreasing the demand for natural construction materials.