Effect of structure on the geotechnical properties of bauxite residue

This paper describes a laboratory program to investigate the mechanical and physicochemical properties of bauxite residue (red mud) at a site in the United Kingdom. The red mud storage facility has been recently decommissioned and has been considered for future rehabilitation and construction activity. Based on a suite of laboratory tests conducted on the red mud, the material has compression behavior similar to clayey soils, but frictional behavior closer to sandy soils. The red mud appears to be “structured” and has features consistent with sensitive, cemented clay soils. Chemical testing suggests that the agent causing the aggregation of particles is hydroxysodalite and that the bonds are reasonably strong and stable during compressive loading. Exposure of the red mud to acidic conditions causes dissolution of the hydroxysodalite and a loss of particle cementation. Hydration of the hydroxysodalite unit cells is significant, but does not affect the mechanical performance of the material. The shape, size, and electrically charged properties of the hydroxysodalite, goethite, and hematite in the red mud appear to be causing mechanical behavior with features consistent with clay and sand, without the presence of either quartz or clay minerals.