Laboratory-prepared iron oxide coatings on sands: Surface characterization and strength parameters

Soils containing iron oxides that are derived from chemical weathering are widespread in geotechnical systems. This work studies the effect of adsorbed iron oxides on the shear strength of laboratory-prepared iron oxide-coated sands. Goethite-and hematite-coated Ottawa sands were synthesized in the laboratory via a heterogeneous geochemical suspension-reaction method. Surface roughness parameters and fractal dimension were determined using atomic force microscopy (AFM), which showed that hematite-coated sands exhibited the roughest surfaces. N₂-adsorption experiments also helped characterize the mineral surfaces. Shear strength parameters were obtained through consolidated drained (CD) triaxial compression, showing an increase in the critical state friction angle ofmore than 5%when the sandswere coated with iron oxides. Iron oxide coatings also increased dilatancy and decreased contractiveness. The experimental results can be attributed to changes in mass-to-mass concentration and intrinsic soil fabric changes due to the presence of iron oxide coatings, as well as to increased roughness and particle-to-particle interlocking.