Experimental investigations on the physical and rheological characteristics of sand-foam mixtures

Sand-foam mixtures have shown potential applications in land stabilization for mine tailings, drilling, and other areas of engineering. A series of laboratory experiments were conducted to examine the effects of foam-water ratio, sand concentration and time history on the physical and rheological properties of sand-foam mixtures. Sand particles of D50 = 0.21 mm diameter were used with sand volumetric concentrations ranging from co = 0.0-0.82. Physical properties such as density, air volume fraction and spreading of sand-foam mixtures with rheological properties including shear stress and viscosity were measured. Two different regimes of low and high concentrated mixtures were identified based on sand concentration with a critical sand concentration of co = 0.6. It was found that the foam spreading rate is independent of foam-water ratio for low concentrated mixtures whereas for dense sand-foam mixtures, the foam-water ratio plays an important role in the fluidity of the mixtures. Rheological study of sand-foam mixture indicated that the yield stress increased with sand concentration. It was found that the viscosity of both foam and sand-foam mixtures decreased with shear rate indicating a shear thinning behavior. A shear banding effect was observed in low concentrated sand-foam mixtures for the shear rate ranging from 20 to 100 s−1. Step-wise loop tests were performed to examine the sample degradation characteristics of sand-foam mixtures. It was found that the effect of time history on sand-foam viscosity is noticeable and viscosity of the sheared sample can be lower than the fresh and un-sheared sample for dense sand-foam mixtures.