Effect of different mixing ratios of polystyrene pre-puff beads and cement on the mechanical behaviour of lightweight fill

A laboratory study on the formation of a lightweight fill material by blending soil with polystyrene pre-puff (PSPP) beads and other binders such as cement is presented in this paper. The effects of different compositions and different ratios between PSPP beads and soil, cement and soil, water and soil on the density, unconfined compressive strength and deformation of the lightweight fill formed are studied. It is observed that the density of the lightweight fill can be effectively controlled by the amount of PSPP beads used in making the fill. With the inclusion of merely 2-6% of PSPP beads (to soil by weight), the density of the lightweight fill formed can be reduced to 700-1100 kg/m³. The shear strength and stiffness of the lightweight fill can be controlled by adjusting the amount of cement used. The unconfined compressive strength of the lightweight fill increases considerably if a cement to soil ratio of 10-15% is used. Compared with the expanded polystyrene (EPS) block geofoam, the PSPP beads mixed lightweight fill has a higher density, but higher shear strength and higher stiffness too. It can be used as a substitute of EPS blocks when irregular shaped volumes are to be filled or when stronger fill materials are required.