Experimental study on the resilient and permanent deformation of a compacted waste foundry sand

The use of Waste Foundry Sands (WFS) as a construction material in geotechnical works is strategic because it allows the consumption of large amounts of this waste worldwide, typically discarded in landfills. Beyond the achievement of environmental requirements, the construction industry needs a comprehensive understanding of its mechanical properties, which is a challenge to enhance the recycling or reuse of WFS. This paper investigates the resilient and permanent deformation of a compacted WFS under repeated load. These features are necessary to understand the behavior of this material in the context of pavement design. A campaign of laboratory tests was carried out based on cyclic triaxial tests to measure resilient modulus (RM) and permanent deformation (PD). Specimens were prepared with different densities, which achieved varying compaction energy (600, 1260, and 2700 kJ/m³) but keeping saturation degree varying in a narrow range. Results demonstrated that the resilient modulus ranges from approximately 80 to 380 MPa, with confining stress controlling its behavior and having a small effect on compaction energy. Permanent deformation reaches almost 3 % after 150.000 load cycles for the maximum confining and deviatoric stresses and is controlled by the confining and deviatoric stress. The WFS reached the shakedown state for all the densities and stress-state evaluated, in a pattern below plastic creep shakedown and plastic limit shakedown. The best models to describe the experimental results were investigated, and the fitting parameters were also found. The authors also demonstrated that the resilient modulus measured on the last 100.000 cycles of permanent deformation tests is similar to the values measured on resilient modulus tests, which allows to characterize the resilient and permanent deformation using only the permanent deformation tests.