AbstractThe prevailing method to separate an expanded polystyrene (EPS) geofoam (geofoam block) roadway embankment and its pavement is the use of cast-in-place reinforced concrete as a load-distribution slab. However, this technique delays the project completion time due to required curing. This study investigates the use of precast concrete panels as an alternative load-distribution slab which promises reduction in construction time and effort. In addition to traditional EPS-precast concrete interface, the effect of interlocking mechanism of various interlock configurations was quantified. In addition to the effects of interface geometry the effect of material hardness on the interface stress-strain behavior was investigated by using two different densities of geofoam blocks. All of the interface shear strength (ISS) tests were also performed using cast-in-place concrete for comparison purposes. Shearing resistance between the EPS and precast concrete was found to be higher than that of the flat EPS-EPS interface recommended by the design guideline. Interlocking improved the interface shear behavior and changed the interface shear mechanism of EPS-precast concrete from purely frictional to frictional-adhesional.