Evaluation of Interface Shear Strength Between Interlocked Geofoam Blocks and Precast Concrete

Abstract

The separation layer between the top of an expanded polystyrene (EPS) block (geofoam block) roadway embankment assemblage and the pavement system is usually comprised of a reinforced Portland cement concrete (PCC) slab. The prevailing construction technology is the cast-in-place method. However, there is a growing consensus that the current state of practice may represent a significant cost, especially to project schedules. As an alternative, this study proposes the use of precast concrete panels. In order to guide design engineers, interface friction properties of traditional flat-surfaced geofoam blocks with a minimum density of 18.4 kg/m3 and precast concrete panels were quantified by using direct shear testing. In addition, four different types of interlock configurations (geofoam blocks with one- and four-square ledges and geofoam blocks with one- and four-triangle ledges) were used to investigate the effects of interlocked geometry and number of ledges in the shear plane between interlocked geofoam block and precast concrete. The interface friction behavior of precast concrete and traditional flat-surfaced geofoam block was found to be purely frictional. The interface friction angle of precast concrete and interlocked geofoam blocks was found to be higher than that of traditional geofoam blocks. Implementing an interlocked configuration, which interrupts the continuous shear plane with ledges, changes the interface friction mechanism of precast concrete and geofoam block from purely frictional to frictional-adhesional. Independent of the geometry of the ledges, adhesion was developed in addition to interface friction. Both adhesion and interface friction angle increased with number of ledges.