Evaluation of Interface Shear Strength Between Interlocked Geofoam Blocks and Cast-in-Place Concrete

Expanded polystyrene (EPS) block (geofoam block) roadway embankment typically involves the construction of cast-in-place reinforced Portland cement concrete (PCC) slab as a traffic load distribution layer since it reduces live load stresses and also provides lateral confinement of the overlying unbound pavement layers. Therefore, in addition to the geofoam block to geofoam block and geofoam block to bedding sand, interface properties of geofoam block to cast-in-place concrete slab should also be investigated for the stability calculations regarding transitional sliding failure mode. In order to enhance the traditional geofoam block to cast-in-place concrete interface shear strength, previously introduced interlocked geofoam block concept has been utilized. Flat-surfaced traditional geofoam blocks were trimmed by a hot-wire to form interlocked geofoam blocks with ledges along their contact surface with the cast-in-place concrete. EPS19 with a minimum density of 18.4 kg/m³ was used in the experimental program. Four different types of interlock configurations (blocks with one- and four-square ledges and blocks with one- and four-triangle ledges) were used to investigate the effect of interlocked geometry and number of ledges in the shear plane. In addition, interface friction properties of traditional geofoam block and cast-in-place concrete surface was also quantified to highlight the improvement provided by the interlocking mechanism. The adhesion bond between traditional geofoam blocks and cast-in-place concrete was close to that of internal shear strength of geofoam blocks. Regardless of the shape, the interface adhesion bond was slightly improved by the number of ledges when compared to that of traditional geofoam and cast-in-place concrete.