Evaluation of Interface Shear Strength Properties of Geogrid-Reinforced Construction and Demolition Materials Using a Modified Large-Scale Direct Shear Testing Apparatus

The interface shear strength properties of geogrid-reinforced Construction and Demolition (C&D) aggregates were determined using a modified large scale direct shear test (DST) apparatus. Comparisons were made between the results of the various C&D aggregates reinforced with biaxial and triaxial geogrids as well as with the unreinforced aggregates by means of the modified and conventional DST methods. The modified DST method employed, sought to increase interlocking between the C&D aggregates with the geogrids and thus ascertains the true interface shear strength properties of the recycled demolition aggregates. Biaxial and triaxial geogrids were used as the geogrid-reinforcement materials. The C&D aggregates tested with the DST were Recycled Concrete Aggregate (RCA), Crushed Brick (CB) and Reclaimed Asphalt Pavement (RAP). The modified DST results indicated that the interface shear strength properties of the geogrid-reinforced C&D aggregates were higher than that of the conventional test method as well as the respective unreinforced materials. Geogrid-reinforced RCA was found to have the highest interface peak and residual shear strength property of the C&D materials. RAP was found to have the smallest interface shear strength properties of the C&D aggregates. The higher stiffness triaxial geogrid attained higher interface shear strength properties than that of the lower stiffness biaxial geogrid. The modified device also showed some increased measured interface coefficients compared to a conventional DST. The geogrid-reinforced recycled C&D aggregates was found to meet the peak and residual shear strength requirements for typical construction aggregates used in civil engineering applications.