Improving the Geotechnical Properties of Recycled Non-Selected Construction Waste Using Geogrid Reinforcement

Aggregates obtained from the demolition of old constructions can be used as a substitute for natural aggregates. The present study aimed to use geogrid and recycled materials to improve the geotechnical properties of such wastes. For this purpose, eight borehole samples of construction and demolition (C&D) waste were taken non-selectively from the Hesar Karaj-Line 4 construction waste landfill. Non-selected C&D waste mostly consists of recycled concrete aggregate (RCA), crushed brick (CB), and regenerated asphalt pavement (RAP). After measuring the properties of the collected samples with standard tests, a series of large-scale modified direct shear tests (DST) were performed to determine their shear strength properties with and without geogrids considering the effects of the aperture size and geogrid strength. Also, impacts of 10, and 20 freeze-thaw cycles, and the moisture content (at the optimum water content, half and 1.5 times that) on the shear strength properties of non-selected C&D wastes were evaluated. The results of DSTs showed a significant improvement in the shear strength of geogrid-reinforced samples compared to those without geogrid. Considering the shear strength test results of natural aggregates, geogrid-reinforced non-selected C&D waste can be used as an economically viable low-energy renewable alternative to these aggregates in road construction and filling projects. The optimum aperture size of geogrid to provide the maximum reinforcement efficiency was obtained at around 25 mm. Furthermore, 20 freeze-thaw cycles led to an 11-22%, and 11-20% increase in the peak friction angles and peak cohesion, respectively, for the non-selected C&D samples.