Geotechnical Properties of Unbound Olive Stone Biochar

Olive stone is a major solid by-product generated from olive oil mills. Due to its promising energy potential, olive stone is a suitable candidate for heat and electricity production via biomass gasification. Olive stone biochar (OSB) is the solid residue left after gasification. Typically, OSB is disposed of as a waste material in landfills. However, there is an opportunity to repurpose OSB as a sustainable geotechnical fill material. In this study, the engineering and environmental properties of OSB were thoroughly evaluated to assess the feasibility of using OSB in construction projects. Furthermore, recycled glass (RG), a mainstream waste material that has been successfully incorporated in civil engineering applications, was subjected to control tests for benchmarking purposes. Geotechnical tests, including particle size distribution, standard Proctor compaction, California Bearing Ratio, hydraulic conductivity, and repeated load triaxial, were conducted on both OSB and RG. The test results indicated that OSB can be satisfactorily used as a geotechnical fill material for pavement subgrade. Environmental test results, including pH, elemental analysis, and leachate analysis, indicated that the implementation of OSB in construction works does not pose negative environmental risks. Instead, the reuse of OSB in civil engineering applications can promote the circular economy of biomass waste, as not only olive stone can be used for energy generation, but also the residue after gasification has the potential to act as a useful construction material.