Characterization and environmental sustainability of open pit coal mine overburden waste rock as pavement geomaterial

As the global economy grows and living standards increase, the use of gravel and sand is expected to nearly quadruple by 2060, putting twice as much strain on the environment as it does now. Local solutions to the global problem are always more sustainable and resilient. In recent times, coal mine overburden (OB) is an unprocessed, highly heterogenous waste of coal mining industries. However, it has proved to be a sound potential alterative of natural aggregate. The associated engineering properties are very site specific and are highly influenced by geology and exposed climate. A comprehensive laboratory testing program oriented at determining the geotechnical and geoenvironmental properties is implemented to investigate the suitability of the OB as pavement material. The load-deformation performance as pavement material is evaluated using 3D finite element modelling and environmental sustainability is assessed through streamlined Life cycle assessment (LCA). This inert geomaterial is acceptable as a pavement material for base and subbase layers with impact value of 28 %, and abrasion value 34 %. The California bearing ratio (CBR) of 76 at unsoaked and 61 at soaked conditions also affirm its choice as an excellent subgrade material. The critical state parameters of the fine aggregate defined the long-term serviceability as a subgrade material. The load-deformation behavior of overburden was found to be similar to the natural aggregate as a pavement material with comparable maximum deflection of 1.20 mm for OB and 1.25 mm for natural aggregate. The LCA revealed that OB are more environmentally sustainable than natural aggregates as base and subbase material. The study highlights the importance of proper characterization and testing of OB to ensure its safe and effective use in construction applications, providing robust local solutions to global problems.