A systematic review exploring the utilization of coal mining and processing wastes as secondary aggregate in sub-base and base layers of pavement

With the rising trend in electricity usage, the amount of waste associated with the mining and processing of coal is also rising rapidly. Over the past few decades, improper utilization of these wastes has led to resource depletion, waste disposal, and environmental pollution issues. The key focus of the present study is to review the literature related to the utilization of untreated and treated coal mining and processing wastes in the construction of sustainable roads. Following a suitable Preferred Reporting Items (PRISMA) framework for systematic review, 67 records are considered for the qualitative analysis. The efficiency of these coal mining and processing wastes as secondary aggregate in the sub-base and/or base layer of pavement is reviewed based on their mechanical (California bearing ratio, Unconfined compressive strength, Flexural strength, and Indirect tensile strength) and durability (Freeze-thaw resistance and Resistance to shrinkage) properties. The effectiveness of chemical stabi-lization on strength gain criteria is also discussed on the basis of microstructural (Scanning electron microscopy and Energy dispersive X-ray spectroscopy) analysis. The findings of the present review suggest that utilization of coal wastes in the construction of bound sub-base and/or base not only addresses the waste disposal challenges but also assists the problems associated with raw material depletion. Additionally, based on the outcomes of past studies, this paper identifies the research gaps and presents future research directions that could open new avenues for the sustainable development of pavement.