Performance of RBI stabilized coal mine overburden material for haul road pavement

This paper presents an extensive laboratory investigation to develop composite materials using coal mine overburden and a stabilizer. The purpose of these composites is to be used as a pavement material for haul road. The physical-mechanical-chemical-micro-structural characteristics of these overburden materials like murrum, sub-soil and top-soil are evaluated before and after stabilization. Top-soil is the outermost layer of soil near the ground surface. Sub-soil is the layer of soil under the top-soil. It is composed of smaller particles such as sand, silt, and clay. Murrum is a very hard homogenous massive material enriched with iron and aluminum. Based on unified soil classification system, murrum is classified as clayey gravels (GC) while sub-soil is clayey sands (SC) and top-soil is organic silty clays of low plasticity (OL). It is found that apart from murrum, other materials are not suitable to be used without stabilization; hence, nine composites are developed using mine overburden and RBI grade-81. Laboratory study shows that the gain ratio of the developed composite is better than the previously developed fly ash-based composites by other researchers. Gain ratio is defined as the percentage increase in mechanical properties of overburden material after stabilization. The gain ratio for CBR and UCS is maximum with the top-soil, followed by sub-soil and murrum. The composite M94RBI6 (94% murrum and 6% RBI) showed highest strength values among all developed composites. All composites showed increased strength due to formation of cementitious gel. Surface morphology confirmed the formation of hydrated gel and Ettringite rods due to pozzolanic reaction.