Medical Waste Incineration Fly Ash as a Mineral Filler in Dense Bituminous Course in Flexible Pavements

Medical waste incineration fly ash (MWIFA) contains heavy metals that are toxic by nature and pose numerous health risks. The paper deals with the suitability of MWIFA as a mineral filler in the bituminous layer as an alternative to conventional stone dust (SD) through an appropriate combination of engineering and environmental assessments. Engineering parameters, such as Marshall stability, stability loss, flow, unit weight, air voids (V(a)), voids filled with asphalt (VFA), and voids in the mineral aggregate (VMA) of the asphalt mixtures, were evaluated with varying filler ratios, from 2% to 10%. All parameters for both fillers at optimum bitumen content satisfied the Marshall Mix Design criteria. The optimum bitumen contents of all filler ratios were within the standard limit recommended by the Bangladesh Roads and Highways Department. It was found that mixes prepared with MWIFA can resist moisture effects, making them durable in the monsoon. The mixes with 5.5% MWIFA as mineral filler performed the best, whereas 9% SD filler was required to achieve similar performance. The environmental test results show no environmental restriction on stabilizing the MWIFA into paving mixtures. The mobility of heavy metals (As, Pb, Cu, Cr, Ni, Cd, Hg, and Zn) from the asphalt-MWIFA mix was insignificant. The cumulative concentrations of heavy metals (Cd, Ni, Zn, Cu, and Pb) from long-term leaching tests were far below the Dutch regulatory limit (U1). MWIFA can be considered an eco-friendly and sustainable mineral filler for the dense bituminous pavement layer.