Engineering and environmental characterization of municipal solid waste bottom ash as an aggregate substitute utilized for asphalt concrete

The preferred management option for the municipal solid waste bottom ash (MSW-BA) around the world is utilization rather than landfilling, but the current environmental quality criteria for bottom ash to be utilized in bulk quantities are rather strict. The purpose of this paper is to analyze the physical and environmental properties of asphalt mixtures containing different amounts of MSW-BA used as an aggregate substitute. The Marshall mix design method, water sensitivity, and wheel track rutting tests were conducted on MSW-BA asphalt mixtures to evaluate the engineering properties of the mix. Leach tests were performed to measure the concentration of heavy metals. The MSW-BA asphalt mixture had relatively lower rutting resistance when compared with the conventional one. The results of the water sensitivity test showed that the MSW-BA asphalt mixtures had a lower tensile strength ratio compared with the conventional asphalt mixtures. It is recommended that the use of the MSW-BA ash in asphalt concrete mixtures be limited to be 20% ash, by total weight of the mix, in binder or base course and 10% in surface mix to ensure satisfactory pavement performance. The test results obtained from the toxicity characteristic leaching procedure testing indicated that, after being mixed with asphalt binder, the concentration of heavy metals and the levels of toxicity were significantly reduced. The concentrations of MSW-BA all along were below regulation limits.