Leaching behaviour of municipal solid waste incineration bottom ash mixed with Hot-Mix Asphalt and Portland cement concrete used as road construction materials

Abstract

One of the beneficial utilisations of municipal solid waste incineration (MSWI) bottom ash (BA) is in the area of road construction sector: for example, the partial replacement of fresh aggregate in Hot-Mix Asphalt (HMA) and Portland cement concrete (PCC). However, the potential leaching of toxic elements (e.g. alkaline elements and heavy metals) from the BA mixed with milled HMA and crushed PCC is still a concern when used as 2nd-cycle recycled materials. This paper presents and discusses the chemical characteristics and leaching behaviour of MSWI BA when used in both HMA and PCC. Chemical analysis of MSWI BA was conducted by using petrographic analysis tools. The leaching characteristics of major alkaline and trace elements from the milled HMA and crushed PCC containing varied amounts of BA were investigated by Synthetic Precipitation Leaching Procedure (SPLP) batch testing. The release of most alkaline and heavy metals (except Mg and Si from HMA and Ca from PCC) is reduced when mixed with the HMA and PCC as adding 10–20% of BA due to the binding effect in asphalt and cement mixtures. The concentrations of most major alkaline elements (e.g. Ca, Al, Si, and Na) from the HMA and PCC with BA increased with increasing elapsed time due to availability controlled leaching. The release of all of the priority elements meets the criteria of the US Secondary Drinking Water Standard (except Al) and the EPA Multi-Sector General Permit for Stormwater Discharges Associated with Industrial Activity.