Use of cement-chelated, solidified, municipal solid waste incinerator (MSWI) fly ash for pavement material: mechanical and environmental evaluations

Abstract

As a by-product from the incineration of municipal solid waste (MSW), fly ash usually contains mobile heavy metals that may engender severe pollution when reused. In this study, fly ash was solidified with cement and a chelating agent to immobilize these polluting elements. The possibility of using the solidified fly ash for pavement materials was also assessed through mechanical and environmental perspectives. According to the results, the strength of solidified fly ash was found proportional to both the cement/fly ash ratio and curing time. This indicated that the increase of fly ash loading reduced the concentration of products from cement hydration, and thus destroyed the structure of the products of hydration. With the increase of freeze–thaw cycles, the compressive strength of cement-stabilized fly ash decreased between days 7 and 14, and then increased between days 14 and 28. Subsequently, the finite element analysis showed that placing the solidified fly ash layer as a pavement material between an unbound base course and subgrade was beneficial to prolong fatigue life and reduce rutting distress of asphalt pavements. Finally, leachability of metals from the mixtures was tested, which showed that leaching concentration decreased as the cement/ash ratio, curing time, and chelating agent content increased.