Evaluation methodology and application for heavy metal leaching assessment in molten slag aggregate concrete.

Molten slag, encapsulating heavy metals in fly ash, has been widely used in subgrade concrete. However, the molten slag aggregate concrete (MSAC) poses a potential risk of heavy metals leaching. For MSAC, this study developed a rapid, accurate closed-vessel agitation method to simulate long-term heavy metal leaching, and determined heavy metal leaching limits for soil and ground water by designing soil column experiment to analyze the migration rule. The closed-vessel agitation method with a leaching solution pH of 4.32 and a liquid-to-solid ratio of 11:1 L/kg was designed. Heavy metal concentrations from the 18-hour closed-vessel agitation method differed by no more than 15% from those of the 64-day semi-dynamic leaching method. Heavy metals from MSAC are transported into groundwater following dilution by soil. The soil dilution multiples for collected loess and lateritic soil were 12-22.9 and 20-50, respectively. This MSAC on top of loess and lateritic soil corresponded to industrial/agricultural and drinking water groundwater standards, accordingly. Moreover, new leaching standards for MSAC heavy metals were introduced, covering applicable soil and groundwater types. The establishment of the assessment methodology facilitates safe promotion of MSAC and other green concretes, ensuring their long-term environmental stability and sustainability.