Activated Carbon Preconditioning to Reduce Contaminant Leaching in Cement-Based Stabilization of Soils

Adding powdered activated carbon (PAC) with cement can enhance stabilization and solidification (S/S) by adsorbing organic contaminants. Simultaneous addition of PAC and cement reduces soil-handling costs, but cement-hydration reactions coat PAC with Ca(OH)(2) before contaminants can be adsorbed onto PAC. Laboratory studies were done on four aged, contaminated soils from manufactured gas plant sites to compare S/S performance with simultaneous addition of PAC and cement versus cement addition after preconditioning with PAC. Ordinary (Type I) portland cement, quicklime, and class C fly ash were the cementing agents tested. Leaching of benzene, toluene, ethylbenzene, and xylenes and naphthalene was quantified using the synthetic precipitation leaching procedure, and unconfined compressive strength was measured. Allowing a 20-week PAC preconditioning time dramatically enhanced leaching and strength compared with adding cement and PAC simultaneously. Adding cement at the same time as PAC resulted in only slight improvements in leaching and strength compared with adding cement alone. The results from this work suggest that PAC is only effective when allowed sufficient preconditioning time before cement addition. (C) 2014 American Society of Civil Engineers.