Environmental performance of reusing a contaminated soil solidified/stabilized by a low-carbon binder as roadway subgrade material

A comprehensive field study was conducted to evaluate the environmental performance of a roadway subgrade consisting of contaminated soil solidified/stabilized with a hydroxyapatite-based binder (termed as SPC in this study). Traditional Portland cement (PC) was used as a control binder for comparison purposes. The environmental properties including soil pH, soil leachability, and chemical speciation of target contaminants including nickel (Ni) and zinc (Zn) were investigated at 1 d, 7 d, 28 d, and 600 d after construction of the roadway subgrade. Furthermore, the field migration distances of Ni and Zn released from the subgrade to the off-site clean soil were investigated after 600-d of exposure to the atmospheric environment. The results showed that SPC solidification/stabilization was not only effective for reducing the soil leachability but improving the chemical stability of Ni and Zn in the contaminated soil. The soil pH was slightly acidic after SPC treatment. The observed maximum distance of Ni and Zn migrated from subgrade to the off-site clean soil was approximately 5 cm at 600 d. The SPC binder exhibited superior performance to PC in terms of immobilization effectiveness of Ni and Zn, soil pH, and curing time.