Cyclic wetting and drying tests on heavy metal contaminated soils solidified/stabilized by cement

Cement solidification/stabilization is a commonly-used method for the remediation of contaminated soils. The stability characteristics of solidified/stabilized contaminated soils under wetting and drying cycles are very important. A series of test programs, unconfined compressive strength (UCS) tests, leaching tests and scanning electron microscopy (SEM) tests are performed to study the long-term stability of solidified/stabilized lead and zinc contaminated soils with cement under cyclic wetting and drying. The test results show that UCS and the leaching characteristics of heavy metal ions of stabilized contaminated soils are significantly improved with the increase of the cement content. UCS of stabilized soils first increases with the increase of times of wetting and drying cycle, and after reaching the peak, it decreases with the increase of times of wetting and drying cycle. When the pollutant content is lower (1000 mg/kg), the leaching of heavy metal ions first slightly decreases under cyclic wetting and drying, then increases, but the change is minor. The concentration of heavy metal ions in the filtrate of the stabilized contaminated soils is higher under a high pollutant content of 5000 mg/kg, and increases with the increase of times of wetting and drying cycle. It exhibits a similar effect of the solidification/stabilization of lead and zinc contaminated soils using cement under a lower pollutant content. Compared with the lead contaminated soils, the zinc contaminated soils can be better stabilized with cement when the pollutant content is higher (5000 mg/kg). The results of scanning electron microscopy (SEM) tests are consistent with those of the UCS tests and leaching tests. The microcosmic mechanism of the changes in engineering of the stabilized contaminated soils under wetting and drying cycles is revealed.