Assessing geo-mechanical and leaching behavior of cement–silica-fume-stabilized heavy metal-contaminated clayey soil

Although cement stabilization/solidification (S/S) is used extensively to remediate heavy metal (HM)-contaminated soils, it may show limited success in some applications. Hence, this study investigated the efficacy of silica fume (SF) as an industrial by-product in enhancing the performance of cement-based S/S. Artificially contaminated soils were first prepared by mixing kaolinite with zinc (Zn) at levels of 0–30 cmol/kg. Cement and cement/SF (CSF) mixture with 15 % cement replacement were used as S/S binders. The agents were separately added to the samples, and then, a set of tests were performed to assess the effectiveness of the treatments. The results show that the addition of sole cement markedly increases the HM retention capability of soil; however, this may be partly lost when the treated samples are acidified. The strength and compressibility potential of cement-treated specimens are also adversely affected by increasing Zn concentration. It appears that the incorporation of SF into the cement matrix reduces the destructive effects of aggressive environment and HM on the behavior of stabilized products. Additionally, based on the toxicity characteristic leaching procedure experiments, CSF blend is more efficient in immobilizing Zn with the lower dosage of binder and shorter curing time of samples compared to sole cement. These observations are mainly associated with both the extended synthesis of pozzolanic phases and maximized packing of particles upon CSF treatment, as is clearly confirmed by the XRD and SEM-EDX analyses. It is concluded that CSF content of 1 wt% per 1 cmol/kg of HM can successfully remediate the zinc-contaminated soils.