Engineering properties of Zn-contaminated soil stabilized with a low-carbon material: Phosphate rock powder-MgO-cement (PMC)

To reveal the engineering properties of Zn-contaminated soil solidified with a new cementitious material, namely phosphate rock powder-MgO-cement (PMC), several series of solidified soil characterization tests including moisture content, dry density, pH value, unconfined compressive strength, and stress-strain curve were conducted. The traditional Portland cement was selected for a comparison purpose. The effects of curing time and Zn2 + concentration on these property indexes were investigated to explore the inhibition mechanism of heavy metal Zn2+ on the stabilization process. In addition, the correlations of unconfined compressive strength with three physical property indexes were analyzed. The results indicated that the PMC stabilizer was far superior to the cement for stabilizing Zn-contaminated soil in terms of mechanical properties and environmental impacts. The normalized moisture content of PMC stabilized soil was greater than the cement stabilized soil, indicating a more complete hydration reaction. A small amount of Zn2+ can promote the hydration reaction, but when the Zn2+ concentration exceeded 0.5 %, the hydration reaction was significantly hindered. The dry density of PMC stabilized soil was about 6 % more than cement stabilized soil under the same conditions. The pH values of PMC stabilized samples were much lower than the cement stabilized soil samples and distributed in 8.0-9.5. The stress-strain characteristic of PMC stabilized soil was softening type and the heavy metal Zn2+ was solidified by adsorption, which could make the stress-strain curve of cement stabilized sample change from brittle type to ductile type.