Abstract: Magnesium phosphate cement (MPC) was used to stabilize or solidify lead-contaminated soils. Unconfined compressive strength test, permeability test and leaching test were conducted to investigate the variation of mechanical properties of lead-contaminated soils treated by MPC under different conditions of curing time and lead concentration. Results show that the unconfined compressive strength increases significantly with curing time, while the hydraulic conductivity and leaching concentration change oppositely. The unconfined compressive strength and leaching concentration under 7-day curing time are satisfied by the regulations. There is a threshold value 500 mg/kg for lead concentration in terms of its influence on unconfined compressive strength and hydraulic conductivity. The unconfined compressive strength and leaching concentration increase with the lead concentration before they reach the threshold value, while the hydraulic conductivity changed oppositely. MIP test results show that the total void volume reduces as the curing time, the total void volume of soil reduces as the lead concentration before they reach the threshold value. SEM test results show that a larger aggregation formation, with a smaller void space in soils as the curing time increases. More obvious aggregation and cementation occurs in soils space as the lead concentration less than the threshold value. MgKPO4·6H2O (MKP) decreases the pore volume of soil pores with the diameter larger than 0.1 ?m, so as to affect the permeability of soil.

Key words: solidification/stabilization (S/S), lead contaminated soil, unconfined compressive strength, hydraulic conductivity, leaching concentration, microstructure