Effect of freeze-thaw cycle on engineering properties and microstructure of stabilized/solidified lead contaminated soil treated by cement

Freeze-thaw cycle tests are conducted to investigate the engineering properties and mechanisms of cement- stabilized/solidified (S/S) lead-contaminated soils with different compaction degrees (90% and 96%). After different freeze-thaw cycles (0, 3, 6 and 10 times), the unconfined compressive strength tests, penetration tests and leaching tests are conducted on samples to investigate the effect of freeze-thaw cycles on engineering properties of S/S samples. The results showed that the freeze-thaw effect depends on the compaction degrees of samples. For the samples with compaction degree of 90%, the permeability and Pb leaching concentration increase with the freeze-thaw cycles, while the unconfined compressive strength decreases. However, little variation is observed for the samples with compaction degree of 96% as the freeze-thaw cycle increases. Scanning electron microscope (SEM) and mercury intrusion porosity (MIP) tests are also conducted to study the micro-mechanism. The results show that the freeze-thaw cycles pose little influence on the microstructure of S/S samples with compaction degree of 96%. Soil particles aggregate and porosity decreases with the freeze-thaw cycles. The inter-particular pores and intra-aggregate pores occupy a fairly large proportion. However, the freeze-thaw cycles enlarge the pore of samples with compaction degree of 90%, and the inter-aggregate pores take large proportion, which is the reason that the engineering properties of S/S samples with low compaction degree is weakened during the freeze-thaw cycles.