An experimental study on microstructure of leachate-polluted stabilized clay

Clay-solidified grouting curtain (CSGC) is a new kind of vertical barrier for remediating unregulated waste disposal sites in China that combines vertical-barrier and cement-based solidification-stabilization treatment techniques. The cement, stabilizing agents and landfill leachate clearly influence penetration. Although CSGC is becoming widely used because it is effective and economical, little is known about how it works. There is no clear consensus on the penetration mechanism, especially under actual continuous leachate percolation. The present work, therefore, studies the microstructure of CSGC under actual continuous leachate percolation. The cement and self-development stabilizing agents (CERSM-B) and their combined effect on the cumulative intrusion and pore size distribution were investigated using mercury intrusion porosimetry and scanning electron microscope images. The experimental results demonstrated that the unhydrated cement particles first create a large pore space. With increasing cement content, cementation products fill the large pores, thus decreasing the total pore volume. Fine-needle hydration ettringite crystal and calcium silicate hydrate gels are found when the cement content is below 15%. Stabilizing agents (CERSM-B) play an important role in the microstructure of CSGC. A close structure of flaky crystals with small, infrequent pores can be observed in samples treated with stabilizing agents (CERSM-B). However, adding too many stabilizing agents (CERSM-B) may increase the continuity of macropores. The peak pore size distribution and corresponding pore size increase with increasing dosage of stabilizing agents (CERSM-B). In engineering applications, the recommended range of cement and stabilizing agents (CERSM-B) is 15–20% percent clay and 7.5–10% cement.