Screening Additives for Amending Compacted Clay Covers to Enhance Diffusion Barrier Properties and Moisture Retention Performance

Abstract

The cover systems in contaminated sites have some problems, including desiccation cracks, which would lead to degradation of the barrier performance. This study presented a systemic laboratory experimental investigation on the liquid–plastic limit, moisture retention, hydraulic conductivity (k), and gas diffusion barrier properties of amended compacted clay by attapulgite and diatomite for controlling desiccation cracks and migration of water and volatile organic compounds (VOCs). The results showed that the attapulgite could enhance the moisture retention and liquid limit of amended compacted clay. Diatomite could reduce the gas diffusion coefficient (Dθ) significantly. The compacted clay amended by the dual-additives component of attapulgite and diatomite could enhance the liquid limit, moisture retention percent, gas barrier property, and hydraulic performance compared with the unamended clay. Based on the experimental data obtained, the dosage of additives was targeted to be 5%. The moisture retention percent of dual-additives (attapulgite 4% and diatomite 1%) amended clay increased by 82%, the k decreased by 25%, and the Dθ decreased by 42% compared with unamended clay. Scanning electron microscopy (SEM), BET-specific surface area test method (BET), Mercury Intrusion Porosimetry (MIP), and thermogravimetric analysis (TGA) indicated the enhancement mechanism of additives-amended compacted clay.

Investigation of Compacted Clay Cover Modified by New Water Retaining Agents

“…Therefore, some researchers use non-environmentally hazardous waterretaining agents to enhance the water-holding capacity of soil and suppress soil cracking. These waterretaining agents including zeolites [32], attapulgite [33], biochar [34], polyacrylamide [35], sodium polyacrylate [36], etc. Zeolite has excellent water adsorption [37][38] and retention properties [32,[39][40].…”

Special Issue on Advances in Soil Pollution and the Geotechnical Environment

“…To comprehend the effect of tidal actions on the nitrogen cycle in siltyclay riparian hyporheic zones, Cai et al [1] carried out the synchronous monitoring of water level and water quality along a test transect during a spring tidal period and measured the permeability and chemical composition of soil samples from drilled holes. Wang et al [2] presented a systemic laboratory experimental investigation on the liquid-plastic limit, moisture retention, hydraulic conductivity, and gas diffusion barrier properties of compacted clay amended with attapulgite and diatomite to control desiccation cracks and the migration of water and volatile organic compounds. Tian et al [3] proposed a calculation method for thermal pore water pressure while considering the overconsolidation effect of saturated clay, which was verified by the relevant experimental data.…”