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

**Min Wang 1, Jiaming Wen 2, Heng Zhuang 1, Weiyi Xia 3, Ningjun Jiang <sup>1</sup> and Yanjun Du 1,\***


**Featured Application: The dual-additives-amended compacted clay covers in this article could apply to the cover system of industrial contaminated sites, municipal solid waste landfill, and industrial solid waste landfill. The dual-additives could enhance the anti-cracking, moisture retention, gas barrier, and hydraulic performance of compacted clay covers.**

**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 (*D<sup>θ</sup>* ) 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 *D<sup>θ</sup>* 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.

**Keywords:** additives; compacted clay cover; moisture retention; gas diffusion barrier; hydraulic conductivity
