*Article* **Evaluation of Performance of Polyacrylamide-Modified Compacted Clay as a Gas Barrier: Water Retention and Gas Permeability and Diffusion Characteristics**

**Yu-Zhang Bi 1,†, Jia-Ming Wen 1,2,†, Hao-Liang Wu <sup>3</sup> and Yan-Jun Du 1,\***


**Abstract:** In this paper, the performance of a gas barrier that consisted of polyacrylamide (PAM) modified compacted clayey soil was experimentally explored. The moisture content and water loss characteristics of the tested soils were adopted as indicative indices of water retention capacity (WRC). The gas permeability (Kp) and gas diffusion coefficient (Dp) of the modified compacted clays were evaluated via gas permeability and gas diffusion tests. The test results showed that the moisture content of the modified compacted clay samples subjected to drying tests increased with increasing polyacrylamide content. Kp and Dp decreased with increasing PAM content. Compared with 0.2% PAM content, the Kp of the sample with 1.0% PAM was reduced by ten times, and the Dp was reduced to ~35%. Compared to the unmodified clay, the liquid limit of the PAM-modified clay increased by 45~55%. Comparison of the liquid limit tests between this study and previous studies revealed that the liquid limit ratio of the zwitterionic polyacrylamide (ZP)-modified soil was much higher than the other material-modified soils. The results of this study are useful to facilitate the application of modified compacted clays as gas barrier materials at industrial contaminated sites.

**Keywords:** compacted clay; polyacrylamide; gas barrier performance; gas permeability; gas diffusion coefficient
