*3.2. WRC*

The evolution of the moisture content with various ZP contents is shown in Figure 4. For the untreated samples, the initial moisture content was 25.6%. It decreased significantly with the increase in drying time from 0 h to 7 h; the moisture significantly decreased from 9% to 13%. After 17.5 h of drying, the moisture content of the compacted clay mixed with ZP of 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% were 4%, 7%, 8%, 9%, and 12%, respectively. The moisture of the soil treated with 1.0% ZP content was 193% higher as compared to the soil with 0.2% ZP. Studies have proven [37] that ZP has a large specific surface area with many hydrophilic groups. Due to the electrostatic attraction between the anions and the penetration disparity induced by the differing concentrations of cations inside and outside, PAM expands linearly to form a three-dimensional network structure [25,26]. Thus, the polymer network of ZP

has a strong physical adsorption effect on water molecules. Accordingly, ZP can effectively improve the WRC of compacted clay and inhibit the evaporation of clay moisture during the drying process. After drying, the moisture content of the clay increased with increasing ZP content, and the modification was the most prominent when the ZP content was 1%.

**Figure 3.** Liquid limit of CCC mixed with ZP. (**a**) Influence of PAM content on the LL of the compacted clay; (**b**) effect of different materials mixed with clay on LL/LLck of the compacted clay [58,59].

**Figure 4.** The moisture content of the compacted clay mixed with different PAM contents.

Figure 5 reflects the influence of ZP content on the water loss of the compacted clay after drying. After 17.5 h of drying at 100 ◦C, the water loss rates of the compacted clay mixed with different contents of ZP were 84%, 71%, 66%, 64%, and 54%, as the ZP content ranged from 0.2% to 1.0%. Therefore, increasing the content of modifier ZP can effectively reduce the water loss rate of clay and improve its WRC. Studies have indicated that the water loss of the clay mixed with various ordinary agricultural and forestry water-retaining agents varies from 55% to 63%, after they are dried for 360 min with a temperature of 60 ◦C [53]. However, when our research used 0.8% and 1.0% ZP for modification, the water loss rates of the clay after drying at 100 ◦C for 17.5 h were 64% and 54%. Furthermore, field monitoring results in the Changzhou contaminated site showed that [18] the highest atmospheric temperature was 45 ◦C, which was much lower than the test temperature of 100 ◦C in this paper. As a result, ZP plays a more prominent role in enhancing the WRC of CCC under low temperatures of 45 ◦C rather than 100 ◦C.

**Figure 5.** Water loss percentage of the compacted clay mixed with different contents of ZP.

Based on the preliminary test results, when the ZP content was than 1%, the clay with the same initial moisture content was too viscous to be blended homogeneously. Therefore, we did not test the soils with ZP content higher than 1.0%.
