## 2 Materials and Methods
### Wet-Dry Cycles  
The compacted specimens were cured for 24 h inside a sealed insulated box to prevent loss of moisture, as shown in Figure 1, before subjecting them to three wet-dry cycles. The wet-dry cycle was initiated by ensuring that the compacted specimens were saturated at the start of the cycle. The saturation state of the specimens was quantified by directly  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**ASTM** & **Soil Property** & **Clay** & **Polyurethane–Clay** \\ \hline D698 [23] & Optimum moisture content (\%) & 31.15 & — \\ D854 [24] & Specific gravity & 2.41 & 2.86 \\ D4318 [25] & Liquid limit (\%) & 73 & 68 \\ D4318 & Plastic limit (\%) & 47 & 48 \\ D4318 & Plasticity index (\%) & 26 & 20 \\ D4943 [26] & Shrinkage limit (\%) & 28 & 29 \\ D2487 [27] & Soil classification & MH & MH with Sand \\ D7928 [28] & D\({}_{60}\) (mm) & 0.00480 & 0.02025 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Soil index properties [21].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Specimen** & **PU Content** & **Initial Void Ratio** & **Compaction Effort** \\ \hline CCL & 0\% & 1.06 & Standard proctor (600 kN-m/m\({}^{3}\)) \\ CPCL & 3\% & 1.44 & Standard proctor (600 kN-m/m\({}^{3}\)) \\ CL & 0\% & 1.44 & Less than the standard proctor \\ \hline \hline \end{tabular}
\end{table}
Table 3: Compaction efforts [21].  
measuring the weight of the compacted specimen. Table 4 shows the target moisture content of the compacted specimens for each moisture content level. Level 1 of the moisture content levels in Table 4 pertains to the saturation level of 100%, while Level 8 pertains to the saturation level of 0%.  
The process for the wet-dry cycles was adopted from the study of [PERSON] and [PERSON] [22]. Air drying was the method used to move the compacted specimen's saturation into a drier state that lasted for a week, similar to the study of [PERSON] and [PERSON] [22]. In addition, the compacted specimens were oven-dried to reach a dry state of 0% moisture content. To restart the cycle, specimens were re-saturated inside the mold by gradually adding water every 2 min until the target weight corresponding to a fully saturated sample was achieved, as shown in Figure 2. The re-saturated compacted specimens were then placed again in a sealed insulated box for 24 h to ensure that the water that re-entered the compacted soil matrix was properly distributed before air drying the specimen to undergo the 2 nd drying cycle. Figure 3 shows the wet-dry cycle of the compacted specimens.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Moisture Content Level**} & \multicolumn{3}{c}{**Target Moisture Content (\%)**} \\  & **CCL** & **CL** & **CCL** \\ \hline Level 1 & 43.98 & 59.75 & 50.35 \\ Level 2 & 37.69 & 51.21 & 43.15 \\ Level 3 & 31.45 & 42.72 & 36.00 \\ Level 4 & 25.16 & 34.18 & 28.80 \\ Level 5 & 18.87 & 25.63 & 21.60 \\ Level 6 & 12.58 & 17.09 & 14.40 \\ Level 7 & 6.29 & 8.54 & 7.20 \\ Level 8 & 0.00 & 0.00 & 0.00 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Target moisture contents of the compacted specimens [30].  
Figure 1: Specimens curing inside an insulated chest.