## 3 Results and Discussion
### Moisture Sensitivity and Ageing Effect
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Source**} & \multicolumn{2}{c}{**Sum of Squares**} & \multirow{2}{*}{**DF**} & \multicolumn{2}{c}{**Mean Square**} & \multicolumn{2}{c}{**F-Value**} & \multicolumn{2}{c}{_p-Value_} \\ \cline{2-13}  & **Dry** & **Wet** & & **Dry** & **Wet** & **Dry** & **Wet** & **Dry** & **Wet** \\ \hline A-Ageing & 4085.5 & 145,359.6 & 1 & 4085.5 & 145,359.6 & 0.169 & 3.585 & 0.686 & 0.075 \\ B-AC Mixture & 50,538.5 & 99,090.9 & 2 & 25,269.2 & 49,545.4 & 1.045 & 1.222 & 0.372 & 0.318 \\ AB & 55,275.6 & 71,102.0 & 2 & 27,637.8 & 35,551.0 & 1.143 & 0.877 & 0.341 & 0.433 \\ Error & 435,115.0 & 729,880.9 & 18 & 24,173.1 & 40,548.9 & & & & \\ Total & 545,014.6 & 1,045,433.4 & 23 & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Two-way ANOVA with interaction results. Therefore and as already mentioned, the effect of ageing in the plastic modified-AC mixture is not obvious. On the one hand, for wet specimens, the ITS has a statically significant increase, on the other, for dry specimens, the ITS has a non-statically significant decrease. The unaged dry specimens results are in line with a previous study [54] that evaluated the moisture susceptibility effect on AC mixtures containing flakes of plastic film collected as urban waste without ageing. Exposure to moisture reduced ITS values by 10% as in this research (12%). The effect of ageing on the plastic-modified materials are not well established yet. [PERSON] [41] studied the effect of two ageing levels (1: 100 \({}^{\circ}\)C for 48 h and 2: 100 \({}^{\circ}\)C for 96 h) on ITS results of AC mixtures containing PP polymers (wet process) and compared the results with the ones from a control mixture. ITS values increased with ageing. However, those variations depended on the ageing level. For the 96 h-ageing level, the increase was less pronounced for the AC mixtures containing PP polymers. In the [PERSON] study, only the temperature effect was evaluated and for a short period of time. In the TEAGE ageing procedure, the specimens (both the dry and the wet ones) are subjected to temperature, watering/drying cycles, and UV radiation during 30 days, which may have a particular role in deteriorating the material (especially plastic film) that thermal ageing may not reproduce accurately. Concerning the isolated effect of nanoclay modification, [PERSON], [PERSON], [PERSON], and [PERSON] [50] assessed the effect of nanoclay on ageing and moisture damage of a gap-graded AC 14 mixture using the ITS test, and compared the results with the ones from a non-modified mixture. They found a significant increase in ITS values with nanoclay modification and with ageing in both dry and wet conditions. Similar results were reported in [52]. Figure 7 presents ITSR values that represent the ratio between the ITS of wet specimens and the ITS of dry specimens presented in Figure 6.  
All ITSR values are considered to be good, they are all above 85% whatever the AC mixture, indicating greater resistance to moisture damage. Once again, it can be explained by the air voids content values as well as by good affinity between the aggregates and the bitumen. The ageing considerably increased (21%) the moisture resistance of plastic modified-AC mixture. For the other two mixtures, the ITSR was near 100% and consequently the water did not deteriorate nor improve them and the ageing effect was minimal. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Control**} & \multicolumn{2}{c}{**Plastic**} & \multicolumn{2}{c}{**Plastic and Nanoclay**} \\ \hline
**Dry** & **Wet** & **Dry** & **Wet** & **Dry** & **Wet** \\ \hline
0.4252 & 0.6727 & 0.3835 & 0.008 & 0.3765 & 0.6261 \\ \hline \end{tabular}
\end{table} 
Table 3: One-way ANOVA (\(p\)-values). Figure 7: Indirect tensile strength ratio (ITSR) values. [PERSON], [PERSON], and [PERSON] [26] studied, among others, the influence of ageing (oven ageing during 16 h) on the ITSR of polymer-modified AC mixtures (six different polymeric products were tested).