# Performance Assessment of Waste Cooking Oil-Modified Asphal Mixtures
## 4 Results and Discussions
### Impact of WCO on Overall Performance of Balanced Asphalt Mixture  
The variation in the overall performance of WCO-modified asphalt mixtures can be examined using the interaction plot. It defines the overall mixture performance by four quadrants: stiff and brittle, stiff and flexible, soft and flexible, and soft and unstable [40]. Stiff and brittle mixtures are expected to have poor cracking resistance (i.e., low CT\({}_{\text{Index}}\)) but good rutting resistance (i.e., high HI-IDT\({}_{\text{strength}}\)). Stiff and flexible mixtures are expected to have good cracking and rutting resistance. Soft and flexible mixtures have good cracking resistance but poor rutting resistance. The soft and unstable mixtures have very poor cracking and rutting resistance. The authors created an interaction plot between the CT\({}_{\text{Index}}\) and HI-IDT\({}_{\text{strength}}\) for the tested mixtures, as presented in Figure 6. The CT\({}_{\text{Index}}\) and HI-IDT\({}_{\text{strength}}\) values are shown in the X and Y axes, respectively, along with their associated pass/fail performance assessment thresholds. Stiff and brittle mixtures are expected to have CT\({}_{\text{Index}}\) < 26.4 and HI-IDT\({}_{\text{strength}}\) >110 KPa (i.e., poor and good cracking rutting resistance, respectively). Stiff and flexible mixtures are expected to have CT\({}_{\text{Index}}\) > 26.4 and high HI-IDT\({}_{\text{strength}}\) > 110 KPa. Figure 4: Cracking performance evaluation of WCO-modified asphalt mixture. Soft and Flexible mixtures have \(\text{CT}_{\text{Index}}>26.4\) and \(\text{HI-IDT}_{\text{Strength}}<110\text{Kpa}\), while the soft and unstable mixtures have \(\text{CT}_{\text{Index}}<26.4\) and \(\text{HI-IDT}_{\text{Strength}}<110\text{Kpa}\). The designed mixture was designed as stiff and flexible mixtures to satisfy the BMD requirements (i.e., the green area). Figure 5: Putting performance evaluation of WCO-modified asphalt mixture. Figure 6: Interaction plot between \(\text{CT}_{\text{Index}}\) and \(\text{HI-IDT}_{\text{Strength}}\) for the evaluated mixtures. The interaction plot is used to study the overall performance of a given mixture and to track the effect of variation in mix proportions (i.e., binder content) or modifier dosage (i.e., WCO oil) on mixture performance. It can be observed that the performance control mixture (i.e., unmodified [0% WCO]) was stiff and flexible, which had a good rutting and cracking resistance. The increase in WCO dosage improves the mixture's resistance to cracking resistance but declines its resistance to rutting. A significant effect can be observed at high WCO dosages. For instance, the modified mixture with 7% WCO increases the cracking resistance of the control mixture by 85% (i.e., from 29.7 to 54.8) but decreases its rutting resistance by 66% (from 114 KPa to 39 KPa). The variation trend indicates that the mixture becomes softer and more flexible with the increase in WCO dosage, as evidenced by its movement to the lower left quadrant (Figure 6). Thus, the designed balanced control mixture becomes unbalanced when using WCO oil at any dosage. Therefore, it shall be redesigned to account for the WCO effect. Several approaches can be implemented to adjust the mixture performance. For example, it is well known that the overall mixture performance relies on the proportions and properties of raw materials. Therefore, adjusting such properties of the control asphalt mixture would address the effect of WCO oil. For instance, performing the following modification would enhance asphalt mixture resistance to rutting using lower binder content, harder virgin binder, higher filler content, higher coarse and fine aggregate angularity, stronger aggregates, higher surface texture aggregates, more cubical shape aggregates, larger nominal maximum aggregate size, higher recycled asphalt pavement content (RAP) [88]. Using a compound modifier consisting of WCO with another modifier would reduce the WCO impact on the performance of the designed asphalt mixture (i.e., enhancing the rutting resistance).