# Performance Assessment of Waste Cooking Oil-Modified Asphal Mixtures
## 4 Results and Discussions  
### Designing Balanced Asphalt Mixture (BMD)  
The Balanced Asphalt Mixture (BMD) design approach is a meticulous process encompassing several stages, including material characterization, performance testing, mixture optimization, and validation [30]. The primary objective of this methodology is to en sure that asphalt mixtures exhibit the desired performance characteristics. This process begins with a comprehensive evaluation of raw materials, particularly asphalt binders and aggregates, to determine their mechanical and physical properties. Afterward, lab-based performance assessment tests and indicators are carried out to assess the resistance of asphalt mixtures to various types of distress, such as rutting, cracking, and moisture damage [30].  
The information obtained from material characterization and performance testing is then utilized in the optimization phase of BMD. This phase identifies the range of binder content that yields the desired performance characteristics. Following this approach, asphalt mixtures can be optimized to achieve the desired performance characteristics while meeting the relevant specifications and standards. Four different approaches were proposed to implement the BMD method, namely (A) Volumetric Design with Performance Verification, (B) Volumetric Design with Performance Optimization, (C) Performance-modified Volumetric Design, and (D) Performance Design [30; 84].  
This study followed approach \"D\", which starts with an initial selection of virgin binder grade and aggregate gradation. Then, the performance of the initial mix design is evaluated at three or more binder contents varied in increments of 0.3 to 0.5%. Firstly, several mixtures were prepared by mixing the selected virgin binder (85/100) and aggregate gradation (Figure 2) at four different binder contents (i.e., 4.0, 4.5, 5.5, and 6.0%). Then, the test specimens were prepared and tested to evaluate the prepared mixtures' performance (i.e., cracking and rutting resistance) using CTIndex and HI-IDTstrength indicators.  
Figure 3 presents the testing results of prepared asphalt mixtures. It can be observed that CTIndex and HI-IDTstrength indicators increased and decreased, respectively, with the increase in binder content. Both indicators have an excellent linear relationship with the variation binder content (i.e., coefficient of determination (R\({}^{2}\)) of 0.97). These findings agree with the reported results in the literature [43; 56]. Such relationships indicated that the CTIndex is increased by 59.2 (i.e., CTIndex = 5923.69 [Pb%] \(-\) 233.68), and the HI-IDTstrength is decreased by \(-\)47.7 kPa (i.e., HI-IDTstrength = \(-\)4776.36 [Pb%] \(+\) 352.38) for each 1% increment in binder content.  
CTIndex and HI-IDTstrength assessment thresholds were used to determine the balanced binder content range. The rutting threshold for HI-IDTstrength (i.e., a minimum of 110 kPa) was used to determine the maximum accepted binder content since increased binder content declined mixture resistance to rutting. It was observed that a binder content of 5.1% satisfies this threshold. Similarly, the cracking threshold for CTIndex (i.e., a minimum of 26.4) was used to determine the minimum required binder content since the decrease in the binder content declined mixture resistance to cracking. It was observed that a binder content of 4.4% satisfies this threshold. Therefore, the designed balanced binder range was 4.4-5.1%. The Balanced Optimum Binder Content (BOBC) was selected as the midpoint of this range (i.e., 4.75%) (Figure 3).