Influence of Balanced Mix Design Approaches on Pavement Design Making Through an Illustrative Example

Laboratory tests have been developed and used over many years to improve the performance-related predictions of volumetric-based asphalt mix designs. Volumetric property requirements were mainly set for improving field pavement performance. These requirements have been established based on specific material properties. However, with the increased use of innovative and recycled materials, these requirements have shifted from guidelines for achieving a better mix design to guidelines limiting innovation and potential improvements. Therefore, it is time to move toward a balanced mix design (BMD), the ultimate goal of Superpave mix design. According to AASHTO PP 105, four major BMD approaches are available providing different levels of freedom compared with the traditional volumetric-based mix design. In this study, BMD approaches are explored using typical northern Nevada materials. An array of performance tests for rutting and cracking were conducted to evaluate the impact of the test selection on BMD. Moreover, the influence of asphalt mixture components (e.g., binder content, reclaimed asphalt pavement [RAP], recycling agents, gradation) on BMD were investigated. The results show that BMD process conversion is influenced by asphalt mixture properties (e.g., mixtures with similar gradation require different BMD approaches to achieve a well-performing asphalt mixture). Binder content was found to significantly influence BMD performance. In addition, it was concluded that asphalt mixtures with higher RAP content do not necessarily imply worse cracking performance. Furthermore, a poor correlation was observed between asphalt mixture costs and performance, where a mixture with the highest cost did not necessarily yield the best overall performance.

Automated summary

Laboratory tests have been developed and used to improve the performance predictions of volumetric-based asphalt mix designs. However, the traditional volumetric requirements have limited innovation and potential improvements, leading to the need for a balanced mix design approach.