Nebraska LTAP


Date of this Version


Document Type



Yazdipanah, F., Khedmati, M., and Haghshenas, H. (2023). Nebraska Balanced Mix Design - Phase I. NDOT Research Report SPR-FY22(002).


Balanced mix design (BMD) is an alternative concept for designing asphalt mixtures that mainly focuses on performance of mixtures rather than only volumetric analysis. Using this concept, it would be possible to account for the incorporation of recycled asphalt mixtures, warm technology, polymers, rejuvenators, and other foreign additives, as well as external effective factors on the mix design such as environmental effects. This project sought to investigate performance-based methodologies for the asphalt mix design by taking a step to develop a preliminary Nebraska BMD framework. With that, selection of appropriate performance tests, finding a functional laboratory aging protocol, and defining performance test criteria were the main long-term goals developed in this phase of study. To this end, three main types of distresses were taken into consideration (rutting, fatigue cracking, and moisture susceptibility), and a set of performance tests including well-established tests (Hamburg Wheel Track (HWT), Illinois Flexibility Index Test (I-FIT), Tensile Strength Ration (TSR)) and surrogate tests (IDEAL-RT, HT-IDT, G-stability, IDEAL-CT) were selected to capture these distresses on two types of high-performance commonly used asphalt mixtures in Nebraska (SLX and SPR). For the fatigue cracking analysis, long-term aging conditioning was conducted using two common aging protocols (NCHRP 09-54 and NCAT). Three types of data were utilized in this study including laboratory performance test results for the lab-compacted and field core specimens, as well as field data based on pavement surface condition monitoring. The validity of the surrogate performance tests was accomplished not only by correlating the field core results with field condition data, but also with correlating every individual surrogate test result to that of a well-established test. Further, the sensitivity, practicality, cost-effectiveness, and variability of different tests were assessed using statistical analysis and review efforts. In terms of rutting and fatigue cracking, IDEAL-RT and IDEAL-CT tests showed the highest correlation to well-established tests as well as significant sensitivity and accuracy in terms of results. For the moisture damage resistance tests, no strong correlation was found between well-established and surrogate tests, except for the G-stability test that showed some potential to be considered for future studies. In terms of long-term aging methods, the NCAT protocol was found to be more severe than NCHRP 09-54, however, selecting an appropriate long-term aging protocol for the Nebraska BMD will be done after long-term data analysis in the next phases of this study. Finally, an initial understanding of each test’s pass/fail criteria was achieved based on the test result values obtained from historically acceptable asphalt mix design in the state.