Quantification of the Role of The Effective Binder in the Performance of RAP – WMA Mixtures

Abstract

Over the past decades, several new technologies/materials (such as WMA, RAP, rubber, polymers, bio-binders…etc.) were incorporated into asphalt mixtures. However, current mix-design specifications evaluate all mixtures containing these different additives/technologies based on volumetric. Further, RAP incorporation in asphalt mixtures is still limited, and the influence of lowered production temperatures on RAP contribution in RAP-WMA mixtures is understudied. To tackle these issues, this study presents a comprehensive evaluation of the effect of production factors ( RAP content and source, binder grade, and production temperatures) on the effective binder in WMA-RAP mixtures, and the role of the effective binder in controlling mixture performance.The experimental program included evaluation of the compaction, cracking, and rutting performance of WMA-RAP mixtures produced with a different combination of the production factors. The Semi-Circular Bend (SCB) test at intermediate temperatures was used for cracking evaluation, while the Indirect Tension Test at High Temperatures (IDT-HT) was used for rutting evaluation. Further, the study included rheological characterization of extracted binder from the mixtures to investigate the role of the effective binder on cracking performance. The results showed that the effective binder properties are changed significantly with changes in the production factors, as measured by the extracted binder rheological properties. Also, the properties of the effective binder showed a direct control of the mixture performance as measured by the IDT-HT strength and the flexibility index obtained from the SCB test. Binder selection limits were developed for lab-produced WMA-RAP mixtures based on the Glover-Rowe parameter. Finally, a validation study was conducted using data from four different projects, including a field project in Texas, FHWA’s accelerated loading facility, a laboratory mixture study in Wisconsin, and a New Hampshire DOT study to confirm the refine the findings of this study.