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Aged asphalt binder in reclaimed asphalt pavement (RAP) or recycled asphalt shingles (RAS) blends only partially with the virgin binder. To better understand this state of blending, the asphalt mixtures in this study were designed, mixed, and compacted using different RAP and RAS contents. The asphalt binders were extracted and recovered from RAP and RAS and then blended with different proportions of a virgin binder. The master curves for the asphalt mixtures and asphalt binder blends were then constructed from the measured data. A locally calibrated Hirsch model was developed to estimate master curves for the asphalt mixtures from the corresponding binder-blend data. Pairwise comparison of the master curves for RAP and RAS and virgin binder showed that degree of blending occurred at 50% to 60% for RAP and at 15% to 30% for RAS.

Asphalt binders are known to exhibit an inherent ability to repair damage. Such self-healing potentially affects the fatigue damage performance of bituminous materials. There are contradicting findings about the effects of aging and polymer modification on healing. The effectiveness of rejuvenating agents also has not been sufficiently addressed. In the present study, three healing indices have been defined to provide a more complete representation with which to quantify the healing potential of binders. These indices have been defined using damage characteristic curves derived from interrupted linear amplitude sweep tests. Initial healing (IH) describes the immediate reduction in the damage accumulated after the rest period. Residual healing (RH) shows the lasting effect of healing and total healing (TH) is a combination of IH and RH. The results demonstrate that IH does not present a complete picture of healing, particularly at low and intermediate levels of damage. While, RH better exhibits the detrimental effect of aging, the healing ability of SBS (styrene–butadiene–styrene) binder at higher damage levels, and the positive effect of the use of the rejuvenating agent. The healing model shows that, irrespective of the healing index and binder, the effect of loading interruptions at higher levels of damage, along with increased stiffness because of aging, prevail over the positive effects of an increase in the duration of the rest period.

Thermal cracking is the prevalent type of distress experienced by asphalt pavements in cold regions. It is widely assumed that when thermal stresses induced in the pavement exceed the tensile strength of the asphalt surface layer, cracking occurs; however, the role of thermal fatigue should not be ignored. To better describe the low-temperature (LT) performance properties of modified asphalt binders, a new parameter, normalised tensile stress (NTS), was defined in this research. NTS values were compared with bending beam rheometer (BBR), direct tension (DT) and semi-circular bending (SCB) fracture test results. The m-value parameter of the BBR test specifies the type of asphalt binder. This classification changes as the loading time changes and is only valid in the linear viscoelastic range. It showed limited sensitivity to changes in the material properties of modified asphalt binders that showed superior LT damage resistance. In contrast, the results from the DT, SCB and NTS parameters were sensitive to the changes. The results of SCB testing and NTS parameters were in agreement with the existing field data. It was also found that the use of sulphur as a cross-linking agent improved the storage stability of styrene butadiene styrene (SBS)-modified asphalt binder and decreased the amount of SBS required to yield a comparable result by about 50%. In contrast to what has been reported by some investigators, the use of polyphosphoric acid as a cross-linking agent intensified the phase separation of bitumen and SBS, and somewhat reduced the efficacy of SBS modification with regard to LT performance.

This paper describes the performance of two pavement sections at the FHWA's Pavement Testing Facility. The sections are classified as thin and thick flexible pavements and were designed according to the new AASHTO design guide. The accelerated loading facility (ALF) was used to load the test pavements. The functional and structural performances of the test sections were evaluated at various stages of the loading history. Roughness, rutting, and cracking were the indicators of functional performance. In situ tensile strains at the bottom of the asphalt layer, pavement surface deflections, and deflections under FWD loading were used for the structural performance evaluation. Pavement temperature, moisture content, and environmental data were also collected. The variation in both functional and structural performance indicators were monitored as a function of 18‐kip‐equivalent single‐axle loads. Performance indicators such as slope variance and present serviceability index were evaluated and monitored as a function of number of load repetitions. The in situ strains, measured by strain gages, were compared to theoretical strains throughout the loading periods. Finally, the actual performance life of the pavement was compared to the design life predicted by the AASHTO design guide.