Because of the sustainability transition in the asphalt industry, it is increasingly popular to apply reclaimed asphalt pavement (RAP) instead of new asphalt. Then, less new material is needed and the amount of waste products is reduced. However, there are questions regarding the performance of asphalt mixtures with high RAP percentages, particularly in terms of potentially excessive high stiffness and a decrease in workability. In the Netherlands, a RAP content of 60% in combination with a softer binder is common practice, but an increase in RAP content means that rejuvenators are often required.

The research objective was to study the multi-scale material properties of hot mix asphalt mixtures with high reclaimed asphalt pavement percentages using micromechanics. At binder level, the DSR test was done and it was also used to select and reject the rejuvenators which are applied at mixture level. The chosen rejuvenators, Neomex HR and Cecabase RWI, were applied to the mixtures with 80% RAP. Besides that, a reference mixture was tested with 65% RAP and a reference mixture of 80% RAP. Further, the results were used to fit a modified micromechanical Hirsch model for RAP mixtures with rejuvenators.

Based on the material tests and comparing it with the reference (65% RAP mixture), it turned out that there is potential to implement 80% RAP mixtures. Both moisture sensitivity and the rutting resistance are improved when a higher RAP content is applied, while the total fracture toughness has remained the same. The stiffness of the 80% RAP mixture is substantially higher, but it is still applicable. The biggest concern is the fatigue resistance, because the fatigue resistance of the 80% RAP mixture without rejuvenator is worse for higher strains.

The application of the rejuvenating additives led to the properties of the 80% mixtures being more similar to the 65% RAP mixture and the workability is improved. However, it did appear that the dosage of the additives is on the high side. The stiffness is lower than the reference mixture, especially the mixture with Neomex HR. Also, the rutting resistance is lower than the reference mixture, especially the mixture with Cecabase RWI. Future research may optimize the dosage to improve results.

The micromechanical Hirsch model provided stiffness results with a reasonably accuracy, although this model used general model coefficients. The simplified Hirsch model with inclusion of the factor Pa could not be simply adopted when it is fit for other types of mixtures. The predicted stiffness for all three mixtures was much higher than it actually is. The adjustment of the fitting parameters, according to the laboratory results of the 80% RAP, led to accurate results making the simplified Hirsch model with inclusion of the factor Pa applicable to the mixtures with 80% RAP and a rejuvenating additive.