Effect of rejuvenators type and dosage on the performance of a highly sustainable balanced mixture design

Reclaimed Asphalt Pavement (RAP) is widely used in US and Europe to reduce the cost of construction and provide sustainable road networks. Utilizing high RAP content, more specifically high amount of aged binder could result in decreasing performance of pavement in terms of low temperature and fatigue cracking. Based on the literatures, two approaches are commonly used to enhance the performance of high RAP mixtures. The first approach is using a softer binder in virgin portion of the total binder content to bring the low-end PG to lower temperature. The second approach is using asphalt binder rejuvenators in RAP before mixing with aggregates to initially enhance the quality of RAP binder and increase its resistant against low temperature and fatigue cracking. Although both types may improve fatigue and low temperature crack susceptibility, negative impact may be observed on rutting resistant, as well. Additionally, in the second approach, contractors are using typical PG but not the true PG of the blended binder to determine rejuvenator dosage. Therefore, the final production may have the correct PG but with possibility of cracking and rutting issues. In this study, a PG 64-28 binder was used in a 12.5 mm mixture with 15% RAP content which was designed with Balanced Mix Design method. Balanced mix design is a recently developed concept that makes balance between performance-based tests and target volumterics by changing asphalt binder content. To use this method, Hamburg test was performed for rutting resistant, SCB test for fatigue cracking, DCT for low temperature cracking and Complex Shear Modulus of the Mixture for blending analysis. Then, in another mixture with the same binder content, RAP content increased to 45%. A PG 52-34 and three different rejuvenators with different dosage were used to investigate three topics: (1) The possibility of using rejuvenators and softer binder in Balance Mix Design. (2) The sensitivity of type and dosage of the rejuvenators in mixtures containing high RAP content (3) Blending analysis of the rejuvenated mixtures using G* of the mixtures versus G* of the binders. Test results and sensitivity analysis indicated that the type and dosage of the rejuvenators does not have significant effect on the performance of high RAP content Balanced Mixture Designs and the new diagram could be an effective tool for determination of the optimum dosage of rejuvenators. It was also concluded that the G* vs G* plot could be an effective tool to qualify the degree of blending.