Abstract:
The purpose of this paper is to report the initial findings of an experimental program to design and assess the properties of recycled hot dense graded asphalt mixes. The mixes include Size 14-mm wearing course mix with and without recycled asphalt pavement (RAP). The RAP contents in the recycled mixes were 10%, 20%, and 30%. Laboratory designs of the recycled mixes were conducted according to current Australian practice, which requires the use of a gyratory compactor to compact the mixes at 120 cycles and the use of lower-grade binder in mixes with >15% RAP content. The mixes, virgin and recycled, were designed to have similar blend gradations and acceptable film indices. The virgin and RAP aggregates were sourced from one supplier to ensure consistency throughout the project. Binder Grade C320 was used for the virgin mix and for the mix with 10% RAP. For the other two recycled mixes, a binder grade C170 (lower viscosity) was used. Results from the limited laboratory design and testing program indicate that despite having similar blend gradations and acceptable design film index values, the mixes vary in most volumetric properties and in stiffness. However, this design approach proved to be successful in producing recycled mixes with up to 20% RAP that meet specification requirements. Results also indicate that the addition of RAP leads to reduction in required binder content to achieve 4% air voids content, also a reduction in the value of voids in mineral aggregate, voids filled with binder, and film index. Further, the addition of RAP results in a stiffer mix, and this effect increases with increasing RAP content.
