RAP use in the creation of new pavement dates back to the Romans, but a renewed interest in the reuse of the asphalt in RAP has undergone a transformation with newer technologies and understanding of Rejuvenation. To comprehend why, one must understand how asphalt pavement ages.
The aggregate in asphalt pavement do not change with age. Since most Reclaimed Asphalt Pavement (RAP) comes from approved projects, quality of the aggregates can be assumed to be high and acceptable. Due to exposure to the elements and traffic over time, the bitumen binder in the RAP oxidizes and changes both physically and chemically. The aged binder becomes stiff, more brittle, and no longer acts as a binder.
For many years, technical requirements dictated that only 10-20% RAP be incorporated into a mix. To incorporate higher levels of RAP, a Rejuvenator / recycling agent additives needs to be added to the mix to soften and restore the properties of the aged RAP bitumen.