Evaluation of the role of reclaimed asphalt pavement preheating on cracking behavior of hot mix asphalt recycled mixtures by digital image analysis

In the last few decades, the need for reducing the exploitation of finite sources has led to an increasing use of reclaimed asphalt pavement (RAP) for the construction, maintenance, and rehabilitation of road pavements. During hot mix asphalt (HMA) plant production, RAP can be added at ambient temperature or preheated into special drums. When designing an RAP mixture, it is essential to dose the correct amount of virgin binder according to the percentage of the reactivated aged one. RAP preheating plays a key role in this process, although no reliable methods are available for achieving an accurate estimation. This article presents an innovative digital image-based methodology, named overlapped digital image (OIA) analysis, to better understand the role of reactivated binder on the cracking behavior of HMA-RAP mixtures. A recycled mixture was produced in the laboratory by adding RAP both at room temperature (25°C) and after preheating (150°C) and subsequently tested according to the Superpave IDT at 10°C and 25°C. The tests were combined with the OIA analysis to identify how the strain patterns and the initiation and propagation of fractures developed, according to the reactivation of the aged asphalt binder. The results show important outcomes in terms of cracking behaviors highlighting the important role of RAP preheating for inducing aged binder reactivation.