Rejuvenation for Roads: BAM Explores How Asphalt Can Be Reused More Frequently

WPB: The Federal Institute for Materials Research and Testing (BAM) is investigating, as part of a project funded by the German Research Foundation (DFG), how biobased rejuvenators can enable asphalt to be reused more frequently and sustainably. Currently, a significant percentage of asphalt material is reused in road construction. However, this often requires increasing the proportion of fossil-based bitumen, and the reuse of reclaimed asphalt is currently limited to only a few cycles.

 Road and highway asphalt layers need to be renewed approximately every 15 years, depending on the level of wear and design. While a high proportion of reclaimed asphalt is already being reused in these processes, the reused material tends to become hard and brittle over time, which can lead to cracks and other surface damages. With each reuse, this tendency worsens. As the use of reclaimed asphalt increases in road construction, the otherwise desirable high reuse rate exacerbates the problem.

 The DFG-funded project “Postcarbon Road,” conducted in collaboration with BAM, Ruhr University Bochum, and the Technical University of Berlin, aims to create an unlimited reuse cycle for asphalt. Instead of relying on fresh bitumen, biobased rejuvenators—so-called “rejuvenators”—are being developed to keep asphalt elastic.

 Fresh Bitumen Worsens the Carbon Footprint

 Currently, fresh bitumen is added to reclaimed asphalt to counteract unwanted hardening. Bitumen, a fossil-based binder derived from petroleum, must be added in increasing amounts during each reuse cycle to maintain the asphalt’s viscosity and elasticity. However, the permissible bitumen content in asphalt is limited. Moreover, this process worsens the CO2 footprint of reclaimed asphalt with every cycle.

 Biobased rejuvenators, such as oils derived from pine resin or cashew shells, offer a potential solution. Preliminary studies have shown, however, that their positive effects are limited to a maximum of four reuse cycles. “We aim to push these boundaries and demonstrate how sustainable rejuvenators can significantly extend the reuse of asphalt,” explains Sandra Weigel, an expert in road construction binders who leads BAM’s work on the DFG project.

 Custom-Designed Biobased Rejuvenators to Preserve Asphalt

 The researchers are developing a specially modified biobased rejuvenator to act as a substitute for fresh bitumen’s rejuvenating effects. The key to long-term effectiveness lies in how well the rejuvenator mixes with the existing aged bitumen in the asphalt. Only with near-complete mixing can viscosity and elasticity be maintained over time.

 “Until now, it has not been possible to reliably determine the degree of mixing, making it difficult to tailor the rejuvenator effectively,” says Sandra Weigel. “We are utilizing infrared spectroscopy and, for the first time, infrared light guides to essentially look inside the mixture and gain a highly precise chemical understanding of the material.”

 Through this approach, the researchers aim to demonstrate how sustainable rejuvenators can be precisely adapted to the composition of reclaimed asphalt, enabling its reuse as often as possible without negatively impacting the CO2 balance.

By Bitumenmag

Asphalt, Bitumen, Road, petroleum