Overview
Throughout Europe polymer modified asphalt (PMA) is used extensively in the past decades for high trafficked roads and premium pavements; especially for surface layers. The addition of polymers contributes to the durability and functionality of these premium pavements, such as noise reducing pavements (the Netherlands) or rutting resisting pavements (Denmark and Slovakia). These pavements are now more and more reaching their end of life. Therefore, the road sector is facing a rapidly increasing source of reclaimed asphalt (RA) that contains polymer modified bitumen (PMB), which offers a potential premium binder contribution. Depending on the hardened state of the combined binder and the deterioration of the aggregate gradation during milling and further pre-processing, it is the challenge to the road sector to ensure – as far as possible – that the PMB containing RA is recycled at its highest practical potential. The goal is to avoid downgrading of RA containing a potential valuable asset.
From a technological perspective, the hypothesis is that the impact of the rheology of the aged polymer modified bitumen predominantly originates from aging of the base bitumen while the polymer remains reasonably inert to oxidative hardening. If the old binder can be recycled into new hot mix asphalt without excessive thermal impact on the polymer (degradation) a positive impact on the properties of a revived binder can be achieved.
From an economic and ecological perspective, the hypothesis is that when RA from premium quality, high trafficked pavements can be recycled into new premium quality pavements, the benefit for National Road Authorities as well as the road sector will be considerable because of the shorter hauling distances (lower carbon footprint) and the fact that less primary resources are needed for premium quality bitumen and aggregate (important for EU countries that are dependent on import of primary raw materials).
In the RECYPMA project we will investigate the possibilities for recycling polymer modified asphalt from surface layers into new high quality surface layers using hot mix recycling. The recycle process will be based on a state-of-the-art-review and laboratory scale experiments. The economic and ecological effects of the of recycling PMA will be evaluated.
The project consists of 5 Work packages. WP 1 is set up for coordination and dissemination. To ensure a diversity that is relevant for Europe, a broad departure is taken through the state-of-the-art review (WP2), followed by gradually focusing to three types of RA asphalt mixtures (one per participating country), one type of polymer modification and one type of pavement application (surface layer) for determining the binder properties in WP3. Based on the results of WP3 three asphalt mixtures will be designed with the reclaimed asphalt in order to determine the asphalt properties and quality. At the end, based on the results of WP 2, 3 & 4, focus is made on a specific road case for estimating environmental and economic benefits (WP5).
Funding
Results
Binder research indicates that the extracted binder from the RA with PMB still contains an active part of polymer that influences the material behaviour as can be expected from a polymer modification. Research on mixtures containing RA with PMB shows, that if proper mix design is used, a good performance in surface layers is realized with respect to water sensitivity, stiffness, rutting resistance and fatigue.
From an economic and ecological perspective, the benefits for National Road Authorities as well as the road sector are considerable because of the shorter hauling distances of aggregates and the reduction of primary resources mainly attributed to the binder. This is especially important for EU countries that are dependent on import of primary raw materials.
The results of the research indicate that there are technical possibilities for recycling of polymer modified surface layers into new premium surface layers and that the benefits of doing so are significant. However still many challenges lie ahead before large scale application is possible, first risks with respect to service life when using RA need to be quantified in more detail (e.g. the assumed relation between SBS (Styrene – Butadiene – Styrene co-block polymer) content and fatigue performance, high stiffness of asphalt containing RA with PMB and the risk of low temperature cracking, etc.), issues related to full scale application (e.g. the risk of degradation of the polymer at high temperatures, mixing time influence on homogeneity and performance of asphalt) need to be explored and finally quality assessment and assurance of the RA has to be managed including the quality of the used aggregates. All three challenges can be met through research while realizing a series of pilot projects. These pilot projects are preferable realized in different European countries to incorporate different recycling techniques and different environmental conditions.