Resource depletion and climate change, amongst others, are increasingly worrying environmental challenges for which the road engineering sector is a major contributor. Globally, viable solutions that comply with the principles of circular economy (CE) are being investigated that can replace conventional asphalt mixtures in a post-fossil fuel society. The use of reclaimed asphalt (RA) is a widely used and well-established method to reduce the environmental and economic impacts of asphalt mixtures while increasing their circularity. However, RA's market supply and demand have not yet been systematically analyzed and established. Moreover, the actual circularity potential and the opportunity of re-circulating RA in a closed-loop model have not yet been methodically defined. To address this, a three-layered framework to quantify and assess the circularity potential (Ω) of RA has been developed. To give stakeholders and legislative bodies a simple method to assess the opportunities available to them to become “more circular”, a novel equation has been formulated. This takes the form of a three-level indicator that considers: technical aspects, the effect of the RA market, and the legislative restrictions. A case study in Germany was structured and undertaken to develop and verify the proposed approach. The results indicate that the available RA is insufficient to cover the needs of asphalt mixture production; even though RA production is significantly lower than the actual need of asphalt mixtures, it is not utilized in its entirety. An impactful step forward is the alteration of the regulations to support the higher utilization of RA in asphalt mixtures, and subsequently, the increased circular opportunity and potential of RA. Thus, Circularity potential (Ω) is a composite indicator that can support stakeholders, designers, and asset managers during the process of decision-making, to follow more circular operational, design, and asphalt pavement management patterns.
Although the benefits of asphalt recycling have been scientifically proven and several best practices are being implemented, further research is required in specific and specialized areas. One of these circumstances is the recycling of Reclaimed Asphalt Pavements (RAPs) that contain asphalt modifiers such as elastomers and/or plastomers. Following the principles of the circular economy and considering the sustainability implications of asphalt mixtures, this paper deals with the multi-recyclability of asphalt mixtures containing 50% RAP with and without a recycled plastic asphalt modifier and rejuvenating agent. The recycled plastic asphalt modifier was made of hard recycled plastics and was introduced to the mixture via a dry method. The research focuses on the characterization of binders via conventional, rheological, and chemical analysis. To control the consistency and variables of the mixtures, the RAP was produced artificially in the laboratory following an ageing protocol for loose asphalt mixtures. According to the obtained results, at all three cycles of binder recycling, comparable properties for (i) the extracted binders from the recycled plastic-modified asphalt mixture, (ii) the extracted binders from the control un-modified mixture, and (iii) the reference bitumen 50/70 were obtained. This was even noticed when a nearly similar quantity of the rejuvenator was needed during the rejuvenator optimization process. Overall, it can be deduced that from the binder-scale point of view, the mixture containing the introduced recycled plastic additive could be recycled for multiple life cycles without any degradation of its mechanical and physical properties.
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
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