The Frontiers of Multi-Recyclability of Bituminous Mixtures with Recycled Plastic under the Scope of Circular Economy

The road engineering sector is increasingly embracing the principles of circular economy and sustainability, leading to the introduction of alternative materials in asphalt pavement. In this regard, the use of recycled plastic as a modifier in asphalt mixtures provides an eco-friendly and cost-effective alternative that improves pavement performance while addressing environmental concerns over plastic waste to a certain extent. While recycled plastic-modified asphalt pavements demonstrated enhanced performance, their recyclability at the end of their service life remains under-explored, which significantly influences the implementation of a circular economic approach. To address this issue, the current thesis aims to investigate the multi-recyclability of asphalt mixtures modified with recycled plastic over two life cycles. To achieve a controlled environment for all the desirable parameters while considering the novelty of the recycled plastic used, the reclaimed asphalt pavement (RAP) was produced using an artificial laboratory ageing protocol, which served as a basis for assessing multiple life cycles. To achieve the main goal of this thesis, a comprehensive experimental campaign was performed to evaluate the binder-scale and mixture-scale performance properties. Additionally, a novel analytical circular economic model was developed, along with a novel indicator, the Product Multi-Recyclability Index (PMRIₙ). This way, it became possible to quantify the product circularity over multiple life cycles for the asphalt mixtures that not only contain recycled materials in an open-loop approach but also over multiple life cycles. The findings revealed that the asphalt mixtures modified with recycled plastic performed comparably, or in some cases, outperformed the conventional mixture over two cycles at a recycling rate of 50%. Overall, it can be concluded that the asphalt mixture containing the recycled plastic modifier can be recycled for multiple life cycles without compromising its mechanical and performance characteristics. The introduced PMRIₙ can be used as a metric to assess the potential recyclability of asphalt mixtures, thereby enabling a plethora of opportunities for the involved stakeholders and the relevant decision-makers towards the actual implementation of the circular economy in the field of bituminous materials.