University of Twente Student Theses


Balancing Materials, researching the circularity of ZOAB

Stevering, T.J.T. (2021) Balancing Materials, researching the circularity of ZOAB.

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Abstract:Balancing materials, researching the circularity of ZOAB is a bachelor thesis carried out for Rijkswaterstaat to gain insights into the circularity of porous asphalt in the current Dutch asphalt industry. The purpose is to Investigate current circularity potential by looking at the closed-loop recycling of porous asphalt in the Netherlands. As well as Indicating the current issues concerning the circularity of porous asphalt and the collecting of the required secondary resources. The questions above have been researched through a combination of literature review and interviews with experts in asphalt recycling and circularity. Furthermore, a case study has been carried out in which a secondary material balance has been used to indicate the circularity of two construction projects. Since one of the projects is a maintenance project and the other a widening project, differences in the circularity strategy have been noticed. These projects can be regarded as representable for Rijkswaterstaat projects. To determine the circularity of a project, it is crucial to map the material flows. The project focuses on porous asphalt and determines circularity based on the percentage of porous asphalt milling that does not leave the system and is not down cycled. This approach is adapted from the guideline “Measuring circularity” (Platform CB'23, 2020), 1 and aims to reduce the quality of the material as little as possible. The data used in the case is provided by the contractors, this data includes quantities of milled asphalt and the asphalt mixture planning. With this information, a percentage of circularity for porous asphalt has been calculated. For the first project, this was 33%. The second project realised a closed-loop circularity of porous asphalt of 56%. The differences can be explained by looking at the strategies. In the first project, porous asphalt mixtures with a maximum of 40% reclaimed asphalt were chosen to use the porous asphalt milling as effectively as possible. This does not necessarily imply closed-loop recycling, but rather the most effective use of material. The second project used porous asphalt mixtures with up to 70% reclaimed materials. This percentage could be achieved through the use of mixtures, including both reclaimed asphalt and PA-stone. A problem is that there is not enough porous asphalt milling in this project to achieve this 56%. Therefore, extra porous asphalt milling has to be imported from other projects. This demonstrates the scarcity existing on the porous asphalt market. It has been noticed that the shortage only occurs for coarse fractions of the asphalt milling. This is due to the breaking of coarse fractions into smaller fractions during recycling. Leading to a shortage of coarse aggregates and a surplus in fine aggregates. The contractor indicated that not the technology, but the availability of material was a limiting factor in the process. Literature determines the current maximum percentage of closed-loop recycling of porous asphalt around 60% (Jacobs, Frunt, & Rering, 2016)2 . The case study showed that 56% circular could be possible, but it will lead to a shortage of porous asphalt milling. This shows that the sector can improve its circularity further, but some challenges have to be overcome. The main conclusion from this report is that to increase the circularity of the asphalt market in the Netherlands, the focus has to be put on the logistical challenges. The level of circularity for a project is difficult to express because it is influenced by many project-specific factors. It, therefore, is key to see circularity as a broader and logistical problem. Balancing the supply and demand for reclaimed asphalt is vital to ensure a more circular economy. It is recommended to integrate circularity on a larger scale than project-wise. Since focussing on circularity in one project leads to compensating on other projects. Lastly, many of the interviewees indicated the need for information. To achieve high circularity in a project, it has to be known what materials will become available to use. As well as more overview of the supply and demand for specific types of secondary materials in projects. Increasing the availability and quality of data can ensure a better logistical process and therefore a more circular industry.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Programme:Civil Engineering BSc (56952)
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