The rapid development of infrastructure has led to various environmental, economic, and societal challenges. The pavement industry, in particular, is known for its high energy consumption, resource utilization, and pollution generation. Despite recent efforts to augment the sustainability and circularity of pavement infrastructure, there remains a lack of comprehensive assessment methods to evaluate the existing practices and technological advancements, which makes the implementation of innovations challenging. This study reviewed twelve existing circular economy indicators and frameworks to understand the challenges associated with their use in evaluating pavement infrastructure. The indicators included Material Circularity Indicator (MCI), Circular Economy Index (CEI), CB’23 framework, Environmental Sustainability and Circularity Indicator (ESCi), Circular Economy Indicator Prototype (CEIP), Material Reutilization Score (MRS), Value-based Resource Efficiency (VRE), Circular Economy Performance Indicator (CPI), Recyclability Benefit Rate (RBR), Reuse Potential Indicator (RPI), Product-level Circularity Metric (PLCM), and Building Circularity Indicator (BCI). These indicators cover different aspects of circularity and sustainability, such as resource efficiency, material circularity, product’s lifetime, preservation of product’s functions, and environmental and economic impacts. However, none of the indicators provide a comprehensive assessment tailored for pavements, encompassing circularity and all three aspects of sustainability. Considering factors such as data availability, overlap of conceptual and methodological approach, and the scope covered, six of the twelve circularity indicators were evaluated in this study, namely, MCI, CEI, CB’23, ESCi, CEIP, and MRS. Since these indicators were not originally developed to assess pavements, appropriate methodological modifications were proposed and validated using three different pavement construction and maintenance methods that are commonly adopted in the Netherlands. In order to map the road to sustainability, the analysis was complemented with the Environmental Cost Indicator (ECI, or in Dutch, MKI) and Net Present Value (NPV). The three case studies adopted in this study included: (a) resurfacing the pavement once in every 12 years with 25% Reclaimed Asphalt Pavement (RAP), hereafter referred as Business As Usual (BAU) scenario, (b) life-extension maintenance by rejuvenating the pavement in years 5 and 10 since construction followed by resurfacing, and (c) use of low-emission technology, i.e., Warm-Mix Asphalt (WMA) with higher RAP 3 percentage (50% by mass) in the mix. An analysis period of 36 years was chosen as per the Federal Highway Administration guidelines and the foreground data was collected from roadway stakeholders. Additional missing information was also gathered from Dutch asphalt product category rule, international databases, and existing literature. The results revealed the strengths and limitations of each indicator. MCI being a mass- based indicator captured the material circularity and product’s service life but failed to represent the environmental and economic impacts. Although CEI indirectly captures the environmental impacts as it is governed by market prices, which takes into consideration the societal and environmental taxes, it is volatile as it is can also be influenced by the supply and demand of raw materials and material quality, potentially overlooking the benefits of using higher percentages of recycled materials. CB’23 provides detailed information by classifying pavement components across different circular economy principles, which aids in targeted improvements but complicates the comparison of alternatives as a whole. ESCi combines MCI and MKI to incorporate circularity and environmental sustainability but requires extensive modelling and lacks economic and social considerations. CEIP, as a questionnaire-based indicator, covers a wide range of circularity principles, but the weighting and scoring of questions is subjective as it is based on the expert opinion leading to concerns of bias in decision making. MRS involves simplified mathematical computations, thereby serving as an attractive choice for quick decision-making. However, it is fundamentally biased to cover only the recycling strategy, and ignores the aspect of lifecycle use, thereby not accounting for durability of the asset. With regards to the case studies, MKI, MCI, ESCi, and MRS indicate that the WMA alternative was the most circular strategy. LCCA, CEI, and CEIP favour the rejuvenation alternative, while CB’23 may favour one alternative when the result of one sub-indicator is designated to be the criterion for decision making. However, since all the indicators cover different aspects of circularity, it is important to complement the results with environmental, economic, and social sustainability indicators for comprehensive and robust assessments. In practice, choosing different alternatives based on the selected indicators can lead to varying end result. Therefore, it is essential to handle these implications carefully and the scope, boundaries, methods, assumptions and any limitations must be clearly stated for transparent decision-making. Future research should focus on improving data quality and developing methods to integrate social sustainability, wherever feasible.

Efficient recycling and the realisation of a circular economy are essential to meet the growing global demand for metals. This thesis investigates the design and evaluation of a singulation system specifically for brass scraps, addressing challenges in their irregular shapes, sizes, and flow behaviours. Singulation, the process of separating particles, is a critical preparation step for automated AI-driven sorting systems to achieve high-definition recycling of alloys. Experiments revealed key factors affecting particle behaviour, including the impact of shape, size, and flow conditions. A detailed analysis of brass particle properties resulted in a proposed system. With both prototype tests and simulation experiments, the realised system for single file singulation achieved effective particle separation, by focusing on mitigating undesired behaviour like rolling and lateral movement. The findings support potential future developments in smart sorting systems for brass scraps and other materials which need automated sorting.

This thesis shows the development of a singulation process for steel scrap particles. This singulation process is part of a sorting line that can sort scrap into different alloy types. This is an essential step in making steel a fully circular product. The new designs are based on an already existing chute used for aluminium singulation. In the report, the scrap properties and their behaviour on the aluminium chute are analysed. These insights are used to create three new designs for a chute that can be used for steel singulation. To evaluate these designs, a Discrete Element Method (DEM) model was used.

The utilization of Recycled Coarse Aggregate (RCA) in concrete has gained signifi-cant traction due to its environmental and economic advantages. However, ensuring the quality of RCA poses challenges as it is influenced by various unpredictable factors includ-ing the high water absorption of RCA, ineffective recycling processes, and the presence of contaminants. The existing body of research on the influence of RCA on the Compressive Strength (CS) of concrete has yielded inconsistent findings, and limited knowledge exists regarding the specific combination of parameters that enable effective control over CS. To address this gap, the present study aims to identify the essential parameters that contribute to controlling CS in concrete through the development of a predictive model. By investigat-ing these crucial parameters, this research intends to extent current knowledge on optimiz-ing the use of RCA in concrete.
To investigate the impact of the crucial parameters on the CS of concrete when uti-lizing RCA, a series of experiments were conducted. The RCA was obtained through the selective demolition recycling technique. The content of RCA was divided through manual separation into unbound stones, Low-Quality Recycled Aggregate (LQRA), and contami-nants. LQRA is composed of residual mortar and stones with mortar attached to their sur-face. The experiments included physical properties tests and optimization of the concrete mix designs. Additionally, relevant literature was consulted to identify the parameters that would serve as variables in constructing the predictive model. Through analysis via re-sponse surface methodology, a predictive model was developed to assess the impact of these critical parameters on the CS of concrete.
The experimental findings confirmed the statistical significance of the predictive model in assessing the impact of critical parameters on the CS of concrete. The level of LQRA was found to have a negative impact on the quality of RCA. The water-to-cement ratio was identified as a significant factor affecting the CS of concrete, with lower ratios yielding higher CS. When using RCA with high LQRA content (up to 65% of the total weight of RCA) as a substitute for natural coarse aggregate, higher replacement ratios re-sulted in lower CS.
In order to further validate the predictive model, Artificial Neural Network (ANN) modelling was incorporated as a non-linear method of assessing the relationship between the variables and the output, which is the CS. The high R2 values obtained from the ANN model demonstrated the robust alignment between the model and the data, strengthening its reliability. The integration of a Pareto chart and model-fitting regression gives a better physical understanding of the results of the predictive model by identifying influential terms and reducing complexity. The resulting model improves interpretability and predic-tive accuracy. The analyses emphasize the significance of integrating ANN and the Pareto chart approach in enhancing model validation and simplification.
These findings offer valuable insights into the parameters that are crucial to the CS of concrete which consists of RCA. By implementing the procedures that assess the quality of RCA, sustainable construction practices can be promoted, and the wider application of RCA can be facilitated on an industrial scale.

Recycled aggregate concrete is emphasized more and more nowadays due to its importance towards the construction industry and general welfare of our planet. Being such a significant feature with regard to universal sustainable development, every aspect of its properties should be evaluated, examined and optimized so that there is a well-known, well-described and ready to use product. This project aimed at correlating some of the established parameters of conventional concrete such as water absorption of the coarse aggregate fraction and the resulting compressing strength, only applied in the field of recycled aggregate concrete. Along with these two properties, a prediction model was sought for which would be able to forecast the mechanical strength of concrete based on its coarse aggregate composition. A series of experiments were performed on samples fabricated for water absorption tests and compressive strength assessment. In total, 112 water absorption samples and over 250 concrete specimens were prepared and examined for the respective attribute. These samples used natural aggregate as the base of the coarse aggregate portion of the mix design, alongside a series of so-called contaminants which replaced the gravel in certain concentrations. These contaminants included bricks, ceramic tiles, glass, wood, gypsum, plastics, mineral fibers and recycled sand concrete and were entirely based upon the C&DW composition globally. Further investigation was done on the inclusion of air within concrete so that contaminated concrete results could be equated to this constant. All water absorption tests were performed according to the current standards and concrete specimens were crushed after 7 and 28 days of curing in order to obtain their strength in compression, while the predictive model was initiated via the Minitab statistical software.
The results indicated some interesting and promising trends. From both sets of experiments, it was evident that the water absorption of the coarse aggregate fraction was not the main contributor towards the strength development of recycled concrete. It had a minor influence, especially compared to the type of contaminant present and how much volume it took. Furthermore, samples with identical water absorption fabricated concretes with different strengths. Overall, plastics and wood had the most negative effect in terms of compressive strength, while bricks, tiles and glass seemed to affect this aspect in neutral or even slightly positive manner. EPS foam in very limited amounts yielded a notable 30 to 35% strength drop, while on the other hand, brick replacing 20% of the NA improved the strength by approximately 7% after 7 days and 2% after 28 days. In the end, based on all experimental input, a predictive model was developed, optimized and validated in several steps so that it was able to predict the water absorption of coarse aggregate, compressive strength after 7 and 28 days and equivalent air content based on the composition of the coarse aggregates. The back-end of the model is provided within the report as a MATLAB code.

Building construction is a material-intensive process known for depleting natural resources, mainly gravel and sand, used in concrete production. At the same time, building demolition generates large amounts of construction and demolition waste (CDW), primarily consisting of end-of-life (EOL) concrete, a significant waste flow occurring in Europe's construction sector. The potential to deal with waste management and the uprising demand for new concrete in construction lies within circular economy-based solutions applied throughout the building's lifecycle. Steering in this direction, the European Union is endorsing a circular economy strategy that aims to utilize EOL concrete derived from CDW to produce new concrete and thus minimize virgin material inputs. These efforts have not been translated to a uniform framework for Europe, where practices, regulations for waste management, and market acceptance for secondary raw materials differ among member countries. In this project, different types of pre-demolition audits, demolition, and waste processing methods for EOL concrete are compared, showcasing the status quo across the EU and the Dutch case study, which portrays innovations that can shape the future of concrete recycling. An integrated LCA and LCC framework is applied from the demolition stage to waste processing and the production of materials for new construction to capture potential environmental and economic benefits and drawbacks at the end-of-life stage (EOL) of the building. The results showcase the pivotal role of BIM-supported pre-demolition audits in combination with selective demolition with benefits that include lower quantity of generated waste allocated to treatment and more components available for reuse. Finally, LIBS, a quality assurance tool for recycled aggregates, shows great potential in supporting a market for secondary raw materials in Europe.

The aim of this research was to investigate the effects of implementing circularity in infrastructural construction projects. As a very polluting sector, circularity is becoming a more and more popular theme in the construction industry. Driven by both governmental regulations of reaching a full circular economy in 2050 and intrinsic motivation, construction companies are slowly introducing practices which contribute to circularity. Unfortunately, not much is yet known about the effects on project process and construction costs when implementing circularity. This research has initiated the first step towards understanding what the effects of circularity are on infrastructural construction projects, providing welcoming insights to both the academic world and practice. Based on a case specific comparison, a circular construction project is more expensive than a regular construction project, due to extra activities which need to be executed before a secondhand material can be applied. Regarding the project process, the circular construction project introduced ''gathering of materials'' as a whole new process step which is constantly interchanging with (re)design until a final design has been completed.

The European construction sector is responsible for the consumption of almost 32% of total raw material for realizing its projects (Benachio, Freitas, & Tavares , 2020). On a national level, this amount results to almost 50% for the Dutch construction industry (Nellssen, et al., 2018). The ever-growing population stresses the need for sufficient infrastructure and services which only results in an increase in demand and eventually an increase in resource consumption. The current trend of linear model, wherein the virgin raw materials are used to construct end products and eventually discarded at its end of life, poses a major threat for raw material extinction, and adds to the problem of excessive resource consumption. A viable solution for this problem is the introduction of circular economy concepts that aim at closing the raw material loops by considering all the current and future life cycle phases of a product in the initial development stages. Since the launch of the Ellen MacArthur Foundation (EMF) in 2010, circular economy (CE) has gained considerable attention. EMF defines circular economy as “a regenerative system that aims to keep materials in a closed loop at their highest value” (Foundation, Cities in the circular economy: An initial exploration , 2017, page 7). CE focuses on much more than reduction of waste through recycling and aims at reducing the consumption of raw materials, designing products such that they can easily be disassembled and reused and extending product lifespan through maintenance and repair. CE differentiates the gradation options that help keep the materials and components within the loop by options such as refuse, reduce, reuse, repair, etc. One of the important parts of any city is its transport infrastructure that can also make use of the circularity principle. For many developed and developing countries, transport infrastructure accounts for the largest proportion of a country’s budget of any public-works program and consequently also play an important part in a nation’s economic and regional development. Studies show that current developing research of circular economy seldom focuses on the assessment of such transport infrastructure. Therefore, the main focus of this study is to understand the barriers of circular economy and to develop an assessment framework that can help the evaluation of transport infrastructure in terms of circularity.

Current linear economic model entails coupling of economic growth with resource constraints and degradation of the Earth. In order to combat these negative aspects and to ensure prosperous and sustainable future, a new economic approach is emerging - Circular Economy. Besides neutralizing threats of the linear model, it also promises additional financial, societal and environmental benefits. This is recognized on (inter)national level with numerous action plans and legislation. However there are almost no actions that are aiming at implementing the notion of circular economy on the level of supply chains/ Therefore, inertia is observed in supply chains in relation to changing towards circularity. This thesis looks at the underlying reasons for this with the research methodology designed around the Social Network Analysis approach. Two main reasons for inertia in supply chains stemmed out of research: differences in perceptions of the actors within a supply chain and diffusion of responsibility phenomenon. Going one level deeper, four causes for these developments were uncovered:
1. Lack of incentives for companies in supply chains for making a change towards Circular Economy.
2. High uncertainties and risks that a change to circularity implies for companies in supply chains.
3. Lack of mutual interests between actors in supply chains for making a change towards circularity
4. Clashes of perceptions on all levels in supply chains, as well as between supply chains and government.