A concept that persistently keeps on being in the centre of attention by numerous governments, institutions, businesses and researchers, is Circular Economy (CE). It is a concept that is currently being promoted by the European Union and by various governments individually, including Japan, the United Kingdom, China, France, Canada, Sweden, The Netherlands, and Finland [
1,
2]. The reason behind this, is that numerous advantages could be exploited by the implementation of a holistic circular economic approach. According to recent publications, the European Commission estimated that the EU manufacturing sector alone could potentially have a benefit of 600 billion euros annual economic growth, if a transition to CE was to be achieved [
3,
4,
5]. Finland’s annual economy is estimated to experience growth of 2.5 billion euros, while when it comes to the global annual economy, the magnitude of the numbers significantly increases and estimates reach values of 1000 billion US dollars per year [
6,
7,
8]. Furthermore, China is recognised as the first country worldwide to actually have implemented legislations related to circular economy [
5]. In other words, lately, the consensus seems to be that CE could be utilized as a means of economic growth that complies with the definition of sustainable development [
4,
5,
9,
10,
11,
12]. The linear economic patterns of “make-use-dispose”, which currently dominate, seem to be agreeably unsustainable [
13,
14]. On the contrary, CE is able to provide alternative energy and materials flow-models, within the economic system; flow-models that are circular and opt to minimise waste production and maximise the service life of each and every material, service or product within a system [
4,
15,
16]. The increasing demands for raw materials, the dependence on other countries, the increasing population and energy demand, and the impact on the planet, comprise the most crucial factors leading to the belief that shifting towards such an economic approach can have great advantages. They are not just limited to environmental gains, but instead, the adoption of CE seems able to deliver economic benefits as well, according to L. Frodermann [
17]. According to Su et al. [
13] and Geng et al. [
18], the adoption of CE can lead to improved competitiveness of enterprises, more efficient use of materials and energy, increased competitive advantage, revenues from “waste” sales, and reduced environmental penalties. Park et al. [
19] and Preston et al. [
20] state that the implementation of CE can lead to more direct relationships with the consumers through collaborative consumption, while reducing the costs through the usage of recycled materials, the utilization of centralized waste management plans and the resale of used products, projecting a more positive corporate image. Sinkin et al. identified the benefits of CE as reduced costs through fewer waste inefficiencies, and increased firm value. Kienbaum Management Consulting [
21] published a report identifying the contribution of CE implementation as reduced costs through less waste pollution, reduced material and energy costs and competitive advantage. Additional income streams from the selling of refurbished products, reduced labour costs, enhanced customer value and differentiation, are the most important benefits of the CE according to Accenture [
22]. Finally, through multiple publications of the Ellen MacArthur foundation (EMF), namely, “Towards the Circular Economy” [
4], “Towards a Circular Economy: Business Rationale for an Accelerated Transition” [
9] and “Towards the Circular Economy Vol.3: Accelerating the scale-up across global supply chains” [
23], the potential benefits of a transition to a CE in Europe are described as annual net material cost savings in the European economy; reduced labour and energy costs, and costs for carbon emissions, along with improved customer interaction and dependency on resource prices. Finally, reduced product complexity and simpler lifecycles with reduced warranty risks and improved product design could be achieved. It thus, becomes apparent that the transition to CE is essential and stakeholders along with governmental bodies should aim towards the support and acceleration of this transition.
Having reported the potential benefits of the implementation of the CE in an economic and environmental perspective, it becomes essential to also highlight some of the most important limitations that could be encountered towards the way of its implementation. Global economic systems are mostly linear. Around 75% of global energy production is based on non-renewable energy resources [
1]. Non-renewable resources are extracted from nature, processed, used, exploited and then are dumped again back into nature in a harmful form [
1]. Along these lines, although sustainable development is a worldwide objective, CE-type initiatives that have been executed and/or will be realized in the not so distant future, will consistently be local or regional at most. Moreover, there is not a global administrative instrument. Be that as it may, gradually—and obviously—step by step, the future could be shaped towards a change, projecting a global improvement aligned with the principles of CE and sustainability [
1,
24]. Strongly rooted in environmental sustainability, the CE framework lacks an elaborated description of the social dimension of sustainability (e.g., the fulfilment of human needs, territorial implications). Its principles are primarily based upon a business perspective and strive equally for environmental and economic benefits. Social benefits are often omitted. Stahel has shown that additional manufacturing processes in a Circular Economy—e.g., refurbishing or recycling, demand more human labour, as these processes cannot often be standardized [
8,
25]. Even if this can create employment opportunities, it is not guaranteed that the jobs are created locally. Moreover, people’s basic needs at a global level may still be further undermined by abuses of power, unhealthy or unfair labour and living conditions or a disrespect of human rights. As such, the circular economy framework does not necessarily fulfil all the dimensions of sustainability [
1]. To achieve a compatible fit, CE initiatives have to be analysed via means of global sustainability net gains in the long-term, before being implemented. When market patterns and their revolving clusters, networks, stakeholders, and the financial investments are directed towards CE, the resulting innovations will have many difficulties to break through in the market. This would happen even if they were economically, ecologically, and socially superior to the prevailing technologies. In other words, the recycling market, just like any other market, has operational patterns, cultures and structures that have already been well-established. CE-based, high-value product reuse, remanufacturing and refurbishment, will have to compete with the aforementioned aspects, plus the managerial aspect of these actions. The economics and business logic of path dependency may prevent many of the emerging CE innovations from penetrating alternative markets [
1]. The material and energy flows extracted from nature travel via many different non-interconnected parts within the economic production-distribution-consumption system before ending up as wastes and emissions within ecosystems. These flows do not necessarily respect pre-defined administrative, geographic, sectoral or organizational borders and/or system boundaries. Innovative business models including designing for multiple life cycles, functional economy and product-service systems have been proposed for the implementation of the CE. However, these have as a prerequisite interorganizational sustainability management. Cooperation is required between the supplier firm and the customer firm and between the producer and consumer [
1,
6,
23,
26]. Circular material flows and renewable energy cascades exhibit a noteworthy opportunity towards more sustainable energy and material exploitation. And this is the case also in the context of entropy. The second law of thermodynamics suggests that all the CE-type initiatives should be thoroughly examined for their net environmental sustainability contribution on a global scale. A cyclic flow does not secure a sustainable outcome [
1]. For instance, in the utilization of forest residues as a source for renewable energy and for replacing fossil fuel combustion, nutrient-rich vegetation parts are extracted from an ecosystem where they could support ecosystem health, biodiversity and forest growth. This process demands energy. The machine manufacturing process also requires energy and materials and produces wastes and by-products. Hence, the sustainability contribution of this circular process can be conflicting. Due to this, and the fact that sustainability can be characterized context-sensitive, it is imperative that CE-related initiatives and processes are carefully examined case-by-case [
1,
10,
27,
28].
Such initiatives in the sector of road engineering, which can be widely observed, are the recycling of reclaimed asphalt (RA), the extension of the service life of asphalt pavements through preventive maintenance, the utilization of wastes in the production of asphalt mixtures, the attempt of increasing the allowed percentage of recycled materials inside the asphalt mixtures [
29] and partially the prioritization of regenerative energy sources. Sometimes however, these practices are already being implemented by the national road authorities or the involved stakeholders not because they serve the principles of circular economy and are beneficial in terms of sustainability, but just because they are economically profitable; and by the rule of thumb are considered as best practices. Again, nothing has been published in terms of asphalt mixtures when it comes to legislative guidelines towards more circular asphalt mixtures. This however, has not stopped some individual stakeholders to move towards this direction. The company KRATON, for example, has moved forward by producing SYLVAROADTM RP1000; an additive derived from Crude Tall Oil (CTO), a renewable raw material, characterized as a by-product of the paper industry. It is able to increase the levels of RA incorporated into the asphalt mixtures while avoiding significant environmental burdens [
10,
30]. Another noteworthy attempt towards more circular products has been made by Tarpaper Recycling, along with Super Asfalt. They have proposed the production of REC100. It is a mobile asphalt plant that ensures 100% utilization of the resources in roofing felt and asphalt waste, in order to produce asphalt mixtures incorporating 100% recycled resources. Finally, the world’s first fully recycled road, has recently been developed and constructed by Eurovia, the VINCI subsidiary, that is specializing in the urban development and transportation infrastructure spheres. This was achieved via the utilization of a mobile continuous asphalt plant, TRX100%, which is capable of recycling up to 100% of asphalt aggregates.