## 1 Introduction  
Circular economy (CE) is a concept promoted by the European Union and several governments individually, which can be defined as an economic model based on the natural cycle, aimed at efficiently using resources through waste minimization, long-term value retention, and reduction of primary resources use [1, 2]. According to [PERSON] and [PERSON] [3], the road engineering industry moves towards more circular approaches. Some standard practices that various stakeholders, companies, asphalt contractors, and agencies are implementing, in line with the circular economy principles, include recycling reclaimed asphalt, extending the service life of their assets (preventive maintenance), and using wastes in asphalt pavements [4]. The road engineering industry's transition to a circular business approach requires managing the resources, energy, and waste more efficiently and sustainably [5]. According to [PERSON] [6], the pavement's sustainability is highly based on the proper selection of materials. Thus, the choice of eco-friendly and low-cost materials is part of sustainability principles in pavements while considering social impacts. [PERSON] et al. [7] state that cleaner production in asphalt mixtures aims to completely or partially replace traditional aggregates and fillers with waste materials or their use as additives modifying the binder's composition. The principal constituents of a typical asphalt mixture are the aggregates, and thus, the utilization of industrial waste and byproduct materials in pavement applications as an alternative for natural aggregates contributes to environmental sustainability [8; 9]. Adjusting asphalt mixtures production with waste materials can also limit the enormous volume of wastes produced from various sources. Furthermore, this solution reduces the consumption of newly mined materials, minimizing the carbon footprint and pavement industry impact on the environment [10]. Although different kinds of recycled materials can be used as aggregates in road construction, it is crucial to know their properties to ensure they meet the same quality standards as natural aggregates to satisfy the same performance standards [11; 12]. This work also aims to study the possibility of using steel slag aggregates (SSA) as a substitute for more than 50% of the natural aggregate in bituminous paving mixes, thus improving the sustainability of the road paving industry. Considering that SSA's mechanical properties may be similar to those of natural aggregates and that this waste is produced in significant quantities, its incorporation in pavements would reduce the volume of this material deposited in landfills, promoting a circular economy. The steel industry, particularly the steel producer, generates significant amounts of wastes, including slag, commonly known as \"steel slag\". According to [PERSON] and [PERSON] [13], steel slag is a waste material produced during the steelmaking process as a byproduct. Steel slag is commonly categorized according to the furnace used for the refinery process, including basic-oxygen furnace (BOF), blast furnace (BF), and electric-arc furnace (EAF). Among these categories, EAF steel slag (used in this work) is the most common type used in road construction [9; 14]. In the last decades, the steel industry in Europe has transitioned towards the electric arc furnace steelmaking technology, being used for approximately 30% of European steel production [15]. In Portugal, there are two steelworks, one located in Seixal (SN Seixal), and the other in Maia (SN Maia), which belong to Siderurugia Nacional (SN) Empresa de Produtos Longos, SA. Both are equipped with an electric arc furnace, in which the primary raw material used in the melting phase is ferrous scrap [16]. Electric-arc furnaces (minimills) use high-power electric arcs instead of gaseous fuels to produce the heat necessary to melt recycled steel scrap and convert it into high-quality steel.