# Physical and Mechanical Properties of Reclaimed Asphalt
## 1 Introduction  
In the context of environmental protection and more sustainable development, new techniques and alternative materials must be researched and integrated into construction processes. Road projects, in particular, require large quantities of conventional materials for new construction and/or rehabilitation of pavements, further depleting already limited natural resources [1]. This has led road engineers to explore alternative materials that are currently considered \"waste materials\" [2]. Therefore, the ability to recycle and use these materials can help reduce the need to obtain and process virgin aggregates for road projects. This, in turn, has environmental benefits, such as reducing energy consumption and greenhouse gas (GHG) emissions during the production and construction process and avoiding the landfilling of construction and demolition (C&D) materials. This also results in financial benefits, such as lower costs for the procurement of materials for the construction of pavement layers [3, 4]. On the other hand, C&D materials can only partially replace conventional materials for road construction due to their relatively lower strength [5]. This is a significant issue, as the response of materials in underlying layers, namely base/subbase and subgrade layers, under various conditions is important for the stability of numerous pavement projects [6]. There are plenty of studies dealing with the technical properties ofC&D materials for road construction, both for surface courses [3; 7] and for base courses and substructures [8; 9]. Moving forward, Reclaimed Asphalt Pavement (RAP) is one of the waste materials that can be rationally reused in new road projects, if its behavior is better understood. RAP is obtained by milling or removing the asphalt layers from road pavements that are either being maintained or rehabilitated. It consists of natural aggregates (93-97% by weight of mixture) covered with aged bitumen and the remaining cured asphalt (3-7%) [10]. RAP did not become of interest to the road industry until the 1970s, due to the petroleum crisis, when its potential for reincorporation into asphalt mixtures to produce new asphalt layers became better understood. From that point on, knowledge about the incorporation of RAP into asphalt layers grew steadily, and today there are standardized testing protocols for asphalt layers treated with RAP [11; 12]. This is also confirmed by [PERSON] et al. [10], who reported that nearly 70% of recent studies on RAP involve its use in asphalt layers. However, as higher percentages of RAP were included in asphalt mixtures, variations were observed in these mixtures, resulting in its use generally being limited to only 15% [13]. This restriction on the use of RAP in asphalt layers has led to an increase in stockpiles of RAP worldwide. In the USA, for example, only one-third of the RAP material is reused per year, while this ratio is one-sixth in Europe [14]. Because of the widespread availability of this potentially sustainable material, research has begun to take a new direction in evaluating the potential of RAP for incorporation into unbound base courses or subbases of road pavements [15]. The suitability of RAP material for use in unbound pavement layers has been systematically investigated by several researchers [16; 17; 18; 19]. However, the mechanical responses and deformation characteristics of the RAP material in unbound pavement layers are not yet fully known due to its special properties. Specifically, although it is widely accepted that the RAP-VA blends have a comparable or better bearing capacity than pure VA [16; 17; 18; 19], other properties are rather questionable. Many studies [16; 20; 21] report that CBR values decrease when RAP is added to VA, but other studies [22] report the opposite result. Additionally, regarding the permanent deformation of RAP-VA blends, there are studies which claim either a significant development [23; 24; 25] or an insignificant development of permanent deformations compared to pure VA [26; 27; 28].