# Evaluation of Mechanical Properties of Recycled Material for Utilization in Asphalt Mixtures
## 1 Introduction  
The increasing amount of waste all over the world has shown that effective measures have to be implemented to reduce their negative environmental impact. Landfilling of waste is not a solution, due to danger of leaching and soil impregnation with potential subsequent contamination of underground water. On the other hand, there are important sustainability benefits associated with the use of recycled material in pavement industry. Recycling helps the environment by reducing resource extraction and the use of virgin material, thereby reducing energy and water use, reducing harmful gas emissions and helping reduce waste to landfills. Buying recycled products also in some cases can reduce cost. Therefore, the idea of using recycled material in pavement construction has attracted the attention of many researchers (e.g., [PERSON] and [PERSON], 2006; [PERSON] et al., 2007; [PERSON], 2008; [PERSON] and [PERSON], 2009; [PERSON] et al., 2011; [PERSON] and [PERSON], 2012; [PERSON] and [PERSON], 2015;[PERSON] and [PERSON], 2016) in the pavement industry to investigate feasibility of the application of some of waste materials as alternative material in pavement construction (1; 2; 3; 4; 5; 6; 7; 8). Among different layers of flexible pavements, asphalt surface layer plays a fundamental role in flexible pavement structure systems as it should withstand varying traffic loads and constantly changing environmental conditions. Moreover, the asphalt surface layer is critical for safe and comfortable driving. Due to the composition nature of asphalt surface layer, application of solid waste in asphalt layer reduces not only environmental issues associated with waste disposal but also the demand for virgin aggregate which will subsequently result in cost savings and economic advantages, representing a value add application for waste material. However, the selection of waste material to be used for pavement construction, particularly asphalt surface layer, is of high importance as the application of waste should not adversely influence the structural and functional aspects of the pavements (9; 10; 11; 12). Among different asphalt components, coarse aggregate properties are identified by the researchers (e.g., [PERSON], 2009; [PERSON] and [PERSON], 2004; [PERSON], 2014; [PERSON] et al., 2015) as the second most important parameter after gradation for the performance of hot-mix asphalt (HMA) because coarse aggregate often forms the skeleton of the asphalt structure and transfers traffic and environmental loads to the underlying base, subbase, and subgrade layers (13; 14; 15; 16). Therefore, the behaviour and performance of asphalt mixture and eventually the asphalt surface layer are directly affected by the material properties and composition of this aggregate skeleton. In fact, the low stiffness of the asphalt mixtures and the excessive rutting in hot-mix asphalt (HMA) pavement surfaces are often attributed to the poor asphalt mixture designs which is primarily controlled by the asphalt binder and aggregate properties (17). Therefore, except for the fine mixes, the selection of coarse aggregate greatly influences the asphalt layer behaviour. In addition, since the aggregate represents the major portion of the asphalt mix, from the viewpoint of environmental preservation and effective use of resources, a comprehensive understanding of the engineering properties of the recycled aggregate can provide enormous benefits. Recognizing this fact, the reported studies and research on the utilization of recycled aggregate such as reclaimed asphalt pavement (RAP), recycled construction aggregate (RCA), recycled glass, etc. have increased all over the world over the past two decades (18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29). Among the recycled aggregates that can be utilized in asphalt mixture, RCA obtained from construction and demolition waste constitute a major part of generated solid waste as a result of renovation and construction projects.