# Limitations on the Use of Recycled Asphalt Pavement in Structural Concrete
## 3 Quality and Homogeneity of RAP Aggregates
### Definition and Origin/Production of RAP Aggregates
As a consequence of infiltration, it must be said that there is an important relationship between asphalt age and properties, such as penetration and viscosity. As asphalt ages and is exposed to the elements, it tends to harden and become brittle, resulting in an increase in viscosity and a decrease in penetration. For \begin{table}
\begin{tabular}{c c} \hline
**Element** & **Test Result (\% by Weight)** \\ \hline SiO\({}_{2}\) & 38 \\ Fe\({}_{2}\)O\({}_{3}\) & 26.8 \\ CaO & 16.3 \\ Al\({}_{2}\)O\({}_{3}\) & 11 \\ SO\({}_{3}\) & 2.9 \\ TiO\({}_{2}\) & 1.8 \\ K\({}_{2}\)O & 1.73 \\ MnO & 0.585 \\ SrO & 0.37 \\ CuO & 0.13 \\ V\({}_{2}\)O\({}_{5}\) & 0.11 \\ BaO & 0.2 \\ Re\({}_{2}\)O\({}_{7}\) & 0.06 \\ ZrO\({}_{2}\) & 0.055 \\ ZnO & 0.045 \\ \hline \end{tabular}
\end{table} 
Table 2: Chemical composition of RAP [33]. this reason, when evaluating the potential of a waste material to leach chemicals to the environment, a number of approaches may be employed. The study reported by [PERSON] at al. [42] found that few pollutant chemicals leached from the stocked RAP and no organic chemicals or heavy metals were found. This indicates that RAP, under most regulatory policies for beneficial reuse of waste in the environment, would pose a minimal risk from a leaching standpoint. Risk evaluation tools, like IWEM (US EPA's Industrial Waste Management Evaluation Model) used by [PERSON] et al. [43], could be used to provide estimates on the content of chemical compositions and to evaluate what types of controls may be necessary to verify potential environmental risks. Such estimates can then be supported by field monitoring in order to make definitive conclusions on the actions to be taken. The use of IWEM in [PERSON]'s study identified, however, some limitations when simulating highly soluble (\"wash-off\") constituents that leach in the short-term and quickly deplete from RAP in the long-term, which could lead to an overestimation of the potential risk. A deeper study of factors that affect RAP leaching, methods of test, and risk assessment approaches can result in a better implementation of RAP and in a maximization of RAP reuse without any type of pollution risk on environment and human health. In Italy, the leaching test becomes fundamental to define the \"bituminous conglomerate granulate\" stated in the Ministerial Decree n\({}^{\circ}\)69 of 28 March 2018 [52]. In this sense, it is important to distinguish the \"bituminous conglomerate\" and the \"bituminous conglomerate granulate\": the first one indicates the unprocessed waste material, while the second one is the definition given to the end of waste (EOW). The EOW material is the waste material that has been processed and has undergone one or more recycling process in order to be used as recycled aggregate. The recycling process includes [53]:  
* Crushing, aimed at obtaining a reduction in the size of the waste;
* Separation, to eliminate unwanted materials in the final product;
* Screening, aimed at separating the grains based on their size to obtain homogeneous particle size fractions. According to the Italian Ministerial Decree n\({}^{\circ}\)69 [52], once the bituminous conglomerate undergoes the recycling process, it must be declared as \"granulate of bituminous conglomerate\". This happens when the following requirements are fulfilled. * The bituminous conglomerate granulate can be used in bituminous mixtures obtained by hot/cold mixing system, and for the production of aggregates to be used in road construction [54]. * The requirements indicated by the standards EN 13242 [54] or EN 13108-8 [55] should be respected (as a function of the intended use).