# Limitations on the Use of Recycled Asphalt Pavement in Structural Concrete
## 3 Quality and Homogeneity of RAP Aggregates
### Minimum Requirements in Italy for RAP Aggregates to Be Used in Concrete  
As mentioned previously, the harmonised standard EN 12620 [58] contains all the essential characteristics with the relative test methods necessary for the assessment of aggregates for concrete. In Italy, the national law for construction (NTC 2018 [70]) imposes the use of this harmonised standard for the qualification of all types of aggregates and refers to the minimum requirements included in the national standards UNI 8520-1 [78] and UNI 8520-2 [79], which are strictly connected to EN 12620 [58]. The list of essential characteristics according to EN 12620 and the relative requirements set up by UNI 8520-1/2 [78,79] is reported in Table 4. Among all the essential characteristics reported in Table 4, a higher focus will be given to the most influential characteristics of the aggregates on the performance of concrete, i.e., the aggregate size, shape and density, resistance to fragmentation (crushing value), and water absorption. Other properties, like durability against freeze-thaw and volume stability, are surely important; however, no information has been found in the literature for RAP aggregates according to the European methods. Starting from aggregate size, EN 12620 [58], in terms of coarse aggregates, requires respecting a ratio between the maximum sieve size (D) and the minimum sieve size (d) equal to 1.4. From the experimental data drawn up from literature [23], it can be noticed that this ratio is generally respected in RAP aggregates. Furthermore, it is known that the distribution of particle size becomes important when the aggregate is used in concrete and it influences its water demand, cohesion, bleeding and the segregation phenomena [75]. In the characteristics related to the grading analysis, it must be evidenced that in UNI 8520-2 [79] there are no references for recycled aggregates origins, which can be considered a limit when trying to prove the different grading size of the aggregate. Aggregate shape is also decisive for workability. Rounded aggregates generally allow a better workability. For this reason, it is important to define the flakiness (FI) [80] and the shape index (SI) [81] of aggregates to prevent any workability issues like the production of concrete with segregation and high sand demand. Low values of FI indicates a low proportion of elongated aggregates, while high values of FI indicates a high proportion of elongated aggregates. Data from literature [6,44] evidence high variability and this is probably due to the origin of RAP. For this reason, and as it can be seen in Table 4, FI varies from 9% to 20%. Aggregate specific gravity can be defined as the weight ratio between aggregate and water at similar volumes [6]. The specific gravity of aggregate will affect the value of density. In RAP materials that contain aggregate and aged bitumen, the density of RAP will be affected by their components and composition. It can be understood that the presence of aged bitumen will reduce RAP density. In UNI 8520-2 [79], in terms of density, there is a clear specification for recycled aggregates based on \"type A\" and \"type B\", which differ from each other in the percentage content by mass. Generally, the minimum density requirement (in terms of oven-dried particle density) is 1700 kg/m\({}^{3}\) and from the values reported in the papers analysed [3,6,23], RAP aggregates have a density between 2186 and 2371 kg/m\({}^{3}\). These results demonstrate that RAP density respects the minimum requirements established in Italy.