# Limitations on the Use of Recycled Asphalt Pavement in Structural Concrete
## 2 Applications and Use of RAP Worldwide  
The majority of RAP is usually destined to return to the roadway structure. This is due to the RAP grading curve, which is characterized by a high percentage of fine and aged bitumen [6]. For this reason, this type of aggregate undergoes a sort of \"closed cycle\", returning again within the road construction, satisfying in this way the basic principles of the circular economy [7]. Indeed, when properly crushed and screened, RAP consists of high-quality and well-graded aggregates coated by asphalt cement that can be used in hot asphalt mix, cold asphalt mix, and asphalt concrete production for base and sub-base construction. In the last few years, studies have been conducted in order to prove the suitability of RAP, also for the production of structural concrete [3; 4; 5; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17]. Unfortunately, only a few results on the use of RAP in structural concrete are available. The analysis of the state of the art evidenced that the majority of papers investigate the use of RAP in asphalt mixture [6; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49] for roads and pavements. Considering the (not-exhaustive) list of examined papers (Table 1), more than half discuss the use of RAP in asphalt mixtures. According to [38], the percentage of RAP used in hot and warm mix asphalt (HMA/WMA) and cold mix asphalt (CMA) in Europe, respectively 51.4% and 3.81%, is significantly higher than the RAP percentage used for other purposes, such as coarse aggregate in structural concrete (about 2%). Furthermore, the amount of RAP deposited on landfills is still high (9.63%), surpassing the percentage of RAP used for structural concrete. In Italy, RAP is still not considered as a valuable resource. According to the Italian Roads and Bitumen Association (SITEB), Italy has made important progress in the reuse of milled asphalt on pavement roads, increasing it from 20% (2014) to 25% (2018) (see Figure 1) [50]. However, Italy still stands behind other countries in Europe that boasts an average of 60% [50]. The countries considered to be the most virtuous, on the other \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Applications**} & \multicolumn{2}{c}{**\% of Papers**} & \multirow{2}{*}{**Main Conclusions**} \\  & **(N\({}_{\text{tot}}\) = 46 Papers)** & & \\ \hline \hline \multirow{4}{*}{Pavements/roads} & \multirow{4}{*}{72\%} & \multirow{4}{*}{\(\bullet\)} & Compressive strength, splitting tensile strength, flexural strength and elastic modulus decreases as the percentage of RAP increases. \\  & & & \(\bullet\) \\  & & & \(\bullet\) \\  & & & \(\bullet\) \\  & & & influences the fatigue resistance. \\  & & & \(\bullet\) \\  & & & \(\bullet\) \\  & & & influences compressive strength, splitting tensile strength, flexural strength and elastic modulus. \\  & & & \(\bullet\) \\  & & & \(\bullet\) \\ \end{tabular}
\end{table} 
Table 1: Use of RAP in different fields and the main research results. hand, are the United Kingdom (90%), Germany (84%), Spain (83%), and the Netherlands (71%) [50]. In the United States, the discrepancy between the use of RAP in HMA/WMA and for the other purposes is even more significant, since the percentage of RAP destined to the production of HMA/WMA reaches the 81.3% of the total production of RAP [51]. The still limited use of RAP in road construction is justified by the reduced mechanical properties of asphalt mixes containing this recycled material. Indeed, replacing virgin aggregate by RAP in asphalt mix can cause a decrease in compressive strength, flexural strength, splitting tensile strength and modulus of elasticity [23; 29; 30; 39]. When included in asphalt mix, RAP also influences fatigue and thermal cracking resistances [38] while showing an increase in the stiffness compared to a mix with virgin aggregates. According to [PERSON] et al.