# Limitations on the Use of Recycled Asphalt Pavement in Structural Concrete
## 4 Mechanical Behaviour of Concrete Containing RAP
### Influence of the Percentage of Substitution of RAP on the Mechanical Properties of Concrete
Furthermore, as was said before, the standard refers generally to the harmonised European standard EN 12620 for the qualification of coarse recycled aggregate for concrete. Differently to the NTC 2018, the previous version of the standard published in 2008 (NTC 08 [106]) referred clearly to EN 8520-1/2 [78; 79] in the definition of additional chemical and physical requirements that recycled aggregate should respect in the function of the intended use of concrete, the maximum percentage of substitution and the class of resistance of concrete. In particular, for the maximum percentage of substitution, EN 8520-2 refers to UNI 11104 [107] for additional information compared to those reported directly in NTC 08. The additional information on recycled aggregate is currently missing in the new standard NTC 2018 and the reference to UNI 11104 can only be inferred because EN 8520-2 is only considered a useful reference by NTC 2018. Therefore, it cannot be certainly said whether UNI 11104 is a mandatory reference and therefore a regulatory gap exists in the current law which should be further investigated. Despite the issue just evidenced, the percentage of replacement indicated in UNI 11104 is a function of the type of aggregate, the class of resistance of concrete and the class of exposure (Table 8). The use of 100% replacement is allowed for concretes with a strength class lower than C8/10. If one refers to UNI 11104 to define the percentage \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Type of Aggregate**} & **Class of Use of Concrete** & **Types of Class of Use of Concrete** & **Class of Resistance of Concrete** & **Percentage of Substitution of Aggregates** & **Applications** \\ \hline \multirow{6}{*}{**RA**} & & GEN 0 & C6/8 & \multirow{6}{*}{100\%} & \multirow{6}{*}{100\%} & \multirow{6}{*}{100\%} \\  & & GEN 1 & C8/10 & & \\  & & GEN 2 & C12/15 & & \\  & & GEN 3 & C16/20 & & \\ \cline{2-6}  & & \multirow{6}{*}{RC} & RC20/25 & C20/25 & \multirow{6}{*}{20\%} & \multirow{6}{*}{Reinforced concrete} \\  & & RC25/30 & C25/30 & & \\  & & RC28/35 & C28/35 & & \\  & & RC30/37 & C30/37 & & \\  & & RC32/40 & C32/40 & & \\  & & RC35/45 & C35/45 & & \\  & & RC40/50 & C40/50 & & \\ \cline{2-6}  & & RC40/50 XF & C40/50 & 0\% & \\ \cline{2-6}  & & FND2 & C25/30 & & \\  & & FND2Z & C25/30 & & \\  & & FND3 & C25/30 & & \\ \cline{2-6}  & & FND4 & C25/30 & & \\ \cline{2-6}  & & FND4Z & C25/30 & & \\ \cline{2-6}  & & FND4M & C25/30 & & \\ \hline \hline \end{tabular} Additional specification requirements and permitted applications to be assessed on a case-by-case basis.  
\end{table} 
Table 7: Percentage of substitution according to British standards (BS 8500-2) [105]. of substitution, the Italian limitations are more restrictive than the European ones: for example, the maximum percentage of substitution for a concrete with a class of resistance lower or equal to C30/37 and an exposure class X0 is 30% for UNI 11104 [107] while it can reach 50% for European standard when a \"type A\" aggregate is used. Experimental studies are needed in support of a possible use of a higher percentage of substitution than what is indicated in the Standards to take advantage of RAP aggregates and to avoid the deposition of unused material that could fit the minimum requirements requested in concrete.