# 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
Aggregate size could constitute the main limit to the non-suitable use of RAP in the mix for mortars because RAP is generally not homogeneous and could not respect the grading requested by the standard. It should also be pointed out that in EN 13139 [63] there are no indications for recycled aggregates in the evaluation of total sulphur content. Furthermore, the content of organic material in the aggregates shall not influence the setting speed of the mortar by extending its time by more than 120 min. In terms of mechanical properties, the compressive strength of the specimens shall not decrease by more than 20% after 28 days, and this could be a limitation considering that a decrease in compressive strength has in general been evidenced for mortar containing RAP depending on the percentage of substitution [40,41]. All these aspects are relevant for the inclusion of RAP in the scope and, consequently, for the application, of this standard. Similarly, EN 13043 [64] specifies the properties of aggregates and fillers obtained from natural or recycled materials for use in bituminous mixtures and in surfaces for roads, airports and other areas subject to traffic. More precisely, this standard does not concern the use of RAP in milled bituminous conglomerates, thus imposing its exclusion if it is used as an aggregate (Table 3). Among the other harmonised standards listed in Table 3, EN 13242 [54] specifies the properties of aggregates obtained through a natural or industrial process or recycled for unbound materials and bound with hydraulic binders, for use in civil engineering works and road construction. By analysing the requirements reported in the standard, attention should be paid to the aggregate size, the content of water-soluble sulphate and the content of organic material, the latter to be evaluated according to EN 1744-1 [65]. Furthermore, the percentage of aggregates should not influence the setting speed of the mortar by extending its time by more than 120 min and the compressive strength of the specimens should not decrease for more than 20% after 28 days, similarly to what is reported in EN 13139 [63]. As mentioned previously, a deeper experimental investigation should be conducted to analyse if the inclusion of RAP in the mix design as an aggregate could influence the setting speed of the mortar and the compressive strength of the specimens. The standard EN 13242 [54] is generally associated to EN 11531-1 [66], which gives more indications on the classification of soils, on the designation of aggregates and their unbound mixtures, and on the criteria for compliance verification when used in civil engineering works and road construction. The other standards reported in Table 3, including the use of recycled aggregates, do not present any particular limitation to the use of RAP in the construction of railways (EN 13450 [67]), or for protective works as armourstone (EN 13383-1 [68]). When focusing on aggregates for concrete, EN 12620 [58] is the reference document for the characterisation and consequent CE marking of aggregates and EN 13055-1 [69] is the reference for lightweight aggregates for concrete. In Italy, the Technical Standard for Construction Works (NTC 2018 [70]), which is a national law, completely refers to EN