A preliminary study on the characterization of Recycled Asphalt pavement (RAP)

The replacement of natural aggregates with recycled ones for concrete production is of vital importance in view of increasing the sustainability of construction materials in accordance with the Circular Economy. The use of crushed Recycled Asphalt Pavement (RAP) as aggregates for concrete will allow the production of more sustainable materials in the construction field. However, chemical, physical and mechanical characteristics of RAP aggregates shall be investigated to optimise their use for concrete production. This issue is one of the tasks of the research project “Sustainable concrete made with recycled asphalt pavement (RAP-CON)” granted by Fondazione Cariplo, currently ongoing. This study reports the first results on the characterization of five types of RAP collected from different Italian Highways. Several properties of RAP as aggregates for concrete were investigated in terms of microstructure, dimensional stability and durability. In particular, morphological observation was carried out by optical and scanning electron microscopy, while open porosity and pore size distribution was evaluated by mercury intrusion porosimetry. Dimensional stability was assessed by preparing cementitious mortar and concrete samples, following the accelerating curing described in EN 1367-4. Lastly, durability was investigated in terms of resistance to freeze and thaw cycles performed in accordance with EN 1367 (parts 1 and 6) in presence of distilled water and salts (1 wt% NaCl solution), respectively. It was found that RAP is a suitable material for aggregates in concrete. Depending on the adhesion between the bituminous binder and the natural aggregates, different durability performances can be achieved. Finally, different results have been obtained as function of types of RAPs, indicating that their characterization before concrete preparation is an important step to ensure the performance of the final product.