Abstract
Reclaimed Asphalt Pavement (RAP) material mainly consists of removed asphalt concretes from existing infrastructures and, to a minor extent, of wasted or rejected mixes during the production processes. Being composed of two valuable non-renewable resources, i.e., aggregates and bituminous binder, its conscious use can ensure the sustainability of asphalt pavement construction. Thanks to the use of RAP material in new asphalt products, the USA saved 4.1 million tons of virgin binder and 78 million tons of virgin aggregates in 2018. Therefore, the use of RAP for the production of new asphalt formulations at the top of the recycling hierarchy is preferable instead of being down-cycled in low-value applications. The RAP material represents one of the most re-used construction products worldwide; in 2018, approximately 88% wt. and 72% wt. of RAP were used in USA and Europe, respectively, as aggregates for Hot, Warm and Cold Asphalt Mixtures and for unbound layers. Several studies have revealed positive responses of the recycled asphalt mixtures with high or very high content of RAP. However, the common practices of many countries still limit the RAP content to a 15–20% wt., on average, in the recycled asphalt mixes. The amount of RAP in asphalt concretes can be significantly increased by applying good management practices of the RAP, either processed or not, as well as novel production technologies and advanced mix design approaches. This manuscript aims to summarize the state-of-the-art of use of RAP aggregates in new asphalt mixtures. The economic and environmental benefits are also discussed.
Highlights
The asphalt concrete removed from an existing road pavement is a fully recyclable material for construction [1,2]
The negative perceptions and the practical issues that limit the common practice to go beyond the average Reclaimed Asphalt Pavement (RAP) content of 15–30% wt. in HMA mixtures can be summarized in four categories that refer to the quality of the RAP aggregates, the technology of the production plant, the mix design methodology and the performances of the final mix containing RAP
Wt.) of RAP in asphalt mixtures, highlighting the possible limitations and restrictions related to the introduction of high quantity of RAP aggregates
Summary
The asphalt concrete removed from an existing road pavement is a fully recyclable material for construction [1,2]. Most of the guidelines and countries or state regulations, such as the European one (EN 13108-8), specify that RAP should be a ready-to-use constituent material for producing new bituminous mixes This statement may involve some additional operations, such as crushing, grading, fractionating and homogenization processes after the removal of the asphalt concrete. Four different techniques can be adopted to remove the existing bituminous layers of pavements and to recycle the obtained material, which are divided based on the energy input of the recycling process and the place where the RAP is used for the production of new materials. The former category can involve the heating of any materials, while the latter can imply the transportation of the materials. This review will focus on hot in-plant recycling of asphalt mixtures containing RAP to represent a complete and extensive overview of the use of RAP, highlighting the related benefit and possible constraints
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