The asphalt paving industry has had great success with recycling asphalt pavements. Recycling of asphalt pavements dates back to 1915 (Kandhal & Mallick, 1997), but it did not become a common practice until the early 1970s when asphalt binder prices increased up as a result of the 1973 Arab Oil Embargo. The asphalt paving industry reacted to this situation by developing recycling technologies that helped reduce the demand on asphalt binder and thereby reduce the costs of asphalt paving mixtures. Many practices initially developed during that period are still in use today and have become part of routine operations for pavement construction and rehabilitation.
Motivations for recycling include economic savings and environmental benefits. Recycling reduces the demand for non-renewable natural resources (both bitumen and aggregates) and thereby also reduces the energy and emissions associated with the extraction and transportation of those raw virgin materials. Recycling also avoids landfilling of old pavement materials removed during rehabilitation. The economic benefit results from materials cost savings resulting from a replacement of a portion of virgin aggregates and bitumen. The bitumen and aggregate components of an asphalt mix represent the greatest proportion of the cost of pavement construction.
For more than three decades, two guiding principles of asphalt recycling have been:
1) Mixtures containing RAP should meet the same requirements as mixes with all virgin materials
2) Mixes containing RAP should perform equal to or better than virgin mixtures.
Recent surveys of the asphalt pavement industry have reported that across the world the average RAP content in new asphalt mixes has steadily increased in recent years with the average RAP content to over 25%. However, the percentage of RAP used in new plant mix varies considerably by countries.
Quality recycled mixes have been successfully designed and produced for many years. The proof is in performance: a recent study comparing the performance of recycled versus virgin mixes based on Long-Term Pavement Performance (LTPP) data from 16 U.S. states and two Canadian provinces shows that overlays containing at least 30% RAP performed equal to overlays using virgin mixtures (Carvalho et al., 2010; West et al., 2011). At the NCAT Test Track, test sections containing 50% RAP using standard Super pave mix design procedures for each layer outperformed companion test sections with all virgin materials in all pavement performance measures through five years of heavy loading (West et al.,
2012; Timm et al., 2016).
The results of observed pavement performance lead to trust and use high RAP in future projects.
