Politique Internationale — What exactly is RAP, short for Reclaimed Asphalt Pavement? Is it innovative technology? How is this a gain in terms of the circular economy?
Brent Morrey — RAP has been around for over 50 years as a recycled aggregate used within asphalt, so technically this is not an innovative technology. The principle is simple: the old pavement is considered as a natural deposit of aggregates (and bitumen) that can be recovered in place. The process consists in incorporating, within the material obtained by crushing the old pavement, a cement, a hydraulic road binder or a hydrocarbon binder and, possibly, a grading corrector as well as water and to mix them intimately in situ or in a plant (stationary or mobile), until obtaining a homogeneous material. It can also be added in a new mix during production in a plant, to replace part of the virgin aggregates and part of the bitumen, because RAP contains bitumen that can be reused.
The benefits regarding circular economy are multiple: less haulage of virgin aggregate materials – closer to market – lower carbon footprint; less virgin asphalt cement – closer to market – lower carbon footprint. Traditionally, this material may have gone to dump, but now asphalt is the most recycled product in the world.
We can talk about innovation in terms of environmental progress. In the beginning, RAP was used primarily as an economic driver while today the environmental benefits (or carbon footprint reduction) are much more recognized.
P. I. — Are these processes used everywhere, by every contractor?
B. M. — Each state jurisdiction specifies the amount of RAP that can be used in different types of HMA (Hot Mix Asphalt). For instance, some jurisdictions do not allow RAP in Stone-Matrix asphalt (eg. New York, California, Georgia, Pennsylvania). In conventional surface-course mixes, some will allow up to 30% RAP (eg. Virginia), and in base-course mixes some will allow up to 40% RAP (eg. South Carolina).
FAA (Federal Aviation Administration) – airport mixes – do not allow for any RAP.
To get the highest percentage of RAP, Colas in the U.S. uses a recycling agent (eg. petroleum-based oil or plant-based oil) to ensure the durability and performance in the road for HMA.
P. I. — What is the RAP of the future? What innovations can you imagine down the road?
B. M. — Future advancements would be to use “cold recycling” methods that would have the same performance as what is produced with a hot mix facility.
In a hot mix asphalt facility, we can use up to 40-60% RAP in a recycled HMA (hot mix asphalt) by reheating the RAP and then use either a petroleum based or plant-based recycling oil to improve the RAP binder and the resulting recycled HMA has the same performance characteristics as a virgin HMA. With cold recycling methods the benefit is no burner fuel is needed as compared to an HMA plant so we now need to research and develop the process(es) and type of recycling agents which will effectively result in a 90- 100% RAP cold recycled mix that can be used soon after being produced and after compaction, can be used as a wearing or base course and have the same performance characteristics and service life as conventional HMA.
P. I. — Do these techniques cost more?
B. M. — Current cold recycling methods do not add any costs, but it is certainly possible that future advancements to improve the performance could – however still lower to those incurred with a hot mix plant, and substantially lower carbon footprint (eg. less than 25kg CO2 per ton).
Ideally, the cost for cold recycled mix should be the same or lower than conventional recycled HMA. The real benefit will be the reduction in CO2 kg/t. It is probable the cost for this future recycling agent/flux oil will be more expensive in addition to the improved production process, however, the overall contribution cost should not make the total cold recycled mix cost more expensive than conventional recycled HMA. In the USA, there is a renewed focus on construction materials’ carbon footprint so anything to lower the carbon footprint is a benefit to the owner.