From waste to resource: The role of bitumen technology in recycled roads
Feb 14, 2019
With the global growth in transport, there is greater demand for the infrastructure sector to deliver cleaner paving solutions, from roads to runways. Asphalt, one of the world’s most recycled materials1, has been exemplary in demonstrating the circular economy in action. The increasing interest in asphalt recycling and the use of Reclaimed Asphalt Pavement (RAP) is rooted in benefits that are well-documented. In addition to reducing construction costs, recycling asphalt can also help to conserve resources.
Impressive results have been achieved in countries such as Germany, where around 90%2 of asphalt is reclaimed and used to construct new and maintain existing roads. Outside of Europe, sustainable construction practices, including the circular economy, have also become a key focus area as society looks to design waste out of the system and keep products and materials in use. In China, for example, the 13th Five-Year Plan3 mandates this new regenerative system at all levels in society to reduce waste and increase resource efficiency.
Embracing the circular economy and maximising the volumes of RAP in new road construction will therefore remain a global priority, but this is only half the story. Sustainable, modern roads must be able to withstand ever-increasing traffic loads and be built with quality and end-performance in mind. This durability is largely impacted by the quantity and quality of a binder used in the asphalt mixture.
To meet the increasing demands of everyday road users in a cost-effective and resource-saving way, reclaimed asphalt needs to be used in combination with conventional bitumen, warm mix asphalt or polymer modified bitumen. However, when using higher quantities of RAP in the asphalt mixture, there are factors that should not be overlooked.
First, as bitumen ages in the pavement it becomes progressively more viscous, hence to achieve the required rheology a lower viscosity bitumen is required. In fact, higher RAP contents will require progressively lower viscosity bitumen in order for the mixture to meet the required final bitumen grade specified for the mixture.
Greater levels of RAP can also make asphalt mixtures more challenging to compact, which can sometimes lead to increased mixing temperatures. Lower mixing temperatures can be achieved by using binders with special additives resulting in reduced CO2 emissions during mixing, while also allowing the earlier reopening of roads to traffic than when using conventional bitumen, so reducing disruption for road users.
Most importantly, these enhanced bitumen products give customers comfort that a road built with a proportion of RAP can deliver very high performance and durability, matching that of conventional asphalt without RAP. Shell has spent years studying the chemistry of bitumen, as well as thoroughly testing bitumen blends with RAP. The result is the development of a specialised polymer modified bitumen, Shell Cariphalte RC, which is an innovative and cost-effective solution, designed for the application and usage of RAP in high-quality surfacing materials. The product not only improves workability but promotes better adhesion and resistance to moisture damage compared when compared to conventional bitumen grades, providing greater durability of the finished asphalt.
Used in combination with RAP in base, binder and surface course layers, Shell Cariphalte RC and other premium products in Shell’s portfolio are being adapted by Shell’s global bitumen R&D centre in Bangalore, India, to render the solutions fit to meet both current and future challenges.
As the pressures on road use grow and the circular economy becomes an engrained approach to doing business, contractors, highway agencies and governments will increasingly seek solutions that maximise how effectively reclaimed asphalt is used. The latest technology and bespoke bitumen solutions can already support road constructors in the quest for making sustainable roads more cost-effective, without having to compromise the road’s performance.
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