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Bitumen for paving applications

30/01/2017 15:08

Bitumen: a binding decision

As the demand for economic and sustainable road networks increases around the world, choosing the right bitumen is more important than ever in ensuring optimum performance.

For nearly a decade, budgets for road maintenance and construction have declined across most of Europe. This makes managing the existing assets crucial, as a poorly-maintained road is likely to require more investment in the long term. For effective pavement management, it is important to consider not only the maintenance technique but also the asphalt mixture or surface treatment used. This is because the components within the mixture – that is aggregate and bitumen – contribute to the end performance of the end product, and ultimately the life of the road.

Building a strong foundation

All roads are not the same, and more importantly they are used differently, with a wide variation of users and client demands. These demands also increase and change over time as our needs become more complex. Therefore, when maintaining an existing road, it must be improved upon to handle greater traffic volumes and loads, as well as to accommodate budgets and future sustainability requirements. “Choosing the right bitumen does a lot to delay the next maintenance cycle, and as a consequence you will have a lower cost over the lifetime of the road,” says Wim Teugels, Crude and Feedstock Specialist at Nynas.

All in the mix

Bitumen can exhibit certain properties, as can a particular aggregate, but it is the material combination that determines the end performance of the asphalt mix. The combination of mineral aggregate and bitumen has to be evaluated prior to job site construction, as this is where binding takes place and also where the asphalt mixture’s end performance properties are determined. “The right mixture design is a key element in providing the optimum solution for specific situations,” explains Wim Teugels.

There is a whole set of different factors that determine whether a specific binder is appropriate for a particular application or not. Criteria like the intended use of the road, environmental conditions and expected traffic levels all have an influence on the selection process.

If a road needs to carry heavy traffic, a binder with higher stiffness at high temperatures will be more appropriate. However, the same binder may not be suitable for roads located in a much colder environment, as they could run the risk of being too stiff at low temperatures, which can lead to cracking. Finding the right balance requires a carefully considered approach from the pavement and asphalt mix design engineer.

Fit for purpose

Test information related to the bitumen and asphalt mixtures are typically used in the selection process, but these are done in laboratory environments. The real test is to evaluate how the asphalt mix behaves after several years and to use this experience to enhance the selection process for the optimum binder related to specific end performance requirements. The industry has been recognising this more and more in recent years, with an increasing desire to communicate the particular performance properties of different bitumens to assist in creating the right mix for the job.

When continually testing the job site material in a lab it is important to have knowledge of the source of material. Using bitumen that has already been tested allows for a more practical indication of performance using data from previous experiences. Information can be made more reliable and allow for better predictions if the quality of the bitumen remains consistent.

As the trend for testing and developing performance-related properties evolves, it will become easier to access the relevant information needed, as having historical data on consistent materials can improve the accuracy of data interpretation. “The important thing to remember is that although all binders within the specifications are fit for purpose, some are a lot more fit for your very specific purpose than others,” Wim Teugels concludes.

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