The bridge builder
When a new bridge is built it involves major investments, strict quality requirements and an ability to efficiently coordinate different technical teams.
The demands placed on the asphalt on a bridge are in some ways different from those for a normal road. In addition to withstanding deformations and cracks, the asphalt must also protect and seal the underlying steel or concrete structure from water and road salt. There are also the strong loads that arise on a bridge as a consequence of vibrations and the effects of wind and weather.
“Another challenge is that extremely strong forces can build up in the interface between the asphalt surface and the bridge’s bearing structure. Even if you’ve laid an asphalt surface and followed all the rules, there can be problems with load resistance and friction if there are any deficiencies in this material transition,” says Professor Nicole Kringos, Director of the KTH Road2Science Center.
This tangible complexity means that there must be a focus on the whole.
“Put simply, it means a pavement system that consists of several layers with a division of function,” continues Nicole Kringos. “Such a system can include not only the asphalt, but also primers and paving membranes, bond coats and paving fabrics. Polymer modification is also often used now.”
Extremely strong forces can build up in the interface between the asphalt surface and the bridge’s bearing structure.
Despite the load, the original asphalt pavement is still in place. It consists of two layers – underneath, a 30 mm mastic asphalt (PGJA11) and then a surface course of 45 mm with an SBS-modified stone mastic asphalt (ABS16), which also has a fibre additive to make the binder thicker.
The polymer-modified binder used on the Öresund Bridge is the same kind – Nynas Endura F2 – as the one used in several other major Swedish bridge projects, including the High Coast Bridge and the Sundsvall Bridge.
Another high-profile bridge project project is the Queensferry Crossing Bridge in Scotland, the longest three-tower, cable-stayed bridge in the world. The 2.7 km long bridge is the centrepiece of a GBP 1.3 billion (EUR 1.44 billion) upgrade to the transport corridor north of Edinburgh that also includes 22 km of new roads and motorway upgrades.
Through a supply contract with the asphalt producer and surfacing contractor Aggregate Industries, Nynas played an important role in this major infrastructure project. This included delivering significant volumes of polymer-modified, penetration and EME grade bitumen throughout the duration of the works over a two-year period. The main demand was for Nypol 103 and Nypave FX 20. These were used respectively in the TS 2010 surface course/bridge-deck and the base/binder course in the interconnecting road network.
St George's Bridge in Doncaster can be found 70 km east of Manchester. When the porous asphalt on the bridge deck needed replacing a couple of years ago, engineers chose an asphalt called Steelflow from asphalt producer Steelphalt. By combining steel slag with a polymer-modified bitumen – in this case Nypol S 89 – they achieved an asphalt surface that was both durable and elastic as well as having the enhanced flexibility needed on a lively bridge deck.
