Successful use of polymer modified binders to improve the durability of highway asphalt surfacings could lead to the greater use of enhanced bitumen for airfield applications.
Extra strength material continues to prove its worth on highway surfacing contracts where clients are keen to invest in durable products that stand the test of time. This is especially true north of the border where TS2010 – a new specification designed to ensure thin surfacings perform well – has been introduced by Transport Scotland.
Now the technology used to provide road asphalt with resistance to deformation and cracking is being developed further with a view to enhancing the performance of airport taxiways and runways too.
High performance products developed by Nynas which are being modified for application on airfields include the binder Nynas Endura Z2. The binder has a good track record on roads and for heavy duty applications such as at docks. One of the earliest contracts was to resurface Oxford Circus and Regent Street in London and more recently has been used to improve the condition of highway within a tunnel at the Dartford Crossing (see story below).
Polymer modified material has been employed on airfields in the past but is not specified as frequently as it is on major highways contracts. A series of successful aviation contracts could change all that.
“Polymer modified binder used within a stone mastic asphalt ensures that a surfacing material has added cohesion and adhesion – and this is particularly important for airfields,” says Nynas asphalt engineering support manager Jukka Laitinen. “We have carried out a comprehensive set of specialist tests, which have included low temperature indirect tensile strength tests after ageing at -18°C. Our modified binders may one day be approved for use on military runways.”
Nynas Endura Z2 has been designed to increase the flexibility of a surfacing to resist loading and sheer forces. For airfield applications it can protect asphalt from rutting – for instance – caused by tightly turning aircraft using taxiways at low speed. The binder can be mixed with hardwearing aggregate to produce an SMA surface course and binder course. Asphalt containing the modified binder can also be engineered to provide enhanced load spreading properties and have improved shear and scuffing strength compared to a standard SMA.
Recent developments with polymer modified binders have also allowed bitumen suppliers like Nynas to develop blends for thin surfacings – such as Nypol 103 – that meet tough new standards including Transport Scotland’s TS2010 specification, written to improve the performance of surfacings in Scotland. Asphalt that meets TS2010 must demonstrate that it is resilient, serves for a long time and provides beneficial surface characteristics from day one. In addition, a thorough dusting of grit on material containing Nynas’ binder ensures the very best of early life resistance to skidding.
Nynas’ Scottish Area Sales Manager Nigel Hardy says: “Our Nypol 103 is a highly modified elastomeric polymer binder with exceptional resistance to permanent deformation and cracking. These characteristic mean it is particularly well suited to the kind of durable asphalt that TS2010 is intended to produce.”
Dartford makes use of Endura Z2
Nynas Endura Z2 binder – which is being developed for heavy duty applications including airfield use – was specified last year within new surfacing laid inside the furthest upstream of Dartford Crossing’s two northbound tunnels.
The tunnel in question is the one that all the heavy goods vehicles use – generating exceptional loads and stresses – and was resurfaced during a total of 14 Friday and Saturday night possessions.
The tunnel deck – of precast concrete panels on elastomeric bearings – is lively and the loads imposed particularly heavy. As well as being durable and flexible, the Nynas Endura Z2 bound asphalt had to remain workable at relatively cool temperatures. Material could not be discharged straight into the paver by delivery truck, as headroom within the tunnel did not allow for tipping. Instead, the asphalt had to be taken in by dumptruck.
Each possession began (overall traffic levels permitting) at 20.00 when men, plant and materials poured into the tunnel’s portals, determined to get at least 100m of carriageway refurbished. Turn around had to be quick: the tunnel had to be reopened by 10.00 the following morning.
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