Coloured surfacings provide not just a decorative alternative to conventional asphalt applications but can also be used to improve visibility and reduce lighting levels within road tunnels.
Pressure on highway authorities to reduce costs and cut carbon emissions associated with street lighting have led many councils to switch off some lanterns at night along lesser used routes or at quieter times. Those responsible for road tunnels however have to exercise a greater degree of caution before suggesting changes to lighting levels, for fear of a negative effect on driver safety.
Specifying more energy efficient luminaires is one way to decrease the financial and environmental impact of lighting. But according to Shell Bitumen, tunnel managers should first of all consider laying coloured asphalt surfacing to improve visibility for motorists and allow lighting levels to be reduced.
The company manufactures a clear synthetic binder known as Mexphalte C into which a coloured aggregate and artificial pigment can be mixed to give a richly coloured or highly reflective road surface. Use of a light grey or white stone in addition to a similarly coloured additive can, the company says, help to improve visibility within highway tunnels.
“Using Mexphalte C to produce an asphalt surfacing within a road tunnel can allow every other light to be switched off without reducing levels of visibility,” says Shell Bitumen’s Technical Manager Lee O’Nions. “Figures relating to the use of the binder in the Markusberg tunnel in Luxembourg, for instance, show big savings of around 40% in terms of electricity usage and a significant reduction in the need for maintenance associated with looking after so many lighting units.”
He adds that very light coloured asphalt manufactured with the binder has been proven to increase luminance within tunnels, compared to asphalt containing dark coloured aggregate.
One of the largest specifiers of the Mexphalte C binder is Tarmac, which uses it to produce a coloured asphalt surfacing known as Mastertint. Tarmac’s Special Products Manager David Parkinson agrees that UK highway authorities should seriously consider the use of coloured asphalts within tunnels. “When laid the product delivers a road surface with a very light appearance, which not only allows lighting levels within tunnels to be reduced but makes drivers feel safer,” he says.
Mastertint has been applied within a number of road tunnels throughout continental Europe but it has yet to be specified within a tunnel in the UK. But both Tarmac and Shell Bitumen are confident that the continued use of the material in other applications in this country, such as on busways, footpaths and public realm schemes (see story below), will lead to its wider application on highways including tunnels.
Shell Bitumen’s Mexphalte C binder can be used to produce asphalt of any colour. More vivid colours are usually achieved by teaming a pigment with an aggregate of a similar hue. Different grades of the binder are available including a polymer modified version used for enhanced durability for application in bus garages for instance, and a low temperature variety.
“The UK market has seen a dramatic increase in the use of coloured asphalt in recent times and the volume of clear binder we have sold has risen by 15% each year for the last three years,” says Mr O’Nions. “The next step for us is to encourage the binder to be used in asphalt specified more widely on highway carriageways.”
But he adds that extra care has to be taken when handling a clear binder to make sure quality levels remain high. “Companies producing asphalt surfacing using Mexphalte C have to ensure their plant and equipment are kept very clean otherwise dirty streaks may appear in the finished material.
“Other clear binders are available but Mexphalte C is one of the longest standing in its field, performs to a high standard and is used widely in materials that have to withstand heavy duty traffic,” Mr O’Nions adds. “Many of the alternative binders available are suitable for aesthetic use only.”
Rainbow of colours displayed around the UK
Recent uses of Tarmac’s Mastertint surfacing featuring Shell Bitumen’s Mexphalte C binder include application on a cycle path outside the Westfield Stratford shopping centre in east London.
Other locations where the material has been specified include Birmingham, where around 2500t of Mastertint containing a green pigment and green aggregate was laid on bus lanes. At London Zoo over 80t of the material containing a whole spectrum of colours including oranges, blues and reds were laid on various pedestrian footpaths. And a series of bright grey and white surfaces were created using a low temperature version of the material at a motorway service station in north Yorkshire.
“Coloured asphalts are proving popular in public realm schemes and there is definitely a value engineering benefit to specifying this sort of surfacing,” says Tarmac Special Products Manager Kiren Sidhu. “When times are hard customers are looking more closely at the longevity of materials and their durability. Mastertint compares well on both fronts to other surfacing products like block paving and resin bound material.”
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