Britpave: The British In-Situ Concrete Paving Association

Deteriorating black top roads offered a whitetopped future

Used extensively in the USA and increasingly on continental Europe, whitetopping offers the beleaguered UK road network a fast, economic, sustainable and long-term reconstruction solution with surprising pollution eating potential reports Rory Keogh for Britpave, the UK infrastructure trade association.

Whitetopping refers to the use of a concrete overlay to resurface an existing distressed pavement surface. The technique has a long history with the first thin white topping overlay being placed in Indiana, USA, in 1918. However, it is only over the last ten years as a result of new technology that use of the technique has significantly increased as hard-pressed national and local road authorities recognise its potential of as a long-term maintenance and reconstruction solution for their crumbling road networks.

The resurfacing technique involves bonding a new concrete overlay onto the existing road. In contrast to other repair and reconstruction methods, if the sub-structure foundation is still sound then no part of the existing road has to be removed. Deformations in the existing surface are milled level and the surface cleaned ready for the new concrete overlay. Not having to dig up the top layer of an asphalt road surface provides substantial time and cost savings. These savings are increasingly attractive to cash-strapped road authorities and to public/private partnership infrastructure models which have a focus on long-term life-cycle costs and performance.

There are two types of whitetopping:

• Ultrathin whitetopping (UTW) with a concrete surface thickness ranging from 50 to 100mm
• Thin whitetopping (TWT) with a concrete surfaced thickness ranging from 100 – 150mm

Thin whitetopping is used where greater strength is required particularly for heavily trafficked roads. Ultrathin whitetopping is designed to renew the surface of worn roads but not to increase structural capacity. Both types offer cost, safety, performance and environmental benefits.

At current prices, concrete often costs less than asphalt. In addition to first cost savings, concrete offers better whole life cost as it requires less maintenance expenditure and provides greater long-term performance. Indeed, whitetopping can extend the life of a road by up to 30 years.

By renewing the road surface, whitetopping improves safety. Not only does it eliminate the rutting and rippling hazards of a deteriorating asphalt road surface, whitetopping provides a much lighter road surface that reflects up to three times more light than asphalt. This not only improves road safety but can also be used to reduce street lighting costs. It has been estimated that in cities whitetopping could reduce the level of street lighting by up to 24%.

Whitetopping also offers a wide range of environmental benefits. Not least of which, according to research carried out by the American Concrete Pavement Association, are fuel savings of up to 20% compared with an asphalt flexible road. Unlike asphalt, concrete contains no VOCs and so does not emit toxins into the atmosphere. In addition, the albedo value of whitetopping, or ratio of surface reflected solar radiation, is much higher than that for asphalt. For a new concrete surface the albedo value is 0.35 – 0.4 compared to 0.05-0.1 for new asphalt. By reflecting more solar radiation, a concrete road surface with a higher albedo value helps to minimise the formation of urban heat islands thereby reducing the energy demands for cooling and air-conditioning.

New developments in concrete technology offer whitetopping a further exciting environmental benefit: the ability to absorb air pollutants. Vehicle exhaust includes a high level of nitrogen oxide air pollutant. However, the addition of titanium dioxide to the concrete means that it actually eats these pollutants. Titanium dioxide (TiO2) is a photocatalytic material that reacts in sunlight to absorb nitrogen oxides and convert them into harmless nitrates that are washed away by the rain. Scientists at Eindhoven University of Technology in the Netherlands have found nitrogen oxide reductions of 35 – 40% in areas paved with concrete featuring TiO2. Researchers at the Public University of Navarre, Spain, are developing a nonoparticle coating for concrete that uses photocatalytic reaction to disintegrate certain pollutants. They report that the coating can reduce 90% of nitrogen oxides, 80% of hydrocarbons and 75% of carbon monoxides. The use of such treated whitetopped road surfaces, particularly in urban areas, therefore offer the tantalising prospect of roads eating the pollutants from the very traffic that use them.

Whitetopping is not new. Indeed, it has been around for nearly 100 years. What is new is the increased recognition of the advantages that this road reconstruction techniques offers. These advantages of cost savings, increased road safety, long-term performance and unrivalled environmental benefits are ones that the hard-pressed UK road authorities would be well advised to examine.

For further information on road construction and maintenance visit: www.britpave.org.uk or email: info@britpave.org.uk