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Hard Wear

Need to get more wear out of your road surfacing? Need to lop a third off your total highway maintenance budget? Paul Thompson discovers how it can be done with a new road preservation system that is helping with the upkeep of the M40.

In these times of economic belt-tightening, everyone is looking for the best way to make a silk purse from a sow's ear – or at least they should be. Contractor, consultant, private sector, public sector – all are waking up to the effects the global economic slump is having on the industry.

In a world where budgets are shrinking and companies are expected to reduce waste and improve their environmental credentials, the time is right for any system or product that can boost these aspects. Of course making a spectacular financial saving helps too.

Now contractors, highway network managers and local authorities have the opportunity to prolong the life of road surfaces, cut down on the amount of newly quarried stone aggregate needed and slash budgets by a third.

Buckinghamshire based surfacing repair and preservation firm ASI Solutions has been given the all clear to use its Rhinophalt road treatment system on the motorway network after four years of trying to gain clearance through the Highways Authorities Product Approval Scheme (HAPAS).

UK Highways (M40) holds the contract to design, build, finance and operate the M40 motorway between Birmingham and London and through maintenance subcontractor Enterprise it is using the Rhinophalt system to help prolong the life of the motorway surface.

In a deal which will see most of the 150km long M40 have its wearing course treated over the next three years, Enterprise and its contracts manager Darren Jones will oversee the spraying of some 3M.m2 of surface course.

"In some places the quality of the surfacing has degraded so much that we can't treat it. It will be fully reconstituted in those areas," says Jones.

The preservation system is a solution rich in pure mineral asphalt which is sprayed onto the road, locking in all the chemicals which help keep the road surface flexible and reduce the likelihood of potholes developing. A fine abrasive grit is then applied (see box).

The two elements of the preservative are applied concurrently from a single pass of an application truck travelling at 6km/h.

For such a simple system the benefits can be profound, says ASI business development manager Steve Isaacs. He claims the initial application of the surface treatment costs 10% of the more traditional plane and relay treatments, but the problem is getting engineers and highway authorities to accept it.

"It is a new concept for engineers," says Isaacs. "It is not surprising that people have had difficulty accepting its performance and use. For years we have expected road surfaces to degrade, potholes to appear and for the road to be repaired. Now we have a system that can rejuvenate the surface before it begins to degrade."The Rhinophalt preservative system is at its most effective when applied soon after a road surface has reached its optimum performance. This is around a year after it has been laid, depending on traffic levels. Its use could help slash between 30% and 50% from conventional road maintenance budgets over a highway's 20 year design life, claims Isaacs.

"The road needs to get into top notch condition. There should be good skid resistance and the texture should still be perfect. By applying the treatment at that point and reapplying it every five years we should be able to maintain that level of performance throughout its design life," he says.

And while it can be difficult for highways authorities to argue that they need more cash to treat a recently opened road, there should be no excuse for failing to write road preservation into term maintenance contracts. Isaacs argues that by not doing so, highway authorities are wasting a golden opportunity to get more for their money while reducing environmental impact.

"What we have here is a sustainable road preservation system that will help reduce plane and relay repairs and help authorities meet environmental targets. By including the system in term maintenance contracts, area engineers can just call it off from the bill of quantities. It could be that simple," he says.

There are limitations to the system though. There is nothing it can do about poor design and its application season in the UK looks likely to be frustratingly short.

"It is not a structural system," says Isaacs, "It can't stop an inadequately designed, overworked section of road from degrading and there are laying limitations."

These limitations mean the Rhinophalt system cannot be laid at temperatures of 10°C and below or during wet weather. It will also mean keeping a close eye on conditions during the overnight laying shift on the M40 (see below). On this project the team is averaging 22,000m2 of treated road surface per 10pm to 6am shift. At that rate perhaps the six-month long laying season is not such a limitation after all.

Click here for M40 route map

A Solvent solution

Over time, bitumen based road surfacing begins to oxidise and degrade as it is exposed to ultra-violet light and road salts. When this happens the binder in the surfacing becomes brittle and cracks under load, eventually leading to the loss of aggregate within the mix.

But by dissolving gilsonite, a naturally occurring mineral asphalt of 98% purity, in a naptha and white spirit based category 3 solvent and applying it to the surface, engineers can slow this degradation.

The solvent softens the uppermost few millimetres of the bituminous binder. A layer of silica grit coats the surface immediately after the solution is applied. This helps regulate the speed at which the solvent evaporates, leaving behind the gilsonite-enriched layer of binder. It also adds skid resistance to the surface.

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