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Hammer time

After taking a fresh look at skid-resistance maintenance in Area 10, A-one+ is making carbon and cost savings. As NCE reports, it’s all being done with a recycling technique that has been around for years.

Delivering more for less is the latest, well worn mantra to the roads sector and it is setting a complex challenge for highways engineers.

Not only must they find ways of extending asset life and achieving best value from shrinking road maintenance budgets, there are also tough targets to meet on carbon and road accident reduction.

The challenge is turning the spotlight on a surface treatment as old as the modern engineered pavement itself - retexturing. This involves the use of an impact or abrading technique, such as bush hammering or shot-blasting, to improve pavement surface attributes.

“By extending the life of surfacing, it generates an immediate cost saving to the Highways Agency, freeing up funds for other priorities”

Phil Reynolds, A-one+

Retexturing is typically used to raise the friction (SCRIM) values of polished aggregate to improve wet weather skid-resistance. It can also increase texture depth - the channels between aggregate - to improve drainage and prevent aquaplaning. Cleaning is another application; removing surface residues such as oil, bitumen or binder film.

A key attraction is that it extends asset life by reworking the existing surface course, with no need to use fresh materials; recycling in its simplest form. It is also ‘green engineering’ already approved for highways use, being listed in the Highway Agency’s Design Manual for Roads & Bridges (DMRB).

Retexturing benefits

Retexturing is providing a number of benefits for A-one+ Integrated Highway Services, a Halcrow/Colas/Costain JV that is the Managing Agent Contractor (MAC) for Highways Agency Area 10.

The roads renewal team has been using state-of-the art bush hammering to complement resurfacing and high friction dressing (HFD) in maintaining skid-resistance across the Area 10 network at compliant levels.

Resurfacing will be carried out where sites require skid-resistance improvement and correction of pavement defects such as cracks, rutting, and potholes. In these cases, the laying of material will provide the best value solution for maintaining road surface appearance, performance and safety to required standards and extending asset life.

Retexturing becomes an option when the road simply needs improvement of surface friction to raise skid-resistance values to above the Agency’s specified investigatory level.

“This is a quick win in obtaining more for less in the present financial climate”

Phil Reynolds, A-one+

After trials 18 months ago, A-one+ has been selectively using KlaruwTex190 (K190) controlled mechanical retexturing, a computer-controlled bush hammering system from Dutch retexturing specialist, Klaruw. Work is carried out by Widnes-based Klaruw RMS, the company’s direct contracting operation in the UK.

The K190 process has key technical advantages. Treatment speed and pressure can be controlled, while ‘floating’ bush hammer tips adapt to pavement surface profile. This ensures consistent results even where there is deformation or wheel track rutting. Coverage can also be controlled, so that retexturing is targeted only where needed and double treatment is avoided. Unlike surfacing work, it is an all-year round process that can be carried out in almost any weather, including rain.

According to Klaruw, K190 bush hammering may extend pavement life by two to five years, or even more, postponing the need for higher cost interventions - overlay or inlay.

Longer life pavement

In terms of asset management, it provides an opportunity to extend pavement life while treating larger areas of the Agency’s network when compared to the higher cost of laying material treatments.

“Retexturing, when suitable, helps maximise the pavement area we can successfully treat to improve skid-resistance,” says Phil Reynolds, A-one+ roads renewal manager for Area 10. “By extending the life of surfacing, it generates an immediate cost saving to the Highways Agency, freeing up funds for other safety improvements and priorities.”

He points out that the bush hammering plant occupies less carriageway area than a resurfacing operation, creating more sharing opportunities for other work during planned traffic management closures. “This is a quick win in obtaining more for less in the present financial climate,” Phil Reynolds adds.

The launch of the Road Surface Treatments Association (RSTA) carbon calculator, developed in association with Nottingham University, now offers a gauge to the likely carbon savings from retexturing. The calculator estimates that Klaruw’s process reduces the ‘Cradle to Laid’ carbon footprint of restoring skid-resistance by potentially up to 90% compared to a 40mm asphalt thin surfacing.

Carbon savings

It generates encouraging numbers on the likely carbon savings made from the 85,000m2 of retexturing completed in Area 10 during 2010/2011.

Phil Reynolds says: “To treat the same area with the current specification for CL942 thin surfacing would require approximately 8,440t of asphalt, generating the equivalent of 422t of CO2 from production, transportation and laying. At 10% of this figure, K190 has provided theoretical CO2 savings of 380t.”

This is not the end of the story. Retexturing delivers on the four criteria for value management - safety, value for money, reduction of disruption and environmental sustainability - used by the Highways Agency to prioritise funding of network maintenance.

A-one+ estimates it has saved in excess of £1M from the retexturing of 15 sites over the past 18 months. It has also saved around £186,000 in repairing network damage (based on a nominal £3,000 average figure for repair per incident). Total numbers of road traffic collision (RTC) and barrier strike incidents available for 11 of the 15 sites treated are down from 80 to 18 for comparable periods pre- and post-treatment.

Shorter possession times

Being quicker to complete than laying material, retexturing also reduces highway possession to help improve journey time reliability. Traffic diversions - typically between 6km and 10km for Area 10 - are implemented for short duration night-time schemes. Quicker treatments reduce the unnecessary fuel consumption and carbon footprint associated with these diversions, as well as the inconvenience to the road user.

In line with Agency standards, the Area 10 roads renewal team monitors the skid resistance of the Agency’s network using SCRIM data collected on an annual basis. This flags up where there may be issues and a need to investigate further.

Investigations look at data collated by the police on personal injury accidents (STATS19) when assessing the requirement for skid-resistance treatment. The team uses other local intelligence, too.

“We also consider our own incident logs of road traffic collisions or damage to barrier, lamp columns and structures which give additional qualifying evidence of the site under investigation,” comments Reynolds.

There are well documented principles in health and safety guidance demonstrating a correlation between the number of minor incidents and those with more serious consequences, he explains.

Judgement helper

These can assist in judgments on whether a site needs treatment. He adds: “This data can prove invaluable in targeting treatments at sites where analysis of injury accidents is inconclusive.”

Use of K190 retexturing by A-one+ in Area 10 was recently recognised by the Chartered Institution of Highways & Transportation, winning Road Safety Project of the Year in the 2011 North Western branch awards.

By offering the option of delaying higher cost treatments with larger carbon footprint, retexturing is a valuable tool in the current economic and environmental climate. It could make more square metres of maintenance and safety improvements possible at a time of limited budgets.

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