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Coppermill Stream Bridge

Key network rail trials demonstrate major gains with new Mac’Ants structural paint stripping system

Network Rail has completed a major bridge stripping evaluation – using an innovative process developed by the Mac’Ants Group – which has demonstrated significant performance and environmental benefits. The project, now completed at the Coppermill Stream Bridge in Walthamstow, north-east London, has highlighted key advantages which, says Mac’Ants – will be recognised by everyone involved in the maintenance and refurbishment of large metal structures, particularly in connection with painting preparation.

The work was undertaken by Shutdown Maintenance Services on behalf of contractor Kier Rail who are Network Rail’s East Anglia Structures Framework contractor. The site, which has two pedestrian and two river crossing bridges – both active and inactive – featured an original coating which was a typical 26% lead content alkyd paint system, the removal of which ahead of maintenance would conventionally be achieved using expendable abrasive blast cleaning. This process has now been significantly enhanced by the Mac’Ants system through the use of blast media centred on thermoset plastic hybrids that offer greater re-use opportunities whilst creating a far more acceptable operating environment. The method dramatically reduces disposal requirements to landfill – potentially by a remarkable 90%.

The Mac’Ants facility has been developed as a mobile unit that is delivered to site on a flatbed trailer. A series of modular units can either be operated from the vehicle positioned at up to 100 metre distance, or simply offloaded using a telescopic handler to bring them closer to the work site if required. The facility connects to a contained or shrouded area on the structure that encapsulates the working surface. The Mac’Ants’ Auriga system then provides extraction, collection and recycling stages with significant benefits at every point, as Mac’Ants’ Director Kent Martin explains –

“Because the process is based on low pressure – some 40 psi compared to a conventional 110 psi – it enables the plastic media to remain useable for longer,” he says. “It also improves noise levels – measurements at the site indicated a reading of less than 50 dbA at the perimeter of a typical pedestrian exclusion zone using a simple Monarflex encapsulation – while creating a far more acceptable working environment within the enclosed area. The work on Coppermill Stream Bridge demonstrated that 30 seconds after the shut down of two blast nozzles in the contained area, the chamber was free of airborne dust,” he explains.

The facility separates re-usable media from that which needs to be removed for disposal – the demonstration even provided good results in this regard where wetted material was present. Benefits relating to speed of stripping compared with conventional alternatives were also noted whilst the profile achieved on the metal structure was readily varied simply by altering the blend of plastic media. Pre-blended hybrid media achieved a profile of up to 130 microns, for example.

“The work at Coppermill has represented the latest in a series of trials that we have undertaken with the Mac’Ants system,” comments Colin Hayter, Senior Construction Manager, South East Territory at Network Rail. “It has demonstrated benefits in terms of cost effectiveness, through reduction in landfill costs, labour requirements and the need to hire ancillary equipment, whilst for the contractor and the external environment alike, the conditions have been significantly improved.”

“We believe that at a time when quality, cost control and safety, health and environmental (SHE) impact are the key considerations with any processing of this type, our development opens up new opportunities for everybody involved in the stripping of large metal structures,” concludes Kent Martin at Mac’Ants. “With the results now qualified and assessed, we are confident that the system has effectively raised the bar for this type of operation which, through the combination of performance and safety, health and environmental (SHE) gains, can only benefit all concerned.”