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To continue to minimise the dead loading of the surfacing its thickness was to be restricted to 60 – 70 mm. This would necessitate the exclusion of the 20mm thick red sand asphalt carpet, traditionally used on the majority of UK bridges. Acting on behalf of Halton council, the firm of consultants Mott MacDonald approached Stirling Lloyd in their search for a waterproofing system that would be able to perform successfully under these circumstances.
Stirling Lloyd's response to this problem was to propose using their Eliminator® two component, liquid spray applied waterproofing system, which is based on methyl methacrylate (MMA) resins in conjunction with their high performance SA1030 Bond Coat. Not only does this well established partnership of products have an unrivaled track record of success worldwide, but the Eliminator® /SA1030 combination has been used successfully on a number of high profile UK projects including the M1 / M62 Lofthouse Interchange, the M62 River Ouse Bridge and the M53 Bidston Moss Viaduct. It is also currently being used on the Ray Hall and Bromford Viaducts on the M6 in Birmingham.
The Eliminator® and SA1030 combination has also been tested in the laboratory and on-site by the British Board of Agrément, and has been approved for use on Highways Agency projects where the sand asphalt carpet is to be omitted (refer to BBA Road & Bridges Certificates R112/99 & R111/99).
Satisfied that the Eliminator® /SA1030 combination would resolve this issue on the structure and assured by its success on numerous previous projects, Mott McDonald approved the products for this prestigious project.
With Mowlem plc as the Principal Contractor, the sub-contract for the application of the system was awarded to Stirling Lloyd Contracts Limited, one of a global network of authorised contractors for the installation of the Eliminator® and SA1030 systems. Work including concrete repairs and the installation of the shock transmission units was undertaken during Autumn 2003 with the remaining work commencing in June 2004.
With traffic congestion levels already heavy on the bridge and no convenient alternative route available, Halton Borough Council stipulated that lane closures could only be implemented overnight and during weekends with the work due to be completed in September 2004. The weekend work began with Mowlem removing most of the existing mastic asphalt surfacing, leaving a 5mm residue. Stirling Lloyd Contract's Ltd then took over the preparation of the substrate. The residue was removed using Bobcat machines fitted with milling equipment then the substrate was captive blasted, completing the preparatory works.
Once the deck preparation had been completed and prior to overall application of the system, adhesion tests to ascertain the bond strength of the membrane to the substrate were carried out by random spot application, at various points on the bridge deck. These confirmed that the values attained easily exceeded the 0.3MPa required by the specification. The spray application of Stirling Lloyd's methyl methacrylate based primer then began. This would ensure that the surface of the deck was sealed and enhance the adhesion of the subsequent Eliminator® membrane.
Once the primer had cured, in typically less than an hour, a second team began the application of the first coat of the Eliminator® membrane, which was pigmented yellow to contrast with the concrete deckand aid visual inspection, especially under artificial light. When the first coat of membrane had fully cured, in approximately one hour, the team who had by then completed the primer application began the spray application of the second coat of membrane, following the yellow coat team down the deck. This second coat was pigmented white to once again aid visual inspection of the membrane and as with the first coat, thickness tests were carried out to verify that the correct thickness had been applied. Once this coat had cured, again within an hour, the membrane's integrity was confirmed using high voltage, non-destructive holiday detection testing equipment.
On completion of the testing the preparation and application of the SA1030 Bond Coat commenced. SA1030 is a proprietary, hot melt, solvent-free bonding coat based on a polymer modified bitumen, designed to give an exceptionally strong bond between the Eliminator® membrane and the surfacing binder course.
Having heated the Bond Coat to within the application temperature range of 175-200 °C, it was then applied to the deck at the minimum required thickness of 1mm. Thirty minutes later once the Bond Coat had cooled, the system was ready to receive the HRA binder course. This was subsequently overlaid with the thin surface course. Amidst the tight scheduling and varying application windows, courtesy of Eliminator®'s rapid cure and speed of application, Stirling Lloyd Contracts Ltd were able to apply the whole system to the area made available to them each weekend – treating up to 1,400m² in their allotted window. This enabled the lane treated to be returned to service in time for the Monday morning rush hour.
There are plans for the construction of a new bridge up stream to ease congestion and reduce the reliance on the Silver Jubilee Bridge, but in the meantime Stirling Lloyd have helped ensure that Halton’s most famous landmark will remain in service for many years to come.
[ Stirling Lloyd Press Release PR04-20 : 10/2004 ]
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