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It was at this time that Stirling Lloyd were consulted by Engineers, the Babtie Group who were looking for a waterproofing system with a proven record of successful applications with thin surfacing. Stirling Lloyd’s recommendation was the Eliminator® /SA1030 combination as not only has it an impressive track record of successful similar projects both in the UK and worldwide, but it had also been tested in the laboratory and on-site by the British Board of Agrément (BBA), and was approved for use on Highways Agency projects where the sand asphalt carpet was to be omitted (refer to BBA Road & Bridges Certificates R112/99 & R111/99). Impressed by the system's track record of applications and following a successful full-scale trial underneath the Viaduct, in which the Eliminator® membrane greatly exceeded the Highways Agency's then new Specification for Highway Works (BD47) tensile adhesion and shear strength requirements, the Babtie Group specified the products for the project. Five years on, with the surfacing still in good condition on the Northbound carriageway, the Highways Agency turned once again to Stirling Lloyd when experiencing similar problems on the Viaduct's Southbound carriageway.
The Chester-bound carriageway required a complete refurbishment following the failure of both its surfacing and existing polyurethane waterproofing membrane. Whilst in part this was attributed to water penetration into the surfacing the absence of a bond between the surfacing and the waterproofing, exacerbated by the pumping action of heavy goods vehicles, coupled with the excessive flexibility of the polyurethane membrane, would seem to be the most likely causes. Prospective waterproofing systems for the work were subjected to full-scale site trials prior to the final decision being taken regarding the most suitable material specification. Adhesion requirements were increased from those specified within BD47 as the reduced surfacing depth would impose greater demands upon the adhesion of the surfacing to the waterproofing and of the waterproofing to the concrete deck. In the trials which were overseen by Atkins, the Highways Agency's Managing Agents for this Construction Management Framework Contract, the Eliminator® /SA1030 Bond Coat system was the only system that achieved results that met the contract specification, with other competitive systems failing to successfully complete the trial. Comforted by the continued success of the 1999 application, as well as its ever growing track record, including some 90,000m² of work during 2004 under the Highways Agency Construction Management Framework on the M6 Ray Hall and M6 Bromford Viaducts, the M5 Bredon Ham and the A38 Aston Expressway, Client the Highways Agency were confident that the Eliminator® /SA1030 combination would resolve this issue for a second time on the structure and specified the products for this project. The specialist sub-contract for the application of the waterproofing and bond coat, based on their performance in the trials and on the Northbound carriageway contract, was awarded to Laser Special Projects Limited, who are based in Worcester and are one of Stirling Lloyd's authorised contractors. The project commenced in early October and as the viaduct was required to be fully open for the Christmas holiday it was critical that the contract programme was met.
Surface preparation involved the input of several specialist contractors'; the first of which, Hansons had the task of planing off the existing Hot Rolled Asphalt (HRA) surfacing to within approximately 15mm of the, not to be replaced, sand asphalt carpet. A team from Laser Special Projects Limited were then able to remove the sand asphalt carpet with ease using wheeled excavators. The polyurethane waterproofing membrane was then removed by contractor's DDC, using machines fitted with milling equipment, followed by a team from CMS who captive blasted the substrate. Once this had been completed Laser Special Projects Limited scarified the isolated areas of the deck where membrane had embedded within low spots. A number of concrete repairs were then carried out using Stirling Lloyd's Metaset Mortar high performance, rapid hardening methyl methacrylate (MMA) resin repair mortar to smooth the surface of the deck. Once the preparatory works were complete and prior to application of the Eliminator® system Laser Special Projects Limited carried out adhesion tests to determine the bond strength of the membrane to the substrate and confirm that it exceeded the enhanced specification. Spray application of Stirling Lloyd's rapid curing, MMA based primer then began. This ensured that the surface of the concrete deck was fully sealed and enhanced the adhesion of the subsequent Eliminator® membrane to the substrate. Once the primer had cured, in less than an hour, the spray application of the Eliminator® membrane began. This was pigmented white to contrast with the concrete deck and has an initial translucence enabling the applicator to visually discern and remedy any potential thin spots. This was backed up by wet film thickness tests being constantly carried out using a gauge pin, which together ensured that the minimum required final thickness of 2mm was attained. Once the membrane had cured, in less than an hour, the membrane's integrity was confirmed using a high voltage, non-destructive holiday detection test which was overseen by a representative from Atkins. On completion of the testing, the application of the SA1030 Bond Coat commenced. SA1030 is a proprietary, hot melt, solvent-free bond coat based on a polymer modified bitumen, designed to give an exceptionally strong bond between the Eliminator® membrane and the HRA binder course. Having heated the Bond Coat to between 190-200 °C, Laser Special Projects Limited then applied it to the membrane at the required thickness of 1mm. Thirty minutes later once the Bond Coat had cooled, the system was ready to receive the surfacing material which was to consist of a 45mm Clause 943 polymer modified HRA binder course followed by a 25mm thin surface wearcourse to give a combined minimum depth of only 70mm. Laser Special Projects Limited applied the full system at such a rate that the 5,100m² of the main deck and 745m² of the adjoining Junction 1 sliproad were fully treated, resurfaced and open to traffic two days ahead of schedule and in plenty time for the Christmas break. With the Southbound carriageway now complete and the Northbound carriageway performing well after six years of service, Bidston Moss is a fine example of where, driven by the need to reduce the depth of surfacing, specialist products with a proven track record can be used to provide a durable waterproofing and surfacing solution without the use of a sand asphalt protection layer. |
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