Weston-super-Mare seafront enhancements
Tarmac and Birse Coastal (a division of Birse Civils), on behalf of North Somerset Council, is modernising the existing sea defences in Weston-super-Mare to bring them up to the recommended standard of protection against possible flooding. At the same time Birse is also upgrading the public spaces on the sea front.
Phase I of the project, located at Marine Lake, started in August 2007 and is now well advanced and due for completion in April 2008. Phase II of the project will be completed in 2010.
By the time Phase I is complete, Tarmac will have supplied 2500m^sup 3^ of ready-mixed concrete to the foreshore area of the site from its plant located a couple of miles away in Weston-super-Mare. Typically, diree deliveries a day have been planned to the project site. This includes 1200m^sup 3^ of specialist Toproc UW microsilica concrete, which is designed specifically for underwater applications. The proximity of Tarmac’s plant to the site has been vitally important to the success of the concrete works, as all Toproc UW micro-silica concrete needs to be supplied and laid during a narrow tidal window of six to seven hours, which presented a major challenge for the team.
A key part of Phase I is the refurbishment of the existing sloping revetment at the western end of Marine Lake. The concrete and rock causeway impounds the lake and plays an important role in the town’s sea defences.
It was originally planned that this refurbishment could be achieved by fixing a sttuctural covering of precast concrete revetment panels. However, early value engineering considered in detail the difficulty of handling and placing the panels – some in excess of 20 tonnes – in the inter-tidal zone. With technical support from Tarmac, the team decided to opt for a ready-mixed concrete solution.
The challenge for Birse Coastal and Tarmac was considerable. The concrete had to be placed in Weston’s intertidal zone (with a tidal range of 15m, it is the second largest in the world), which meant the material needed to resist wash-out. As it was also being installed on an incline of 1:2, it also needed to be capable of full compaction without slumping down the slope and to ultimately receive and retain a tamped finish. Long-term durability was also an essential property, with the concrete face having to resist impact loads from waves and tidal abrasion during its lifetime.
To ensure that the solution met both performance and aesthetic demands, Tarmac worked closely with Birse Coastal, prior to the award of the contract, to provide a solution in Toproc UW. This is a cohesive micro-silica concrete that is resistant to wash-out and, because of its thixotropic nature, also has sufficient workability to allow placement and finishing while resisting slippage. Toproc UW typically achieves a compressive strength of 30-40MPa within 24 hours and 70-90MPa within 28 days. This high compressive strength gives Toproc UW excellent abrasion resistance.
The long-term durability of Tarmac’s Toproc concretes range has been proven in many high abrasion applications and, in addition to its plastic properties, was a key factor in its selection for the Weston-super-Mare project.
Copyright The Concrete Society Mar 2008
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