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Factory floor to ocean’s door – sea defence proves concrete's diversity

Aggregate Industries brought its bespoke design and concreting processes straight from the factory to the site of its work to protect Littlehaven’s seafront from the stormy tides of the Tyne.

When Aggregate Industries was asked to deliver an aggregate solution for an ageing seawall at Littlehaven, it offered a chance to demonstrate the durability and flexibility of concrete.

The new defence was part of a major civil engineering scheme costing more than £5.3m to replace the original seawall, which was protruding seawards at its centre, leaving it susceptible to structural damage and wave overtopping.

The project, initiated by South Tyneside Council, included designer Royal Haskoning and contractor Galliford Try.

The challenge was to provide a coastal defence which could offer genuine improvements, transform the beach, promenade and defences along a stretch of South Shields seafront and turn the neglected coastline back into a desirable visitor destination.

Concrete meets design needs

Concrete fulfilled the design ambition for a decorative finish through concrete casting on site.

Aggregate Industries supplied Articimo ready-mixed concrete for this project, sourced locally from its Gateshead plant.

Bespoke, decorative Ure Valley gravel aggregates were exposed in the surface of the concrete and the design also incorporated an integral colour additive, supplied by SLP Colourtone, to enhance the look of the seawall and provide further integration with the local amenities.

“The curved formation reduced the risk of overtopping to protect South Shields’ frontage from coastal erosion and sea flooding”

The base concrete was a specifically designed mix, to a C35 strength classification, which incorporated blast furnace slag to enhance both chloride resistance to embedded steel and long-term durability to freeze thaw, as well as constant wetting and drying in a marine environment.

Aggregate Industries created two bespoke colour shades - unique to this project - to complement and blend into the beach surroundings.

The seafront’s new defence configuration featured a stepped concrete apron leading to beach level, a wide promenade and a backing flood wall.

Collectively these provided a wider sea defence system than the original vertical seawall, while the curved formation reduced the risk of overtopping to protect South Shields’ frontage from coastal erosion and sea flooding.

Methods parchuted from factory

The client wanted to achieve a precast quality finish using concrete cast in situ, so Aggregate Industries brought techniques and processes directly out of the factory and on to the site, including specialist concrete finishers and acid etching.

The consistency of both colour and aggregate exposure was critical to the visual appearance.

On site, the project team began by pouring the Articimo ready-mixed concrete into formwork. It was then floated off to leave a smooth closed surface.

A surface retarder spray applied to the concrete prevented the top layer from setting and ensured that the surface layer could be washed and removed the following day. This exposed the decorative aggregate contained within the concrete.

“Last December’s storms caused widespread destruction across the North-east’s coast, posing the first real, rigorous test of the new seawall”

This look was further enhanced by acid washing the concrete to remove any remaining cement paste from the exposed aggregate, leaving a clean finished surface.

The two bespoke colour shades used both complemented and blended with the existing environment, creating the illusion of a transitional landscape.

To protect and preserve this two-tone colour effect - and the appearance of the exposed aggregate - the surface was then sealed using a clear sealer.

To enhance the durability of the cast concrete, micro fibres were included to reduce bleed rate, increasing the long-term performance of the finished structures. This complemented the bespoke street furniture and artwork, high-quality landscaping and feature lighting, all of which helped revitalise the seafront.

The test of the Tyne

Last December’s storms caused widespread destruction across the North-east’s coast, posing the first real, rigorous test of the new seawall as it faced the elements.

The storm caused the highest tide observed by the River Tyne gauging station since the 1953 coastal surge, which also ravaged the area.

Yet despite these extreme conditions, Littlehaven’s seawall withstood a severe battering, with water levels reaching halfway up the stepped apron and some breaking water and spray up to the promenade level.

The performance and protection exceeded the project team’s original expectations, which is largely due to the wide natural beach that has developed much quicker than expected in front of the concrete defence.

Neil Cochrane is specification manager at Aggregate Industries

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