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Up to strength

Dry spray guniting equipment was used with great success as part of strengthening work on a Staffordshire road bridge recently, upgrading the crossing to carry vehicles up to 40t.

The A50 Burton Bridge spanning the River Trent has 32 brick built arches, 25 of which needed their load bearing capacity increased to meet Highways Agency requirements. The strengthening method needed to be highly durable since 30,000 vehicles cross the bridge every day.

In the event, subcontractor Concrete Construction Techniques achieved the strength by spraying a polymer modified mortar blending Portland cement, graded aggregate and additives over reinforcing steel mesh.

A concrete cover of 90mm depth lined a total area of 1.188m2 under the arches. The sprayed concrete lining also served to overcome the problem of spalling. The bridge was starting to crumble, 72 years after an upgrade in 1926 when the crossing was lengthened.

Before spraying, accumulated grime and loose concrete had to be removed by high pressure water jetting. Steel reinforcing was then fixed in place across the underside of the bridge with 5,500 resin anchored steel dowels.

The layer thickness achieved using dry spray was such that we could control the spray rate much more finely than we ever could with wet concrete, says Concrete Construction Techniques director Bill Jones. We were very pleased with the outcome. The bridge is now up to standard and unless another weight limit increase is needed, it will not need repair for years.

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