Sprayed concrete delivers essential repair to retaining wall

High performance webercem spray DSF by Saint-Gobain Weber has been specified by BAM Ritchies for the repair of a concrete retaining wall on the approach to Blair’s Bridge.

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Located in Redding, now part of the Falkirk district of Stirlingshire, Central Scotland, this was once a collier village with an extensive tract called Redding Moor.

BAM Ritchies, the geotechnical division of BAM Nutall, a leading supplier of civil engineering works and infrastructure projects, was commissioned by Falkirk Council to repair the retaining wall approaching Blair’s Bridge. The bridge carries a railway line and is crossed by the busy B805 road. The wall had suffered progressive concrete spalling over its full length with exposed reinforcement covering an area of up to 200m².

Following a detailed survey of the structure, the repair methodology devised by BAM Ritchies and technical advisors at Saint-Gobain Weber, called for the weak and delaminated concrete to be removed by hydro-demolition. This technique uses high pressure water jets to effectively break out large areas of defective concrete, clean the remaining substrate and remove corrosion. The surface was made ready for the installation of 69mm stainless steel formers which were fixed into position to match the movement joints in the wall capping beam.

webercem spray DSF was applied to the structure incorporating A252 steel reinforcing mesh to the full 69mm thickness and hand trowelled to provide a flat profile. A final flash coat was applied to give a uniform texture to the wall.

Around 40 tonnes of the economical webercem spray DSF was used in this project. This is a polymer-modified, cement-based concrete mix which contains inert limestone aggregates and dust suppressants. The formulation has been designed especially for dry process spray application to give high early strength, reduced rebound and waste, and maximise application thickness. webercem spray DSF contains alkali glass fibres that offer better strain relief and stress distribution and help to reduce shrinkage cracking. Conformity testing to BS EN 1504-3 meets the requirement of a Class R4 repair product and complies with Highway Agency specifications for repairs to highway structures. It offers high-build – up to 150mm thickness can be applied in one pass on vertical and overhead faces – and has low permeability to water and chlorides. 

BAM Ritchies incorporated movement joints, 20mm wide, using polysulphide mastic sealant. The company’s concrete team led by Patrick Carden, works manager, completed the works within the three week period commissioned by the Council. 

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