Following the decommissioning of an exposed gas pipe at the Menai Suspension Bridge, Mapei products were specified for the repairs required for two corbels of the bridge.

The main contractor appointed by Wales and West Utilities, Taziker Industrial Ltd, contacted Specialist Concrete Finishing and Repairs Ltd (SCFR Ltd) for the repairs. Access was made possible via a mobile elevating work platform from ground level; Taziker removed the redundant pipe and its surround first, allowing access to SCFR Ltd to carry out the repairs.

The material specification Mapei provided consisted of guidelines for substrate preparation, preparation and protection of the steel reinforcement and the concrete repairs to fill the voids in accordance with BS EN 1504 and Highway Specification 5700.

For the protection of the steel reinforcement against corrosion, Mapei recommended the installation of Mapeshield I 10/10 pure zinc anodes for galvanic cathodic protection. Made up of a multi-layered zinc core with a large surface area, and covered with a special conductive paste, the system is then kept active over the years.

After connecting Mapeshield I 10/10 to the reinforcement steel with metallic strays, a difference in potential is created between the steel and the zinc which stops corrosion and impedes its formation, even if the surrounding environment is particularly aggressive, for example due to the presence of chlorides.

To reinstate the voids, Mapei recommended the application of Mapegrout T60, a sulphate-resistant, R4 class fibre-reinforced mortar mixed with water and internal curing admixture Mapecure SRA to reduce hydraulic shrinkage and the formation of micro-cracks. When mixed, a workable mortar with thixotropic consistency was formed, which was then applied by hand to the vertical surface of the two corbels.