webercem spray RS provides vital reparation to sea defence
High performance webercem spray RS repair concrete has been specified for the protection of a 1930’s sea wall damaged by decades of continuous tidal erosion.
Shepway District Council has responsibility for a number of beaches along the coastline from Folkestone down to Dungeness, an area of approximately 20 miles. Coronation Parade, on an exposed part of this coastline, is a concrete structure located on Sunny Sands beach in Folkestone. It spans 340m and was built in the late 1930s as a sea defence, providing prevention of cliff erosion whilst protecting a number of homes and businesses. At the eastern end is a National Grid Interconnector that allows sharing of electricity between the United Kingdom and Europe.
Due to the continuous tidal action, and the rocks which act as a barrier to reduce the effect of the wave forces, the concrete has suffered from impact damage and from chloride ingress. This in turn has led to corrosion of the steel reinforcement with associated concrete spalling. Concrete Repair Association (CRA) member, Birmingham City Laboratories, part of Birmingham-based Acivico professional services provider, carried out all the testing and analytical services prior to designing the repair. Main contractor Concrete Repairs Limited, Surrey, addressed the poor condition of the structure using hydro-demolition, a technique that uses high pressure water jets, to effectively break out large areas of defective concrete, clean the remaining substrate and remove corrosion from the reinforcing steel.
The requirements for carrying out these repairs, and for reinstating the concrete with sufficient cover to the reinforcement, had to include a repair method that would work within the short low tide cycle. To meet this criteria a sprayed concrete repair method was specified using webercem spray RS by Weber. This is a polymer-modified, rapid setting, dry-sprayed concrete which is ideal for permanent repairs where time constraints, such as tidal flow, demand early strength gain. This rapid setting capacity prevents wash out from the tidal water flow and minimises the penetration of chlorides. Research shows that salt penetration into webercem spray RS is limited to 10mm whereas fresh, traditional concrete absorbs chlorides faster than hardened concrete as the crystalline structure has not yet fully formed.
webercem spray RS contains inert limestone aggregates, dust suppressants and accelerators. This product has passed the stringent freeze/thaw test required for durability and the bonding adhesive standards of BS EN1504. This formula is designed for dry-spray processes where the material is blown by air to the nozzle and mixes with water on exit from the lance. This reduces rebound on contact with the substrate surface and allows high build material application. The dry-spray process fires the material at the substrate at over 80mph giving good compaction with very few voids.
This highly technical product gives an initial set in just 15 minutes and in six hours has a compressive strength of 10-15 N/mm². It has been designed by Weber specifically for use in marine applications, repairs to river bridge abutments or piers, and structural repairs to concrete beams, columns and soffits. This product meets the standards contained in Exposure Class XF4 for long term durability being exposed in flood plain environment.
One of the challenges in this project was to achieve a good finish to the repairs of the arches on the concrete structure. Despite the rapid setting nature of the product, the specialist teams of applicators managed to float the repairs before the sprayed material had hardened to achieve an excellent finish to the webercem spray RS concrete.
Mike Balletta, infrastructure manager, Concrete Repairs limited, says: “This project has been extremely complex logistically, having to work around the tides and then into the winter months. This harsh environment has required innovative ways in which to use plant, equipment and materials, especially when specifying a repair material with which to reinstate the concrete with sufficient reinforcement. After considering various options webercem spray RS was the natural choice and our decision has proved to be correct with the material performing exactly as planned. We are extremely pleased with the results as is Shepway District Council.”
An impressed current cathodic protection (ICCP) system was also specified in order to further protect the steel reinforcement from corrosion and to ensure the structure withstands the harsh conditions it is subjected to for a further 75 years.