Saint-Gobain Weber sprayed concrete holds back the tides at West Bight promenade
The high performance weber.cem spray RS manufactured by Saint-Gobain Weber, a leader in the formulation of innovative, high strength construction mortars and concrete repair systems, has been used in the vital reparation of the sea wall fortification of the Outer Bight. Here critical protection is offered to the navigation channel of Newhaven harbour from where the Newhaven – Dieppe ferry and cargos operate.
With a twice-daily battering by the tides, this impressive Victorian wall has been subjected to enormous hydraulic power over its 100-year life. Remedial action is being undertaken using the rapid sprayed concrete specifically developed by Saint-Gobain Weber for repairs to structures in tidal zones. The rapid setting qualities of weber.cem spray RS enables remedial work to be carried out between the tides and this advanced concrete repair product is predicted to defend the Newhaven wall for another 100 years.
The curved sea wall around the Outer Bight sees waves driven from both the south and south east direction to meet at a point where a set of steps had been cast for access to the sandy area. Over time the original concrete substrate, subjected to massive pressure at the point of wave convergence, has suffered with weak surface areas being eroded and substantial lateral and vertical cracks being opened to further wave and water damage. Fissures up to 500mm deep, running for several metres along the wall face, have had to be repaired to avoid the real possibility of a breach of the defences.
John Howarth, operations supervisor for Newhaven Port, recognises the crucial role played by the sea wall in protecting the harbour entrance.
“Local patch repairs have been applied over time but a major remedial programme became inevitable. This is a dynamic location with sand and water movement and it is not unusual to see waves breaking 60ft above the top of the wall!” Allan Cummins, AJC Contractors of Worthing, West Sussex, a marine contractor, and their engineering consultant Tony Mackin, proposed the weber.cem spray RS system and associated structural works which have now applied to the first 60 metre section. “I am extremely impressed with the Saint-Gobain Weber product,” reports John Howarth.
weber.cem spray RS is a dry sprayed concrete able to achieve rapid set, and is ideal for permanent concrete repairs where time constraints, in this case the tides, demand early strength gain. Initial set is achieved in just 15 minutes and in six hours a compressive strength of 10-15N/mm² is achieved. This prevents washout from the next tidal flow. The material contains inert limestone aggregates, dust suppressants and chemical accelerators as well as a blend of cements that better resist the chemicals in seawater. The formulation is designed for dry spray application where the material is pumped dry through to the nozzle where a high pressure water flow carries the material to the substrate surface mixing with the weber.cem spray RS on its journey from the nozzle. At Newhaven the material has been delivered at 100psi. The amount of water added at the nozzle is critical: too little and the larger aggregate in the material will rebound from the surface, too wet and the material will slump. When correctly mixed and applied, a depth of up to 150mm of weber.cem spray RS can be achieved in a single application.
At Newhaven the repair process has been to cut out all cracks and damaged material to provide a sound key substrate free from all loose aggregate. Stainless steel pins have been driven into the original substrate every 300mm along the fissure opening and 40mm in from the desired finished surface level. Steel mesh reinforcement is anchored to these pins and the spray application of the weber.cem spray RS commences in 150mm layers until the surface level is achieved. A further layer of steel mesh reinforcement covers the whole wall surface. Yet another 100mm depth of weber.cem spray RS is applied to establish a new defensive surface. AJC Contractors, in conjunction with Eastbourne Scaffolding Ltd., designed and erected an intricate scaffold arrangement across the wall face and the pump and materials station was established on the decking above the wall. Lighting allowed work during night tides.
After the rapid initial curing, compressive strength increases to 30N/mm² in 24hours and up to 40N/mm² in three days and is fully cured after 28 days at 50N/mm² at which time the static modulus of elasticity is 30kN/mm². Tensile strength of 4-6N/mm² is achieved after seven days and the flexural strength of 6-8N/mm². The critical bond strength with concrete substrate of weber.cem spray RS is >2N/mm².
The prediction that these repairs will give long lasting protection to the wall is made on the basis that in the areas of greatest damage the original hand mixed concrete has a nominal compressive strength of 40N and in some of these areas, at least 25mm of surface material has been lost. “Where we are applying 100mm of Saint-Gobain Weber’s repair concrete, even if we were to lose 25mm through abrasion in the next 100 years, we would still have more protection left in place than we do at present.”
The weber.cem spray RS product manufactured in the Bedfordshire plant by the multinational construction products manufacturer Saint-Gobain Weber is the solution to holding back the ravages of the weather and tides of the English Channel.
Further information and technical support is available on 08703 330070 or visit www.netweber.co.uk.
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