Dun Laoghaire Harbour

St. Michaels Pier supports the passenger terminal servicing the HSS fast ferry from Dun Laoghaire harbour to the Port of Holyhead in Wales. Maintenance surveys revealed that the large diameter cast in-situ concrete piles supporting the structure were suffering from severe spalling and corrosion to the reinforcing steel.

Norfolk Marine Ltd carried out a comprehensive survey, highlighting the piles affected, the extent to which concrete cover was lost, and the severity of corrosion to the reinforcing bar, the results of which were evaluated to design an effective repair solution.

A fabric formwork pile repair system was elected as the most cost efficient solution due to ease of installation to the large 1.6m diameter piles. The piles concrete together with the exposed repair was cleaned by using HP water to remove all marine growth and lose material. Spacers were fitted to the cleaned piles and the fabric formwork sock zipped around its circumference and suspended from the pier sought. A micro concrete was then pumped into the formwork.

Fabric formwork is preferable for marine concrete pile repairs as the porous fabric allows the free water in the concrete mix to bleed down to a water cement ratio of 0.4.This gives a significant improvement in strength and durability over concrete placed in conventional shuttering systems.

With design of concrete thickness and a mix design incorporating GGBS and fiber reinforcement giving enhance resistance against the ingress  chloride/ sea salts a long lifespan can be obtained.

Subsequent laboratory testing of concrete samples taken on site at Dun Laoghaire resulted in 28 day compressive strengths of 50N/mm2 and above.

Norfolk Marine liaised closely with the Harbour Master to ensure the entire project was completed safely and with no disruption to the harbour’s ferry schedule.