Garden Island Sydney

Concrete repairs at Garden Island Dry Dock

Client: Australian Department of Defence and Australian Defence Industries (ADI)

Location: Potts Point, Sydney

Task: Long lasting repairs were required to the reinforced concrete walkways built into the sides of the inner and outer caisson of the Dry Dock.

Andersal Project Manager: Henk van den Heuvel

Special Challenge

Previous attempts at repair had failed. The concrete and reinforcement is subject to one of the most hostile environments: Cyclical soaking in salt water followed by drying quite dramatically.

The structure is regularly filled with seawater and the resulting chloride ions had been absorbed into the concrete and were above threshold levels, thus attacking the steel reinforcing and causing it to rust. Without repair the corrosion would have continued unabated resulting in considerable future expense and risks to the safety of personnel.

Solution

The full scope of concrete repair work required was difficult to assess without a survey of the various concrete surfaces as well as detailed diagnostic testing.

As the structural steel members are exposed to a high chloride environment over the reinforcement, repair of the structure using high-strength pourable grouts was only half of the remedial process.

It was suggested the use of a buried anode protection system called Galvashield® XP. These sacrificial anode units are attached directly to the repaired steel reinforcement and each unit provides galvanic protection within its sphere of influence. This technology extends the maintenance cycle of the structure and protects the reinforcement members that have commenced corrosion but have not yet produced visible spalling.

Andersal also arranged the latest technology in silanes, permanent water repellent for concrete in any aggressive environment. The product Dry Treat 100N CI® incorporates a migrating corrosion inhibitor which travels to the reinforcement and sets up a passive layer around it. The application of silane affords protection equivalent to approximately 120mm of additional good quality concrete cover. Silanes have been used with great success on bridges, car parks and commercial structures such as the Sydney Opera House and the Anzac Bridge.

The solution is designed to ensure a trouble free life of 20 years in a marine grade environment with the newly placed 80MPa repair mortars.