HMAS Stirling at Garden Island in Western Australia is the home port of the Australian Navy’s entire submarine group and around half of its major surface vessels. With the navy’s operational capability reliant on access to wharves and piers, the role of these maritime structures is crucial, however, most were constructed between 30 and 45 years’ ago.
At that time there was less knowledge and emphasis on durability and many of those concrete design and construction practices have proven to be inadequate for the long-term and were showing signs of sea salt chloride-initiated corrosion.
This situation led to redevelopment works commissioned by the Department of Defence and the remediation project at HMAS Stirling by managing contractor Doric Group. Under Doric, Duratec Australia was awarded the contract in August 2017, and the works completed in December 2019. The aim was to extend the service life of these maritime structures to 2055 through a challenging program, accommodating shipping and other base activities, with minimal disruption and a range of tidal conditions.
- Armament Wharf: concrete repair, cathodic protection (CP), joint sealing, protective elastomeric coatings, replacement of jetty and dolphin access way, light pole replacement and trial pile repairs.
- High Level Bridge: concrete repair, CP, custom finger plate joint replacement, replacement of pile caps and fixing straps, repainting of vehicle guard rail.
- Moresby Harbour: concrete repair, joint repairs, protective silane coatings and a trial pile repair.
- Oxley and Parkes Wharves: concrete repair, CP, joint repairs, protective silane and elastomeric coatings and light fittings replacement/protective coatings to flood light towers.
- Diamantina Pier: joint repairs, protective silane coatings and replacement of light fittings/coating repairs to flood light tower.
- Diamantina to Parkes Service Tunnel: concrete repair.
GHD would provide design, including investigation, repair option analysis, specification, technical inspections and quality support. Given the age of the structures, much of their construction was unavailable or inaccurate so GHD conducted extensive research to re-establish asset history. Information was obtained from GHD team members’ own experience; published research papers; and by contacting personnel involved in the original construction; and via social networking, GHD obtained construction photographs in the 1970’s from the project manager involved in the construction of the High Level Bridge. This detective work reduced uncertainty and some investigations and assisted repair evaluation.
Durability investigations included detailed visual inspection on ground level, via boat and elevated working platform; concrete core sampling for chloride and carbonation; half-cell potential measure; concrete breakout for reinforcement condition and section loss assessment; underwater diving inspection including ultrasonic pile thickness and cathodic protection potentials measurement; and timber and termite specialist inspection and testing.
The work included conventional and cathodic protection concrete repair, protective coatings, bridge expansion joint replacement, pile strengthening repairs, fender system replacement, and piling and steel work repairs.
The repair specifications called for the extent of works to be identified with pre-repair surveys and recording of inspection results. The defects were checked and certified prior to the approval of any works. A trial repair was also conducted to establish the extent of concrete breakout required.
The extent of concrete remediation was carried out with a make-safe program undertaken to remove all likely delaminations that could cause injury. A marked up drummy survey was carried out and location and quantity verified by GHD prior to breakout commencing. Breakout was carried out to the specification requirements on the extent of reinforcement corrosion and delineation saw cuts were installed at the perimeter of the repair area. All the final measurements, post-breakout, were undertaken and verified by GHD for the purposes of repaired documentation and commercial reimbursement.
As a result of all this hard work, Duratec Australia and GHD won three categories (Marine, Wharves and Mega Projects (>$10M in value) and was announced the overall winner of the Australasian Concrete Repair and Remedial Building Association’s (ACRA’s) Excellence Awards. The Concrete Institute of Australia congratulates our Silver Members Duratec and GHD on their exception wins.