Client – Melbourne Water
Consultant – Infracorr Consulting Pty Ltd
Contractor – John Holland -KBR joint venture
The Patterson Lakes retaining wall backs onto approximately 820 properties along the canals in the picturesque suburb of Patterson Lake, located 35 km south-east of Melbourne. The retaining wall was constructed in 1970 from reinforced concrete blocks, corrosion of the steel reinforcement was imminent due to a marine environment and tidal influences.
John Holland-KBR Joint Venture was engaged by Melbourne Water to extend the service life of the 6.4 klm retaining wall for another 50 years, they partnered with Infracorr Consulting to develop a corrosion protection design.
Working closely with JH-KBR JV and Melbourne Water, Infracorr developed a range of concept designs. Two issues that created some challenges were that the wall was not electrically continues and that the reinforcement was tightly congested throughout the structure.
The Hybrid corrosion protection option was the preferred option over impressed current, ground anode and galvanic-only concept designs. Over 16,000 anodes were installed by the contractor over a 12-month period.
Infracorr Consulting liaised with Concrete Preservations Technology [CPT] in the United Kingdom and developed a customised geometrical anode that was narrower (to eliminate risks of touching reinforcement during installation) and longer (to reduce the number of drill holes required during rehabilitation.
The Hybrid CP system utilizes zinc alloy anodes installed into drilled holes, with the anodes initially powered using a small power supply. The high initial current passivates the reinforcement, restoring the alkaline (high pH) environment to the concrete. Following this initial phase, the power supply and temporary cables are removed, and the anodes are then connected to the reinforcement to provide ongoing galvanic protection.
In conjunction with concrete patch repairs and protective coatings, the Hybrid CP system was chosen to provide long-term protection to the concrete retaining wall.
Hybrid CP was adopted over traditional ICCP primarily as it is very suited to this type of environment and its inherent benefits of significantly reducing requirements for monitoring and maintenance and hence major savings in the associated costs.
The repair works are designed to provide an additional 50 years of life to the structure.