Bridges

The Queen Street Bridge over Laverton Creek in the west of Melbourne is a 35-year old bridge consisting of inverted ‘T’ beams which are simply supported on four large pier walls and situated in a marine environment. Routine visual inspection revealed cracking and severe delamination and spalling in parts of all four pier walls. A detailed diagnostic investigation supplemented by a load rating assessment taking into account the identified defects was undertaken to establish the condition of the bridge with a view to identifying suitable remedial options. The diagnostic investigation included visual inspection of the various components, non-destructive tests carried out on site and compressive strength, volume of permeable voids and chloride tests on concrete cores extracted from the pier walls. The condition assessment revealed that the severe deterioration of the pier walls can be attributed to the lower quality of the concrete and subsequent chloride-induced corrosion of the steel reinforcement. Following consideration of various remedial options a combined repair system of coated reinforced concrete jackets and encased sacrificial (galvanic) anodes was used in the four pier walls to mitigate the deterioration caused by the chloride-induced corrosion of the steel reinforcement. The reinforced concrete jacket which also strengthened the piers was constructed using a self-compacting fly-ash concrete, and in order to further enhance its protective capability, a zinc-based sacrificial (galvanic) corrosion protection system, namely, Galvanode DAS (distributed anode system) anodes with self regulating voltage and current output were encapsulated within the reinforced concrete jacket. Monitoring over the past 3 years shows that the combined system performs very satisfactorily with the embedded anodes only required to make a small contribution at this stage to the performance of the overall system. This paper presents the findings of the diagnostic investigation and provides details of the construction of the protective system and its subsequent monitoring and performance.