MARKHAM durability and remediation project – the Bledisloe Wharf: how MARKHAM arrested the deterioration of a major concrete marine structure in Ports of Auckland, New Zealand.
The Ports of Auckland were monitoring the deterioration of the Bledisloe Wharf, and in 1999 were coming to the conclusion that the wharf should be replaced. A cathodic protection system was in the process of being installed to the wharf beams, but the decision was made to discontinue this due to cost. There was also the issue that
cathodic protection did not protect other vital aspects of the structure such as pile caps, piles, upper and lower faces of the deck, and the key edge beam.
Routine inspections discovered a severe chloride contamination and with the profile of the penetration extending in beyond the lower reinforcing strands and stirrups. There were many sites where corrosion was evident or rust stains were seeping out of the concrete.
Compounding the problem were two factors. A ship had regularly discharged bilge water with contaminants that effectively sealed the lower surfaces of the I-beams with a deposit in appearance similar to a varnish. Secondly tidal washing and splashing combined with salt contaminated rainwater which was leaking through the deck and running down the sides of the beams caused moisture and chlorides to be encapsulated within the concrete by the impermeable coating of “varnish” on the lower flange of the beam.
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