Bledisloe Wharf – Port of Auckland

Adding Life to Concrete – How MARKHAM arrested the deterioration of a major concrete marine structure at the Port of Auckland.

OBJECTIVE

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.

SOLUTION

After independent testing, AQURON 7000 was selected to combat corrosion of reinforcing steel, in view of delaying the need to replace the Bledisloe Wharf. The intent was to secure a few more years’ active life from the structure. This was applied in 2001.

The bottom of the beams, piles and other elements were high pressure water-blasted and with sand for the more difficult areas to clean. Then the AQURON treatment was applied to every exposed surface of the structure using high pressure spray equipment and a barge below deck.

Current system name for this treatment: CIVIL-TECT.

Soon after this work was completed, areas where corrosion or rust staining had been evident were tagged. Beams were inspected and any defects were recorded photographically and by detailing on plans.

RESULTS

An inspection of the wharf by Beca Consultants, Ports of Auckland, and MARKHAM team 10 years after applying the AQURON 7000 system confirmed there was no evidence of any further ongoing corrosion to the Bledisloe Wharf. Even the tagged sites appeared to be entirely dormant with none of the previous rust stain emissions.

Another major benefit was that the deck was effectively waterproofed. Before the inspection, a very wet weather pattern had been saturating Auckland and heavy rain was falling during this inspection in a pontoon beneath the wharf. Only one small leak point through the deck was observed where previously leakages had extensively stained the soffit panel junctions and down the sides of the beams.

This was an excellent outcome, and even at that time exceeded the expectations of extension of service life.

As at 2021, the Bledisloe Wharf is still in use and is in fact being extended. A remarkable win for Port of Auckland, and a very major saving in replacement costs.