Bridges

The Auckland Harbour Bridge (AHB), built in 1959 and widened in 1969, has some 125,000 m2 of external steel surfaces which have been maintained using a ‘patch and recoat’ philosophy. This has been carried out since 1998 by Total Bridge Services (TBS) under a performance-specified maintenance contract using moisture-cured urethane coatings. TBS is a joint venture between TBS Farnsworth, Opus International Consultants Ltd and Fulton Hogan. In 2012 a maintenance alliance was formed (AHB Alliance), between the NZ Transport Agency, TBS and Beca. The Alliance commissioned the authors to develop a deterioration model for the existing coatings, review the existing maintenance regime and potential protective coating systems, investigate alternative maintenance strategies, and make recommendations towards developing an optimised strategy to provide corrosion protection within more restrictive environmental protection requirements.This paper summarises the findings of the initial report and some subsequent investigations including analysis of 15 years of audit adhesion testing, and the possible use of a high ratio calcium sulfonate alkyd overcoating system to avoid the need for abrasive blasting and so reduce the environmental impact of maintenance painting.