Extended performance is quite reasonably expected of our reinforced concrete structures, some like marine structures are in aggressive environments, they may be many decades old, of critical importance in terms of function and/or location, and irreplaceable, etc. such that repair and protection is necessary during their service lives.
Chloride ion induced corrosion of reinforcement steel is the most common cause of deterioration of prestressed, post-tensioned, or reinforced concrete structures exposed to marine or saline environments.
During the lifetime of a reinforced concrete structure three basic periods with respect to corrosion and corrosion protection of reinforcement can be defined:- the initiation time (t0) where some limited corrosion may commence; the corrosion onset/pit growth period until the commencement, at the activation time (t1) of serious, damaging corrosion; and, the propagation period (t2) when reinforcement corrosion proceeds.
Various repair and protection technologies and approaches are possible during the initiation (t0), corrosion onset (t1) and propagation periods (t2) of a reinforced concrete structure. The paper will summarise the main repair (remediation) and protection technologies and approaches but focus mostly on the ‘do nothing’ and patch repair options that have been engineered to lead to successful long service life extension of various marine reinforced concrete structures.
The ‘do nothing’ approach is often not considered and field experiences of this approach on various marine reinforced concrete structures around Australia will be cited.
There are increasing perceptions that conventional concrete patch repairs (without galvanic anodes) in marine and saline environs are not durable and crack, delaminate and spall within a matter of years. There are also increasing perceptions that incipient anode formation can be induced by such repairs. Reminders will be provided of the fundamentals of conventional concrete repair (without anodes) most particularly the electrochemistry and the effects on such of the various components of conventional concrete patch repair not only on the durability of the repairs themselves but also on incipient anode management. Field experiences of many decades of actual patch repaired marine structures around Australia will also be discussed.
Poor experiences with concrete patch repairs have occurred and the likely reasons for these will be explored. A recent poor experience with patch repairs incorporating galvanic anodes on a marine exposed concrete bridge will also be presented.