Civil Engineering Reference
In-Depth Information
Keys (courtesy Florida DoT).
recommended to use a bulk zinc anode at low tide level to protect the lower
steel and to reduce the consumption of the zinc coating anode.
Many of the piles it has been applied to are prestressed. The use of
galvanic zinc anodes means that the risk of hydrogen embrittlement of the
prestressing is minimised.
The main advantage of thermal sprayed metal anodes are that they do
not change the profile or dead load of the structure or require excavation of
concrete. Most other galvanic anodes have at least one of these drawbacks.
While the thermal sprayed galvanic zinc anode was developed for application
in a marine splash and tidal zone environment, it has been used inland in de-
icing salt exposure conditions. In this case a humectant of hygroscopic salts
was developed (Bennett, 1998). This was designed to reduce the electrical
resistance of the cover concrete and the anode/concrete interface to boost the
current flow of the anode in dryer inland conditions. A proprietary system
with protective/cosmetic top coat is also offered in Europe.
In monitored galvanic anode bridge systems in Florida, sections of rebar
have been isolated from the network and connected via an ammeter to the
rest of the steel. This allows monitoring of protective current flows into a
particular area. Similarly, areas of anode have been isolated and current flow
measured to determine how much current the anode delivers. Occasional
coring can be used to assess the amount of anode consumed and the anode
replaced when necessary. Large-scale galvanic systems are in place protecting
many piles in Florida where over 50,000 m
2
has been applied.
