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Harbor
Cathodic Protection System Installation
Anode Installation. A mesh ribbon of titanium was used with a mixed
metal oxide coating as an anode (Figure 31). The ribbon is 1/2 inch
(1.25 cm) wide and approximately 0.05 inch (1.2 mm) thick. The contractor
embedded the ribbon in a grid pattern in saw cut slots in the bottom
surfaces between the curb and the outside pile girder and between
the track slabs (Figures 32 and 33). The slots were ¾ inch
(2 cm) deep and 3/16 inch (0.5 cm) wide. When drain holes, pipe
hangers, or other obstructions were encountered the ribbon slots
were shifted to clear the obstructions by at least 1 inch (3 cm).
The longitudinal slots were spaced 13 inches (33 cm). Both ends
of the anode ribbon terminated at holes the same depth as the slot
and approximately 1 inch (3 cm) in diameter where ends of anode
was welded to a 1/2-inch (1.25 cm) wide, titanium header ribbon
(Figures 34 and 35). The header ribbon was connected to a Number
12 AWG (2.7 mm diameter) lead wire via a mechanical copper fastener
and completely sealed with epoxy.
The mesh was grouted into place using polymer modified, Sikatop
123 Plus® ensuring the anode was in good electrical contact
with the concrete (Figure 36). The objective was to use a grout
that was as good an electrical conductor as the surrounding concrete
with a maximum resistivity of 25,000 ohm-cm. The anode ribbon was
held in place with small wedges (golf tees) or Dow? backer rod until
the grout was in place. The contractor had to go back and apply
grout to the open lengths after removing the tees and backer rod.
NFESC engineers tested all components of the anode installation
and found no electrical contact with any metal in the wharf.
The lead wire and its connection to the header ribbon was contained
in 1 inch (3 cm) polyvinyl chloride (PVC) conduit starting at the
point where the header ribbon emerges from the concrete. The conduit
ran to the closest transverse girder where it teed into another
conduit that ran along the transverse girder at the end of a span
(between transverse girders). The latter acted as a common carrier
for all anode lead wires from each span. Each span’s conduit
proceeded toward the curb under the outboard pile girder where they
teed into a 2-inch (5 cm) conduit running longitudinally under the
curb deck alongside the pile girders. The 2-inch (5 cm) conduit
is a common carrier for all anode lead wires from individual spans.
Each conduit tee has a watertight access plate allowing wire connection
and inspection. All wire-to-wire connections of leads below deck
were solder joints that were sealed. The 2-inch (5 cm) conduit was
routed to a junction box for each segment. Conduit was mounted securely
by nonmetallic clamps or straps spaced at 6 feet (2 m) intervals.
Figure 31. Titanium mesh, anode ribbon.
Figure 32. Saw cutting grid slots for titanium ribbon anode.
Figure 33. Anode grid slots under the curb slab.
Figure 34. Fitting titanium header ribbon.
Figure 35. Welding header ribbon to anode mesh ribbon
Figure 36. Grouting anode slots with Sikatop 123 Plus©.
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