Civil Engineering Reference
In-Depth Information
anode-copper connections failed at some point in time. This type of failure
is discussed in more detail below. Summarising the inventory, in 33 out of
52 well-documented cases, the CP system worked well without failures or
unforeseen maintenance.
Figure 6.5
provides the probability of failure as a
function of time, for anode failure, anode-copper connection failure and
reference electrode failure. For anode failure, ranges are shown. The lower
boundary represents the two cases of full anode replacement, the upper
boundaries represent all cases including local anode disbonding.
6.4 Degradation of anode-copper connections
The connections between the primary anode (e.g. platinum wires or silver
wire fabric used as primary anodes in coating systems) and the copper cabling
are sensitive to accelerated corrosion. If the copper comes in ionic contact
with the concrete, anodic polarisation dissolves the copper in a short time,
causing loss of electrical connection. One option to protect a connection
is by manually applying an isolating material around it, usually a polymer
resin, like epoxy. The epoxy-encapsulated connection is then embedded in
the concrete and the remaining space is filled with mortar (cementitious or
epoxy). The absence of accelerated corrosion in the connection depends on
the perfection of this isolation. Water ingress through the isolation provides a
conduction path from the copper to the concrete pore system and promotes
corrosion. Another option is to connect bare copper wires and primary
anodes in connection strips inside a junction box, which is supposed to be
watertight. In this case, water leakage into the junction box may provide a
conduction path to the concrete and promote accelerated corrosion.
0.50
0.50
0.50
0.45
0.45
0.45
connections fail
0.40
0.40
0.40
anode
fails
0.35
0.35
0.35
0.30
0.30
0.30
REs fail
0.25
0.25
0.25
0.20
0.20
0.20
0.15
0.15
0.15
0.10
0.10
0.10
0.05
0.05
0.05
0.00
0.00
0.00
0
0
0
2
2
2
4
4
4
6
6
6
8
8
8
10
10
10
Age (years)
(all related to conductive coatings, see text), anode-copper connection failure and
reference electrode failure.
