Page 255 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

CORROSION CONTROL OF BRIDGES 233

2
So far, over 2.0 million m of reinforced and prestressed concrete structures have
been protected worldwide.
Anode selection and application have proven to be a challenge in designing CP
systems for concrete structures with adequate life. The anode for concrete bridge
deck should have the following features:

1. Capability to withstand traffic loads.
2. Resistance to environmental factors such as moisture and temperature fluctua-
tions.
3. Design life equal to or greater than that of wearing surfaces.
4. Sufficient conductive surface area to minimize or completely prevent mature
deterioration of the surrounding concrete.
5. Economical.

Over the past few decades, several anode configurations have been used in concrete
bridge decks and substructures:

1. Coke–asphalt anode system used high silicon iron anode and required wear sur-
2
face. The estimated cost for this anode system is $92/m with service life of
20 years (29).
2. Nonoverlay slotted anode system used platinized-niobium–copper wire anode
laid in regularly spaced slots designed to distribute CP current evenly to the
rebar mat and was filled with a conductive polymer concrete. Estimated cost is
2
$92/m and 15 years of service life.
3. Conductive polymer mound anode system used platinized-niobium copper wire
anode with the conductive polymer mounded on wire anode and rigid concrete
2
overlay on top. Estimated cost is $137/m with a service life of 20 years.
4. Activated titanium mesh secured to the concrete and covered with either con-
2
ventional concrete or latex-modified concrete overlay at a cost of $137/m and
service life of 35 years.
5. Other anode systems specially developed are sprayable conductive polymer
coatings, metallized zinc coatings, and conductive paints. Typical primary
anode for the conductive polymer or paints is platinized niobium wire attached
2
to the concrete prior to application. Estimated cost is $76/m with a service life
of five years.
6. Metallized zinc used either small stainless steel or copper plates epoxied to the
2
concrete surface to make a connection to power service. Cost is $137/m service
life 15 years.

Some problems with the CP system are the following:

1. Debonding of the conductive coating in environments where concrete is con-
stantly wet or when the materials applied before the concrete is dry.