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TECHNICAL PAPER

somewhat inconclusive [11] . The ability of the activated titanium
anodes themselves to operate at high current densities (up to
220 mA/m ) for short periods is well established but can give
2
rise to acid attack of the surrounding cementitious material [10] .
This needs to be considered particularly when such anodes are
not applied to the surface of a structure but inserted in holes
drilled into the concrete and embedded in a cementitious repair
mortar with or without a graphite-based backfill. The inclusion of
saturated lithium hydroxide in the cementitious mortar has been
suggested for the use of discrete titanium oxide anodes which
decreases the risk of acidification of the encasement mortar
allowing current densities in excess of 220 mA/m 2 [12] .

All these ICCP systems require the installation of external
Figure 4: Activated mesh anode fixed on the steel reinforced concrete power supplies such, as transformer rectifiers. To comply with
element prior to the application of a cementitious overlay CP standards (see later) carefully controlled long-term current
distribution and zoning of the anodes to deliver the required
a 0.2 mm coating in less than 6 years . The reported failure current are essential requirements with the necessity of continual
[9]
mechanism involves gradual increase in the resistance of the monitoring of the systems.
coating owing to zinc corrosion so that the current distribution is
likely to become ineffective [11] . A range of thickness 0.2-0.4 mm 3. CORROSION CONTROL WITH THE USE OF
is recommended for optimum performance [10] and the current GALVANIC ANODES
density should not exceed 10 mA/m over significant timescales.
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This should ensure a lifetime of the order of 25 years for a A parallel development since the early 1990’s has been the
0.4 mm coating thickness. introduction and gradual establishment of galvanic anodes,
firstly, to control the formation of incipient anodes, often
Activated titanium electrodes with proprietary electrocatalytic described as the ‘ring effect’, around the periphery of patch
coatings are available in several forms, the most widely used repairs, simply by attaching galvanic anodes to the exposed
being an expanded mesh which is normally attached to the steel around the perimeter of patch repairs prior to the
surface of reinforced concrete by means of non-metallic fixings application of the repair material (Figure 5). Subsequently,
and covered with a cementitious overlay of appropriate low more and more applications of continuously improving galvanic
resistivity (Figure 4). A variety of such overlays, applied by anodes have been established with anodes placed in a grid
different means, have been used and their performance is formation (Figure 6) or along the exposed steel reinforcement
critical to the durability of the anode system. Some failures have where applicable (Figure 7).
occurred due to disbondment of the overlay and these have
generally been attributed to deficiencies in surface preparation, That galvanic anodes control steel reinforcement corrosion
pre-treatment or application procedures. Evidence as to whether adequately was demonstrated elegantly in large slabs in India [13] .
the substrate/overlay bond strength may be significantly These had dimensions of 1 m x 1 m x 0.25 m. Some had nine
affected by sustained application of CP in certain instances is galvanic anodes attached to the steel members in a 3 x 3 grid

Galvanic Alkali activated
anodes encasing mortar
to keep zinc Alkali activated
active encasing mortar
to keep zinc active

Figure 5: Alkali activated galvanic anodes, as in inset, attached to steel Figure 6: Chains of alkali activated galvanic anodes, as in the inset,
reinforcement prior to the application of the repair material placed in drilled holes in the concrete in a grid formation to control
corrosion of the steel reinforcement

64 THE INDIAN CONCRETE JOURNAL | APRIL 2021