In this study, data from galvanic and hybrid electrochemical treatments applied to structures is
analysed. It is shown that the protection of steel in concrete using galvanic anodes finds theoretical support
from a basis of improving the environment or maintaining a benign environment at the steel. Protection current
output responds to the aggressive nature of the environment and, as a result, galvanic anodes have substantially
longer lives than originally predicted. Monitoring is preferably focused on monitoring the effect of
the protection on the condition of the structure and may be achieved by monitoring either steel corrosion rate
and/or steel corrosion potential. Monitoring is preferably combined with a risk management option such as a
facility to apply a temporary impressed current treatment to arrest active corrosion if a risk is identified. An
allowance for new galvanic protection criteria has been made in the latest European standard on Cathodic
Protection of Steel in Concrete

Christian Christodoulou (7175462)

Gareth K. Glass (7175465)

S.P. Holmes (7175459)

English

Loughborough University Institutional Repository

   This item was submitted to Loughborough’s Institutional Repository (https://dspace.lboro.ac.uk/) by the author and is made available under the following Creative Commons Licence conditions.      For the full text of this licence, please go to: http://creativecommons.org/licenses/by-nc-nd/2.5/  1 INTRODUCTIONCorrosion of steel in concrete is an electrochemi-cal process and electrochemical techniques havebeen used to control corrosion.  The simplest of the-se techniques is galvanic protection.  In this case agalvanic anode is connected to the steel and the an-ode corrodes while delivering a protection current tothe steel.  Another technique is a hybrid treatment inwhich a high protection current is briefly impressedoff a galvanic anode before galvanic protection isapplied (Holmes et al. 2011a).  This work looks atdata from such systems and considers their perfor-mance.2 RESULTS2.1 Galvanic AnodesGalvanic anodes were installed at the edge ofpatch repairs on a car park deck suffering from de-icing salt induced corrosion.  Figure 1 shows an as-pect of the installation process. The anodes were in-stalled in drilled holes (25mm diameter by 40mmdeep) in the parent concrete and were encapsulatedin a proprietary putty and connected to the steel.Figures 2 - 3 shows the potential changes relativeto an arbitrary reference at some distance from theedge of the patch repairs where the anodes wereconsidered to have no influence on the potentials(Christodoulou et al. 2011).Figure 1  Installation of a galvanic anode at an area ofconcrete repair.Anode polarisation effect at 14 Days-450-400-350-300-250-200-150-100-5000 200 400 600 800 1000 1200 1400Distance from Patch (mm)PotentialChange(mV)700 mmFigure 2  Change in potential induced by anodes in-stalled in concrete repairs.Protection of Steel in Concrete Using Galvanic and HybridElectrochemical Treatments.G.K. GlassConcrete Preservation Technologies, Nottingham, UKChristian ChristodoulouAECOM, Birmingham, UKSteven Holmes1Concrete Preservation Technologies, Nottingham, UKABSTRACT: In this study, data from galvanic and hybrid electrochemical treatments applied to structures isanalysed.  It is shown that the protection of steel in concrete using galvanic anodes finds theoretical supportfrom a basis of improving the environment or maintaining a benign environment at the steel.  Protection cur-rent output responds to the aggressive nature of the environment and, as a result, galvanic anodes have sub-stantially longer lives than originally predicted. Monitoring is preferably focused on monitoring the effect ofthe protection on the condition of the structure and may be achieved by monitoring either steel corrosion rateand/or steel corrosion potential. Monitoring is preferably combined with a risk management option such as afacility to apply a temporary impressed current treatment to arrest active corrosion if a risk is identified. Anallowance for new galvanic protection criteria has been made in the latest European standard on CathodicProtection of Steel in Concrete.Anode polarisation effect at 60 Days-200-180-160-140-120-100-80-60-40-2000 200 400 600 800 1000 1200 1400Distance from Patch (mm)PotentialChange(mV)Figure 3  Change in potential induced by anodes in-stalled in concrete repairs.Potential measurements were taken at both 14 and60 days.  The locations did not coincide because ac-cess was limited by parked cars. The data shows thatin  both  cases,  the  anodes  had  a  dominant  influenceon the potential changes to a distance of about600mm.2.2 Hybrid treatments.A hybrid treatment briefly impresses a high cur-rent off a galvanic anode using a battery or tempo-rary power supply for a period of about a week to ar-rest active corrosion before connecting the anode tothe steel to continue delivering galvanic protection.A Hybrid AnodeTM consisting of a discrete galvanicanode with an impressed current connection is gen-erally  used.  Figure  4  shows  an  example  of  such  ananode temporarily fitted in a drilled hole with a tita-nium connection detail.Figure 4  A galvanic anode with a titanium connec-tion temporarily fitted in a hole.Data was collected from hybrid treatments ap-plied to bridge piers and abutments suffering fromchloride induced corrosion. Figure 5 shows the ef-fect  of the treatment on open circuit  steel  potentials(Holmes et al. 2011b). The steel potential shifted tomuch more positive values after 60 days of protec-tion in this example.Figures 6 - 8 shows the logged currents, tempera-ture and potentials obtain on a bridge structure overa 4 year period. The current output was subject todaily and seasonal fluctuations arising from changesin the temperature with higher temperatures result-ing in more current. Flooding occurred after 530 and840 days and this again caused the current output toincrease and the potentials to fall.-600-550-500-450-400-350-300-250-2000 5 10 15 20 25 30Elapsed Time (min)SteelPotential(mVvsSCE)Potential Prior To Treatment(4% Cl-)Potential Decay After 60 daysFigure 5  Effect of hybrid galvanic anode treatmenton steel potentials.Whiteadder bridge galvanic current and temp to May 200900.511.522.530 100 200 300 400 500 600 700 800Time (days)Current (mA/m2 )-30-20-100102030Air Temperature (°C)TemperatureLower zoneUpper zoneRiver in flood causes current torise to 4.5 and 2.5 mA/m2 forlower and upper zonesFigure 6  Protection current, steel potential and tem-perature from a bridge structure.Whiteadder bridge -  Reference Electrodes 1-6 (Upper Zone)-260-240-220-200-180-160-140-120-1000 100 200 300 400 500 600 700 800Time (days)Steel potential (mV vsAg/AgCl)Ref 1 Ref 2Ref 3 Ref 4Ref 5 Ref 6River in flood and piers underwater causes current to increaseand steel potential shifts morenegative to -430 mVFigure 7  Steel potentials from a bridge structure.Whiteadder bridge -  Reference Electrodes 1-6 (Upper Zone)-260-240-220-200-180-160-140-120-100500 600 700 800 900 1000 1100 1200Time (days)Steel potential (mV vs Ag/AgCl)Series1 Series2Series3 Series4Series5 Series6Figure 8 Steel potentials from a bridge structure.Figure 9 shows an example of steel potentials andcorrosion rates obtained on a bridge subject to hy-brid galvanic anode treatment (Glass et al. 2008).The potentials shifted to more positive values overthe first two years of operation while the corrosionrates were all below 1mA/m2.Steel corrosion potentials andrates in a 2006 bridge installation-300-250-200-150-1000 100 200 300 400 500 600 700Time (days)Potential (mV vs SCE)01234 Corrosion Rate (mA/m2)Corrosion ratePotentialPotential (mV vs SCE) Corrosion Rate (mA/m2)Potential (mV vs SCE) Corrosion Rate (mA/m2)Figure 9  Steel potentials and corrosion rated fromprotected bridge elements.3 DISCUSSION3.1 Basis for Galvanic protection.The protective effects of electrochemical treat-ments are broadly described as chloride extraction,re-alkalisation and a negative steel potential shift.These are summarised in Table 1 and tend to be re-lated to different electrochemical treatments (Mietz1998). However all mechanisms operate in any con-tinuous treatment.Re-Alkalisation(CEN.TS14038-1)Chloride Ex-traction(prCEN.TS14038-2)Cathodic Pro-tection(EN12696:2012)ProtectionobjectivePassivatingenvironment(restore highpH)Passivating en-vironment (re-move chloride)Potential(adequate pola-risation)TreatmentTimeTemporary(3-14 days)Temporary(6-10 weeks) PermanentCurrentDensity 0.8 - 2 A/m2 0.8 - 2 A/m2 3-20 mA/m2Table 1  Summary of protective effects and associ-ated treatments.Both carbonation and chloride induced corrosiondamage result from a reduction in the pH at the steel.In the case of chloride induced corrosion this reduc-tion in pH is localised.  Chloride induced corrosionis sometimes termed autocatalytic (self-accelerating)(Glass et al. 2008).  A pit nucleation event at the siteof corrosion initiation leads to the formation of solu-ble iron ions.  These react with water to produce ironhydroxide and positive hydrogen ions.  Chlorideions act as a charge balancing species.  Hydrochloricacid is effectively produced.  Corrosion propagatesbecause a macro-corrosion cell is formed.  The gen-eration of acid at a corroding site is balanced by thegeneration of hydroxide away from the corrodingsite.The dominant effect in the cases of continuouselectrochemical treatments is most probably an im-provement in the environment at the steel (Chris-todoulou et al. 2010). The evidence for this comesfrom the long time required to achieve protectionand the low protection current densities relative tothe localised steel corrosion rate at which protectionis achieved (Glass et al. 2008).  Much less current isrequired to prevent corrosion initiation than that re-quired to arrest an existing corrosion process.Specific evidence from galvanic systems comefrom the observation that zinc, thermally applied toconcrete surfaces does give adequate protection inaggressive subtropical marine conditions. If it canprotect steel in aggressive conditions, then it shouldalso be able to protect steel in less aggressive condi-tions (Holmes et al. 2011a).Galvanic current output tends to fall with time asthe anode is consumed (Fig. 6).  As a result galvanicprotection is not generally achieved by sustaining anadequate  level  of  steel  polarisation.   Indeed  somegalvanic anode systems are only installed as a corro-sion prevention system and rely on concrete patchrepairs to arrest active corrosion.3.2 Responsive Behaviour.Galvanic protection does not have a user control-lable protection current output. However the protec-tion current output of a galvanic anode varies withtemperature and moisture content in the same waythat the corrosion rate of steel varies with these fac-tors.  This is termed responsive behaviour. As shownin Figures 6 to 8 current from galvanic anodes in-creases in wet an hot environment  which are alsomore aggressive to steel.In cold and dry periods, the current output falls.As  a  result  the  life  of  the  anode  is  increased.   Theservice life of an anode is not determined by a max-imum current density, but by a much lower averagecurrent density (Holmes et al. 2011a).3.3 Monitoring.Monitoring the performance of galvanic anodes ispreferably focused on monitoring changes in thecondition of the structure that arise as the result ofthe protection because galvanic protection does notgenerally sustain high levels of steel polarisation.Examples include corrosion potential as a functionof time and/or distance from an anode or edge of therepaired area and/or corrosion rate (Christodoulou etal. 2011).Figure 5 provides an example of how the opencircuit steel potential shifted to substantially morepassive (positive) values after a period of protection.Figure 2 provides an example of the effect of the an-odes on the change in potential in the concrete nearthe edge of a concrete repair area.  Figure 9 providesan example of how the corrosion rate changed withan increasing period of treatment.Corrosion rates up to 2mA/m2 are generally con-sidered to be very low or passive.  An acceptancecriteria might include demonstrating that the corro-sion rate at a selected locations representing areas ofhigh corrosion risk is less than 2 mA/m2.  Such a cri-terion is suited to a treatment primarily aimed at ar-resting existing active corrosion such as the hybridelectrochemical treatment described above [4].Some galvanic protection methods are aimed atpreventing incipient anodes from forming.  In thiscase the treatment is preventative. One acceptancecriterion in this case is to measure the effect of theanodes on the potential through the concrete along aline extending away from the edge of a repaired areaand to show that the influence of the anodes domi-nates the potential changes to a distance of 300mm.3.4 Acceptance of Galvanic Technology.The use of galvanic anodes to provide protectionhas recently been added to the European Standard onCathodic Protection of Reinforced Concrete (BS EN12696:2012).  Criteria such as those suggestedabove are allowed for galvanic anodes.Monitoring is preferably combined with a riskmanagement option in the event that monitoringshows evidence of active corrosion.  This is a re-quirement imposed by the revised European Stand-ard.  Such an option could be to include a facility toapply a temporary impressed current treatment to ar-rest active corrosion if active corrosion is identified.One advantage of the technique is it is much lesscomplex than other electrochemical techniques andimprovements have been made (e.g. the hybrid an-ode system described above) to overcome the lim-ited power in galvanic anodes.  Thus the number andvariety of case histories is growing rapidly.4 CONCLUSIONSThe protection of steel in concrete using galvanicanodes finds theoretical support from a basis of pro-tecting the steel by improving the environment ormaintaining a benign environment at the steel.  Gal-vanic protection is not generally achieved by sus-taining an adequate level of steel polarisation.Protection current output responds to the aggres-sive nature of the environment and as a result gal-vanic anodes have substantially longer lives thanoriginally predicted because the anode is not con-sumed in cold and dry conditions.Monitoring the performance of galvanic anodes ispreferably focused on monitoring the effect of theprotection on the condition of the structure and maybe achieved by monitoring either steel corrosion rateand/or steel corrosion potential. Monitoring is pref-erably combined with a risk management optionsuch as a facility to apply a temporary impressedcurrent treatment to arrest active corrosion if a risk isidentified.Galvanic protection is increasingly being usedbecause it is less complex than other electrochemicaltechniques.  There are now a significant number andvariety of case histories of galvanic and hybrid ap-plications. An allowance for new galvanic protectioncriteria has been made in the latest European stand-ard on Cathodic Protection of Steel in Concrete.5 REFERENCESChristodoulou, C., Glass, G., Webb, J., Austin, S. andGoodier C., “Assessing the long term benefits of ImpressedCurrent Cathodic Protection” Corrosion Science 52 (2010) p.2671-2679.Christodoulou C., Glass G., Webb J., Austin S. and GoodierC., 2011, “A new approach for the patch repair of car parks us-ing galvanic anodes”, Concrete Solutions 4th InternationalConference on Concrete Repair, 26-28 September 2011, Dres-den.Glass, G.K., Roberts, A.C., Davison, N.,  “Hybrid corrosionprotection  for chloride contaminated  concrete”  Proceedingsof  the  Institute  of  Civil  Engineers, Construction Materials,161 (2008) p. 163-172.Holmes S.P., Wilcox G.D., Robins P.J., Glass G.K. andRoberts A.C., 2011a “Responsive behaviour of galvanic anodesin concrete and the basis for its utilisation” Corrosion Science53 p. 3450–3454.Holmes S.P., Wilcox G.D., Robins P.J., Glass G.K. andRoberts A.C., 2011b “Long term assessment of a hybrid elec-trochemical treatment”, Materials and Corrosion 62, p. 1-7.Mietz J. 1998, Electrochemical Rehabilitation Methods forReinforced concrete Structures, A state of the Art Report, Eu-ropean Federation of Corrosion publication number 24, p.1.

Protection of steel in concrete using galvanic and hybrid electrochemical treatments

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Protection of steel in concrete using galvanic and hybrid electrochemical treatments

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