Life Extension of Bridges, 2010

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1 INTRODUCTION

Cathodic protection (CP) is a very useful tool to repair reinforced concrete bridge structures when suf-fering of chloride induced corrosion. Chloridescommonly derive from de-icing salts and/or were

formerly used as concrete admixture. Chloride con-taminated reinforced concrete structures mainly suf-fer from cover concrete delamination and loss of re-inforcement cross-sections. Conventional repair methods involve removing all of the chloride-contaminated concrete causing an increased amountof material to dispose and used to reinstate the struc-ture. Using CP there is no need to remove all of thechloride-contaminated concrete reducing the timefor access, repair and traffic management. It is onlynecessary to remove spalled concrete and to reinstateheavily corroded reinforcement bars.

CP involves polarizing the reinforcement in an elec-trical circuit. The electrical circuit converts the rein-forcement into the cathode and an inert electrode(e.g. mixed metal oxide coated titanium) forms theartificial anode which can be installed discretely or on the surface. Additionally a secondary effect of aworking CP system is that it causes chloride ion dif-fusion from the steel to the anode, enhancing corro-sion protection. The main benefit for the structure isthat it is not necessary to remove all of the chloride-contaminated concrete. This is beneficial not only

because it reduces the volume of concrete removed but also because it often eliminates the need to sup- port the structure during the work, Lambert (1998).

Three different CP systems installed on freeway and bridge structures in the UK are described.

2 M4 ELEVATED FREEWAY - LONDON

2.1 General

The M4 is a major elevated freeway into the west of London. It carries 87,000 vehicles per day into and

out of the capital of England. It was constructed di-rectly over an existing major highway that carries anadditional 51,200 vehicles per day. Both run througha residential area with private dwellings directly ad-

jacent to the twin level route. The elevated freewayis 3.5 miles long and is made up of pre-stressed

beams supported on 120 bents using two half jointsat each bent, see Figure 1. It was constructed in 1967and has long showed its age. Every winter, hugequantities of de-icing salts are liberally applied to

prevent ice forming on the freeway.

Sustainable and cost effective solutions to life extension of bridges

C. P. Atkins, P. Lambert, R. Brueckner, R Merola & A. R. Foster Mott MacDonald, Altrincham, United Kingdom

ABSTRACT: In order to minimise costs and disruption associated with repair it is necessary to minimise the

amount of concrete removed wherever practical. Cathodic protection (CP) can be used as a repair techniquefor chloride contaminated concrete. The main benefit is that it is no longer necessary to remove all the chlo-ride contamination. This paper presents an outline of a number of UK based projects where CP has formed akey part of a maintenance strategy.

Figure 1. Twin half joints contribute to the problems.

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Bridge Maintenance, Safety, Management and Life-Cycle Optimization – Frangopol, Sause & Kusko (eds) © 2010 Taylor & Francis Group, London, ISBN 978-0-415-87786-2



These have penetrated the leaking joints and passedinto the concrete.

2.2 The Challenge

Levels of chloride of over 5% by mass of cement(17.5kg/m3

or 30lb/yd3) are regularly recorded, with

one value double this. The reinforcement is corrod-ing, and concrete has spalled. The shape of the struc-ture means the majority of work has to take placewithin lane closures. For most of the structure thiscan only take place at night when the traffic volumesare lowest. The residential area means that you can-not make any significant noise at night to carry outrepairs. The acceptable level of noise is roughlyequivalent to loud speech.

In the first instance the structural capacity was as-sessed and all loose concrete removed to prevent thisfalling onto vehicles. Then a repair strategy had to

be developed for the most heavily chloride contami-nated half-joints. A standard mesh and overlay CPsystem could only be used in conjunction with shut-ting the whole freeway. To install anodes from thesoffit required a total length of drilling of approxi-mately 600 feet. The estimated duration was over 30days per crossbeam. The persistent traffic during theday meant the drilling would have to be carried outat night but the noise limits prevented night work.

2.3 The Solution

On reviewing the reinforcement details it was notedthat there was an area running along the crossbeamthat contained no reinforcement. This was close tothe main inaccessible reinforcement. If it were pos-sible to install anodes in this location the risk of hit-ting steel was dramatically reduced so the works be-came more manageable.

The lengths of holes required reduced from 600 to

60 feet so it became shorter in duration. The shorter duration meant that the works became significantlycheaper. The neighbourhood would be less dis-rupted. Site safety would improve as there would befewer people working for shorter periods. The only

problem was that no one had ever attempted this be-fore. A specialist sub contractor was appointed tocarry out a trial. The coring started at one end andremained on course, coming out within 2 inches of where it was predicted. The core drifted down under gravity, but as all the crossbeams to be protectedwere on a camber this was not considered a problem.

Due to the success of the coring trial it was decidedto use this approach on site. The coring was success-fully carried out over three night shifts. A detaileddesign was produced that split the upper section of the crosshead into two zones. Anodes were fixed to

a titanium conductor bar at different locations tovary the current distribution in accordance with thereinforcement. Reference electrodes were also fixedto the conductor bar to allow for monitoring the sys-tem. This was then pulled through the core hole and

grouted into place. The manufacturers recommendedgrout did not flow sufficiently to enable its use so a post tensioned duct grout was employed instead.

It was still necessary to repair the cantileveredcrossbeams, but this was still limited by the noiseand traffic problems. The contractor came up withan innovative approach adapting an airport baggagehandling truck to provide a mobile soundproofed en-closure that could be raised into position and movedaround during night work, see Figure 2. This meantthat hydro-demolition and shotcrete reinstatement

could be carried out at night without disturbing thelocal residents.

2.4 Cost Implications

The installation of the first pier was completed inMarch 2008. The estimated cost savings, assumingdrilling from the soffit was possible, were 20%, re-ducing the cost of repair to approximately US$600,000 per crosshead. The estimated cost of cross-

beam replacement was US$ 10 million. Due to thesavings involved another eight piers were able to berepaired within the next twelve months. At present

prices the cost of fixing the entire viaduct reducesfrom US$ 1.2 Billion to US$ 72 Million by employ-ing this technique. The repair system has provedsimpler and more efficient to install than any option

previously proposed. The approach saves time andmoney, improves site safety and minimises the dura-tion of the road works and the noise generated dur-ing repair. Both environmental and sustainability is-sues have been addressed in a positive andquantifiable manner.

Figure 2. Modified airport vehicle becomes mobile sound-

proof enclosure.

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3 SILVER JUBILEE BRIDGE, RUNCORN

3.1 General

The Silver Jubilee Bridge in Runcorn, UK, was con-

structed in the 1960s and is a Grade II listed struc-ture (Figure 3). It is part of a major highway route in North West England that carries over 90.000 vehi-cles per day on four lanes. The original design car-ried a single lane in each direction, plus a singleovertaking lane along the middle. This was thenwidened to carry two narrow lanes in each directionduring the late 70s. Due to the lane width and thesignificance of this route over the River Mersey traf-fic management with the current volume of traffic isdifficult. A closure would result in a diversion of atleast 40 miles. Partial closure would result in heavy

congestion combined with night work next to livetraffic so it has been crucial to maintain the integrityand durability of the structure. The bridge is such asignificant restriction that a second structure, theMersey Gateway, is to be constructed.

The central span of the bridge is a 1082 feet longsteel arch structure with two 250 feet side spans andis the largest of its type in Europe. The deck is rein-forced concrete supported on structural steelwork.The original surfacing was hand placed mastic as-

phalt. This provided some degree of waterproofing,

but was left in place for over 40 years, until a newwaterproofing and surfacing system was installed in2005. By this time the bridge deck was heavily chlo-ride contaminated and corroding in many areas. Theapproach viaducts have four main beams supported

by reinforced concrete piers. The ends of the beamswere precast, and the central spans were cast in

place at the same time as the deck. The approachspans are a total of 1713 feet in length.

The highways in this part of England are subjectedto chloride-based de-icing salts during the winter months. Although the deck of the approach viaductsis waterproofed and has not degraded significantly,there are joints over every third pier that have de-

graded with time, allowing chloride-contaminatedwater to leak onto the substructure. Chlorides have penetrated the concrete cover, and levels at the rein-forcement have reached 2% by mass of cement – more than enough to cause corrosion.

3.2 Repair History

Over the past 15 years Mott MacDonald’s Materialsand Corrosion team have been tasked with develop-ing effective methods of stopping or controlling cor-rosion on the Silver Jubilee Bridge, Coull (2003).

This has required pushing the boundaries of corro-sion engineering to achieve a durable and reliablerepair at the lowest practical cost, Lambert (2007).Most of the areas protected to date have been acces-sible from underneath the bridge, see Figure 4. Thishas meant that although access has sometimes beenextensive, it has been relatively straightforward.

Several repair strategies have been employed at theSilver Jubilee Bridge, such as patch repairs, electro-osmosis protection and cathodic protections systems.The patch repairs carried out were mainly performed

to ensure public safety. While reinforcement sectionloss was not significant enough to warrant structuralconcerns, the public was at risk from falling delami-nated concrete from under the approach viaducts.Loose and delaminated concrete was removed andthe steel and exposed concrete overcoated using a

polymer-modified cementitious mortar containing anamino alcohol corrosion inhibitor. The mortar coat-ing minimized any further corrosion of the rein-forcement and prevented significant further ingressof the contaminants. This repair method has been

performing adequately and prevented significant

section loss over the previous 10 years, Baldwin(2003).

An electro-osmosis system has been specifically de-veloped to control moisture levels in a pier of the

bridge by the application of controlled low voltageDC pulses. The system is capable of reducing mois-ture levels in concrete to between 60% and 70% RH,and maintaining this level irrespective of externalweather conditions. An additional benefit to the re-moval of excess free moisture is the associated re-duction in dissolved salts, particularly chloride, pre-

sent within the pore solution of the concrete, withthe overall effect of reducing chloride ions to belowcritical levels with respect to chloride-induced cor-rosion. The system is also designed to negatively po-larise the reinforcement resulting in a degree of ca-thodic protection, helping to reduce the corrosion

Figure 3. Silver Jubilee Bridge, Runcorn side.

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Figure 4. Original pier located under a joint in the deck above.

risk of embedded steel during the transition periodfrom high to low relative humidity (typically severalmonths), and providing additional protectionthroughout the life of the installation, Lambert(1997).

3.3 Mesh and Overlay CP

The first cathodic protection system was installed in1993 and represented the first commercial use of coated titanium mesh with a dry-mix shotcrete over-lay for CP systems in England. The basic mesh and

overlay system was also used on the next two con-tracts, but in 1998, another innovative approach, ahybrid system, was used. This hybrid system com-

bined discrete anodes with mesh and overlay. In anunusual step, dry-mix shotcrete was used for theconcrete repairs, while wet-mix shotcrete was used

for the overlay to minimize dust and noise disruptionto a neighbouring school.

In 2000 a cathodic protection system and patch repairs were used during a repair contract which in-

cluded extensively contaminated areas next to theabutment and locally affected areas at the highestsections of the approach viaducts. To reduce costs,locally affected areas with difficult access were

patch repaired using hand-applied mortar containingcorrosion inhibitor to protect against the ring anodeeffect.

The systems installed after 2000 were designed byreviewing the operating criteria of the existing sys-tems. By employing this technique it was possible toreduce the quantity of anodes used, in some cases by

a factor of 3. In addition the lower current demandmeans larger zones can be used, which reduces thenumber of monitoring probes and power supplies.As an example one system installed in 1995 used 7zones to protect one 30m long beam. Four of thesezones had multiple layers of anode mesh. Therewere 24 reference electrodes and 6 graphite potential

probes installed. In 2005 four similar beams were protected as a single zone, with a single layer of mesh anode and 4 reference electrodes.

3.4 Innovative CP Solution

The remaining heavily chloride contaminated bridgeelement to be protected is the deck; however, thereare limitations in respect of the suitability and acces-sibility. The bridge deck is 131 feet above the River Mersey and the Manchester Ship Canal and trafficmanagement is restricted. A mesh and overlay sys-tem would certainly be able to provide the current,

but the vibrations in the deck caused by trafficwould mean there was a risk that the sprayed con-crete overlay would debond. Discrete anodes could

be installed by roped access, but would require drill-

ing holes into the deck at depth. If the holes weredrilled marginally too deep there was a risk of drill-ing into live traffic. A galvanic system as previouslyinstalled in combined systems would fall under thesame restriction. The application of corrosion inhibi-tors could provide a time limited protection but a du-rable solution was required. What was needed wasan anode system that could be surface mounted andsecurely fixed but did not require an overlay. Such asystem did not exist in the UK market.

The only other solution would involve the removal

and replacement of the bridge deck. Aside from thetraffic chaos associated with its closure, the envi-ronmental consequences of this cannot be tolerated.The deck is approximately 1000m

3of concrete. The

embodied energy in the deck concrete is estimated to be around 6 TJ, equivalent to the energy produced

a) before repair

b) 10 years after repair

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by 1200 barrels of oil. This does not consider the as-sociated disruption to traffic and the local popula-tion, Atkins (2006).

After extensive research, a cassette system for instal-lation on jetties and harbours was identified thatshowed promise. The anodes sit in a foam filledglass reinforced polymer tray which can be mounted

on a concrete surface using bolts, see Figure 5. Inthe environment of jetties and harbours the foamnever dried out as it was wetted by the tide but onthe bridge this would not happen. Moisture is neces-sary to act as transport medium for the current to thereinforcement protected. Following several discus-sions about the purpose and the requirements for asuitable system to be installed on a bridge weworked with the manufacturers to refine the cassettesystem. The developed calcium nitrate impregnatedglass fibre foam is able to remain moist simply by

being in contact with the atmosphere.

The responsible authorities accepted the proposal of a trial installation of a 197 feet section of the bridgedeck. Cassettes are installed at 20 inches (500mm)centres, which is the maximum allowable spacing of anodes using the existing operating data showed thiswould provide an acceptable amount of current. Themonitoring data of the initial 6 months showed thesuccessful cathodic protection of the trial section,and the remaining 920 feet is being protected in thesame way.

4 M4 THEALE RAILWAY BRIDGE, LONDON

4.1 General

The Theale railway bridge crosses the M4, a major freeway leading to central London. The north abut-

ment of the railway bridge is suffering from rein-forcement corrosion and cathodic protection has

been identified as a remedial measure. The structureis adjacent to a main railway line and so access waslimited, see Figure 6. In addition the concrete sur-faces have been vandalised.

4.2 Cathodic Protection

Based on the access restrictions between railway andabutment and the likelihood of vandalism it wasconsidered that an embedded anode system would bethe most robust, while maintaining a surface that can

be easily cleaned. A mesh and overlay system wasconsidered as too susceptible to vandalism andcleaning the rough surface from time to time was notintended to be included in the maintenance budget of the client.

Figure 6. Finished CP system at Theale.

Figure 5. Cassette System installed on deck soffit.

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The access restraints did not favour the installationof a mesh and overlay system. Having reviewed theinformation available a system consisting of MMOcoated titanium ribbon anodes embedded into 20mmdeep x 5mm wide slots cut vertically into the surface

of the concrete was chosen. Additional protectionwas required to tie reinforcement in the corbel andthis was provided using discrete anodes.

5 CONCLUSIONS

Repair strategies are mainly governed by access re-strictions at the structures. The Intranode Cassettesystem installed at the Silver Jubilee Bridge waschosen as to be the most suitable system to with-stand bridge vibrations, reducing installation timeand avoiding long lasting traffic management. The

system designed for the M4 in London was gov-erned by access and noise restrictions. Every struc-ture needs to be assessed for their local restrictionand the most appropriate system needs to be identi-fied by the engineer.

Conventional systems such mesh and overlay anddiscrete anodes can be used most of the time, how-ever, to go one step forward and reduce the envi-ronmental footprint a little thought and research isnecessary. Innovative CP systems are able to reduceinstallation time and the amount of materials used as

well as a significant life extension of bridges. For specific site and CP system requirements trafficmanagement, working at height and exposure to vi-

bration and noise can be limited.

Over the years that CP systems have been designed,installed and subsequently monitored, it was ob-served that they have generally exceeded the per-formance criteria with ease, Lambert (2009). After the first 12 months of operation, cathodic protectionsystems stabilize and require little intervention. Theoldest systems continue to operate at a current den-

sity of approximately 4 mA/m

2

on the steel surface – about 20% of the design output. The monitoring probes continue to give consistent and stable read-ings.

The experience gained from each system was usedto refine the design of the following applications, re-sulting in bigger zones, less anodes and referenceelectrodes, and the development of hybrid protectionsystems to overcome local difficulties.

REFERENCES

Atkins, C.P., Buckley, L.J. & Lambert, P., 2006. Sustainability

& Repair, Concrete Communication Conference, UCL/The

Concrete Centre.Baldwin, N.J.R. & King, E.S., 2003. Field Studies of the Effec-

tiveness of Concrete Repairs, Phase 4 Report: Analysis of

the Effectiveness of Concrete Repairs and Project Findings.Research Report 186, Health and Safety Executive, Sud-

bury, UK.

Coull, Z.L., Atkins, C.P., Lambert P. & Chrimes, J., 2003. The

Evolution of Reinforced Concrete Repair Techniques at the

Silver Jubilee Bridge, Latincorr 2003, Universidad de

Santiago de Chile.

Lambert, P., 1997. Controlling Moisture, Construction Repair:

Concrete Repairs 6.

Lambert, P., 1998. Economic Aspects, Chapter 10, Cathodic

Protection of Steel in Concrete, Editor: P.M. Chess, Pub:

Spon.Lambert, P. and Atkins, C., 2007. Maintaining the Silver Jubi-

lee Bridge – Cathodic protection for a critical causeway,Concrete International.

Lambert, P., Foster, A., Atkins, C. & Brueckner, R., 2009.Adaptive Design of Cathodic Protection for ReinforcedConcrete, Proceedings of 17th IBAUSIL 2009, University of Weimar.

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Life Extension of Bridges, 2010

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