corrossion of steel reinforcement

7/24/2019 CORROSSION OF STEEL REINFORCEMENT

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A

PROJECT REPORT

ON

CORROSSION OF STEEL REINFORCEMENT

GUIDED BY

MS SMITA PATEL

SUBIMITTED

BY

Amin Jay B

(096!0"06#0$%DIPLOMA (SEM&'I% CI'IL

SUBIMITTED BY

SIGMA INSTITUTE OF TECNOLOGY

) ENGINEERING* (POLYTECNIC%

AT +AGODIYA ROAD

'ADODARA


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Certifcate

This is to certify that Mr. Amin Jay B

having Enrolment No: 09648006!0"have com#lete$ %art&' '(% %ro)ect *or+having title corrosion of steelreinforcement. ,e has -n$ergone the#rocess of sho$h yatra literat-res-rvey an$ #ro/lem (enition. ,e iss-##ose$ to carry o-t the resi$-e '(%%art&'' *or+ on same %ro/lem $-ring1emester&2' for the nal f-lllment ofthe '(% *or+ *hich is %rere3-isite tocom#lete (i#loma Engineering.

GUIDED BY ,a- ./

D,a12m,n2

MS SMITA PATEL


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ACKNOWLEDGEMENT

Reinforced concrete structures have the potential be very

durable and capable of withstanding a variety of adverse

environmental conditions However, failures in the structures do still

occure as a result of premature reinforcement corrosion. The

maintenance and repair of bidg for their safety requires effectiveinspection and monitoring techniques for assessing the

reinforcement corrosion.

Engg need better techniques for assessing the condition of the

structure when the maintenance or repair is required. These method

need to be able identify any possible durability problems within

structure before they become serious.This paper review all the

electrochemical and non-destructors from the point of view of

corrosion assessment and their application to bridges, bldg. andother civil Engg structures.

The authors to thank the e!ican "#$%E&T'%-#($

erida, pro)ect *++, the ater $ational "ommission "$'/

for meteorological data and the de "iencia y "0$'"1T/,

"ontracts 234-'+ *2+, 4*5-(' and 466-(' for financial

support in conducting various phases of this investigation..The

assistance of (. 7uintana,andfrom "#$%E&T'%-#($, 8nidaderida in the work and theiruseful comments is sincerely

appreciated.


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A3421a52

"ommon types of corrosion occurring are (itting,

"revice and #ntergrannular corrosion. The two most common

causes of reinforcement corrosion are chloride ions and

carbonation by atmospheric carbon dio!ide. #n wet and cold

climates, reinforced concrete for roads, bridges, parking

structures and other structures that may be e!posed to deicing salt

may benefit from use of epo!y-coated, hot dip galvani9ed or

stainless steel rebar, although good design and a well-chosencement mi! may provide sufficient protection for many

applications. Epo!y coated rebar can easily be identified by the

light green color of its epo!y coating. Hot dip galvani9ed rebar

may be bright or dull grey depending on length of e!posure, and

stainless rebar e!hibits a typical white metallic sheen that is

readily distinguishable from carbon steel reinforcing bar. ore

techniques like "athodic protection and E"E are also employed.

8se of :ly 'sh too delays the effect of chlorides and carbon


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dio!ide.

'N(E

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! A$mi;t-res 'n 7oncrete 8 7atho$ic %rotection 9

4 1teel 5e#lacement 9

< 7oncrete Mi;es "0

6 The %revention of 7orrosion on 1tr-ct-ral

1teel

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%ainting "8 7orrosion %rotection %hiloso#hy "4

9 7orrosion 'n&hi/iting A$mi;t-res " 5eferences

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GUJARAT TECNOLOGICAL

UNI'ERSITY INDUSTRY DEFINED PROBLEMPROJECT (IDP%STATEMENT FORM

STUDENT PARTICULAR

FIRST NAME 7 JayLAST NAME 7 AminMOB NO 7 !$#!$"#698EMAIL 7)ay.amin"!?yahoo.com

COLLAGE NAME SIGMA INSTITUTE OF TECNOLOGY

) ENGINEERING* (POLYTECNIC%

ADD At.bakrol, ajwa nimeta road, Ta: Wagodia, Di!t.: "adodara, G#jarat, $ndia

BRANC 7 CI'IL

SEMESTRE YEAR 7 6T SEM

SIGNATURE OF 7STUDENT

INDUSTRY PARTICULAR

NAME 7CONTECT ADD 7MOBILE NO 7

EMAIL 7&&&&&&&&&&&&&&&&INDUSTRY&&&&&&&&&&&&&&&&&&&&&NAME 7ADD 7


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$NT%OD&CT$ON

&teel-reinforced concrete is widely used in construction. The corrosion of the steel

reinforcingbarsrebars/ in concrete limits the life of concrete structures. #t is one of the main causes for

thedeterioration of the civil infrastructure. "orrosion occursin the steel regardless

oftheinherentcapacity of concrete to protect the steel fromcorrosion; accelerated corrosion results from

the loss of alkalinity in the concreteor the penetration of aggressive ions such as chloride ions/.

ethods of corrosion control of steel-reinforced concrete include cathodic pro-ection,

surfacetreatments of the rebars epo!ycoating,galvani9ing, copper cladding,protective rustgrowth,

surface o!idation,and sandblasting/.

'TEEL '&%(ACE T%EATMENT

&teel rebars are made of mild steel because of low cost. &tainless steel is e!cellentin corrosion

resistance,but its high cost makes it impractical for use in concrete./The coating of a steel rebar withepo!y is commonly used to improve corrosionresistance, but it degrades the bond between rebar and

concrete, and the tendencyof the epo!y coating to debond is a problem.:urthermore, the cut ends of

therebar and areas of the rebar where the epo!y coating is damaged are not protected from corrosion.

0n the other hand, galvani9ed steel attains corrosion protection byits 9inc coating,which acts as a

sacrificial anode.


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used are epo!y coating and galvani9ing because of their long history of usage.

ADM$)T&%E' $N CONC%ETE

The methods and materials for corrosion control of steel-reinforced concrete are reviewed. The

methods are steel surface treatment, the use of admi!turesin concrete, surface coating on concrete, and

cathodic protection.'dmi!tures are solids or liquids that are added to a concrete mi! to improvetheproperties of the resulting concrete. 'dmi!tures that enhance the corrosion resistance of steel

reinforced concrete include those that are primarily for corrosion inhibition The latter are attractive

because of multifunctionality. The former are mostly inorganic chemicals such as calcium

nitrite,copper o!ide, 9inc o!ide, sodium thiocyanate, and alkaline earth silicate/ that increase the

alkalinity of the concrete, although they can be organic chemicals such as banana )uice. 'dmi!tures

primarily forstructural property improvement can be solid particles such as silica fume,yashand slag,

and solid particle dispersions such as late!. &ilica fume as an admi!ture is particularly effective for

improving the corrosion resistance of steel-reinforced concrete due to the decrease in the water

absorptivity,and not so much because of the increase in electrical resistivity.>ate! improves corrosion

resistance because it decreases water absorptivity and increases electrical resistivity. ethylcellulose

improves corrosion resistance only slightly.

"ar-bon fibers decrease corrosion resistance due to a decrease in electrical resistivity.However,

the negative effect of the carbon fibers can be compensated by addingeither silica fume or late!, which

reduce water absorptivity.The corrosion resis-tance of carbon fiber-reinforced concrete, which typically

contains silica fume forimproving fiber dispersion, is superior to that of plain concrete. shows the

effects of silica fume, late!, methylcellulose, and short carbon fibers as admi!tures on the corrosion

potential E, measured according to'&T "56 using a high-impedance voltmeter and a saturated

calomel electrodeplaced on the concrete surface; Ethat is more negative than ?42 m% suggests+2@

probability of active corrosion/ and the corrosion current density # , determined by measuring the

polari9ation resistance at a low scan rate of 2.*6 m%As/of steel-reinforced concrete in both saturated"a0H/ and 2.3 $ $a"l solutions. The saturated "a0H/ solution simulates the ordinary concrete

environment; the$a"l solution represents a high-chloride environment. &ilica fume improves the

corrosion resistance of rebars in concrete in both saturated "a0H/ and $a"lsolutions more effectively

than any of the other admi!tures, although late! is effective. ethylcellulose slightly improves the

corrosion resistance of rebar in concrete in "a0H/ solution. "arbon fibers decrease the corrosion

resistance of rebars inconcrete, mainly because they decrease the electrical resistivity of concrete. The

negative effect of fibers can be compensated by either silica fume or late!.#nstead of using a corrosion-

inhibiting admi!ture in the entire volume of concrete, one may use the admi!ture to modify the

cement slurry that is used as acoating on the steel rebar."ompared to the use of rebars that have been

eitherepo!y coated or galvani9ed, this method suffers from its labor-intensive site-orientedprocess.0n


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the other hand, the use of a shop-coating based on a cement-polymer composite is an emerging

alternative.0f all the admi!tures described for improving the corrosion resistance of steel-reinforced

concrete, the most widely used are calcium nitrite, silica fume, and late!.


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CAT*OD$C +%OTECT$ON

"athodic protection is an effective method for corrosion control of steel-reinforcedconcrete.#t

involves the application of a voltage to force electrons to go to the steel rebar, thereby making the steel

a cathode. 's the voltage needs to be constantly applied, the electrical energy consumption is

substantial. This can be alleviated bythe use of carbon fiber-reinforced concrete.'s the steel rebar is

embedded in concrete, the electrons need to go through the concrete in order to reach the rebar.

However, concrete is not very conductingelectrically. The use of carbon fiber-reinforced concrete for

embedding the rebarfacilitates cathodic protection, as the short carbon fibers enhance the conductivity

of the concrete. :or directing electrons to the steel-reinforced concrete, an electrical contact that is

connected to the voltage supply is needed on the concrete.

0ne choice of an electrical contact material is 9inc, a coating deposited on the concrete by

thermalspraying. #t has a very low volume resistivity thus requiring no metal mesh embed-ment/, but

it suffers from poor wear and corrosion resistance, the tendency to o!idi9e, high thermal e!pansion

coefficient, and high material and processing costs. 'notherchoice is a conductor-filled polymer,thatcan be applied as a coating withoutheating, but it suffers from poor wear resistance, higher thermal

e!pansion coeffi-cient, and high material cost. 1et another choice is a metal e.g., titanium/ strip or

wire embedded at one end in cement mortar that is in the form of a coating on the steel-reinforced

concrete. The use of carbon fiber-reinforced mortar for this coatingfacilitates cathodic protection, as it

is advantageous to enhance its conductivity.

Bue to the decrease in volume electrical resistivity associated with carbon fiberaddition 2.C3

vol. @/ to concrete, concrete containing carbon fibers and silica fume reduces the driving voltage

required for cathodic protection by *5@ compared toplain concrete, and by 45@ compared to concrete

with silica fume. Decause of thedecrease in resistivity associated with carbon fiber addition *.* vol.@/ to mortar,overlay embedding titanium wires for electrical contacts to steel-reinforced concrete/ in

the form of mortar containing carbon fibers and late! reduces the driving voltage required for cathodic

protection by *2@ compared to plain mortar overlay.#n spite of the low resistivity of mortar overlay

with carbon fibers, cathodic protection requires multiple metal electrical contacts embedded in the

mortar at a spacing of** cm or less.

'TEEL %E+LACEMENT

The replacement of steel rebars by fiber-reinforced polymer rebars is an emerging technology that isattractive because of the corrosion resistance of fiber-reinforced polymer. However, this technology

suffers from high cost, the poor bonding between concrete and the fiber-reinforced polymer rebar, and

the low ductility o the fiber-reinforced polymer.


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Cement

e used the same brand Typ e #A## cement for (hase ## as was used in (hase #. The chemical analysis of the

cement in Table .* is for the (hase # cement and was provided by the supplier.

#gnition >oss 2.+2@

#nsoluble Residue 2.C2@

'teel %einor-ement

Reinforcement was $o. ,


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The average was 2.4 while the median value was 2.. 0nly one mi! had the value of 2.3,

e!ceeding the limit, but the mi! was still used due to the minimal divergence from the ma!imum. Theintended ma!imum slump for the mi!tures was .2 inches.

#n order to maintain individual mi! characteristics, the slumps were allowed to vary. 'll values

were below the ma!imum and ranged from *.2 to C.3 inches. hen the consistency is affected by theadmi!tures it is possible that the set time of the mi!ture could also be altered. :or the new study, the set

times of the mi!es were measured. The results of this testing are in &ection 3.4.C.

The air content of concrete mi!tures must also be controlled to achiev e a desired product. The

B'& and B&& mi!es did not use any air entraining admi! ture. The commercial inhibitors and the control

mi!es used air entraining admi!tures per recommendations of the manufacturers. The air content isrecommended to be .3@ with a range of ?*@ to F4@ for concrete with a ma!imum aggregate si9e of CA5

inch and e!posure to Gsevere conditions I2J. 'll but two mi!es were within this range. Th e deviant

mi!es were both below the lower limit. Datch si9es were *.2, *.*, and *.43 c.f., depending on the number o f

specimens required for testing. Table . shows the mi! proportions for the corrosion specimens.

The prevention of corrosion

on structural steelwork

The cost effective corrosion protection of structural steelwork should present little diffi cultyfor common applications and environments if the factors that affect durability are recognised at the

outset. This note aims to give specifi ers an insight into the factors involved. #n dry heated interiors no

special precautions are necessary. here precautions are required modern durable protective coatingsare available which, when used appropriately, provide e!tended maintenance intervals and improved

performance.

Te -orro!ion /ro-e!!

ost corrosion of steel can be considered as an electrochemical process that occurs in a series

ofconsecutive stages. The details of this process can be summarised by the following equationK-

:e F C04 F4H 40 L 4:e4 04 H4 0

#ronA&teel/ F 0!ygen/ F ater/ L Rust :rom this it can be seen that for iron and steel to corrode it isnecessary to have the simultaneous presence of water and o!ygen. #n the absence of either, corrosion does

not occur.


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Wat ae-t! te rate o -orro!ion0

The principle factors that determine the rate of corrosion of steel in air are the time of wetness and the

presence of atmospheric pollution typically present as suplhates and chlorides.

1 Time o wetne!!

This is the proportion of total time during which the surface is wet, due to rainfall, condensation, etc.

1 '#l/ate!

These originate from sulphur dio!ide gas that is produced during the combustion of fossil fuels.

1 Cloride!

These are mainly present in marine environments. The highest concentrations of chlorides are to be found in

coastal regions and there is a rapid reduction when moving inland.

Doth sulphates and chlorides increase corrosion rates. They react with the surface of the

steel to produce soluble salts of iron that can concentrate in pits and are themselves corrosive.

Decause of variations in atmospheric environments, corrosion rate data cannot be generalised,however, environments and corresponding corrosion rates are broadly classifi ed in D& E$ #&0 *4+

(art 4 and #&0 +44C

Te ee-t o de!ign on -orro!ion /re2ention

#n e!ternal or wet environments, design can have an important bearing on the corrosion of steel

structures. #n dry heated interiors no special precautions are necessary. The prevention of corrosion should

therefore be taken into account during the design stage of a pro)ect. The main points to be considered areK

1 To a2oid te entra/ment o moi!t#re and dirtThe key here is to avoid the creation of cavities and crevices; so welded )oints are preferable tobolted )oints. >ap )oints should be avoided or sealed where possible. 'dditionally drainage holes to

prevent standing water may have to be incorporated.

1 Coating a//li-ation

The design should ensure that the selected protective coatings can be applied effi ciently.

Typically this might involve ensuring adequate access for painting or adding drainAvent holes to sealedcomponents, which will be sub)ect to hot dip galvani9 ing.

Te a//li-ation o /rote-ti2e -oating!

&urface (reparationK-The surface preparation of steel is concerned with the removal of mill-scale, rust and other

contaminants to provide a satisfactory substrate for coating and is generally considered to be a two stage

process.

The first stage of any surface preparation is to remove residues of grease, oil or marking inks.

The second stage is to remove any mill scale and rust and is generally done by either hand and power toolcleaning or abrasive blast cleaning.


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+ainting

(ainting is the principle method of protecting structural steelwork from corrosion.

(aints are made by mi!ing, pigments the coloured part/, binders the film forming component/ and the

solvent which dissolves the binder/.

(aints are usually applied one coat on top of another and each coat has a specific function or purpose.

The primer is applied directly onto the cleaned steel surface. #ts purpose is to wet the surface and toprovide good adhesion for subsequently applied coats. #n the case of primers for steel surfaces, these

are also usually required to provide corrosion inhibition.

The intermediate coats or undercoats/ are applied to MbuildN the total film thickness of the system.


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Ke4 +oint!

5. #n dry heated interiors no special precautions are necessary.

6. The corrosion of steel can be considered as an electrochemical process

7. :or steel to corrode it is necessary to have the simultaneous presence of water and o!ygen.

8. The principle factors that determine the rate of corrosion of steel in air are the time of wetness and the presence of atmospheric pollution.

9. The prevention of corrosion should therefore be taken into account during the design stage of a pro)ect.

. (ainting is the principle method of protecting structural steelwork from corrosion.

;. Hot dip galvani9ing is the most common method of applying a metal coating to structural steel


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epo!y coated reinforcement over the last few years, due in part to vigilant inspection.

Cement and $n-rea!ed Con-rete Co2er o2er te %einor-ing 'teel

any times, both sulfates and chlorides are present in an aggressive environment, such as sea water.

T!B0T specifies Type ## cement for any structure where durability in a sulfate e!posure environment is a

concern. The depth of concrete cover over the reinforcing steel, neglecting effects of cracking, is directly

related to the time it takes for the chlorides to penetrate to the level of the reinforcing steel and initiatecorrosion. #ncreasing the amount of concrete cover over the reinforcing steel, taking into account theP

location in the structure and the effects the increased depth of cover will have on fle!ural crack width, is one

method utili9ed to protect the reinforcing steel. Type ## cement increases the resistance of the concrete tosulfate attack in an attempt to keep the cover intact to protect the reinforcing steel.

De-rea!ed +ermeabilit4

Becreasing the concrete permeability is vital in increasing the durability of a reinforced concretestructure. 's concrete permeability decreases, the time it takes forchlorides to penetrate to the reinforcing

steel level and initiate corrosion increases. >owered permeability can be achieved by lowering the

waterAcement ratio or with the addition of fly ash or silica fume to the concrete mi!. The presence of fly ashor silica fume lowers the permeability of the concrete by filling up the interstitial spaces between the cement

particles with the smaller fly ash or silica fume particles. T!B0T has routinely allowed the contractor the

option of replacing 42 to C3 percent of the cement with fly ash for economy. 0n a few e!perimental

pro)ects recently, T!B0T has specified concrete permeability instead of a mi! design to allow the contractormore latitude to achieve the desired result. #n these cases, fly ash was necessary to achieve the required

permeability value. &ilica :ume has been tried on a couple of pro)ects but concrete workability and

finishing problems and cost associated with it have prevented its use by nT!B0T on any more than a trialbasis.

oderately lowering the waterAcement ratio can also lower concrete permeability however, lowering

the waterAcement ratio too much can also cause problems. :or e!ample, greatly reducing the waterAcementratio in a bridge deck through the use of high range water reducers to maintain workability can lead to

e!cessive plastic shrinkage cracking on the surface and thus actually lead to increased permeability.

Corro!ion>$nibiting Admit#re!

'n inorganic corrosion-inhibiting admi!ture, calcium nitrite, has been used on a limited basis to

deter corrosion of the reinforcing steel once chlorides have penetrated to the reinforcing bar level. This

admi!ture is considered a set accelerator by the 'merican &ociety of Testing and aterials '&T/ and it

can change the workability characteristics of the mi!. #n warm climates, such as in Te!as, a set retardingadmi!ture is usually necessary when calcium nitrite is used in the mi! to maintain a suitable time period to

place and finish the concrete. (roduct information from the supplier indicate s calcium nitrite works bestwhen the waterAcement ratio is less than 2.2 but this usually requires the use of a superplastici9ing admi!ture. 'lso, the effectiveness of calcium nitrite is greatly diminished with waterAcement ratios above 2.3.

The mi! usually does not release bleed water so continuous fog misting during finishing operations is also

necessary. Through e!perience, it has been determined at T!B0T that a moderately low dosage rate ofcalcium nitrite, about 4 gallons per cubic yard of concrete, achieves a good balance between corrosion

protection and maintaining concrete workability.


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Con-rete 'ealer!

T!B0T has also sponsored studies on a number of concrete sealers and has tried several of them in

the field. &ome of the best results have been achieved with silane and silo!ane penetrating concrete sealersand these are sometimes used on bridge decks in the northern parts of the &tate. &ealer penetration in most

cases is only a few millimeters and they must be reapplied on the surface of bridge decks every few years to

maintain their effectiveness. 'chieving the required sealer penetration on reduced permeability concretecan be difficult.

Epo!y waterproofing is sometimes used on interior bent or abutment caps under open )oints in thebridge slab to provide another layer of protection to the substructure in aggressive environments. :ollowing

proper application procedures is essential to the successful performance of this barrier.

Catodi- +rote-tion '4!tem!

T!B0T e! periences with cathodic protection systems have been less than favorable. :or e!ample,

in 0ctober of *+55, five 3/ different cathodic protection systems were installed and monitored on the 8.&.5 issouri-(acific Railroad overpass structure in Dig &pring, Te!as. The types of systems, location in the

structure and the results of monitoring are shown in Table *.

#mprovements in cathodic protection systems since *+55 have led T!B0T to revisit the issue. The

7ueen #sabella "auseway, in (ort #sabel, Te!as, has been retrofitted with four different cathodic protection

systems. The systems have been installed during the past year and data is unavailable.

"athodic protection is not a corrosion protection method used by T!B0T currently and there are no

plans for its use in the future. T!B0T s limited e!perience with in- service performance of cathodicprotection has been poor. The cost to install and maintain these systems compared to bridge rehabilitationand replacement costs in Te!as are high.

Con!tr#-tion Detail!

"onstruction details are an important method used by T!B0T to lessen the impact of aggressive

environments on highway structures. &ealed )oints, sealed e!pansion )oints or eliminating some or all of the)oints altogether in the bridge deck help to protect the substructure from chloride contaminated water

draining down from above. The key is to minimi9e, as much as possible, the conditions under which

corrosion can initiate and progress. Brip pans to catch runoff and avoiding details that could pond water are

good insurance against corrosion induced damage. #f chloride contaminated water must contact thestructure, then it should be drained from the structure as quickly as practical. Qoints between precast

elements or cold )oints between cast-in-place parts should be as watertight as possible.


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+re2ention o -oating in -orro!ion

&teel in concrete is usually protected against corrosion by passivation of the steel arising from the

high alkalinity of the pore solutions within the concrete. ' stable o!ide layer is formed on the steel surfacewhich prevents the anodic dissolution of iron. >oss of durability in reinforced concrete only occurs if this

stable o!ide layer is rendered unstable if depassivation occurs/ due to the ingress of chlorides to thesteelAconcrete interface or carbonation of the concrete reducing the alkalinity of the pore solution at the

steelAconcrete interface. Burable reinforced concrete therefore must be designed to resist carbonation and to

e!clude chlorides from any source I*J. Reinforcing steel should be embedded in concrete specified in

accordance with current standards. #n particular the mi! design and minimum cover must be observed andsuited to corrosivity of environment. #n many cases this will provide sufficient corrosion protection to the

reinforcing steel, provided that the concrete is correctly placed, compacted and cured.

$evertheless there is significant evidence that some of these conditions are not fulfilled and that

problems of steel and concrete deterioration are due either to inadequate design or to incorrect site practice.There are circumstances in which it is difficult to achieve the specified design life without additional

corrosion protection measures. (roblems arise if

the concrete cover and the concrete quality is - by design or otherwise - reduced relative to the

necessary values for the surrounding environmental conditions e. g. by e!treme filigree elements/;

special structures have to be erected, e. g. connections between precast and cast in place elements or

heat insulated )oints between the structure and e!ternal structural elements e. g. balconies/;

non-dense or dense lightweight concrete is designed to reach a required thermal insulation as well as

low ownweight;

structures are e!posed to high concentrations of chlorides e. g. in marine structures and bridge or

parking decks due to the use of deicing salts/.

#n such cases designers may consider modifications to the concrete mi! design in order to decrease

permeability. "oatings and surface treatments to limit chloride ingress into the concrete, the use of corrosion

protected reinforcement and of more corrosion resistant materials for the reinforcement e. g. stainlesssteels/ and addition of inhibitors to the fresh concrete and cathodic prevention by impressed current my also

be considered. This publication gives a survey of corrosion protection of reinforcement that prevent or

retard corrosion and which might be proposed and used for new structures but also as preventive and as

repair measures for e!isting reinforced concrete structures.

A//li-ation o -oated reinor-ement

Epo!y coating is one of the most widely used techniques for protecting reinforcing bars against

corrosion inside the concrete. The effectiveness of and Qapan I6J. >ater this method has spread also to

"anada, iddle East and Europe. Epo!y-coated rebar has been in frequent use in the 8nited &tates since themid-*+2s. There the main application is in the decks of highway bridges sub)ect to deicing salts but all

over the world the product has also been used as reinforcement in many other fields of concrete

constructions e. g. garages, substructures of marine bridges and offshore structures. The consumption ofepo!y-coated reinforcement in 8&' has increased gradually to about 432.222 tons yearly in *++2. #n


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Europe the application concentrates on single pro)ects.

Man#a-t#re o te -oating

There are two types of epo!y-coatingsK liquid and powder coatings. Decause of better corrosion

protection efficiency IJ electrostatic spraying of epo!y powder to the straight lengths of rebar currentlyaccounts for the ma)ority of coated rebar. 'fter cleaning the steel by abrasive blasting in electrostatic

spraying the electrically charged powder particles are sprayed onto a preheated steel surface F4C2O"/

where they melt to form an even and uniform powder film. 'fter a heat catalysed irreversible reaction thepowder starts to gel. 'fter the film is solidified the coated bars are cooled in water or air.

's a result an uniform coating without pores and cracks is the best. E!periences showed that fusionbonded epo!y-coatings render rather even thicknesses, even across the ribs on ribbed bars.

ith regard to failures in application of epo!y-coated bars in substructure of marine bridges some

producer use chromated bars to improve adhesion between steel and epo!y.

Mode o a-tion

The purpose of the coating is to isolate and insulate the steel from the corrosive environment. The

coating act solely as a barrier against the environment. The epo!y-coatings used today to protect reinforcing

steel contain no corrosion inhibitive pigments.

To provide adequate protection the coatings should have a minimum thickness. $evertheless it

should not be so thick that it empedes fle!ibility and bonding of the coating between steel surface andconcreteK 'ccording to 8& standard '&T ' 3-5* the thickness of epo!y powder coating in order to

fulfil fle!ibility, bonding and corrosion protection requirements should be between*C2=m and C22=m.

#f there are defects on the coating through which aggressive agents can penetrate the barrier,corrosion concentrates on these areas. #ntegrity of the coating therefore is essential for effective corrosion

protection. The film therefore must be free from pores, cracks and damaged areas.

+ro/ertie! o -oating

0wing to their chemical composition epo!y resins e!hibit several physical properties such as highductility, small shrinkage in polymerisation, good abrasion resistance, good heat resistance and outstanding

adhesion on metal surfaces if sufficiently pretreated.

Epo!y resins normally e!hibit good durability against solvents, chemicals and water. The long-termdurability of most epo!y-coatings in concrete are good. Thin epo!y coatings until 432=m are not

completely impermeable to o!ygen and moisture, but diffusion ca be reduced by sufficient thickness and

density. "hloride permeability in a defect free coating is considerably lower than that of water vapour ando!ygen if a powder epo!y-coating has a thickness of *C2- 432=m IJ.

Epo!y-coatings have no electrically but a electrolytical conductivity in the presence of water andAorincreased temperatures. 'reas beyond the coating can act as anodes and cathodes of corrosion elements if

adhesion is removed. Dut

the epo!y-coating will not soften or deteriorate in the highly alkaline environment,


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it has an e!cellent adhesion to a well pretreated steel reinforcement, ensuring no delamination as a

result of corrosion forces.

Corro!ion /rote-tion bea2ior

#n numerous accelerated corrosion tests on natural e!posure epo!y-coated and untreated or in other

way protected steel bar reinforcement have been compared. &ound epo!y-coating provided considerable

long-term protection to the steel when e!posed in carbonated concrete and concrete with a high

concentration of chloride. The use of epo!y-coatings free of essential defects guarantees completeprotection in carbonated concrete and a significant reduction in the rate of deterioration of reinforced

concrete containing high levels of chloride.

The corrosion prevention ability of liquid epo!y-coatings is not quite as good as that of powder

epo!y-coatings. >iquid coatings may have many holidays or are more permeable to water andAor chloride

ions.

"racks in the concrete did not increase corrosion of epo!y-coated bars with an undamaged coating.

However, the use of coatings in chloride containing concrete does not provide complete protection."orrosion of the steel may be initiated at breaks in the film. #n concrete with high levels of chloride an

attack was observed to be spreading from points of defect in the coating. There was very little bonding

between the steel an the coating. :ilm disponding appears to be a consequence of a cathodically controlledunderfilm corrosion I*2J. This caused a systematic break-down of the coating and cracking of concrete.

These results indicate that epo!y barrier coatings may have a finite tolerance limit for chlorides.

Catodi- +rote-tion a! a Corro!ion Control Alternati2e

corrosion of reinforcing steel in concrete is a widespread and enormously costly problem in all

parts of the 8nited &tates. $umerous concrete structures including bridge decks and substructures, parking

garages, balconies and others are deteriorating as a result of reinforcing steel corrosion. %irtually anyreinforced concrete structure is susceptible to the ravages of corrosion if sub)ected to the right

environment.

The corrosion process that takes place in concrete is electrochemical in nature, very similar to a

battery. Electrochemical corrosion is corrosion which is accompanied by a flow of electrons between

cathodic and anodic areas on a metal surface. #n concrete the electro-chemical corrosion reactions are most

often triggered when three factors chloride, o!ygen and moisturemeet at the reinforcing steel surface. '

sort of natural battery develops within the reinforced concrete structure, generating a low-level inters- nalelectrical current. The points where this current leaves the metal surface and enters the concrete electrolyte

are called anodes. The current leaving the concrete and return- ing to the steel does so at the cathodes. "or-rosion or o!idation rust/ occurs only at anodes.

hen corrosion of reinforcing steel occurs, the rust products occupy more volume than the originalsteel, causing tension forces in the concrete. &ince concrete is relatively weak in tension, cracks soon

develop as shown in :igure *, e!posing the steel to even more chlorides, o!ygen and moistureand the

corrosion process accelerates. 's corrosion continues, delaminationsseparations within the concrete and

parallel to the surface of the concrete occur. Belaminations are usually located at, or near, the level ofreinforcing steel. Eventually concrete chunks break away or spall off.


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%isual signs of corrosion-induced damage on many types of reinforced concrete structures arebecoming more and more prevalent. #n many parts of the country one can hardly drive across a bridge or

enter a parking garage that doesnNt have some de- gree of corrosion damage.

The rate of concrete deterioration at any given time is dependent on many factors including

corrosion rate, reinforcing steel concentration, concrete properties, cover and the environment, to name afew. 0nce corrosion has begun there is one thing for certainit will only get worse and it will do so at an

ever-increasing rate. 8ltimately, if corrosion is allowed to continue, structural integritycan be compromised

due to loss of section of the reinforcing steel andAor loss of bond between the steel and the concrete, and re-

placement may be the only solution.

#n order to mitigate or control a corrosion problem provide low future maintenance and longterm protection/ specific information is needed for any given structure. :ortunately, proven technology andscien- tific methods are available to evaluate corrosion of reinforcing steel and other embedded metals/

and associated damage on reinforced concrete structures. These techniques are designed to determine the

e!tent of damage, define the corrosion state of steel in undamaged areas, evaluate the cause, or causes, ofcorrosion, and determine the potential for the steel to corrode in the future resulting in further damage. #t is

only after this information is obtained through a detailed corrosion condition evaluation that a suitable

repair and protection specification can be developed for a corrosion-plagued structure. #t is important topoint out that concrete itself can deteriorate regardless of the condition of embedded reinforcement. E!-

amples of this include free9eAthaw damage and alkali-silica reactions. %arious concrete tests are therefore

often conducted as part of an overall evaluation.

'lthough there are similarities between corrosion of conventionally reinforced concrete structures

and pre-tensioned or post- tensioned structures, the ma)ority of this article applys to conventionally

reinforced concrete structures only, particularly with respect to the applicability of cathodic protection.


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Catodi- +rote-tion

hat is cathodic protectionS &imply put, cathodic protection "(/ is a widely used and effectivemethod of corrosion control. any people, engineers included, think cathodic protection is some kind of

voodoo. 0thers believe "( is so complicated and e!pensive that it has no practical use in the concrete

rehabilitation industry. Then there are those who say "( doesnNt work or that it is unreliable in the longterm. The facts, however, show that "( is not so complicated, is often the most cost-effective course of ac-

tion, has practical application on reinforced concrete structures, and that it most defi- nitely works. 0f

course, performance of "( systems, like all other corrosion protection systems, is directly dependent on

sound specifications, proper installation, and monitoring and maintenance. ith "(, one cannot simplyinstall it and forget it.


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:or decades, cathodic protection has been successfully used to protect pipelines, ship hulls, off shore

oil platforms, heat e!chang- ers, underground tanks, and many other fa- cilities e!posed to a corrosive

environment.


25/36

is galvani9ed. However, once all the 9inc is consumed, the base steel will be susceptible to corrosion in thesame way as plain reinforcing steel.

'nother e!ample of a sacrificial anode in concrete is aluminum for e!ample, bal- cony railings/ in

contact with reinforcing steel. This situation is similar to galvani9ed reinforcing steel, although it is not a

favorable or intentional application of sacrificial anode protection. #t is well known that corrosion of

embedded aluminum in concrete can occur and crack the concrete. The situation can be made worse,however, if the aluminum is in contact with reinforcing steel. 'luminum, being more active than steel, can

act as a sacrificial anode to protect the reinforcing. Hence, misapplication or acciden- Tal application of

sacrificial anodes can have undesirable consequences.

's stated earlier, cathodic protection has evolved as the only proven procedure for effectively

mitigating and controlling corrosion of steel in e!isting chloride-contaminated conventionally reinforcedconcrete structures. The characteristics, relevant design parameters, development of necessary

components, limitations, installation procedures and performance history of many types of "( systems for

concrete structures containing mild reinforcing steel have been e!- tensively researched and documented.The widespread use of cathodic protection and the need for design, installation, testing, performance and

maintenance guidelines, prompted the $ational 'ssociation of "orrosion Engineers $'"E/ to compile

and issue a standard recommended practice for G"athodic (rotection of Reinforcing &teel conventionalmild steel/ in 'tmospherically E!posed "oncrete &tructures. #n addition, standard specifications forcathodic protection of reinforced concrete bridge decks will soon be available from the 'merican 'sso-

ciation of &tate Highway and Transportation 0fficials ''&HT0/.

'ele-tion o C+ or Corro!ion Controlon %einor-ed Con-rete 'tr#-t#re!

's discussed earlier, "( is not always needed nor is it necessarily applicable on every structure. The

first step is to have a concrete and corrosion condition survey conducted in order to define the cause and

e!tent of the problem. ith the results of a thorough condition survey at hand, the en- gineer must analy9e

the data and make a determination on the type of repair and protection method to use. #f cathodic protec-

tion is chosen then another determination must be made in order to choose the most appropriate system forthe conditions encountered.

To select and design a proper repair and protection scheme it is imperative that the cause, or causes,

of the distress are properly diagnosed and fully understood, and that the e!tent of damage is determined.Defore selecting cathodic protection for a given structure a number of issues need to be considered.

&ome of these includeK

#s the owner looking for long term rehabilitation say greater than *3 or 42 years/S "athodic

protection is usually most cost effective when long term rehabilitation is desired. The amount of

damaged concrete is another factor in choosing "(. #f only a small amount of delamination and spalling has


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occurred, "( may not be the most appropriate choice for future protection. &imilarly, if the ma)ority of a

concrete structure is badly deteriorated, replacement may be in order. The in-between situations require

consider- ation of other information gathered from the condition survey. 0ne advantage of "( is thatremoval of sound concrete is not required, thus a considerable cost savings may be reali9ed. #t may be a

viable alternative to removing two or three inches of concrete over a large area in order to prevent future

corrosion.

The corrosion rate of the reinforcing steel must also be considered. #f the corrosion rate is high in

areas which are yet undamaged, conventional repairs will not aid in controlling future corrosion. 'ctually

stopping or slowing the rate to an acceptable level may be necessary, and "( is the only technique which ispresently available for accomplish- ing this.

The chloride concentration in the concrete throughout the structure is also important. #f sufficientchlorides are present at the reinforcing steel depth in many areas of the structure, "( may be theeconomically viable alternative. However, if the chloride content is relatively low, or if the chlorides are

generally located only in isolated areas of the structure, another corrosion protection system may be most

appropriate.

'nother factor to consider is whether or not the concrete distress was solely caused by corrosion ofreinforcing. :or e!ample, if free9eAthaw or alkali-silica reaction problems are encountered, "( is not the

way to go. &uch deterioration will continue with or without cathodic protection. #n fact, in the case of alkali-

silica reactions, recent research indicates that "( current can actually accel- erate the reactions.


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There are many things to consider in selecting a suitable rehabilitation plan for a deterioratedconcrete structure. ' few of the most important issues related to "( have been mentioned here. #n many

cases, a life cycle cost analysis is useful in selecting the most appropriate rehabilitation method.

's discussed earlier, once "( has been selected, the e!act type of "( system must be chosen. The

type of anode is one of the most critical components of a "( system. The particular application may

preclude the use of some of the available anodes and "( systems. The type of surface to be protected topsurface, soffit, vertical, etc./ and its ge- ometry, concrete cover over reinforcing steel, the environment in

and around the structure, and structural considerations, such as whether the structure can support the ad-

ditional dead load resulting from some "( systems, are all important factors in selecting a specific "(

system.

There are several different types of impressed current and sacrificial anode "( systems. :or thepurposes of this article, some typical "( systems used on bridge decks and substructures are shown. &ome

of these systems are also widely used on other types of structures and other systems, not shown here, are

also being utili9ed.

:igures C through 6 show some of the typical "( systems used on bridge decks. Driefly, shows acoke asphalt "( system, :igure shows a mounded conductive polymer "( system 3 pre- sents a titanium

based anode mesh system. Doth the mounded conductive polymer and titanium mesh anode systems require

a cementitious overlay as shown. 'll "( systems require some amount of embedded instrumentation formonitoring purposes.

'#mmar4

Reinforcing steel corrosion has caused an enormous amount of damage on many different types of

concrete structures, and is an ongoing problem throughout the 8nited &tates. :ortunately, proven methodsare available to evaluate corrosion of reinforcing steel and the associated damage on reinforced concrete

structures. These tools allow one to determine the e!tent of damage, define the corrosion state of steel inundam- aged areas, evaluate the cause, or causes, of corrosion, and determine the potential for the steel to

corrode in the future resulting in further damage. 0ther methods are also available to investigate concrete

deterioration processes unrelated to reinforcing steel corrosion. #t is only after the required information is

obtained through a detailed concrete and corrosion condition evaluation that a suitable repair andprotection specification can be developed for a deteriorated reinforced concrete structure.


28/36

"athodic protection is a widely used and effective method of corrosion control for reinforced

concrete structures. "athodic protection supplies a source of e!ternal current to counteract the corrosioncurrent. Hence, corrosion stops, or at least, is greatly mini- mi9ed.

#n the authorNs opinion, those involved in recommending or specifying concrete repair and

protection systems owe it to their cli- ents to become familiar with "( and to consider its application whenappropriate.

'lmost any atmospherically e!posed reinforced concrete structure or portion of reinforcedconcrete structure of almost any ge- ometry can be cathodically protected. How- ever, e!isting structures

must be considered individually with regard to the need for and applicability of "(. Remember, not all

structures are good candidates for "(, but "( is the only system that can truly retard or mitigate

corrosion. Defore selecting cathodic protection for a given structure a number of issues need to be

considered. #f "( is chosen then several other points must be taken into account in order to choose themost appropriate system for the conditions encountered.

A new look at re/airing -orro!ion damaged -on-rete


29/36

'rc-spraying of 9inc on concrete for the cathodic protection of steel reinforcement

Every year building owners and managers are faced with the costs of repairing and patching

concrete that spalls when the reinforcing steel corrodes, usually due to the presence of salt. Removal,

patching and the application of waterproofing membranes are some of the treatments that, alone or incombination, have traditionally been used to rehabilitate corrosion-damaged concrete. However, there are

concerns about the effectiveness of using such approaches to deal with reinforcement corrosion when the

concrete is contaminated by salt, because contamination remains and corrosion continues unless virtuallyall the concrete is removed.

&acrificial cathodic protection is regarded by many as a possible rehabilitation alternative which, if

applied before damage occurs, can reduce repair costs significantly. ith this method of protection, a 9inc

film is sprayed on the concrete surface; the 9inc, rather than the reinforcing steel, then becomes the site ofcorrosion activity.

hile cathodic protection has shown promise in :lorida in preventing corrosion of coastal bridges,

until recently, no equivalent research had been carried out in the more severe and varied "anadian

climate. To assess the viability and potential of this new rehabilitation strategy, a team of researchers from#R" and initiated laboratory and field investigations.

#n one of the field studies, undertaken in partnership with the inistry of Transportation of 7uebecin *++C, seven reinforced concrete columns of a ontreal bridge were flame-sprayed with 9inc. $ow,

more than 42 months later, the 9inc continues to protect the bridge columns.

#n another field study, $R" researchers, in partnership with the #nternational >ead inc Research

0rgani9ation, metali9ed driving surfaces in an 0ttawa parking garage with 9inc. :or the most part, high

levels of protection were provided by the metali9ing, although in e!tremely wet areas the 9inc sacrificed

itself more rapidly than in dry areas, indicating that more 9inc needs to be applied in areas where watercollects.

"urrent work at $R" involves metali9ing alloys 9inc in combination with other materials, such as

magnesium or aluminium/ onto concrete. Researchers e!pect that these materials will prove more

effective than pure 9inc in providing protection to concrete in dry environments.


30/36

Corro!ion +rote-tion !4!tem!

#ndustrial :urnaceNs "orrosion protection began in the late *++2Ns as a spin off to what we were

already doing with refractory lining systems and how they themselves protect a steel shell against heat and

corrosion.That evolved into what we are now doing today as supplier and installers of specialty flooring

and lining systems. 0ur corrosion protection systems protect steel, concrete floors, walls, tanks, ceilings,

and other applications.

0ur crew can offer plants the complete package, with e!perienced personnel being able to handle

pro)ects ranging from floor resurfacing to complete concrete and steel restoration. 0ur e!perience helps to


31/36

catch problems before they evolve into time-consuming e!pensive overhauls. #f a complete overhaul is

needed, our customers benefit from knowing the )ob is going to be done right the first time, eliminating

any unplanned costly down time.

0ur product line has successfully performed inK

U


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U (olymer "oncreteK e carry four variations of polymer concretes which are commonly used forbuilding or rebuilding trenches, sumps, pumps and machinery pads. These products are both

pourable and trowelable and are e!tremely acid and alkaline resistant. Their built-in fiber

reinforcement virtually eliminates cracking and tremendously increases its impact resistance.#nside our *22,222 square foot warehouse is a casting shop which services municipalities with pre-

cast polymer concrete shapes for their sewer systems.

U Traditional fiberglass and "arbon mat reinforced installation systems

'tr#-tr#l %einor-ement

Detter grade of concrete with lower wAc ratio and well compacted.

' polymeric coating is applied to the concrete member to keep out aggressive agents. ' polymeric

coating is applied to the reinforcing bars to protect them from moisture and aggressive agents.

:ly 'sh - 8sing a :ly 'sh concrete with very low permeability, which will delay the arrival of

carbonation and chlorides at the level of the steel reinforcement. :ly 'sh is a finely divided silica rich

powder that, in itself, gives no benefit when added to a concrete mi!ture, unless it can react with the

calcium hydro!ide formed in the first few days of hydration. Together they form a calcium silica hydrate"&H/ compound that over time effectively reduces concrete diffusivity to o!ygen, carbon dio!ide, water

and chloride ions.

odified quality of steel reinforcement which are less susceptible to corrosion such as special

grade of stainless steel, "R& "orrosion Resistant &teel/,TT steel etc.

(re-applied impermeable coating Epo!y, "E"R# V "DR# coating/ &tainless steel or gladded

stainless steel is used in lieu of conventional black bar

A$mi;t-res @Nitrites an$ Nitrates for concreting *hich are to /e a$$e$ in the greenconcrete.


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Electrochemical in)ection of the organic base corrosion inhibitors, ethanolamine and guanidine, into

carbonated concrete.

0ther inorganic inhibitors, which are known to be migratory in nature. The migration process

is diffusion through water and diffusion through vapour phase.

&tructural design aspects of corrosion control involve factors such as configurational geometrical/

considerations that minimi9e or, if possible, eliminate e!posure to corrosives

"onclusion


34/36

ethods of corrosion control of steel-reinforced concrete include steel surface treat-

ent, the use of admi!tures in concrete, surface coating on concrete, and cathodic

(rotection

ReferencesK

1. Building Code Requirements for Reinforced Concrete, ACI 318, ACI Manual of ConcretePractice, Part 3 American Concrete Institute, Detroit, Mi.

. !Corrosion of Metals in Concrete, ACI R, ACI Manual of Concrete Practice, Part 1.

3. !Control of Crac"ing in Concrete #tructures, ACI $R, ACI Manual of Concrete Practice,Part 3.

$. !Design and Construction of %i&ed 'ffs(ore Concrete #tructures, ACI 3)*R, ACI Manualof Concrete Practice, Part $.

). Perenc(io, +.%., !Corrosion of Reinforcing #teel, A#M #P 1-C, 1$, //. 1-$01*.

-. +(iting, D., ed., Paul lieger #2m/osium on Performance of Concrete, ACI #P01, 1,$ //.

*. Ber"e, 4.#., Pfeifer, D.+., and +eil, .5., !Protection Against C(loride InducedCorrosion, Concrete International, 6ol. 1, 4o. 1, 188, //. $$0)).


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corrossion of steel reinforcement

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