corrossion of steel reinforcement
TRANSCRIPT
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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'%-#($, 8nidaderida in the work and theiruseful comments is sincerely
appreciated.
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A3421a52
"ommon types of corrosion occurring are (itting,
"revice and #ntergrannular corrosion. The two most common
causes of reinforcement corrosion are chloride ions and
carbonation by atmospheric carbon dio!ide. #n wet and cold
climates, reinforced concrete for roads, bridges, parking
structures and other structures that may be e!posed to deicing salt
may benefit from use of epo!y-coated, hot dip galvani9ed or
stainless steel rebar, although good design and a well-chosencement mi! may provide sufficient protection for many
applications. Epo!y coated rebar can easily be identified by the
light green color of its epo!y coating. Hot dip galvani9ed rebar
may be bright or dull grey depending on length of e!posure, and
stainless rebar e!hibits a typical white metallic sheen that is
readily distinguishable from carbon steel reinforcing bar. ore
techniques like "athodic protection and E"E are also employed.
8se of :ly 'sh too delays the effect of chlorides and carbon
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dio!ide.
'N(E
15.N
7NTENT %AE
N
" 'NT5(7T'N
! A$mi;t-res 'n 7oncrete 8 7atho$ic %rotection 9
4 1teel 5e#lacement 9
< 7oncrete Mi;es "0
6 The %revention of 7orrosion on 1tr-ct-ral
1teel
""
%ainting "8 7orrosion %rotection %hiloso#hy "4
9 7orrosion 'n&hi/iting A$mi;t-res " 5eferences
!
!9
!
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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 # , deter- mined 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 $a"lsolutions more effectively
than any of the other admi!tures, although late! is effec- tive. ethylcellulose slightly improves the
corrosion resistance of rebar in concrete in "a0H/ solution. "arbon fibers decrease the corrosion
resistance of rebars inconcrete, mainly because they decrease the electrical resistivity of concrete. The
negative effect of fibers can be compensated by either silica fume or late!.#nstead of using a corrosion-
inhibiting admi!ture in the entire volume of con- crete, one may use the admi!ture to modify the
cement slurry that is used as acoating on the steel rebar."ompared to the use of rebars that have been
eitherepo!y coated or galvani9ed, this method suffers from its labor-intensive site-orientedprocess.0n
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the other hand, the use of a shop-coating based on a cement-polymer composite is an emerging
alternative.0f all the admi!tures described for improving the corrosion resistance of steel-reinforced
concrete, the most widely used are calcium nitrite, silica fume, and late!.
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CAT*OD$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 con- crete/ 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 con- crete 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 cor- rosion 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 corro- sion 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 con- crete 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 an- odes.
hen corrosion of reinforcing steel oc- curs, 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 corro- sion continues, delaminationsseparations within the concrete and
parallel to the sur- face 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 dam- age 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 in- cluding
corrosion rate, reinforcing steel con- centration, 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 corro- sion problem provide low future mainte- nance and longterm protection/ specific in- formation is needed for any given structure. :ortunately, proven technology andscien- tific methods are available to evaluate cor- rosion of reinforcing steel and other em- bedded metals/
and associated damage on reinforced concrete structures. These tech- niques 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 po- tential for the steel to corrode in the future resulting in further damage. #t is
only after this information is obtained through a de- tailed corrosion condition evaluation that a suitable
repair and protection specification can be developed for a corrosion-plagued structure. #t is important topoint out that con- crete 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 con- crete structures
and pre-tensioned or post- tensioned structures, the ma)ority of this ar- ticle applys to conventionally
reinforced concrete structures only, particularly with respect to the applicability of cathodic pro- tection.
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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 ca- thodic 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, how- ever, 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 moni- toring and maintenance. ith "(, one can- not 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.
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is galvani9ed. However, once all the 9inc is consumed, the base steel will be susceptible to corrosion in thesame way as plain rein- forcing 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
favor- able or intentional application of sacrificial anode protection. #t is well known that cor- rosion of
embedded aluminum in concrete can occur and crack the concrete. The situa- tion can be made worse,however, if the alu- minum is in contact with reinforcing steel. 'luminum, being more active than steel, can
act as a sacrificial anode to protect the rein- forcing. 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 cor- rosion of steel in e!isting chloride-contami- nated conventionally reinforcedconcrete structures. The characteristics, relevant de- sign parameters, development of necessary
components, limitations, installation proce- dures and performance history of many types of "( systems for
concrete structures con- taining mild reinforcing steel have been e!- tensively researched and documented.The widespread use of cathodic protection and the need for design, installation, testing, per- formance and
maintenance guidelines, prompted the $ational 'ssociation of "or- rosion 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 protec- tion 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 pro- tection 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 en- countered.
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 se- lecting cathodic protection for a given struc- ture a number of issues need to be consid- ered.
&ome of these includeK
#s the owner looking for long term reha- bilitation say greater than *3 or 42 years/S "athodic
protection is usually most cost ef- fective when long term rehabilitation is de- sired. 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 appropri- ate 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 re- quired, 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 control- ling 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 con- crete throughout the structure is also impor- tant. #f sufficientchlorides are present at the reinforcing steel depth in many areas of the structure, "( may be theeconomically vi- able 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 protec- tion 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 prob- lems 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 se- lecting 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 select- ing a specific "(
system.
There are several different types of im- pressed current and sacrificial anode "( sys- tems. :or thepurposes of this article, some typical "( systems used on bridge decks and substructures are shown. &ome
of these sys- tems 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 conduc- tive 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 dif- ferent types of
concrete structures, and is an ongoing problem throughout the 8nited &tates. :ortunately, proven methodsare available to evaluate corrosion of reinforc- ing steel and the associated damage on rein- forced concrete
structures. These tools al- low 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 avail- able to investigate concrete
de- terioration processes unrelated to reinforcing steel corrosion. #t is only after the required in- formation is
obtained through a detailed concrete and corro- sion condition evaluation that a suitable repair andprotection specification can be developed for a deteriorated reinforced concrete structure.
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"athodic protection is a widely used and effective method of corrosion control for re- inforced
concrete structures. "athodic pro- tection 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 con- sider its application whenappropriate.
'lmost any atmospherically e!posed re- inforced concrete structure or portion of re- inforcedconcrete 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
struc- tures are good candidates for "(, but "( is the only system that can truly retard or miti- gate
corrosion. Defore selecting cathodic protection for a given structure a number of issues need to be
considered. #f "( is cho- sen then several other points must be taken into account in order to choose themost ap- propriate system for the conditions encoun- tered.
A new look at re/airing -orro!ion damaged -on-rete
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'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.
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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
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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$$e$ in the greenconcrete.
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Electrochemical in)ection of the organic base corrosion inhibitors, ethanolamine and guanidine, into
carbonated concrete.
0ther inorganic inhibitors, which are known to be migratory in nature. The migration process
is diffusion through water and diffusion through vapour phase.
&tructural design aspects of corrosion control involve factors such as configurational geometrical/
considerations that minimi9e or, if possible, eliminate e!posure to corrosives
"onclusion
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ethods of corrosion control of steel-reinforced concrete include steel surface treat-
ent, the use of admi!tures in concrete, surface coating on concrete, and cathodic
(rotection
ReferencesK
1. Building Code Requirements for Reinforced Concrete, ACI 318, ACI Manual of ConcretePractice, Part 3 American Concrete Institute, Detroit, Mi.
. !Corrosion of Metals in Concrete, ACI R, ACI Manual of Concrete Practice, Part 1.
3. !Control of Crac"ing in Concrete #tructures, ACI $R, ACI Manual of Concrete Practice,Part 3.
$. !Design and Construction of %i&ed 'ffs(ore Concrete #tructures, ACI 3)*R, ACI Manualof Concrete Practice, Part $.
). Perenc(io, +.%., !Corrosion of Reinforcing #teel, A#M #P 1-C, 1$, //. 1-$01*.
-. +(iting, D., ed., Paul lieger #2m/osium on Performance of Concrete, ACI #P01, 1,$ //.
*. Ber"e, 4.#., Pfeifer, D.+., and +eil, .5., !Protection Against C(loride InducedCorrosion, Concrete International, 6ol. 1, 4o. 1, 188, //. $$0)).
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