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BIPOLAR CONCRETE PENETRATING CORROSION INHIBITORS

EPCO®KP-200

Bipolar Concrete penetrating corroion in!i"iting a#$i%t&re

'SES For protection of reinforcement against chlorides. As an admixture to concrete for protecting reinforcement steel in structure exposed to aggressive corrosion like marine structures,

foundations, jetties, docks, mooring berths, bridges, sewerage systems, chlorinating plants,

chimneys, cooling towers, power plants, refineries & buildings.

PROPERTIES E!"#$#% is a hi#tech corrosion inhibitor system that works on the 'ipolar

(nhibition )echanism *'.(.)+ which inhibits corrosion of steel in concrete at both the poles.

afe to concrete, safe to environment.

!onforms to -" pecifications.

EPCO®KP-(00

S&r)ace applie# "ipolar concrete penetrating corroion in!i"itor

'SES (n repairs and rehabilitation of concrete structures, to protect the embedded reinforcementagainst chlorides. Also for structures and foundations exposed to salinity.

PROPERTIES

/hen surface applied it diffuses through the concrete by virtue of its affinity for steel

Corroion Control*

From the literature survey and case studies it has been reported that 01 of failure of structures

is on account of corrosion of embedded steel reinforcement in concrete. 2herefore corrosioncontrol of steel reinforcement is a subject of paramount importance. First and foremost for

corrosion control is the good 3uality of concrete through good construction practices. (t is a very

vast subject touches the fundamentals of choosing constituents material and good rules to be

followed during various stages or production of concrete, in particular the use of lowest possiblewater4cement ratio having regard to workability. (n view of the general availability of

superplastici5ers, it should be used to cut down the /4! ratio to make dense concrete.

roper mix design, use of right 3uality and 3uantity of cement for different exposure conditions

is to be adopted. -ecently it has been reali5ed that lower /4! ratio which has been always

associated with lower permeability is not enough to make impermeable concrete contributing tohigh durability. 6se of supplementary cementitious materials such as fly ash, ground granulated

blast furnace slag *gg"+, silica fume etc. are re3uired to be used as admixtures or in the form of

blended cement in addition to lowest possible /4! ratio to make concrete dense. 2hese materials

improve more than one properties of concrete, which will eventually reduce corrosion of reinforcement. 2ests on mortar containing ggbs have shown that water permeability is reduced

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by a factor up to 7. (t is also reported that 8 per cent ggbs educed the diffusion of chlorideions into the concrete by as much as 7 times. ilica fume contributes to the all#round

improvements in the 3uality of concrete, which are responsible for reducing corrosion of steel

reinforcement. 2he improvement in the microstructure of hydrated cement paste is ultimatelyresponsible for protecting the steel reinforcement from corrosion.

(n short it can be said that if we make good concrete with low permeability and improved

microstructure, it will be durable by itself and also it can take care of the reinforcementcontained in it o a great extent. (t is always not possible to make such ideal concrete, particularly,

in view of the complex environmental and exposure conditions. Further the inherent long term

drying shrinkage and micro cracks in concrete, the problems become more serious. 2his demands

certain other measures to control the corrosion of steel reinforcement. 2hey are listed and brieflyexplained.

7. Metallurgical methods

%. Corrosion inhibitors

9. Coatings to reinforcement

0. Re-alkalization

:. Chloride removal

8. Cathodic protection

;. Coatings to concrete

+,( etall&rgical et!o#*

teel can made more corrosion resistant by altering its structure through metallurgical processes.

ifferent methods such as rapid 3uenching of the hog bars by series of water jets, or by keeping

the hot steel bars for a short time in a water bath, and by such other process the mechanical properties and corrosion resistance property of steel can be improved. 2here are many situations

where stainless steel reinforcements are used for long term durability of concrete structures.

+,2 Corroion in!i"itor*

!orrosion inhibitors, which come in powder, gel and li3uid form, retard the rate of the corrosion

reaction. 2hey are widely used in many industries to effectively reduce the corrosion rate of steeland other metals. !ommercial products for the control of corrosion of steel reinforcement in

atmospherically exposed concrete were first produced in the 7<;=s. 2hey increase the time to theonset of corrosion and then act to reduce the rate of corrosion. 2hey can be introduced into the

concrete mix at the time of construction4 repair or *in a suitable formulation+ applied to thesurface of an existing concrete structure. 2here are three main types of inhibitors>

+,2,( Ano#ic in!i"itor. /!ic! retar# t!e corroion reaction at t!e ano#e* !orrosion can be

prevented or delayed by chemical method by using certain corrosion inhibiting chemicals such asnitrites, phosphates, ben5oates etc. At low dosage there is concern that they will suppress

generali5ed corrosion but may fail to eliminate all anodic sites. "f the available materials, the

most widely used admixture is based on calcium nitrite but have proved to be deleterious at highchloride concentrations. (t is added to the concrete during mixing of concrete. 2he typical dosage

is of the order of 7#9 litres per m9 of concrete depending on chloride levels in concrete.

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Fig 10 Corrosion inhibiting effects of calcium nitrite

As mentioned earlier, in the high p? of concrete, the steel is protected by a passivating layer of ferric oxide on the surface of steel. ?owever, the passivating layer also contains some ferrous

oxide, which can initiate corrosion when the chloride ions reach the steel. 2he nitrite ions present

in the corrosion#inhibiting admixture will oxidi5e the ferrous oxide to ferric oxide, thus

stabili5ing the passivating layer even in the presence of chlorides. 2he concentration of nitritemust by sufficient to cope up with the continuing ingress of chloride ions.

!alcium nitrite corrosion inhibitor comes in a li3uid from containing about 9 per cent calciumnitrite solids by weight. 2he more corrosion inhibitor is added, the longer the onset of corrosion

will be delayed. ince most structures in a chloride environment reach a level of about ; kg of

chloride iron per m9 during their service life, use of less than 7@ litres4 m9 of calcium nitrite

solution is not recommended.Fig. 10 shows that without an inhibitor the reinforcing steel starts to corrode when the chloride

content at the rebar reaches a threshold level of .; kg4 m9. Although the corrosion process starts

when the threshold level is reacted, it may take several years for staining, cracking and spallingto become apparent and several more years before deterioration occurs. Adding calcium nitrite

increases this corrosion threshold. /hen you add %#litres4 m9, corrosion will not begin untilover ;.;#kg4 m9 of chloride is present in the concrete at the rebar.

+,2,2 Cat!o#ic in!i"itor

/hich retard the reaction at the cathode and seek to prevent oxygen reaching the reinforcing

steel. At low dosages, they are effective at reducing corrosion rates but are generally less

efficient than the anodic type.

+,2,+ Bipolar in!i"itor

2hey retard the corrosion process both at the anode and the cathode. 2hese combine the benefits

of both anodic and cathodic inhibitors at relatively low dosages. (n this category organic)igratory bipolar corrosion inhibitors are the most widely used.

)igratory 'ipolar !orrosion inhibitors are organic inhibitors. 2hey protect the steel at both the

anodic and the cathodic sites. 2he 'ipolar corrosion inhibitor chemistry involves migration of itsmolecules by electron density distribution to both the anodic and 77 cathodic sites of the steel.

'y virtue of its high vapour pressure, very high affinity and virtue of diffusion these inhibitors

migrate towards the steel in concrete and get deposited in a monomolecular layer. 2his is trueeven in dense concrete. 2his barrier coating then raises the chloride threshold concentration for

corrosion. Further more the inhibitor within the concrete matrix reduces the rate of chloride ion

migration towards steel. (t also dislodges previously absorbed chloride ions and water molecules

on the steel surface.2he basic advantage of the product lies in the ease of use. tudies have proved that addition of

these types of corrosion inhibitors has no deleterious effect on the properties of concrete.

!oncrete penetrating corrosion inhibiting admixture upon addition into the concrete matrix plays

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a major role in inhibiting the corrosion process. 2he European !ommittee for standardi5ation*!E+ pr. EB 7:0#< recommends application of !oncrete penetrating corrosion inhibitors as a

proven corrosion control strategy. ?-##888 *trategic ?ighway -esearch rogramme+ has

recommended these types of corrosion inhibitors for concrete structures subjected to chloride#induced corrosion. Ceneral 'uilding !orporation of Dapan has evaluated this product in concrete

extensively and has reported rebar life extension by six times. 2wo codes available

internationally for testing these types of inhibitors are A2) C 7< & D( A 8%:.2hey are available, both as surface applied inhibitors and as admixed inhibitors. urface applied

inhibitors are used by spraying on the complete surface of the structure being repaired so that

protection to the unexposed reinforcement is taken care of. Admixed inhibitors are used in the

fresh mortar4concrete being placed for strengthening the structure.pecification for surface applied !orrosion inhibitor

Base Bipolar ater "ae# Organic in!i"itor, Concrete penetrating t1pe,

Colour Colorle Ha1 li3&i#

pecific !ravit" (,0( 4 (,02 at 25o C

#iscosit" at $%0C ((-(2 ec "1 6or# B7 C&p,

p& ini$&$ 8,5

'osage To "e pra1e# at t!e rate o) 7$2 9 ltr

(o)icit" Non-to%ic . Eco-)rien#l1,

EvaluationS!o&l# pa :IS - ;205 tan#ar#Speci)ication )or A#$i%e# corroion in!i"itor

Base Bipolar Organic in!i"itor, Concrete penetrating t1pe,

Colour Bro/ni!

pecific !ravit" (,05 4 (,0< at 25o C

#iscosit" at $%0C ((-(2 ec "1 6or# B7 C&p,

p& ini$&$ 8,0

'osage + =g per c&"ic $eter o) concrete,

(o)icit" Non-to%ic. Eco-)rien#l1,

*ffect on concrete

properties

o adverse effect on physical properties in fresh & hardened concrete inthe absence of any other admixtures. ?owever it is Essential to carry out

trial mix with desired admixtures along with )igratory !orrosion(nhibitor.

Compatibilit" for

&igher (hermal

C"cles

Co$pati"le )or !ig!er t!er$al c1cle No #eleterio& e))ect

e>en at !ig! te$perat&re, E))ecti>e e>en at !ig!er te$perat&re,

E>al&ation S!o&l# pa AST-G-(08 tan#ar# ? :IS - ;205

S!o&l# pa tropical cli$ate tet @t!er$al c1cle

+cceptance Criteria,

)igratory 'ipolar !orrosion (nhibitor should be tested as per A2)#C#7<4 D( # 8%: from

reputed laboratories like !(- & (.(.2.(ropical Compatibilit":

)aterial shall have evaluated test reports indicating significant reduction in corrosion rate after minimum of < thermal cycles at 8o! followed by @ weeks of accelerated corrosion. *inear

polari5ation method+2he inhibitor shall be non#toxic & safe to plant and human life.

2he principle of most inhibitors is to develop a very thin chemical layer on the surface of the

reinforcement. 2here is a very wide range of corrosion protection performance from differentinhibitor formulations, even with generic classifications. (ndependent evaluation and certification

of performance is desirable. ?owever, such evaluations need to be representative of field

concretes and conditions. As the true effect of an inhibitor can only be evaluated from corrosionrate measurements before and after application and by reference to a control area, such

systematic evaluations are lengthy processes and are in their early stages.

kp200

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