Rapid Chloride Permeability Testing_tcm45-590139

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orrosion o f reinforcing steel dueto chloride ingress is one of themost common environmental

at tacks that lead to the deteriorat ion ofconcrete structures. Corrosion-relateddamage to bridge deck overlays, park-ing garages, marine structures, and man-ufacturing plants results in millions of

dollars spent annually on repairs. Thisdurability problem has received wide-spread at tention in recent years becauseof its frequent occurrence and the as-sociated high cost of repairs.

C hlorides penetrat e crack-free con-crete by a variety of mechanisms: cap-illary absorption, hydrostatic pressure,diffusion, and evaporativetransport. Of these, diffusionis predominant. Diffusionoccurs when the concentra-tion of chloride on the out-

side of the concrete memberis great er than on the inside.This results in chloride ionsmoving through the concreteto the level of the rebar. Whenthis occurs in combinationw ith wetting and drying cy-cles and in the presence ofoxy gen, conditions a re rightfor reinforcement corrosion.

The rate of chloride ioningress into concrete is pri-

marily dependent on the in-

ternal pore structure. The pore struc-ture in turn depends on other factorssuch as the mix design, degree of hy-dration, curing conditions, use of sup-plementary cementitious materials, andconstruction practices. Therefore, w her-ever there is a potential risk of chloride-induced corrosion, the concrete shouldbe evaluated for chloride permeability.

Tes t i ng fo r c h lo r i de

permeab i l i t yFor specification and quality-con-

trol purposes in projects, we prefer atest that is simple to conduct and thatcan be performed in a short time. Therapid chloride permeability test meetsthese goals. First d eveloped by Whitingin 1981 (Ref. 1), RCPT has had results

that correlate w ell w ith results from theclassical 90-day salt ponding test.

Standa rdized testing procedures arein AASHTO T 277 or ASTM C 1202.The RCPT is performed by monitoringthe amount of electrical current thatpasses through a sample 50 mm thickby 100 mm in diameter in 6 hours (seeschematic). This sample is typica lly cutas a slice of a core or cylinder. A volt-age of 60V DC is maintained across

the ends of the sample throughout thetest. One lead is immersed in a 3.0%salt (NaCl) solution and the other in a0.3 M sodium hydroxide (NaOH) so-lution (Ref. 2).

Based on the charge that passesthrough the sample, a q ualitative rat-ing is made of the concrete’s perme-

ability, as shown in Table1. Versatile and easy to con-duct, the RCPT has beenadopted as a standard andis now w idely used (Ref. 3).

The test, how ever, ha s anumber of drawbacks:

The current that passesthrough the sample duringthe test indicat es the move-ment of all ions in the poresolution (that is, the sam-ple’s electrical conductiv-ity), not just chloride ions.Therefore, supplementarycementit ious materials (suchas fly ash, silica fume, or ground

granulated blast-furnace slag)

C

By Prakash J oshi andCesar Chan

Rapid ChloridePermeability Test ingA test that can be used for a wide range

of applications and quality control purposes if

the inherent limitations are understood

Underside of a corroded and spalled bridge deck, Cedar Creek

Bridge, British Columbia. About 65 mm of concrete t hickness has

been lost, and the concrete above the spall is also delaminated.



or chemical a dmixtures (such as w aterreducers, superplasticizers, o r corrosioninhibitors0 can create misleading re-

sults largely due to the chemical com-position of the pore solution, ratherthan from the actual permeability. Asa result, some researchers do not rec-ommend the RC PT to evalua te the chlo-ride permeability of concrete contain-ing these materials (Ref. 4).

The conditions under w hich themeasurements are taken may causephysical and chemical changes in thespecimen, resulting in unrealistic val-ues (Ref. 5). For exa mple, the high volt-

age applied during the test increasesthe temperature of the sample, whichcan accelerate hydration, particularlyin younger concretes.

The test h as low inherent re-peatability and reproducibility charac-teristics. The precision statement inASTM C1202-97 indicates that a sin-gle operator will have a coefficient ofvariation of 12.3%; thus the resultsfrom two properly conducted tests onthe same material by the same opera-tor could va ry by as much as 42% (Ref.

2). The multilaboratory coefficient ofvaria tion has been found to be 18.0%;thus two properly conducted tests onthe same material by different labora-tories could vary by as much as 51%.For this reason, three tests are usuallyconducted and the test results averaged,which brings the multilaboratory aver-age down to 29%.

Canad ian Indus t ry P rac t i ceDespite these drawbacks, this test

method ha s been w idely used for spec-

ification and quality control purposes.In Canada, the RCPT has been speci-fied on various projects to qualify con-

crete mixes in bridge deck overlays a ndparking structures. The RC PT has evenbeen incorporated as a part o f the stan-dard in C SA S413-94 Parking StructureDesign-C (Ref. 6). Clause 7.3.1.2 de-fines low-permeability concrete as hav-ing “ w ater/cementing ma terials ra tio no texceeding 0.40, and a n average coulombrating not exceeding 1500 based on atest of three specimens tested in accor-dance with ASTM C1202.” The RCPThas also been used to compare the ef-

fectiveness and performance of varioussystems, such as sealers, membranes,and corrosion inhibitors, intended to re-duce the ingress of chloride ions or re-duce corrosion in concrete structures.

AMEC Earth & EnvironmentalLimited has for a number of years used

the RCPT for chloride permeabilitytesting on numerous diverse projects.The following list shows the applica-tions of the RC PT and provides someexamples of projects.

Qualifying a mix for a particularapplication

The concrete for a bridge deck re-

habilitation project in Calgary had aspecified compressive strength of 45MPa at 28 days and a specified maxi-mum of 1000 coulombs passed at 28days, with penalties for lower RCPTresults. Although the concrete achieveda 5-day field-cured compressive strengthof 30 MPa and a 7-day lab-cured com-pressive strength of 39.0 M Pa, the RC PTresult at 33 days was 2525 coulombson a field-cured sample. We recom-mended further moist curing and test-ing at a later age, recognizing that the

chloride permeability values would im-prove with further hydration. In con-trast, the shotcrete used for the con-struction of the C.O.P. Bobsleigh StartFacility in Ca lgary w as specified to havea low chloride permeability—the max -imum typically specified by the Min-istry of Transportation in Ontario forlatex-modified shotcrete is 1500 coulombs.RC PT results show ed wha t qualified asa very low permeability of 1394 coulombspassed at 37 days.

Determining the effectiveness ofsurface sealers

We conducted RCPT on concretecore samples from a parking structurein Vancouver to determine the effec-tiveness of a deep penetra ting sealer. Test

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

20 40 60 80 100 120 140 160 180 200

C o u l o m b s P a s s e d

Age (days)

Mix C

Mix B

Mix A

The RCPT setup is simple and provides results relatively quickly.

Coulombs passed vs. age for several bridge deck concrete mixes investigated at AMEC.



and 1366 coulombs passed) and un-sealed (4066 and 3211 coulombspassed) locations a nd concluded t hatthe sealer continued to provide im-proved resistance to chloride pene-tration.

Comparing field-cured samples with

lab-cured samplesOn a bridge deck project in Cal-

gary, we conducted RCPT on concretesamples cured in the field and in thelab. The lab-cured sample passed 990coulombs at 28 days, while the field-cured samples passed an average of2119 coulombs at 28 days.

Determining the effectiveness ofcorrosion inhibitors

RC PT w as conducted on 28-da y-

old concrete samples conta ining tw ocommercial ly avai lable corrosion-inhibiting admixtures. The object ofthe test was to evaluate the perform-ance of these concrete mixes comparedwith a control sample with no corro-sion inhibitors. Test results showed

Rating of chloride permeability of concrete according to the RCPTChloride Charg e pass ing , Typical conc rete t ypepermeabilit y coulombs

High > 4000 High w-c ratio (> 0.6) conventionalPC concrete

Moderate 2000 to 4000 Moderate w-c ratio (0.40 to 0.50)conventional PC concrete

Low 1000 to 2000 Low w-c ratio (< 0.40) conventional

PC concreteVery low 100 to 1000 Latex-modified concrete,

internally sealed concrete

Negligible < 100 Polymer-impregnated concrete,polymer concrete

Determining the field performance of a surface sealer with age

To determine t he effectiveness ofa sealer after 15 years of service in aCalgary parking structure, we tookcores from both originally sealed (2088

results indicated 1846 and 1671 coulombspassed for sealed samples and 5983 and8263 coulombs for unsealed samples,thereby proving the effectiveness of theapplied sealer in reducing the ingress ofchlorides into the concrete.



that 2470 coulombs passed for onecorrosion-inhibiting admixture, 3209coulombs passed for a second brandof corrosion-inhibiting admixt ure, an d1211 coulombs pa ssed for the controlsample witho ut the corrosion inhibitor.This verified tha t by cha nging the chem-istry of the pore water solution, cor-

rosion-inhibiting admixtures increasethe appa rent chloride permeab ility asdetected by RC PT, rendering th e re-sults invalid.

Evaluating the performance ofrepair materials

We conducted RCPT on a rapid-set-ting repair grout consisting of pre-blendedcementitious material. According to theproduct literature, the repair materialcontained a corrosion-inhibiting chemi-

cal that was not in the form of calciumnitrite. A very low coulombs-passed valueof 177 was obtained for a well-consoli-dated sample, demonstrating tha t the re-pair grout is well suited for structural re-pairs of pavements, parking structures,bridges, loading docks, and tunnels.

Evaluating the chloride permeabilityof concrete with age

One of the most important factorsaf fecting the permeability o f concrete isthe internal pore structure, which in turn

is dependent on the extent of hydrationof the cementitious materials. The cur-ing conditions and the age of the con-crete thus largely determine the easewith which chloride ions can move intoa concrete. Reference 7 reports chloridepermeability with time of moist curingfor pla in and silica fume concretes. From7 to 28 days, at a water-cement ratioof 0.50 for the plain mix, a chloridepermeability reduction of 18% is ob-tained; at a water-cementitious materi-

als rat io of 0.47 for the silica fume mod-ified concrete mix, a chloride perme-ability reduction of 56% is obtained.

At AM EC, w e tested concrete sam-ples from a bridge deck rehabilitationproject in Vancouver where a maxi-mum of 1000 coulombs passed at 28days was specified. The samples weremoist cured a t a ll ages up until the timeof testing. RCPT was conducted onthree different samples that had slightdifferences in the amounts of super-plasticizer and silica fume. Results of

the tests are shown in the graph at the

bottom of page 002. Note that thesemixes did not reach the required 1000coulombs passed at 28 days but did soat later ages. These test results pointout the importance of proper moist cur-ing and that chloride permeability canbe significantly reduced with concreteage. At 90 days and later, there is al-most no difference in chloride perme-ab ility amo ng the va rious mixes tested.

As previously mentioned, the RCPThas been incorporated as a standard inCSA S413-94 for the specification oflow-permeability concrete in the con-struction of parking structures, stipu-lating an average coulomb rating notexceeding 1500 at 28 days. But this stan-dard also includes a note that, at thedesigner’s discretion, testing can be doneat later ages, up to 91 days, providedthat the concrete in the structure willnot be exposed to de-icing salts until

later ages. Thus the standard recognizesthat concretes containing supplemen-tary cementitious materials w ill continueto have permeability reductions. It isimportant that designers and contrac-tors recognize that the resistance to chlo-ride permeability in concrete, unlikecompressive strength, should not berigidly embraced at early ages (even upto 28 days) in specifications and test-ing, unless chloride exposure on thestructure is expected within this timeperiod. The use of supplementary ce-

mentitious materials and proper curing

are essential to pro duce concrete w ithsignificantly lower chloride permeabil-ity, but this increased concrete qualitycan be observed only at later ages.

The Rapid Chloride PermeabilityTest ha s gained w ide acceptance a s arelat ively easy a nd q uick test method.As we have noted, though, there aremany limitations to the authenticity ofthe test results. Designers and con-

tra ctors should be a w are of t hese lim-itations when qualifying a particularconcrete mix for certain applicationsor w hen interpreting RC PT results.The use of supplementa ry cementitio usmaterials and rigorous moist curingwill significantly reduce the chloridepermeability, particularly at concreteages past 28 day s, and this longer timeto achieve the desired qualities shouldnot be overlooked. If the limitationsinherent t o R CP T are understood , this

test ca n be used for a w ide range ofapplications, testing, and q uality con-trol purposes.

Prakash Joshi has over 20 years of expe-

rience in quali ty assurance, qualit y con-

trol , inspection, and testing w ith AMEC

Earth & Environmental L td. in Burnaby,

Bri ti sh Col umbia. Cesar Chan, an engi-

neer-in-training wit h AM EC Earth &

Envi ronmental , has assisted on specialty

testi ng for dif ferent types of cements,

mineral and chemical admi xt ures, and

steel and syntheti c fi bers.

Rapid Chloride Permeability Test:strengths and weaknessesAdvantages Is relatively quick—can be used for quality control

Has simple and convenient setup and procedures Provides results that are easy to interpret

Correlates well with 90-day chloride ponding test

Disadvantages May not represent the true permeability (or potential permeability)

for concrete that contains supplementary cementitious materials or

chemical admixtures

Ma y a llow measurements before a steady state is achieved

Can cause physical and chemical changes in the specimen, resulting

in unrealistic va lues

Ma y not be suitable for concretes tha t conta in conducting materials

(such as steel or carbon fibers)

Has low inherent repeatability a nd reproducibility



References

1. D. Whiting, “ Ra pid Determination ofthe C hloride Permeability o fCo ncrete,” Report N o. FHWA/RD -

81/119, August 1981, Federal H ighw ayAdministration, O ffice of R esearch &Development, Washington, D .C .

2. “ Standa rd Test M ethod for Electrical

Indication of Concrete’s Ability toResist C hloride Ion Penetration,”ASTM C 1202-97, Annual Book of

ASTM Standards, Vol. 04.02, pp.

639–644.

3. K.D. Stanish, R.D. Hooton, andM. D.A. Thomas, “ Prediction of Chlo-

ride Penetration in Concrete,” Testing

the Chl ori de Penetrati on Resistance of

Concrete: A L iteratu re Review, FH WAContract DTFH61-97-R-00022.

4. C. Shi, J. Stegemann, and R. Caldwell,“ Effect o f Supplementary Cementing

Ma terials on the Specific C onductivityof Pore Solution and Its Implications

on the Rapid Chloride PermeabilityTest Results,” (AASH TO T277 andASTM C 1202) July–August 1998, pp.389–394.

5. R. Feldman, G. Chan, R. Brousseau,and P. Tumida jski, “ Investigation ofthe Ra pid Chloride Permeability Test,” ACI Materials Journal, May–June1994, pp. 246–255.

6.“ Pa rking Structures—Structures D e-sign,” CSA S413-94, Ca nadia n Stan-

dards Association, December 1994.7. P. Plante and A. Bilodeau, “ Ra pid

Chloride Ion Permeability Test D ata on

Concrete Incorporating SupplementaryCementing Materials, Fly Ash, SilicaFume, Slag and Natural Pozzolans inConcrete,” S-114, Proceedings, Third

International Conference, Trondheim,Norway, 1989, American ConcreteInstitute.

Publication #C02L037, Copyright © 2002 Hanley-Wood, LLC. All ri ghts

reserved

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Rapid Chloride Permeability Testing_tcm45-590139