Polarization Induced Deterioration of Reinforced Concrete With CFRP Anode

7/23/2019 Polarization Induced Deterioration of Reinforced Concrete With CFRP Anode

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Polarization Induced Deterioration of Reinforced Concrete with CFRP Anode

Ji-Hua Zhu 1, Liangliang ei 1, !iaochang Zhu 1, Hongfang "un 1,#, Lu$ing %ang & and Feng 'ing1,#1 

(uangdong Pro)ince *e+ Laorator+ of Durailit+ for !arine Ci)il ngineering, "chool of Ci)il

ngineering, "henzhen .ni)er/it+, "henzhen 01232, (uangdong, China4 -!ail/5

zhu6h7/zu8edu8cn 9J8-H8Z8:4 liangwei8/zu7g;ail8co; 9L88:4 /zuzhu;c7g;ail8co; 9!8Z8:& 

De$art;ent of Ci)il and n)iron;ental ngineering, Chal;er/ .ni)er/it+ of %echnolog+,

(othenurg "-<1& =3, "weden4 -!ail5 tang8lu$ing7chal;er/8/e

#

Author/ to who; corre/$ondence /hould e addre//ed4 -!ail/5 /unhf2>7/zu8edu8cn 9H8"8:4

?ingf7/zu8edu8cn 9F8'8:4 %el8@Fa?5 3-B00-&3B>-&<2 9H8"8:4 3-B00-&30>-31== 9F8'8:8

Acade;ic ditor5 Federico ella

Recei)ed5 B !a+ &210 @ Acce$ted5 &3 June &210 @ Puli/hed5 10 Jul+ &210

Abstract: %hi/ $a$er in)e/tigate/ the deterioration of reinforced concrete with caron fier reinforced

 $ol+;er 9CFRP: anode after $olarization8 %he /teel in the concrete wa/ fir/t /u6ected to

accelerated corro/ion to )ariou/ e?tent/8 %hen, a $olarization te/t wa/ $erfor;ed with the e?ternal

attached CFRP a/ the anode and the /teel reinforce;ent a/ the cathode8 Caron fier reinforced

;ortar and conducti)e caron $a/te a/ contact ;aterial/ were u/ed to adhere the CFRP anode to the

concrete8 %wo current den/itie/ of 1&<< and &< ;A@;&, corre/$onding to the /teel reinforce;ent/

were a$$lied for &0 da+/8 lectroche;ical $ara;eter/ were ;onitored during the te/t $eriod8 %he

deterioration ;echani/; that occurred at the CFRP@contact ;aterial interface wa/ in)e/tigated +

/canning electron ;icro/co$+ 9"!: and '-ra+ diffraction 9'RD: techniue/8 %he increa/e of

feeding )oltage and the failure of onding wa/ o/er)ed during $olarization $roce//, which ;ightha)e re/ulted fro; the deterioration of the interface etween the contact ;aterial and CFRP8 %he

for;ation and accu;ulation of EaCl cr+/tal/ at the contact ;aterial@CFRP interface were inferred

to e the ;ain cau/e/ of the failure at the interface8

*e+word/5

 $olarization4 interface deterioration4 reinforced concrete4 CFRP anode

1. Introduction

Reinforced concrete /tructure/ ;a+ /uffer fro; $re;ature failure induced + the corro/ion of the

reinforcing /teel e;edded in the concrete, which i;$lie/ that a huge in)e/t;ent in /trengthening,re$air, and rehailitation of the degraded /tructure/ in order to reach their targeted /er)ice li)e/8

Chloride ingre// i/ one of the ;a6or cau/e/ of /teel corro/ion, which can lead to concrete cracing

due to the e?$an/ion e?erted + corro/ion $roduct/ G1,&8 %he corro/ion of /teel + chloride in

concrete i/ generall+ under/tood a/ an electroche;ical $roce// G>8 Eowada+/, )ariou/ well-

de)elo$ed ;ethod/ are a)ailale for deter;ination of the chloride diffu/i)it+ G< and /teel corro/ion

control G08 A;ong the;, i;$re//ed current cathodic $rotection 9ICCP: i/ con/idered one of the

;o/t effecti)e ;ethod/ G3,B and u/uall+ $ro)ide/ /ufficient $rotection G8 In an ICCP /+/te;, a

cathodic current i/ a$$lied to the reinforcing /teel, re/ulting in the /hifting of the /teel $otential

toward/ a le)el at where the corro/ion rate i/ negligile G3,B8

It i/ of crucial i;$ortance to /elect a /uitale anode for the deli)er+ of the $rotection current fro;the /urface through the concrete to the /teel rear8 Different t+$e/ of anode ;aterial/ ha)e een

de)elo$ed, including ther;al-/$ra+ed zinc anode/ G=, ther;al-/$ra+ed titaniu; anode/ G12,11,

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titaniu; ;e/h G1& and conducti)e $aint or o)erla+ coating anode/ G1>,1<8 Indu/tr+ i/ /till looing

for new anode ;aterial/ to /ati/f+ the reuire;ent/ of ond efficienc+, in/tallation con)enience, and

lower co/t8

Caron fier reinforced $ol+;er 9CFRP: i/ generall+ con/idered a/ a lightweight ;aterial with

e?cellent ;echanical /trength and electrical conducti)it+ G108 ecau/e of the/e ad)antage/, CFRP

ha/ een increa/ingl+ u/ed in ci)il engineering, e/$eciall+ in /tructural /trengthening of concrete/tructure/8 Howe)er, the re;arale electrical conducti)it+ of CFRP wa/ le// recognized in ci)il

engineering8 It i/ re$orted that CFRP can e u/ed a/ the anode ;aterial of ICCP /+/te; in

electroche;ical re$airing of reinforced concrete /tructure/8 (ad)e et al8 G13,1B re$orted the te/t

re/ult/ of reinforced concrete /tructure/ lolli$o$ /$eci;en/ and ea;/ with CFRP /er)ing a/ an

i;$re//ed current anode8 an Egu+en et al8 G1 /tudied the $erfor;ance of CFRP faric and rod/

a/ i;$re//ed current anode/ in calciu; /olution and concrete8 Con/euentl+, the idea of co;ining

the CFRP/ dual functional characteri/tic/ of oth ;echanical $ro$ertie/ and electrical conducti)it+

wa/ $ointed out which ;a+ lead to a no)el ;ethod of reno)ating /tructure/8 %he re$orted re/ult/

G1=,&2 co;$ared the ulti;ate /trength/ of /$eci;en/ with CFRP $erfor;ing dual role/ 9oth

/trengthening and anode ;aterial: again/t control /$eci;en/ in which CFRP wa/ onl+ u/ed for

/tructural /trengthening8

%he ao)e /tudie/ ;ainl+ focu/ed on the efficienc+ of u/ing CFRP anode in ICCP again/t /teel

corro/ion, wherea/ degradation of the /+/te; i/ al/o critical, e/$eciall+ for the long-ter;

 $erfor;ance in the /er)ice life $eriod8 %he degradation de$end/ on )ariou/ a/$ect/ including the

 eha)ior of anode and contact 9adhe/i)e: ;aterial/, a/ well a/ the interface eha)ior of oth

anode@contact ;aterial and concrete@contact ;aterial8 Recentl+, Zhu et al8 G&1 in)e/tigated the

 eha)ior of CFRP anode in the /i;ulated ICCP /+/te;8 Eo /ignificant degradation in electrical and

;echanical $ro$ertie/ wa/ found of CFRP /u6ected to anodic $olarization at the /elected a$$lied

current den/itie/, which de;on/trated that CFRP could e /ucce//full+ u/ed to /i;ultaneou/l+ carr+

out the dual function/ of i;$re//ed current anode and /tructural /trengthening8

In the $re/ent $a$er, a great intere/t ha/ een de)elo$ed in /tud+ing the deterioration of ICCP

/+/te; of reinforced concrete with CFRP anode8 Polarization te/t/ with large current den/itie/ were

ado$ted to accelerate $o//ile deterioration $heno;ena clo/e to the CFRP anode8 Influence of

initial corro/ion le)el/ and different contact ;aterial/, a/ well a/ $olarization e?tent/ were /tudied8

2. Experimental Program

%he following e?$eri;ental $rogra; wa/ carried out in thi/ /tud+8

?ternal current wa/ i;$re//ed to induce the corro/ion of /teel/ e;edded in concrete /$eci;en/8Polarization wa/ then a$$lied to the corroded /$eci;en/ with CFRP anode and ;onitoring the

electroche;ical $ara;eter 9feeding )oltage:8 !icro/tructural change/ at the CFRP@contact ;aterial

interface were e?a;ined after $olarization $roce//8

2.1. Specimen Preparation

ighteen reinforced concrete c+linder/ were $re$ared, each with a dia;eter of 2 ;; and height of

&>2 ;;, a/ /hown in Figure 1a8 %he concrete wa/ ;i?ed u/ing <03 g@;> of Portland ce;ent

9Conch >&80, Anhui Conch Ce;ent CK8 L%D, uhu, China:8 %he water to ce;ent ratio wa/ 28<0

and the /and ratio wa/ 28>B8 %he coar/e aggregate wa/ cru/hed /tone with a ;a?i;u; /ize of >2

;;8 %he fre/h concrete wa/ cured in a cha;er at a te;$erature of &0 C and relati)e hu;idit+ of

=0M for & da+/ after ca/ting8 Ried /teel 9HR>>0, "haoguanIron CK8 L%D, "hao+ang, China:

with a dia;eter of 13 ;; wa/ $laced a?iall+ in the center of the c+lindrical concrete /$eci;en/8 A

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hole of 180 ;; in dia;eter and 12 ;; in length wa/ drilled at the end of each /teel rod to allow

electrical connection with an e?ternal wire8 An 2 ;; /eg;ent of each /teel rod wa/ e?$o/ed for

te/ting and the re/t wa/ /ealed + e$o?+ re/in for i/olating8 %hu/, the /urface area of /teel

 $artici$ating in $olarization $roce// wa/ <2&2 ;;&8 After & da+/ of curing, the c+linder/ were cut

to e?$o/e a $lanar /urface for the adhe/ion of CFRP anode8

Figure 1. "che;atic )iew of te/t /etu$ 9a: c+lindrical concrete /$eci;en/4 9b: corro/ion

acceleration4 9c: $olarization /+/te; of concrete /$eci;en/ with CFRP anode8 9.nit5 ;;:

Clic here to enlarge figure

2.2. Corrosion Acceleration Process

Accelerated corro/ion of the /teel wa/ a$$lied $rior to the $olarization $roce//8 %he i;$re//ed

current ;ethod wa/ u/ed to introduce accelerated corro/ion to the in-concrete /teel, which $la+ed

the role of anode while a /tainle// /teel $late wa/ u/ed a/ the cathode Figure 1 8 %he /$eci;en/

were i;;er/ed in >80M EaCl /olution during the accelerated corro/ion $roce// with the /olution

le)el ;aintained &2 ;; ao)e the e?$o/ed $art of the ried /teel, a/ /hown in Figure 1 8 A

con/tant current of &0 ;A $er /$eci;en wa/ i;$re//ed for &< h, < h, and =3 h to introduce three

corro/ion le)el/ to the total of 10 /$eci;en/ 9%ale 1:8 %he )oltage etween anode and cathode wa/

;onitored e)er+ &2 ;inute/ with a data logger8

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Table 1. Para;eter/ u/ed for corro/ion acceleration and $olarization te/t8

Clic here to di/$la+ tale

2.3. Polariation Process

"che;atic )iew of the $olarization /+/te; with CFRP anode i/ /hown in Figure 1c8 CFRP wa/

adhered to the $lanar /urface/ of the concrete /$eci;en/ + contact ;aterial/8

Co;;ercial CFRP /tri$/ were u/ed in thi/ /tud+, /ince thi/ ind of ;aterial ;aintained good

 $erfor;ance a/ anode in $re)iou/ /tudie/ G&18 According to the infor;ation gi)en + the

;anufacturer, CFRP /tri$/ are ;ade of ;ulti-la+er caron fier/ ounded + LA!-1&0@LA!-&&3

la;inating e$o?+ 9Pro-"et Inc8, a+ Cit+, !I, ."A:8 ach la+er con/i/t/ of weft-war$-nit caron

fier/ co;ined + the e$o?+8 %he caron fier u/ed in CFRP wa/ %ora+ %B22 with )olu;e fraction

of 32M8 %he CFRP $late/ were ;achined to &0 N 102 ;;& to e co;$atile with the $lanar /urface/

of the /$eci;en/, a/ /hown in Figure 1c8

%wo ind/ of contact ;aterial/ were u/ed to adhere CFRP to the concrete /$eci;en/8 Kne i/ a

;ade-in-laorator+ caron fier reinforced ;ortar 9are)iated to ;ortar in thi/ $a$er: and the

other i/ a co;;ercial conducti)e caron alu;ino/ilicate $a/te 9are)iated to $a/te in thi/ $a$er:8

%he ;ortar wa/ $re$ared + u/ing caron fier/ of length >O0 ;; in the a;ount of 180M of ce;ent

 + ;a//, fine ri)er /and, and ce;ent with a water to ce;ent ratio of 28<0 and ce;ent to /and ratio

of 1828 !eth+lcellulo/e in the a;ount of 28<M of ce;ent + ;a// wa/ fir/t added to water a/ a

di/$er/ing agent to di/$er/e caron fier/ unifor;l+ efore adding ce;ent and fine /and8 %he

co;;ercial conducti)e caron-alu;ino/ilicate $a/te ha/ a good conducti)it+ due to the gra$hite

 $article/, with a )olu;e re/i/ti)it+ of 2821O28221 Kh;c;8

%he $olarization te/t /tarted after B da+/ of adhering CFRP to the concrete to allow h+dration of the

ce;ent8 %wo con/tant current/, i8e8, 0 and 12 ;A, were a$$lied corre/$onding to $olarization

current den/itie/ of 1&<< ;A@;& and &< ;A@;&, re/$ecti)el+, relati)e to the /urface area of /teel8

%he te/t duration wa/ &0 da+/ for all /$eci;en/8 %he feeding )oltage etween the /teel and the

CFRP wa/ $eriodicall+ ;ea/ured with a high i;$edance ;ulti;eter during the te/t8

%he 1 /$eci;en/ were di)ided into three grou$/ and laeled according to the corro/ion le)el,

 $olarization current, and t+$e/ of contact ;aterial, a/ /hown in %ale 18 %he lael C&<I0!, for

e?a;$le, define/ the /$eci;en with a corro/ion ti;e of &< h 9C&<:, $olarization current of 0 ;A 9I0:,

and caron reinforced ;ortar 9!: a/ the contact ;aterial8 %he conducti)e caron-alu;ino/ilicate

 $a/te i/ indicated + P in the lael/8 It /hould e noted that the /$eci;en/ with I2 are the control/$eci;en/ without $olarization, which were $re$ared for co;$ari/on $ur$o/e/8

2.!. "icrostructure Anal#sis

!icro/tructure o/er)ation/ were $erfor;ed + Digital Ca;era, "canning lectron !icro/co$e

9"!:, and '-ra+ Diffraction 9'RD:8 'RD ;ea/ure;ent/ were conducted on a ruer D ad)ance

in/tru;ent with a Cu*Q /ource at <2 and &22 ;A8 %he in/tru;ent ha/ uilt-in $ha/e identif+ing

/oftware to anal+ze the 'RD /$ectra8 "! wa/ $erfor;ed on a Hitachi "-><22E /canning electron

;icro/co$e with accelerating )oltage of 10 and woring di/tance of a$$ro?i;atel+ 12 ;;8

efore loading the /$eci;en into the "! cha;er, the /$eci;en/ were /$utter-coated with gold to

for; a conducti)e /urface8 %he corro/ion de$th wa/ a//e//ed to reflect the influence of the

 $olarization $roce// on CFRP, according to which the corro/ion rate 9corro/ion de$th@duration ti;e:

wa/ al/o e/ti;ated8 %he corro/ion de$th wa/ ;ea/ured + re;o)ing the corroded $art of CFRP with

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a nife and then ;ea/uring the thicne// of the re;aining un-corroded $art8 %he corro/ion de$th

wa/ then calculated + /utracting the un-corroded thicne// + the initial thicne//8

3. $esults and %iscussion

3.1. Accelerated Corrosion o& Steel

Corro/ion wa/ introduced to the /teel i;edded in the concrete /$eci;en/ u/ing an accelerated

corro/ion ;ethod /o that, when $olarization wa/ a$$lied, the /teel had alread+ /uffered fro;

corro/ion to /i;ulate real-life condition/8

%he ;ea/ured )oltage etween the ried /teel anode and the /tainle// /teel cathode i/ $re/ented in

Figure &8 %he )oltage of grou$ C&< /how/ no /ignificant change during the corro/ion acceleration

 $roce//, with the )oltage di/triuted o)er the range 0O3 8 !eanwhile, the )oltage of grou$/ C< 

and C=3 decrea/ed with ti;e, fro; 3 to at the eginning down to <O0 at the end8 %he )oltage

dro$ indicate/ the decrea/e of re/i/tance etween the anode and cathode8

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Figure 2. !ea/ured )oltage etween ried /teel anode in concrete and /tainle// /teel cathode in

/olution during the $eriod/ of accelerated corro/ion for 9a: &< h4 9b: < h4 and 9c: =3 h8

Clic here to enlarge figure

3.2. Feeding 'oltage during Polariation

%he feeding )oltage of the $olarization /+/te; with CFRP anode wa/ $eriodicall+ ;onitored during

 $olarization $roce//8 %he feeding )oltage cur)e/ are /hown in Figure >8 %he feeding )oltage /ee;/

to e a//ociated with the corro/ion le)el, $olarization current den/it+, and the t+$e/ of contact

;aterial/8 For grou$ C&<, the feeding )oltage of C&<I0! and C&<I0P /tailized at around 0 during

the fir/t 10 da+/, and then increa/ed to &B80 , which i/ four ti;e/ ;ore than the original )oltage a/

/hown in Figure >a8 At the $olarization current of &< ;A@;&, C&<I12! and C&<I12P eha)ed

differentl+8 %he )oltage for C&<I12! /howed an initial increa/e fro; 0 to &2 in the fir/t fi)e da+/,

and then re;ained /tale o)er the following 10 da+/8 C&<I12P /howed a $ea at a$$ro?i;atel+ 1&

da+/8 Howe)er, in general, the )oltage /howed an increa/ing trend8 For grou$/ C< and C=3, the

re/ult/ in Figure > ,c /how that, at a current den/it+ of 1&<< ;A@;&, the )oltage increa/ed )er+

/lowl+ fro; & to 12 4 while at &< ;A@;&, the feeding )oltage increa/ed ;ore, fro; & to &B 8

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Figure 3. Feeding )oltage etween /teel in concrete and CFRP for grou$ 9a: C&<4 9b: C<4 and 9c: C=3

during $olarization te/t8

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Clic here to enlarge figure

(enerall+, the ;ea/ured feeding )oltage indicate/ an effecti)e electrical connection, although the

re/i/tance increa/ed during the te/t $eriod8 %he increa/e of feeding )oltage /hould e related to the

lo// of electroche;ical acti)it+ of the /+/te; G&&8 %he underl+ing ;echani/; will e di/cu//ed in

the following /ection/8 !oreo)er, the /$eci;en/ with current den/it+ of 1&<< ;A@;& had ;ore

/tale electrical connection/ than tho/e with &< ;A@;&

 at the /a;e corro/ion le)el and with the/a;e t+$e of contact ;aterial8

3.3. Inter&ace Examination

An increa/e of feeding )oltage wa/ o/er)ed during $olarization $roce//, a/ /hown in Figure >,

indicating a degradation of electrical connection8 %o in)e/tigate the failure ;echani/;,

;icro/tructure o/er)ation/ were $erfor;ed u/ing digital ca;era, "!, and 'RD on /$eci;en/

C&<I2P, C&<I0P, and C&<I12P with caron $a/te and C&<I2!, C&<I0!, and C&<I12! with ;ortar8

%he detached interface/ are /hown in Figure <, where the failure /urface of CFRP i/ indicated +

white arrow/ and the failure /urface of the contact ;aterial/ + lac arrow/8 Kf the /$eci;en/ withcaron $a/te a/ the contact ;aterial, the CFRP anode of C&<I2P 9no $olarization current a$$lied:

/ee;ed to ha)e fractured fro; the in/ide of the contact ;aterial, /ince $art of caron $a/te wa/ /till

attached to the CFRP /urface8 "$eci;en C&<I0P, to which a 0 ;A current wa/ a$$lied, /howed a

/;ooth failure interface etween CFRP and caron $a/te, indicating a reduction of adhe/i)e

 onding of the caron $a/te8 hen the current increa/ed to 12 ;A, the failure /till occurred on the

interface etween CFRP and caron $a/te8 In addition, the CFRP /urface /ee;ed ;ore corroded8

Figure !. Photogra$h/ of the failure interface etween CFRP and caron $a/te of /$eci;en 9a:

C&<I2P4 9b: C&<I0P and 9c: C&<I12P8 %he lac arrow/ indicate caron $a/te /till attached to the

concrete4 the white arrow/ /how the CFRP/ $eeled fro; the caron $a/te8

Clic here to enlarge figure

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"i;ilar failure $heno;ena were o/er)ed for /$eci;en/ C&<I2!, C&<I0!, and C&<I12! with ;ortar a/

the contact ;aterial 9Figure 0:8 In the/e /$eci;en/ the CFRP /ee;ed ;ore /e)erel+ corroded than

for the /a;$le/ with caron $a/te a/ the contact ;aterial, /ince ;ortar u/uall+ contain/ ;ore $ore/

than $a/te due to the u/e of aggregate and the e?i/tence of a tran/ition zone, which $ro)ide/

additional $ath/ for ionic tran/$ort8

In oth ca/e/ 9caron $a/te and ;ortar a/ contact ;aterial:, the failure after a$$lication of currentoccurred at the interface etween contact ;aterial@CFRP indicating that the interface wa/ the

weae/t $art of the /+/te;8 %hu/ the failure ;echani/; will e related to the che;ical change of

 oth contact ;aterial/ and CFRP, e/$eciall+ the $art clo/e to the interface region8 %hu/ the

;icro/tructure of tho/e two $art/ wa/ /tudied in the following /ection/8

Figure (. Photogra$h of the interface etween CFRP and ;ortar of /$eci;en 9a: C&<I2!4 9b: C&<I0!

and 9c: C&<I12!8 %he lac arrow/ indicate ;ortar /till attached to the concrete4 the white arrow/

/how the CFRP/ $eeled fro; the ;ortar8

Clic here to enlarge figure

3.!. Contact "aterials

%he che;ical change and ;icro/tructure of the contact ;aterial at the interface were in)e/tigated

 + 'RD and "! techniue/8

For the caron $a/te contact ;aterial, %he 'RD /$ectra and identification of the three /$eci;en/

/u6ect to )aried current with $a/te a/ contact ;aterial are /hown in Figure 38 %he C&<I2P /a;$le

con/i/ted of three cr+/talline $ha/e/5 gra$hite 9C: i/ the conducti)e con/tituent which $ro)ided the

conducti)it+ of the contact ;aterial4 trona GEa>H9CK>:&&H&K i/ the cr+/talline $roduct for;ed

during the hardening of the contact ;aterial4 and halite 9EaCl: diffu/e/ fro; the EaCl /olution8

hen the current wa/ increa/ed fro; 2 to 0 ;A and 12 ;A, the gra$hite $ea/ /howed no

/ignificant change8 Howe)er, the height of the EaCl $ea increa/ed, indicating ;ore halite 9EaCl:

wa/ $roduced8 %rona GEa>H9CK>:&&H&K di/a$$eared, which ;ight e due to the acidification

effect around the anode region which con)erted trona to EaCl, water, and CK &8

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Figure ). 'RD /$ectra identification of caron $a/te /u6ect to )aried current den/itie/8 (-(ra$hite

9C:, H-Halite 9EaCl:, %-%rona GEa>H9CK>:&&H&K8

Clic here to enlarge figure

%he corre/$onding "! re/ult/ are /hown in Figure B8 A/ /een in Figure Ba, when no current wa/

a$$lied 9C&<I2P:, the adhe/i)e $art 9/olule /ilicate: of the caron $a/te and conducti)e gra$hite

 $article/ were onded fir;l+ and for;ed a den/e /tructure8 A /;all a;ount of diffu/ed Cl 928M:

wa/ detected Figure Bd8

hen 0 ;A current/ were a$$lied, the onding etween adhe/i)e $a/te and gra$hite $article/

a$$ear/ to e roen and a ;ore $orou/ /tructure for;/ 9Figure B :8 %he $ore/ ;a+ ha)e $ro)ided

;ore incur/ion $athwa+ for anion/ to reach the CFRP anode8 %he content of Cl increa/ed to <8&1M

co;$ared with that of C&<I2P, co;ining the 'RD re/ult, in the for; of EaCl cr+/tal/8

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Figure *. "! i;age/ of the caron $a/te/ of /$eci;en 9a: C&<I2P4 9b: C&<I0P and 9c: C&<I12P8 %he

ele;ent anal+/i/ re/ult/ 9D": of the corre/$onding area indicated + rectangular fra;e and 1 and &

are /hown in 9d:4 9e: and 9& :8

Clic here to enlarge figure

hen 12 ;A current/ were a$$lied, /;ooth $article/ with /ize of ten/ of ;icron/ and the loo/efeature/ around the /;ooth $article/ were o/er)ed a/ indicated + lac arrow/ Figure Bc8

!eanwhile, the content of Cl increa/ed to 0=8>&M 9/;ooth $article: and &833M 9loo/e feature:8 %he

loo/e feature ;aterial /ee;/ to ha)e a /i;ilar co;$o/ition to the original caron $a/te 9no current

a$$lied:, and it ;ight e the re;aining unreacted $art of the $a/te8 %he ele;ent Cl ;ight co;e

fro; the /urrounding region /ince the detecting area of D" i/ of ;icron/8 %he /;ooth $article/

were /u$$o/ed to e the EaCl cr+/tal/ either fro; the diffu/ion of the EaCl /olution u/ed or the

Chlorination of trona GEa>H9CK>:&&H&K8 %hu/ the for;ation and accu;ulation of EaCl cr+/tal/ at

the contact ;aterial@CFRP interface wa/ e/ti;ated to e the ;ain rea/on for the failure of onding8

For the ;ortar contact ;aterial, the 'RD re/ult/ are /hown in Figure 8 %he uartz 9"iK&: $ha/e

wa/ found in all /$eci;en/, which i/ the do;inant co;$onent of the /and u/ed8 Li;e/tone 9CaCK>:wa/ al/o detected in all /$eci;en/, originating fro; the caronation of the h+dration $roduct Ca

9KH:&8 In C&<I2!, cr+/talline halite 9EaCl: wa/ detected, which i/ /u$$o/ed fro; the diffu/ion of

 EaCl /olution8 herea/ in C&<I0! and C&<I12!, the content of EaCl increa/ed with current,

indicating the a$$lied current accelerated the ;o)e;ent of EaCl fro; /olution to the anode8

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Figure +. 'RD /$ectra identification of ;ortar $a/te/ /u6ect to )aried current den/itie/8 S-Suartz

9"iK&:, C-Li;e/tone 9CaCK>:, H-Halite 9EaCl:8

Clic here to enlarge figure

%he ;icro/tructure and ele;ent anal+zing re/ult/ of /$eci;en/ with ;ortar contact ;aterial are/hown in Figure =8 At the /a;e age, ;ortar with no current a$$lied 9C&<I2!: /how/ a t+$ical firou/

;or$holog+ of h+dration $roduct, /uch a/ CO"OH foil ;atri? and Ca9KH:& and ettringite fier/

9Figure =a:8 Howe)er, when current wa/ a$$lied, the firou/ /tructure al;o/t 9C &<I0!, Figure = : or 

totall+ 9C&<I12!, Figure =c: di/a$$eared, re$laced + a ;ore den/e /tructure con/i/ting of

agglo;erated irregular /ha$e $article/, which i/ the later h+dration characteri/tic/ of ce;entitiou/

;aterial/8 %hu/ the a$$lied current a$$ear/ to accelerate the h+dration of ce;entitou/ ;aterial/8

%he D" re/ult/ /how that the content of the ele;ent Cl increa/ed fro; &8M to &=82M for

C&<I0! and 118B2M for C&<I12!8 Co;ining with the finding in 'RD, the increa/ed content Cl ;a+

 e fro; the EaCl accu;ulation at the anode /urface when current a$$lied, which will reduce the

 onding area etween contact ;aterial@CFRP8 !oreo)er, the content of ele;ent Ca wa/ ;ea/uredand found to decrea/e with increa/ing current, fro; 1>80BM 9C&<I2!: decrea/ed to 283>M 9C&<I0!:

and 28<2M 9C&<I12!: according to the uantification of D" re/ult/, which /ugge/t/ the tran/$ort of

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cationic Ca& to the cathode8 It i/ nown that the onding co;$onent in ce;entitou/ ;aterial i/

;ainl+ CO"OH, where Ca i/ the i;$ortant con/i/ting ele;ent8 %he lo// of Ca will cau/e the

degradation of CO"OH and thu/ the failure of onding ca$ailit+, which i/ con/i/tent with the

finding in Ref G&>8 Con/euentl+, oth the accu;ulation of EaCl and the lo// of Ca at the anode

will cau/e the lo// of /hear /trength of the interface and the increa/e of electrical re/i/tance o)er

ti;e8 Further /tud+ of the ;echani/; will e a focu/ of future /tudie/8

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Figure ,. "! i;age/ of the ;ortar fro; /a;$le 9a: C&<I2!4 9b: C&<I0! and 9c: C&<I12!8 %he

ele;ent anal+/i/ re/ult/ 9D": of the corre/$onding area indicated + rectangular fra;e are /hown

in 9d O & :8

Clic here to enlarge figure

3.(. CF$P Anode

%he influence of the $olarization $roce// on CFRP wa/ a//e//ed + the corro/ion de$th, fro; which

the corro/ion rate 9corro/ion de$th@duration ti;e: wa/ al/o e/ti;ated8 After &0 da+/ of $olarization,

the corro/ion de$th/ of C&<I2P, C&<I0P, and C&<I12P were a$$ro?i;atel+ 2, 2, and 2821= ;;,

re/$ecti)el+8 %he calculated corro/ion rate i/ a$$ro?i;atel+ 28B T;@da+8 In co;$ari/on, the

corro/ion de$th of the ;ortar /erie/ wa/ 2, 2811= ;;, and 281>3 ;; for C &<I2!, C&<I0!, and

C&<I12!, re/$ecti)el+, with a calculated corro/ion rate of a$$ro?i;atel+ 0 T;@da+8 Con/euentl+, the

CFRP anode u/ing caron $a/te a/ the contact ;aterial can /ur)i)e an order of ;agnitude longer

than the one u/ing ;ortar, which ;a+ e related to the different $ore /tructure/ of the contact

;aterial/, con/i/tent with the o/er)ation + digital ca;era 9Figure < and Figure 0:8 %he corro/ion

;echani/; on CFRP ha/ een /tudied in G&<8 It wa/ found that Cl& and ;ore o?idizing HClK will e $roduced at the anode 9CFRP: region during electrol+/i/ when ClU e?i/t/ in the electrol+te,

which will deco;$o/e the e$o?+ in CFRP into $owder/ and cau/e a rough /urface of CFRP a/

o/er)ed in Figure < and Figure 08 e /hould al/o note that the failure occurred at the interface

 etween contact ;aterial@CFRP in/tead of concrete@contact ;aterial8 %hi/ indicate/ that the anode in

thi/ $olarization /+/te; i/ CFRP in/tead of contact ;aterial /ince onl+ the electron@ion e?change

in/tead of electron e?change or ion e?change can cau/e da;age8 %he electron@ion e?change at the

interface i/ a t+$ical feature of anodic reaction8

Additionall+, although the CFRP wa/ corroded u$ to 281>3 ;; in de$th, the weae/t $art of the

 $olarization /+/te; where fracturing occurred wa/ /till at the interface etween the CFRP and the

contact ;aterial rather than in/ide the CFRP, according to Figure < and Figure 08 %hi/ indicate/ that

the corro/ion of CFRP i/ not the $ri;ar+ cau/e of the degradation of the contact ;aterial@CFRP

interface during &0 da+/ of $olarization8

!. Conclusions

An e?$eri;ental in)e/tigation wa/ carried out to /tud+ the interface deterioration of reinforced

concrete /$eci;en/ with CFRP anode after $olarization8 %wo contact ;aterial/ of caron fier

reinforced ;ortar and conducti)e caron $a/te were u/ed to attach the CFRP anode with concrete8

%he feeding )oltage wa/ ;onitored during $olarization $eriod8 %he underl+ing degradation

;echani/;/ at the interface etween the CFRP anode and contact ;aterial/ were re)ealed + ;ean/of "! and 'RD techniue/8 a/ed on the re/ult/ and anal+/e/, the following conclu/ion/ can e

drawn8

18 %he feeding )oltage increa/ed e)en though an effecti)e electrical connection wa/ /till ;aintained

o)er the $olarization $eriod8 %he increa/e of feeding )oltage indicate/ a deterioration of the

electrical connection in the /+/te;, /ince the current re;ained con/tant during the te/t $eriod8 %he

deterioration wa/ found re/ulting fro; deterioration of the interface etween the CFRP anode and

contact ;aterial8

&8 %he deterioration of the interface wa/ con/idered ;ainl+ cau/ed + the che;ical change of

contact ;aterial/8 For caron $a/te contact ;aterial, the for;ation and accu;ulation of EaCl

cr+/tal/ at the contact ;aterial@CFRP interface wa/ e/ti;ated to e the ;ain rea/on for the failure of 

 onding8 For ;ortar contact ;aterial, oth the accu;ulation of EaCl and the lo// of ele;ent Ca at

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the anode are ;ain rea/on/8 %he deterioration of the interface led to the lo// of /hear /trength of the

interface and the increa/e of electrical re/i/tance o)er ti;e8

>8 %he CFRP with ;ortar a/ the contact ;aterial wa/ corroded ;ore /e)erel+ 90 T;@da+: than that

with caron $a/te a/ the contact ;aterial 928B T;@da+: after &0 da+/ $olarization8 %hu/, fro; the

a/$ect of durailit+ of CFRP, the caron $a/te /ee;/ ;ore $rotecti)e for CFRP than ;ortar when

the electrical connection i/ en/ured8

<8 Large current den/itie/ were ado$ted in the $re/ent te/t/ to achie)e $o//ile interface

deterioration of the $olarization /+/te; in a relati)el+ /hort $eriod8 Further re/earch with $ractical

current den/itie/ i/ nece//ar+ efore /ite a$$lication to in)e/tigate the long-ter; eha)ior of

reinforced concrete ICCP /+/te; with CFRP anode8

Ac-noledgments

%he re/earch wor de/cried in thi/ $a$er wa/ /u$$orted + the Eational a/ic Re/earch Progra;

of China 9i8e8, the =B> Progra;: 9Pro6ect Eo85 &211C21>32<:, the Chine/e Eational Eatural"cience Foundation/ 9Pro6ect Eo8 012B&>B, 01<B&3=, and 01<2>3<:, and the Eatural "cience

Foundation of "Z. 9Pro6ect Eo8 &21<&1:8

Aut/or Contributions

Ji-Hua Zhu controlled the whole $ro6ect and $re$ared the ;anu/cri$t8 Liangliang ei and

!iaochang Zhu are re/earch /tudent/ who carried out the laorator+ te/t8 Hongfang "un contriuted

in the ;icro/co$e anal+/i/ and $re$ared the ;anu/cri$t8 Lu$ing %ang wa/ in)ol)ed in the de/ign of

 $olarization te/t8 Feng 'ing contriuted in de/igning the te/t $rogra;8 All author/ were in)ol)ed in

the te/t re/ult/ anal+/i/ and in the finalizing of the ;anu/cri$t8

Con&licts o& Interest

%he author/ declare no conflict of intere/t8

$e&erences

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9htt$5@@creati)eco;;on/8org@licen/e/@+@<82@ :8