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1 Journal of the Korean Ceramic Society Vol. 44, No. 9, pp. 524~528, Determination of Critical Chloride Content of Ordinary Portland Cement Concrete by Linear Polarization Technique Hong-Sam Kim, Hai-Moon Cheong, and Tae-Song Ahn Road Research Team, Expressway & Transportation Technology Institute, Korea Expressway Corporation, Gyeonggi , Korea (Received August 23, 2007; Accepted August 31, 2007) x w msp p gj p y ½y Á w Á k w œ m» q ( ; ) ABSTRACT The results of evaluating steel corrosion in concrete containing chloride content of various levels indicated that the more chloride content in concrete leads to the lower potential and higher corrosion current density. However, the open circuit potential of steel varied with time and exposure condition, and the corelation between the open circuit potential and corrosion current density was not obvious. In order to determine the critical threshold content of chloride of steel corrosion in concrete, the concept of average corrosion current density was employed. The range of critical chloride content in portland cement concretes was about 1.56~1.77% (Cl, %, wt of cement content) along with water-cement ratio, and higher water-cement ratio resulted in reduction in critical threshold chloride content. Key words : Chloride, Critical threshold content, Portland cement, Steel corrosion, Linear polarization 1. gj p œ sy y e yùp ye sww wš, œ ph 12 ~ w w e y w t kv š Ì 20 ~ 60 Å yv (Y-Fe 2 O 3 nh 2 O) x w ky» l y š. 1) ù gj p t w kv v gj p y, y eny, e gj p yw e w q š y k w». t y x, v 3~8 ƒ. 2) ù w t w ƒ wš ww v ƒ w q w gj p ³ w z ƒ ƒ w. Corresponding author : Hong-Sam Kim hskim68@ex.co.kr Tel : Fax : gj p y k k,. ù gj p w y gj p w ƒ. x, g j p w y y w y (critical threshold chloride content) w. w, gj p ù y w w. Haussmann Gouda ph œ e w x l Cl /OH ó0.6 w y w. 3,4) wr, Lambert Page gj p y y w»yw w Cl /OH ƒ 3 ƒ ƒw šw gj p w p y y w j ƒ š š. 5) ù, gj p Cl OH d» p gj p y t» ùkü x. 524

2 y ew gj p w, gj p,,, p C 3 A, Ÿ yy. p, p C 3 A ù Ÿ yy p š y w š j y œ ph w e. w y j w Alonso y w w wš. 6), k k y w» w. Haussman Gouda k k (shift) w. ù, Peterson Clear m t k k w., Hope k k(depassivation) wš. gj p sƒ w, w w»y w» sƒwš y m - p gj p y w. 2. x 2.1. gj p w r msp p( w OPC w) 3.15 š ƒ 3,120(Blaine, cm 2 /g) S p w. 2.59, 2.59 w, œ j» gj p v Ì š w e 13 mm, 2.67 w. gj p w 187 kg š wš - p 40, 50 60% y g, v 15 ± 1.5 cm, œ» 4.5 ±1.0% t w. œ» y w» w p 0.15% AE ƒw. 10 mm x w ó m û w z ó š e w q w, gj p k t No r r w z, m Áò w. gj p y p 0, 0.2, 0.4, 0.6, 0.8, 1.2, 2.4%(Cl ) y w gj p x w. kx z 5 t gqw w w. e l k w gj p œ k w. x w msp p gj p y gj p sƒ gj p w sƒ ASTM C 876 w d w,»yw d wù d z w w d w., (Eoc, z ) e (SCE) w 0.1 mv/s w w gj p k w w. w d mv/s, Eoc» ±20 mv. œ kx z 95% w e w. 3. š 3.1. y y gj p w y wš w, w l. y ù y yw» w y l q w» w w d q w. gj p y en y y w t kv q. y y» w msp p w gj p - p w w Fig gj p j yw, Fig. 1. Change of half cell potential with different chloride contents and ages(opc 40). 44«9y(2007)

3 526 ½y Á w Á k Fig. 2. Variation of half cell potential with various chloride contents and ages(opc 60).» z» ù kü. ù, - p 40% y y 0.6% w k ( 0.2 V(vs. CSE) ) ùkü, y ùkû. wr y y ƒ 2.4% 0.29 V(vs. CSE) w ùkû. wr, - p 60% ƒ w w w - p 40% yƒ j ù kû gj p gj p gj p mw w y e w» gj p w w ƒ w. w» w - p 40% msp p gj p w w ùkü Fig. 3. gj p ƒ w ƒ f w, y k ( 0.2 V(vs. CSE) ) ƒ ƒ ù. k w 0.1 µa/cm w 2 ùkü 0.29 V(vs. CSE). wr, - p ƒ 60% msp p gj p(opc 60), w Fig. 4. ƒ y k w ƒ w Fig. 3. Relation between open circuit potential and corrosion current density of rebar in concrete(opc 40). Fig. 4. Corelation between open circuit potential and corrosion current density of rebar in concrete(opc 60).. w l yw ƒ w. ƒ û w ƒw, Broomfield ew. 8) w Broomfield gj p v Ì y w, w, y, w j š wš. w Pourbaix ph wš q w» wš. 6) 3.3. gj p y gj p w y w w wz

4 x w msp p gj p y 527 Fig. 5. Pre-mixed chloride content and corrosion current density of rebar(opc 40). Fig. 7. Pre-mixed chloride content and corrosion current density of rebar(opc 60). Table 1. Critical Threshold Chloride Content and Average Corrosion Current Density of Rebar Corrosion in Concrete with Varing Water-cement Ratio(OPC) W/C (%) Critical chloride content (%, wt of cement) Average corrosion current density (µa/cm 2 /day) Icorr=0.027 Exp (0.734 Cl%) Icorr=0.025 Exp (0.822 Cl%) Icorr=0.033 Exp (0.709 Cl%) Coef. of determination Fig. 6. Pre-mixed chloride content and corrosion current density of rebar(opc 50).» w» gj p y w» v w. x 95% w, yw š w» w (1) s³ wš 0.1 µa/cm 2 /day w. w Alonso Andrade w. 7) I corr t Average I corr = total time (1) Critical corrosion rate : Average I corr 0.1 µa/cm 2 /day (2) - p gj p y w» w gj p w p w 7 y w w gj p x 7, 14, d w Figs. 5 ~ 6 w ùkü. Fig. 5 - p ƒ 40% msp p gj p y y ƒw ƒ j w, d w w x» ù s³ (average Icorr) y y w ƒ 0.98 w ƒw ùkû. m w y p 1.77%. w w - p ƒ 50 60% w w msp p gj p y y s³ w Table 1 gj p y p 1.56~1.77% ùkü. w msp p gj p y w» w - p ƒ 44«9y(2007)

5 528 ½y Á w Á k» d l w w w. y y gj p sƒw yw w y w j ùk û. s³ l w msp p gj p y - p p 1.56 ~ 1.77%, - p ƒ ƒ w y w. msp p gj p y w» w - p ƒ 30, 40, 50% msp p gj p w»s x w ùkü. Acknowlengement Fig. 8. Comparison of result by Nilsson and this study. 30, 40, 50% msp p gj p w w Nilsson 9) w Fig. 8. Nilsson - p 40 50% y 1.5 ~ 2.0%( p ) šwš ù x w - p 1.67 ~ 1.77%( p ) - p 40% sƒ ù - p 50% j s ƒ. wr, x 95% w w e x š w q, x w ƒ { û x p 0.5 ~ 0.7%. ù x ƒ» x w» l x y w q. 4. m sp p w gj p y w» w s³ w. w s³ y w y w yw w q m ƒ wš w m» s ƒ k ww 2005 w» ( y: 05 w» D-11) w w,. REFERRENCES 1. ACI Committee 222, Corrosion of Metals in Concrete, ACI Journal, J. P. Skalny, Materials Science of Concrete, The American Ceramic Society Inc., D. A. Hausmann, Steel Corrosion in Concrete. How Does It Occur?, J Mater Prot, (1967). 4. V. K. Gouda, Corrosion and Corrosion Inhibition of Reinforcing Steel, Br Corrosion Journal, (1970). 5. P. Lambert, C. L. Page, and P. R. W. Vassie, Investigation of Reinforcement Corrosion. Electrochemical Monitoring of Steel in Chloride Contaminated Concrete, Materials and Structures J (1991). 6. M. Pourbaix, Lectures on Electrochemical Corrosion, Plenum Press, New York, C. Alonso, C. Andrade, M. Castellote, and P. Castro, Chloride Threshold Values to Depassivate Reinforcing Bars Embedded in a Standardized OPC Mortar, Cement and Concrete Research, (2000). 8. J. P. Broomfield, Corrosion Rate Measurements in Concrete Bridges by means of the Linear Polarization Technique Implemented in a Field Device, ACI Fall Convention, Minnesota, L. O. Nilsson, HETEK, A System for Estimation of Chloride Ingress into Concrete. Theoretical Background, The Danish Road Directorate, Copenhagen, Denmark, Report No.83, w wz