w y wz 10«3y 265~271 (2010.12.) Journal of Korean Society of Urban Environment y w w gj p ü e y y y w y Á½k * w m œw Á* w y œw (2010 9 9, 2010 12 7 k) Effect of Chloride Ion Diffusion Coefficient and Critical Chloride ContentGon the Service Life of Concrete Structures for Reduction of Environmental Load Su-Ho Bae ½ Tae-Dong Kim* Department of Civil Engineering, Andong National University *Department of Environmental Engineering, Andong National University (Received 9 September 2010 : Accepted 7 December 2010) Abstract Factors such as the surface chloride content, the critical chloride content for steel corrosion, and the diffusion coefficient for chloride ion in concrete may significantly influence the service life of concrete structures exposed to chloride environment. In this paper, the effects of water-cement (W/C) ratios on the critical chloride content for steel corrosion and the diffusion coefficient for chloride ion were investigated through the laboratory and the field exposure test. For this purpose, the test specimens were made of concrete with W/C ratios of 31%, 42%, and 50%, and then chloride ion diffusion and critical chloride content tests were carried out for them. It was observed from the test result that both the critical chloride content for steel corrosion and the diffusion coefficient for chloride ion were strongly influenced by W/C ratio. Finally, the service life of existing concrete structures was predicted by using the measured values for the chloride ion diffusion coefficient and critical chloride content. Key Words : Environmental load, Service life, Diffusion coefficient for chloride ion, Critical chloride content, Watercement ratio wy gj p w ü» ù eƒ w, ew» sgj p y wƒ ƒw., y w w» w ü y dw ü Á œw w. gj p t y, y y y wy gj p ü j w e. gj p ü w y y y e - p w sƒw. w - p 31%, 42% 50% w gj p œ w z y y y x ww., - p ƒ 31~50% ü x s x y ƒƒ 0.96~1.63 kg/m 3, 2.53~3.97 kg/m 3 ùkûš, y - p x j w ùkû. w, y y y de w» gj p ü sƒw, gj p y w w ü - p 40% w w ùkû. : y w, ü, y y, y, - p Corresponding author E-mail : shbae@andong.ac.kr 265
266 yá½k I. w y ù w ƒ ew gj p l en y ³ w ü j w.» gj p ù eƒ, ew» sgj p y wƒ ƒw., y w w» w gj p ü y dw ü œw w q. wy gj p ü dw» w gj p y, t y (Gj rv, 2006). y gj p - p,, p,, y w š, y gj p w, p, yy, y, t»k w (Trejo Pillai, 2003). wr, gj p ü y y j» ü dw w sƒ š, w ƒ v w., y y p x w z gj p ü e w sƒw. w ³ y NT BUILD 492(1999) w - p y p sƒw š, w x w s x w y s ƒw., ü y y d gj p ü e w sƒw» w Life-365 program (Benz Thomas, 2001) w - p x gj p ü sƒw. 1. II. x p w H t m sp p w, Table 1. ù w, w, Table 2 3. ywy y š y gj p š ùvk š AE (t x K ) t p Table 4. gj p ü x w D19 x (SD 30A) w, œw w y w y ASTM D 1141 (1990) Table 5 w. 2. x 2.1. x gj p - p(w/c) x Table 1. Physical properties of cement Density Setting time (min) Fineness Compressive strength (MPa) (g/cm 3 ) Initial Final (m 2 /kg) f 3 f 7 f 28 3.15 250 370 340 23.5 33.0 40.0 Table 2. Physical properties of fine aggregate Specimen Density (g/cm 3 ) Absor-ption Unit mass (kg/m 3 ) Mass of passing No. 200 sieve River sand (Nakdong river) 2.60 1.47 1597 2.2 2.43 F.M. Table 3. Physical properties of coarse aggregate Specimen G max (mm) Density (g/cm 3 ) Absorption Unit mass (kg/m 3 ) F.M. Crushed rock (Andong) 25 2.65 0.58 1648 7.27
y w w gj p ü e y y y w 267 Table 4. Properties of chemical admixture Type Specific gravity ph Solid content Quantity (by mass of cement) Main component Superplasticizer 1.21 8 41 0.2 ~ 2.0 Sodium salt of a sulfonate naphthalene Table 5. Chemical constitution of artifical seawater (kg/m 3 ) NaCl MgCl 2 Á6H 2 O Na 2 SO 4 CaCl 2 KCl 24.53 10.40 4.09 1.16 0.695 Fig. 1. Details of prism test specimen (mm). y y sƒw» w g j p w x w, t v 180 ± 20 mm 210 ± 20 mm, t œ» 4.0 ± 1.5% w, W/C 31%, 42% 50% gj p w x(φ100 200 mm) ƒ x x (Fig. 1) w. ƒ x x gj p ü j» w gj p x ƒ ƒ W/C w (Cl ) 0.3, 0.6 0.9 kg/m 3 ƒw. x xz 24 w z t w, x w» w x 14 ¾ 20 o C x w. wr, y p y sƒ x gj p w q w» w x œ ƒ w. Table 6 W/C gj p wt ùkü. 2.2. y y sƒ gj p œ d (28, 91, 182, 273 365 )¾ t ww z»yw x w y d w.»y w x Andrade (1993), Dhir (1990), NT BUILD 492 (1999) Zhang Gj rv (1994), ³ y NT BUILD 492 w y x ww. gj p r Ì 50 mm w, 10% NaCl, 0.3 M NaOH w (Figs. 2 3). y e wz œ e w 30 V œ w y ü 24 d w.»yw x óù z gj p r w 2 ƒ w w, 0.1 N AgNO 3 w s³ en¾ d w. d w y w. D = RT --------- zfe X d a X d ------------------------ t (1) Table 6. Mix proportions of concrete Specimen Cylinder Prism W/C Cl (kg/m 3 ) Target slump (mm) Target air content S/a Unit mass (kg/m 3 ) W C S G SP (C %) 31-210 ± 20 40 165 525 652 996 1.5 42-180 ± 20 4.0 ± 1.5 43 166 400 744 1006 1.2 50-180 ± 20 48 167 336 855 944 1.2 31 0.3, 0.6, 0.9 210 ± 20 40 165 525 652 996 1.5 42 0.3, 0.6, 0.9 180 ± 20 4.0 ± 1.5 43 166 400 744 1006 1.2 50 0.3, 0.6, 0.9 180 ± 20 48 167 336 855 944 1.2
배수호 김태동 268 Fig. 2. Detail of migration set-up. Fig. 4. Cyclic wet and dry salt water method. Fig. 3. Arrangement of migration set-up. 여기서, E = U 2 ------------ L, a = 2 --RT ------- erf zfe 1 1 Fig. 5. Seashore exposure test. c c 2 d ------0 염소이온 확산계수 (m /s) 이온의 원자가 패러데이 상수 양극과 음극 사이의 전압차(V) 기체상수 욕액의 온도 시편의 두께 염소이온의 침투깊이(m) 실험 지속시간 비색법에 의한 반응 농도(N) 음극셀의 염소이온 농도(2N) 철근부식 촉진시험 및 해양 폭로시험 본 연구에서 사용된 철근부식 촉진시험법인 염수 건 습반복법은 Fig. 4와 같은 수조에 철근 콘크리트 시험 체를 배치하여 적절한 순환장치에 의해 수조 내로 염 수의 침지와 건조를 반복시킴으로써 콘크리트 내의 철 근부식을 촉진시키는 시험법이다. 콘크리트 배합 시에 염분을 혼입하거나 콘크리트 피복두께를 감소시키면 D: z: F: U: R: T: (K) L: (m) Xd : t: (s) erf : error function cd : c : 0 2.3. 2 철근부식이 더욱 촉진된다. 이 때 철근의 부식 개시 시 기를 감지하기 위하여 철근에 리드선을 연결하여 주기 적으로 자연전위 측정 등에 의한 모니터링을 하여야 한다. 한편, 해양 폭로 공시체는 재령 14일까지 약 20 C의 실험실에서 기건양생 후 경북 영덕군 금곡리에 위치한 동해안의 비말대에서 시험 전까지 콘크리트 내의 철근 부식이 발생할 때까지 약 3년간 폭로시켰다(Fig. 5). 철근부식 모니터링 및 부식 임계 염화 물량 평가 콘크리트 내의 철근부식이 시작되었을 때, 철근 주 위의 염화물량을 측정함으로써 합리적인 부식 임계 염 화물량을 평가하기 위하여 철근부식 촉진시험이 진행 되는 동안 각 시험체에 대해서 자연전위 측정에 의한 모니터링을 실시하였다(ASTM C 876, 1991). 이에 따 라 철근부식이 감지되었을 때 시험체를 파괴하여 부식 임계 염화물량을 평가하였다. 콘크리트 내의 철근부식 임계 염화물량을 평가하기 위하여 부식 모니터링에 의하여 부식이 감지된 콘크리 트 시편을 위, 아래로 할렬하여 부식된 철근 주위의 콘 크리트에서 상, 하 부분의 모르타르를 부위별로 약 5 g 씩 채취하여 분말 시료를 조제한 후 이를 No.100체 (0.15 mm)로 쳐서 통과된 것을 염화물량 평가를 위한 o 2.4.
y w w gj p ü e y y y w 269 Fig. 6. Compressive strength of concrete. Fig. 7. Diffusion coefficient of concrete. w. w y sƒw. 1. III. x š Fig. 6 y p y sƒ gj p W/C ùkü. Fig. 6 gj p W/C ƒ wš ƒw ƒ ƒw ùkù, x gj p t yw ùkû. Fig. 8. Critical chloride content of concrete. 2. y p Fig. 7 - p gj p y ùkü, y - p ƒ wš ƒw ùkû., y y w (2) txw. D () t = D ref t ref m ----- t (2)», D (t) t y y, t ( ), D ref» ( m 28 ) y y, m y y y ùkü. - p 31%, 42% 50% w 28
270 yá½k Table 7. Input parameters used for durability analysis W/C Diffusion coefficient at 28 days ( 10 12, m 2 /s) Diffusion coefficient decay constant Surface chloride content (kg/m 3 ) Critical chloride content (kg/m 3 ) Concrete cover (mm) 31 9.9 0.21 13.0 42 13.8 0.29 13.0 50 17.2 0.31 13.0 * Laboratory test results ** Field exposure test results 1.58 * 50 3.92 ** 100 1.39 * 50 3.34 ** 100 1.11 * 50 3.09 ** 100 y y ƒƒ 9.9 10 12, 13.8 10 12 17.2 10 12 m 2 /s ùkûš, - p w (m) ƒƒ 0.21, 0.29 0.31 ùkû. 3. y sƒ Fig. 8(a) w x 3 w ü x y ùkü. ü x y 0.96~1.63 kg/m 3 ùkûš, - p ƒ w ƒw ùkû. Fig. 8(b) 3 w s x w x x y ùkü, y 2.53~3.97 kg/m 3 ùkûš, ü x - p ƒ w ƒw ùkû., y W/C x j w ùkû. wr, gj p w w y gj p v ̃ y e w w ùkû. w, ü x y x x gj p w y y w k v q k yƒ» w ü x gj p ü f x x» q. 4. y y y ü e w y y y gj p ü e w sƒw» w Life-365 program w. Table 7 y y, ü x s x y Fig. 9. Expected service life of concrete structures. ü w w ùkü. Fig. 9 gj p ü w
y w w gj p ü e y y y w 271 ùkü, ü - p ƒ š v ̃ j ƒw ùkû., - p gj p v ̃ gj p ü j w e ùkû. w, gj p ü y y ƒ š y j ƒw, - p ƒ gj pƒ š z j gj p y w w ü ƒ w - p w ùkû. IV. 1. gj p y y - p ƒ š ƒw w ùk ûš, y - p ƒ j ƒw ùkû. 2. - p ƒ 31~50%, ü x s x y ƒƒ 0.96~1.63 kg/ m 3, 2.53~3.97 kg/m 3 ùkûš, y - p x j w ùkû. 3. gj p ü w, ü y y ƒ š y j ƒw, - p ƒ gj pƒ š z j g j p y w w ü - p 40% w w ùkû. 2007w w w w. References 1. Andrade, C. 1993. Calculation of Chloride Diffusion Coefficients in Concrete from Ionic Migration Measurements. Cement and Concrete Research. Vol. 23, pp. 724-742. 2. ASTM C 876. 1991. Standard Test Method for Half- Cell Potentials of Uncoated Reinforcing Steel in Concrete. American Society for Testing and Materials. pp. 616-621. 3. ASTM D 1141. 1990. Specification for substitute Ocean Water. American Society for Testing and Materials. pp. 439-440. 4. Benz, E. C. and Thomas, M. D. A. 2001. Life-365 Service Life prediction Model. The Silica Fume Association. 5. Dhir, R.K., Jones, M.R., Ahmed, H.E.H. and Seneviratne, A.M.G. 1990. Rapid Estimation of Chloride Diffusion Coefficient in Concrete. Magazine of Concrete Research. 42(152). pp. 177-185. 6. Gj rv, O.E. 2006. Durability Design of Concrete Structures in Marine Environment. IABMAS. pp. 949-950. 7. NT BUILD 492. 1999. Chloride Migration Coefficient from Non-Steady-State Migration Experiments (Concrete, Mortar and Cement Based Repair Materials). 8. Trejo, D. and Pillai, R. G. 2003. Accelerated Chloride Threshold Testing: Part ASTM A 615 and A 706 Reinforcement. ACI Materials Journal. 100(6). pp. 519-527 9. Zhang, T. and Gj rv, O.E. 1994. An Electrochemical Method for Accelerated Testing of Chloride Diffusivity in Concrete. Cement and Concrete Research. 24(8). pp. 1534-1548.