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Title |
Time Dependent Evaluation of Corrosion Free Life of Concrete Tunnel Structures Based on the Reliability Theory
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Keywords |
부식 ; 염소이온 확산계수 ; 표면 염소이온농도 ; 부식 발생 임계농도 ; 몬테카를로 시뮬레이션 ; Corrosion ; Diffusion ; Surface chloride ; Chloride threshold ; Monte carlo simulation |
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Abstract |
This study predicted the probability of corrosion initiation of reinforced concrete tunnel boxes structures using the Monte Carlo Simulation. For the inner wall and outer wall in the tunnel boxes, exposed to airborne chloride ion and seawater directly respectively, statistical values of parameters like diffusion coefficient D, surface chloride content CS, cover depth c, and the chloride threshold level Clim were examined from experiment or literature review. Their average values accounted for 3.77×10-12 m2/s, 3.0% by weight of cement, 94.7mm and 45.5mm for outer wall and inner wall, respectively, and 0.69% by weight of cement for D, CS, c, and Clim, respectively. With these parametric values, the distribution of chloride contents at rebar with time and the probability of corrosion initiation of the tunnel boxes, inner wall and outer wall, was examined by considering time dependency of chloride transport. From the examination, the histogram of chloride contents at rebar is closer to a gamma distribution, and the mean value increases with time, while the coefficient of variance decreases with time. It was found that the probability of corrosion initiation and the time to corrosion were dependent on the time dependency of chloride transport. Time independent model predicted time to corrosion initiation of inner wall and outer wall as 8 and 12 years, respectively, while 178 and 283 years of time to corrosion was calculated by time dependent model for inner wall and outer wall, respectively. For time independent model, the probability of corrosion at 100 years of exposure for inner wall and outer wall was ranged 59.5 and 95.5%, respectively, while time dependent model indicated 2.9 and 0.2% of the probability corrosion, respectively. Finally, impact of Clim, including values specified in current codes, on the probability of corrosion initiation and corrosion free life is discussed.
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