Monitoring Corrosion of Reinforced Mortar using Guided Mechanical Waves Benjamin L. Ervin Advisor: Dr. Henrique Reis Department of Industrial and Enterprise Systems Engineering University of Illinois at UrbanaUrbana-Champaign What Causes Corrosion? Corrosion in Reinforced Concrete Metallic corrosion in U.S. Number one infrastructure estimated at $276 billion annually durability problem affecting Aesthetics $22.6 billion estimated for Serviceability infrastructure Safety Highway bridges are 37% of All geographic areas vulnerable infrastructure, with majority being reinforced concrete Bridge collapse Annual direct costs of reinforced concrete bridge corrosion is estimated at $4.2 billion Indirect costs estimated at 10 times the direct costs • • • Chlorides and CO2 penetrate concrete, primarily by diffusion Chlorides break down oxide layer CO2 reacts with concrete (carbonation) • Lowers pH • Destroys oxide layer • • Chlorides present from: • Deicing salts on roads • Marine atmosphere • Ground salts • Admixtures (e.g. accelerants) CO2 is in atmosphere Sea water Road salt Concrete carbonation at Wrigley Field (Chicago, IL) resulted in spalling of large concrete chunks in 2004 Corrosion Process Guided Mechanical Waves Combination of compressional and shear waves continually interacting with boundaries to form a composite wave Interface pressure affects amount of wave energy leaked into surrounding concrete Deleterious substances ingress to rebar depth Rust product builds at interface creating pressure Tensile hoop stresses created in concrete cause cracking Loss of cross-section and degradation of concrete affect bond strength Experimental Procedure 1. Accelerate corrosion (impressed current) while monitoring using guided waves 2. Convert wave energy to attenuation 1 2 3. Conduct pullout test to find bond strength 4. Form relationship between attenuation of guided wave and bond strength of corroded specimen 1 Amplitude (Volts) 0.5 0 t1 4 3 E t = ∫ V ( t )2 dt -0.5 t0 -1 200 300 400 Tim e (µs) ⎛E ⎞ Attenuatio n (dB ) = 10 * log ⎜⎜ o ⎟⎟ ⎝ Et ⎠ 500
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