Modeling of carbonation in tensile zone of plain concrete beams damaged by cyclic loading

Concrete in bridge structures is constantly subjected to CO2 ingression as well as fatigue damage caused by repeated vehicle loads. This paper presents a general modeling process for carbonation in fatigue-damaged concrete beams. The key point of considering effects of fatigue damage on concrete carbonation is determining diffusivity of CO2 in fatigue-damaged concrete. To do so, residual strain was chosen as an indicator to evaluate fatigue damage states and a Fictitious Distributed Crack Mode of fatigue-damaged concrete beams was proposed to incorporate residual strain into diffusivity of CO2. Subsequently, the partial differential carbonation equation for fatigue-damaged concrete beams was established and a Keller Box Scheme was implemented to solve it. The numerical solutions were verified by accelerated carbonation tests for concrete beams damaged by cyclic loading. Finally, through parametric study for usual ranges of various influencing factors, a simplified carbonation model for fatigue-damaged concrete beams was proposed. Model predictions of carbonation depths were in acceptable agreement with test results as well as numerical solutions. The simplified model could be used to design concrete cover and help accurately predict or estimate initiation time of corrosion of steel bars in concrete structures.