Application of the 3D chemo-hygro-thermo mechanical model on existing bridges exposed to chlorides and mechanical damages

Abstract

Bridge engineering world practice has showed that implicit method of service life prediction, relying on sufficient quality and depth of concrete cover, do not guarantee a 100- year structure lifetime without major, complex and expensive repair works. Bridges exposed to harsh combination of mechanical (static, dynamic, cyclic loading) and environmental (sea salts, de-icing agencies, freeze - thawing cycles, etc.) actions are particularly vulnerable. Two such case studies: Krk Bridge and Maslenica Bridge located in aggressive maritime environment will be analysed in the paper including in-service performance and comparison between measured values on bridges and numerical results obtained by two numerical models for service life prediction: the 3D chemo-hygro-thermo mechanical (3D CHTM) model implemented into the finite element code MASA and the Life-365 model. Both models are capable to realistically predict chloride content in concrete after long-term exposure to seawater. However, the 3D CHTM model, which considers cracks and damage in concrete, anticipates the beginning of steel reinforcement depassivation much more precisely than the other model which doesn’t take concrete damage and cracks into account.

Assessment of Performance Indicators of a Large-Span Reinforced Concrete Arch Bridge in a Multi-Hazard Environment

“…Measured chloride profiles after 13 years of exposure are compared with numerical results using two service life prediction models: the Life-365 and the 3D chemo-hygrothermomechanical (CHTM) model [39,40]. The Life-365 model calculates chloride penetration into uncracked concrete according to Fick's second law, assuming diffusion as the dominant transport process, where the chloride diffusion coefficient is time-dependent and is determined based on the concrete mixture [41].…”

“…The comparison with measured data (Figure 6) led to the conclusion that both models are able to realistically predict the chloride concentration in concrete after a long period of time (more than 10 years). However, the 3D CHTM numerical model, which considers cracks in the concrete, predicts the depassivation time much more accurately [18,39,40]. Life prediction analysis combined with other testing methods leads to the conclusion that a service life of 100 years can be achieved with the designed concrete quality and concrete cover depth.…”

“…Life prediction analysis combined with other testing methods leads to the conclusion that a service life of 100 years can be achieved with the designed concrete quality and concrete cover depth. However, cracks and damage in the concrete that occur during construction and exploration shorten the depassivation time to less than 10 years [18,39,40]. It should be noted that both models assume constant boundary conditions: surface chloride concentration, water saturation, relative humidity, and temperature, while chlorides penetrate into concrete by diffusion.…”