The Economy of Preventive Maintenance of Concrete Bridges Due to Corrosion

The current practice for physical evaluation and delayed maintenance of deteriorated concrete bridge is fundamentally wrong. This research presents a new approach for the evaluation of the condition states of steel reinforced concrete bridge members, which is based on their chemical conditions instead of the physical deficiencies such as cracks and delamination. Using the proposed chemical based inspection approach, a more effective and economic preventive maintenance plan could be achieved. The available non-destructive evaluation (NDE) methods and preventive maintenance measure are identified. Since the chloride induced corrosion is the major factor that dictates the service life of the steel reinforced bridge element, a refined equation for estimation of the diffusion coefficient of chloride ions into concrete is proposed. A Finite Element Analysis (FEA) model that accounts for time-dependent and temperature-dependent diffusion coefficient was developed and verified against experimental data produced by several researchers. The results of the numerical analysis showed good agreement with experimental data. After validation against experimental data, the FEA model was used to evaluate the effectiveness of the preventive maintenance measures, such as surface sealers and overlays. The chloride profiles derived from the FEA model was then used as an indicator to select appropriate preventive maintenance measures at the right time based on the chloride concentration at the surface of the steel. A simplified concrete bridge deck element is selected to compare the life-cycle cost of a bridge deck with different concrete mix design and different maintenance strategies under various exposure conditions. For cost-effective management of concrete highway bridges, the following measures should be taken, depending on the exposure conditions: 1. For severe exposure conditions, such as coastal area or cold regions that require a large amount of deicing salt, carbon steel reinforced bridge decks have a short service life. Therefore, a well-planned preventive maintenance strategy needs to be implemented in order to postpone or eliminate the needs of major rehabilitation and replacement. In such case, the use of stainless steel could be the most economical solution for the long run. In addition, the use of integrated overlay made of high performance concrete or cathodic protection systems may reduce the life-cycle cost based on a 75-year expected service life. 2. For moderate exposures, the use of overlays and surface sealers has been deemed cost-effective. However, the life-cycle cost is very sensitive for sealer application since it needs to be reapplied frequently. Thus, the effectiveness of the sealer should be closely monitored by the Non-destructive Evaluation (NDE) methods. 3. For mild exposures, the corrosion may not be the most critical deterioration mechanism for the bridge deck element. The riding surface of the bridge deck needs to be replaced periodically due to other deterioration mechanisms such as erosion, fatigue cracks, etc. In conclusion, this research shows that it is not only economical, but also necessary to allocate more funds to perform in-depth, chemical oriented non-destructive tests and active preventive maintenance