**5. Concrete bridges**

Known for their longevity and low maintenance costs reinforced concrete (RC) bridges are designed to maintain their service life over long periods of time. But they deteriorate from the same elements as steel bridges: poor construction, and outdated designs for today's traffic loads. Subject to aggressive factors, such as over loading, vibration, extreme weather, freeze thaw cycles, chlorides in de-icing salts, plus air borne chlorides in marine environments the service life of the RC bridge is degraded. As the Federal Highway Administration has stated "Salt contamination is probably the most significant single contributor to bridge deterioration". These five primary elements are the contributing factors to the deterioration of RC bridges.

### **5.1 Elements of deterioration on concrete bridges**

For reinforced concrete bridges there are two primary elements, or factors, that contribute to the deterioration of concrete structural members: salts and loads exceeding the original design criteria.

#### *5.1.1 Deterioration from water and salt*

The effect of salt on the decks and substructure of an RC bridge can be significant. The chloride ion as a major component of sodium chloride and calcium chloride is the most destructive element to an RC bridge in the corrosion deterioration process on the reinforcing bars, which expands and induces high tensile stresses in the surrounding concrete. Hairline cracks enlarge from freeze/thaw and traffic causing delamination and spalling of concrete. Water seepage (with salt) through faulty deck joints cause deterioration in abutment back walls, beam seats, pier caps, concrete pads, and end diaphragms.
