Bridge inspections are a critical part of highway safety. It always makes the news when an inspection calls for repairs that close a bridge, but what specifically have the inspectors found in a situation like this? Here are five of the most common problems that are identified during bridge inspections.
1- Corrosion
Exposed structural members and reinforcement weaken rapidly when they begin to corrode, causing the entire structure to become weaker and more dangerous. Some areas are exposed by design, while others become exposed as a result of crumbling concrete or flaking paint.
Corrosion can also impact the bolts, pins, and brackets hidden from view to passing motorists, making thorough, routine inspections even more important to the long-term health of the bridge.
2- Carbonation of Concrete
A completed concrete bridge would seem an unlikely candidate for any type of chemical reaction to be taking place, but that is exactly what happens during carbonation. A reaction between the carbon dioxide in the air and two components of cement – calcium hydroxide and calcium silicate – lowers the pH of the concrete.
Over time, the increased acidity of the concrete will begin to corrode the steel reinforcement bars and any other steel components of the bridge, either by direct contact or even as acidic water drips onto the steel from above. This accelerates corrosion and is often the cause of the corrosion described above.
3- Alkali-Silica Reactions
Another chemical reaction can take place within the cement. Alkali-silica reactions, also known as “concrete cancer”, take place when the chemical composition of the cement interacts with the aggregate used to make the concrete. This process forms a gel inside the aggregate.
When the water reaches the aggregate, the gel inside absorbs water and swells. The expansion of the aggregate particles begins to break the concrete apart, causing spalling and, ultimately, the failure of the concrete. This process may be accelerated as the shelling concrete exposes reinforcement steel.
4- Creep and Shrinkage
Even very old concrete can change shape with the constant pressure of traffic. In time, it can move enough to create pressure at the joints between sections of concrete. That is why we often see modern bridges built with expansion joints that allow some room for movement while maintaining a watertight joint.
Likewise, concrete can continue to shrink for many years after it is poured as a result of interactions with moisture at the particle level, creating gaps and other problems at joints.
5- Freeze/Thaw Damage
Freezing and thawing is the natural enemy of concrete. Any type of opening where water can enter a concrete surface can swell in size as that water freezes, breaking the concrete apart and creating a cycle of ever-larger gaps.
Freezing and thawing are exacerbated by other processes above and by the use of ice-melting materials such as salt.
Proper inspections can extend bridge life, reduce damage to vehicles, and lower the risk of catastrophic events by finding problems before they come to a head. Be proactive and have local bridges inspected in your area.
