You see a lot of roadways covered in asphalt, but have you noticed that once you pass onto a bridge, it typically changes to concrete? That’s right—most bridges are made of concrete even if the surrounding road is asphalt. One reason for this is that asphalt is a little flexible. ReadCivil, a publication for civil engineers, says, “Asphalt isn’t structurally suited for creating a span, since it is flexible, and when it is heated, actually becomes plastic (in the sense it flows).” Because bituminous asphalt pavements are not rigid, they act a little like very cold butter. These pavements are sticky and thick, and although they seem hard, they do flow under heavy pressure. This means an asphalt surface would not be able to hold its own weight or additional weight for a bridge or overpass structure.
Another reason asphalt surfaces are typically not used for a bridge is because it would add a significant amount of weight to the roadway. Roadways and overpasses/bridges are designed separately because they serve very different purposes, from crossing a city roadway to crossing a body of water or a train track. This requires a different level of design and execution.
Additionally, asphalt on a bridge or overpass could hide underlying problems, according to California-based expert American Asphalt. They state that water intrusions or structural defects could go undetected and cause a safety hazard for users of the overpass. “Left unnoticed and unattended by inspectors, these hidden weaknesses could result in potentially dangerous consequences for drivers.”
Concrete bridges, on the other hand, can support their own weight and the additional weight of traffic. This is because they’re installed with reinforcement bars or mesh, which makes them lighter and more durable for an overpass or bridge. ReadCivil states, “Most concrete bridges have steel supporting girders or prestressed concrete beams with steel cables and reinforcing bars integral to them, columns, pile caps, and piling, so the mass of concrete plus the traffic load can be safely supported.” Some bridges may be built with wooden beams or planks and are reinforced with steel beams, cables, and other structural-reinforcement items. Before steel and concrete, bridges were typically made of stone blocks placed in an archway. The stones were arched toward each other, supported by stacked columns. This technique was simple and durable.
Today’s concrete bridges are inspected often, typically at least every two years. Concrete bridges require less maintenance than asphalt bridges because resurfacing isn’t a necessity. However, paving contractors must take great care in the transition areas between bridge and roadway to ensure overall smoothness between the surfaces. Because the asphalt surrounding the bridge will require resurface work, paving crews must be able to work confidently with both concrete and asphalt to ensure there is proper clearance between the two pavements and that the roadway is safe and smooth. Go Pave Utah’s experts know how to work with both concrete and asphalt, which means a transition to either pavement will be seamless when our crew is in charge.
