One of the main challenges associated with using reinforced concrete is the tendency of rebar to corrode. Bridges, overpasses, parking structures, and more can all collapse as a result of corrosion. De-icing salt and maritime conditions can accelerate the corrosion process, leaving structures with a shockingly short lifespan. Innovations are being worked on that would allow concrete to heal itself, or to indicate where cracks are forming. The idea behind this is that the sooner cracks can be identified, the sooner they can be filled, delaying the corrosion process for as long as possible.
However, new methods exist to help protect rebar. A new bridge spanning the St. Croix River between Wisconsin and Minnesota is utilizing these recent advancements. In fact, this technology has given the bridge an estimated lifespan of 100 years. First off, the rebar is coated in a plastic piping; next, all spaces are filled in using grout. This allows the rebar to be firmly protected against corrosion. The rods are placed near the surface of the road. Less corrosion leads to less cracks in the concrete, which mean less repairs. Additionally, the rebar is protected from corrosion, so any cracks that do
occur are less likely to be life-threatening.
Fewer repairs have many benefits for infrastructure owners. First off, repairs are often costly. Second, repairs tend to mean road and bridge closures. Third, the environmental impact of cement is very negative and very large. Essentially, higher durability translates into saved money and time, as well as reduced environmental impact.
This new bridge is not just impressive for it's incredible lifespan: it also has some deep roots. Its location on the river is in a place where the water is about 25 feet deep. The workers were tasked with not only getting the foundation to the bottom of the river, and not only with getting through the 85 feet of muck under the water, but with hammering the foundation into the 26 feet of bedrock below the muck and water. This deep-set foundation results in an interesting fact. The bridge is almost as deep under the water as it comes out above the water.
Source: Pioneer Press