Old bridges need new money to replace.
Credit: Phil’s 1stPix/Flickr
By itself, concrete is a very durable construction material. The magnificent Pantheon in Rome, the world’s largest unreinforced concrete dome, is in excellent condition after nearly 1,900 years. And yet many concrete structures from last century – bridges, highways and buildings – are crumbling. Many concrete structures built this century will be obsolete before its end.
Given the survival of ancient structures, this may seem curious. The critical difference is the modern use of steel reinforcement, known as rebar, concealed within the concrete. Steel is made mainly of iron, and one of iron’s unalterable properties is that it rusts. This ruins the durability of concrete structures in ways that are difficult to detect and costly to repair.
While repair may be justified to preserve the architectural legacy of iconic 20th-century buildings, such as those designed by reinforced concrete users like Frank Lloyd Wright, it is questionable whether this will be […]
This article, I believe, is off-base. True about the C02. But the prime difficulty with bridges are two. One is that their load limits have been surpassed as larger and heavier trucks were allowed on bridges not designed for those loads back in the 50’s. Second is most bridges are made using prestressed concrete. A little explanation is in order. Concrete is strong on the push, not the pull, and steel is strong on the pull, not the push. Taking advantage of this, crafty engineers pulled with tremendous force on the steel and cast the concrete around that taught assembly. The result, called prestressed concrete, had a much improved load limit.
I believe the problem can be due to those two factors…. in bridges. To think all of that all reinforced concrete has a short lifespan, in my estimation, is bogus.
I am no engineer, but we all know one or two. To imagine that they never thought about rust is………… silly.
Bridges designed for 40 ton trucks see 80 ton loads, and then truck passing to boot.
It also merits comparison with Mexico, that designs for and allows 100 ton trucks. Are their bridges falling down? This bridge thing is world wide. I believe our bridge problem is more of a reflection of a profound disrespect for the limitations of regulation than that generations of engineers never thought of rust.
The Romans did do it better than our high energy Portland cement, with less CO2
see: http://newscenter.lbl.gov/2013/06/04/roman-concrete/