Here's Brian Potter, author of Construction Physics on Twitter:
Here's Brian Potter, author of Construction Physics on Twitter:
It is not a mystery why our concrete lasts only a few decades, it's understood perfectly well - chlorides make their way into the concrete and cause the steel reinforcing to corrode. The corroded steel has a larger volume, and so spalls the concrete.
This is overwhelmingly the cause of failure of modern concrete. Roman concrete was unreinforced and doesn't have this problem. It's not uncommon today to build long-lifespan structures either unreinforced, or with stainless steel reinforcing, to prevent this type of failure.
I think this vibes with the common engineering idiom I've heard paraphrased as "anyone can build a bridge that will never fall down, but an engineer can build a bridge that will only barely not...
I think this vibes with the common engineering idiom I've heard paraphrased as "anyone can build a bridge that will never fall down, but an engineer can build a bridge that will only barely not fall down." Historically the way to build things given a relative lack of material science and structural engineering knowledge was to just massively overbuild with absurd safety factors. Reinforced concrete gets you a gigantic boost in bang-for-your-buck in terms of material strength, but means you're turning "artificial rock" into "artificial rock that critically depends on easily corroded structural members."
You can still do it "the hard way" today, but it means on a fixed budget you'll have one supremely overbuilt bridge instead of five that are "good enough" based on your predicted usage and lifespan. Build the Brooklyn Bridge for horse carriage traffic and you're going to have to awkwardly retrofit it for vehicular traffic in a few decades. Likewise, it's probably unwise to engineer a forever bridge for ICE cars today when who knows what the transit of thirty or forty years from now might look like.
Here's Brian Potter, author of Construction Physics on Twitter:
I think this vibes with the common engineering idiom I've heard paraphrased as "anyone can build a bridge that will never fall down, but an engineer can build a bridge that will only barely not fall down." Historically the way to build things given a relative lack of material science and structural engineering knowledge was to just massively overbuild with absurd safety factors. Reinforced concrete gets you a gigantic boost in bang-for-your-buck in terms of material strength, but means you're turning "artificial rock" into "artificial rock that critically depends on easily corroded structural members."
You can still do it "the hard way" today, but it means on a fixed budget you'll have one supremely overbuilt bridge instead of five that are "good enough" based on your predicted usage and lifespan. Build the Brooklyn Bridge for horse carriage traffic and you're going to have to awkwardly retrofit it for vehicular traffic in a few decades. Likewise, it's probably unwise to engineer a forever bridge for ICE cars today when who knows what the transit of thirty or forty years from now might look like.