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Comment by toss1 | Hacker News Reader

>>if moisture gets to the steel rods, the reinforced concrete beams crack.

Exactly; and the crucial intermediate step in there is the moisture causing the steel to oxidize, the iron oxide increasing the volume of the rebar, and thus putting the concrete in tension from the inside, and since concrete really sucks in tension (but is great in compression), the concrete cracks.

I'm mystified that iron-based rebar is even still allowed in construction, when fiberglass-based rebar is readily available and proven to work better.

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I asked this question here a while back and the answer I got was that at failure steel rebar stretches rather than breaks catastrophically and thats a very important safety factor when calculating dynamic loads, a fiberglass rebar structure would fail far more catastophically.

At, finally an answer that makes sense —Thx!

I'm sure adding a bit of kevlar in the rods would solve that problem, but modeling will still be difficult...

We have no data on such solutions and we keep building bigger, taller, more complex structures so there may be some resistance to new solutions, but I'm sure someone is working on them, as we reach the limits of the old ones.

And this is one of the big issues with RAAC (Reinforced Aerated Autoclaved Concrete, extensively used in the UK in the 60s and 70s. The concrete is aerated (think expanded polystyrene) so it is compressible. That means that you don't see any cracking on the surface as tye rebar corrodes. There is no obvious warning of imminent collapse. The panic in the UK last summer after RAAC ceilings in 2 UK schools collapsed (thankfully during the holidays) was because they had been recently inspected- one the week before.

The social flow on effects spread even wider.

Large numbers of low cost social housing used RAAC as a roofing solution that exists to this day. Councils that still manage low rent housing for people on assisted incomes are taking the financial hit for insurance and replacement.

Arguably worse is the situation of those people who scrimped and saved and bought their way out of povety and purchased the house they previously rented.

What was once an investment of their life savings into capital that would grow in value is now money lost in a house scheduled for demolition that has zero value with a defect no insurer will cover.

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