zlacker

I spoke with a builder, and the concrete starts to decay in 50 years. Until then it's like new. It lasts much longer than that, 100+ years is not a problem.

>>GoToRO+(OP)
I suggest the builder may have suffered from some motivated reasoning.

Concrete not starting to decay until 50 years has passed is the exception, not the rule.

>>GoToRO+(OP)
The problem, as per the article, isn't concrete. It's rusting steel inside reinforced concrete.

>>GoToRO+(OP)
To be clear, the article is discussing reinforced concrete—concrete made with steel rebar, which rusts.

Unreinforced concrete can and does last for many hundred years. Reinforced concrete, not so much.

FTA:

“Early 20th-century engineers thought reinforced concrete structures would last a very long time – perhaps 1,000 years. In reality, their life span is more like 50-100 years, and sometimes less. Building codes and policies generally require buildings to survive for several decades, but deterioration can begin in as little as 10 years.”

>>wonder+82
Only if you have poorly mixed concrete.

The kind of concrete they use in buildings is not the same as the concrete they use in sidewalks.

>>oxfeed+34
We only use reinforced concrete. The type of work where simple concrete is enough are very rare.

>>oxfeed+34
Unreinforced concrete is largely useless for modern construction, because it basically has negligible tensile strength. You can't make beams, columns, or even pre-fabbed wall panels of any useful strength without reinforcement.

One of the reasons unreinforced concrete may last a lot longer is because its only going to exist in places that don't subject it to tensile stresses. That being said, changes like differential settling can create these stresses after construction.

'Deterioration' can mean many things in terms of concrete.

>>GoToRO+R7
It may start to lose it's strength after 50 years, as designed, if kept under designated conditions.

As for decay, IIUC, it loses pH gradually, from the time you mix it, and that pH is the most important protecting factor that stops the steel from rusting.

Obviously though, a lot of factors have a huge factor on lifetime, including composition, construction, environmental conditions ...

>>GoToRO+R7
Simple concrete is enough in almost all cases for what we do - if we use enough of it. Rebar allows dramatically reducing the amount we use in most cases, with this predictable trade off

It’s rarely physics, almost always economics.

>>lazide+qk
Plain concrete is simply not allowed by code for many applications. So even if you could theoretically justify the design, you couldn’t get the permit to build it.

Physics, economics, and bureaucratics is a good summary of structural engineering. The last one can’t be ignored.