I learned recently that reinforced concrete buildings only last about 50 years. Moisture and oxygen seeps into concrete and corrodes the rebar.
Maintaining concrete is a matter of having routine structural inspectors come out to poke and prod the concrete. Worn traffic areas get patches and sealants. Areas with a lot of runoff get seals to direct water in ideal ways. Etc.
0. https://www.sika.com/en/construction/structural-strengthenin...
A farm near where I grew up had a big barn, built in the 1700s that was in daily use until the mid 80s. Due to a family/inheritance dispute, maintenance ceased in the 90s. At some point, the roof leaked and that set in motion things that resulted in collapse last year.
https://www.tracesofwar.com/sights/12168/German-Coastal-Batt...
This condition can be detected and fixed before failure.
Buildings only last 50 years or so before being torn down and rebuilt.
https://www.mynicehome.gov.sg/article/dealing-with-spalling-...
Anyway, the sequence is that micro cracks form on the concrete and expose the steel, then the exposed steel rusts and pushes more concrete away, exposing more steel. This too can be fixed before it becomes a problem.
People on this thread claiming a collapse in 60 years are probably not civil engineers. People claiming that reinforced structures will outlast the Pyramids at Giza are definitely not civil engineers.
What I don't agree is on the classification of that as a "fatal flaw". Looks like we are in serious disagreement on the goal of our constructions.
It's not a fatal flaw in terms of building a perfectly serviceable structure.
It's a fatal flaw in terms of building a structure that lasts the ages like the pyramids.
Like all engineering problems, the solution is greatly dependent on your goals.
Over time however, carbon dioxide from the atmosphere slowly seeps into the concrete (anything that's only intermittently wet fares the worst here), turning the calcium hydroxide into calcium carbonate. While this has the beneficial side effect of actually increasing the strength of the concrete itself, it also lowers its pH value, which means the rebar is no longer protected against corrosion once the carbonation process reaches the rebar.
Most concrete structures with long design lifetimes made of concrete (some dams, levees, bridges - but not all by any stretch) will use design techniques to minimize or remove the use of rebar, such as compression only designs , or ‘overbuilding’ so expected corrosion still leaves the structure strong enough over it’s design life.
Generally, concrete is a strongly base compound and protects rebar from corrosion. Over time however it can be influenced by the environment, with those base compounds reacting and leaving a less protective environment. Some environments do it faster than others.
If the covering concrete is strong enough/thick enough, the pressure caused by the rebar turning to rust inside the concrete won’t crack it - if the rebar was structurally important (pretty much always or why use it?) it still weakens the structure though, sometimes dangerously.
Attempts to mitigate the risk where weatherproofing is not an option and rebar is essential for structural reasons like concrete roadways and bridges have had their share of disasters. epoxy coated rebar for instance can lead to unpredictable and sometimes rapid failures in exactly the types of environments it was expected to help in [https://www.fhwa.dot.gov/publications/publicroads/99novdec/r...]
https://partridge.com.au/concrete-cancer-what-is-it-and-what...
Some other failure modes include the Alkali-Silica reaction (sometimes confusingly named concrete cancer too, though fundamentally different) [https://en.m.wikipedia.org/wiki/Alkali–silica_reaction]
The more dependent a design is on an element that can corrode, and the tighter it’s design tolerances, the more fragile it is. The more overbuilt it is, and more conservative the design, the more expensive it is.
Taking a low margin design and then not maintaining it is a recipe for this kind of disaster [https://www.google.com/amp/s/www.independent.co.uk/news/worl...] and lots of dead people.