The first house I owned was built in 1928, and by the time I bought it the foundation and basement floor had significant problems. An inspector told me that the concrete had probably been made with “creek sand” containing a significant fraction of organic matter that, over time, had decayed away and left the concrete porous and weak. Not hard to imagine similar problems in countries like Russia and China (and Turkey).
I think everybody has covered most all the reasons concrete eventually fails … I’ve just one or two more to add:
Adding too much water to the concrete mix !!!
The batch plant generally sends the concrete truck out to the job site with the exact amount of water mixed in that the specifications call for … but this mix tends to be glompy and hard as hell to place and finish … so once the truck arrives at the site, the concrete foreman almost invariably adds more water in … thus allowing a smaller crew to take less time to get the job done, and more profit …
Freezing …
This doesn’t really apply to the OP’s case … if our concrete gets frozen in the first couple of weeks after the pour … the shit will just fall apart right away, within months it will be obvious and get the jackhammers out … 'cause we’ll have powdered limestone instead of concrete shortly thereafter …
Word to the wise:
The lowest bid for concrete work may or may not be your best value … be on-hand when the concrete truck arrives and if you hear the foreman tell the driver “add ten gallons” … jump in and say “NO” … you’re paying for 3,500 #/in[sup]2[/sup] concrete, not 1,500 …
It takes three weeks for concrete to come to strength … so don’t roll ten-wheelers over the concrete until that time has past … and have a guard on-site the first evening, unless you want all the neighbors’ kids names scratched in permanently …
I was on a building site a few years ago and watched a guy in a hard hat taking a bucket full of concrete from the delivery truck before the pour. I asked him about it (cos I am nosy like that) and he showed me some cubes that they had made from previous deliveries. At some point, they crushed them with a hydraulic press to determine the strength - if it was too low, or, apparently, too high, they had to dig it up at the supplier’s expense and do it again.
Core sample … sits on a shelf three weeks and then placed in a hydraulic press …
The inspector should of had a thermometer and a slump tester … slump is the measure of how much water is in the mix … and he was just watching making sure no one threw any empty flour tins into the pour … probably more tests that I didn’t notice since I was the guy with the muck rake …
You misunderstood the point.
We inspect stuff at 40 years because out of thousands of buildings *any *failures, even minor ones, are one too many. How many Roman structures are still standing? 1 or 2 out of tens of thousands.
After 40 years sitting at the edge of an ocean we find some surface cracks. Which we fill. Buildings aren’t falling down after 40 years.
One other difference is that the Romans didn’t build cantilevered balconies. A 6" thick slab of concrete sticking 10 or 15 feet out into space attached to the building only along one edge. If they had done so they would have fallen down in minutes. Since they didn’t know anything about tension support via rebar or the equivalent.