I’ve always thought of concrete as a relatively durable material and yet in Russia and China concrete apartment buildings built 40-60 years ago are already "crumbling" after several decades. Is this a characteristic of the way they were made or is concrete not all it’s cracked up to be as a “permanent” material.
Not long at all, hopefully.
It’s a matter of construction quality and maintenance. The best concrete will eventually succumb to the weather but it could take a very long time. Quality concrete, proper reinforcement, and simple maintenance like painting will enable a building to survive a century or more, assuming proper design in the first place. The buildings in the linked article were built on the cheap, and saving money is a common reason for concrete construction in the first place. Without maintenance even steel superstructures and masonry won’t last forever.
Here in Florida the laws require an inspection of mid- and high-rise condos every 40 years. At these inspections it’s common to find surface cracks in the concrete structure. It’s also common to find cantilevered balconies where water has gotten down into the embedded rebar which expands as it rusts, cracking the concrete and leaving the balcony rather weakly attached to the building. :eek:
The fix is simple: the weakened concrete is jackhammered away, any rusted rebar is cut out and replaced, then new concrete is applied to cover. In the case of extensive balcony corrosion, they’re all sliced off the side of the building then new ones built in place after fresh rebar is first drilled into the floor slabs then set in place with a concrete / epoxy mix.
Once redone, the whole structure is good as new for another 40 years. The start of the building boom here was 70 years ago now. Plenty of early buildings are coming up on their second inspection and are looking good, at least structurally.
It’s certainly possible that truly craptacular concrete, shitty inadequate design, and insufficient or non-existent rebar will produce early and catastrophic failure. As can an utter lack of maintenance, such as letting basements fill with water and stay that way.
Bottom line: Not a first world problem. Definitely a less-than-first-world problem.
It very much depends on how good the quality control was at the construction stage. There have been many cases around the world where the concrete was substandard (usually with too much, or the wrong type of sand). This may also involve some bribery and corruption within bot supplier and customer.
Properly built, they should outlive most of us.
The dome on the Pantheon is coming up on its 1900th birthday. The Flavian Amphitheatre is in rather sorry shape, but most of the damage was caused by earthquakes; the remaining structure seems sound.
That was my first thought too - apparently, I guess, rebar is the problem.
There have been numerous problems over the last century with concrete buildings -
the apartments that crumbled in a recent Turkish earthquake were built with sand stripped from a beach - apparently the salt caused problems.
Apartments in Taiwan several decades ago that collapsed in an earthquake - the builder dumped empty cooking oil cans (presumably those square metal ones) into the forms to reduce the amount of expensive concrete used.
Some tall apartments in Mexico city several decades ago simply fell over during their earthquake, because the seismic waves in the old swamp basin turned the ground below them to mush- so poor foot construction, not bad concrete.
Balconies, and bridges, and other items expose to the elements and stresses, and containing rebar, are susceptible to cracks and rebar corrosion. Properly build, sheltered from excessive weather, concrete structures should last for centuries; oh, and keep them away from earthquakes.
For engineered structures like highways and bridges the usual intended design life is 100 years +, meaning that every bit has to demonstrably be able to function with maintenance at last that long. In many cases if you make the century there’s nothing likely to go wrong after that for a long time.
Normal buildings may not have an intended design life, and an implied expectation that they will cost more to maintain than knock down after 20-30 years. Or they can be built on the basis that once they are up its someone else’s problem. If cheaper materials or methods are used, or maintenance cut, then that optimistic lifespan can be severely shortened.
A major risk is rusting of any reinforcing inserts, which expands and then spalls. Even though it should be under inches of concrete, lack of waterproofing and drainage, hair-thin cracks caused by settlement etc can allow water to penetrate. It happens out of sight so may not be noticed until it gets really bad.
What’s up with this? Why were the Romans so much better at concrete than modern Floridians? 40 years is pitiful.
I’m not a civil engineer, but I suspect the answer is that the Romans, not having access to modern modeling methods, overbuilt the crap out of everything, since they had no way of determining how much concrete or whatever was just enough to support the structure. We could certainly build buildings today that would last millennia, but no one’s terribly interested in paying 5x as much for whatever apartment building they’re putting up to ensure that.
Roman structures tended to be massively overbuilt combining fired brick with concrete to form relatively low stress structures. They had almost no notions of the modern engineering calculations for stress and strain and so used empirical knowledge and rules of thumb based upon previous successful construction without consideration for optimizing the amount of material or space used. They also didn’t build skyscrapers or other structures more than three or four stories high, albeit not so much because of structural stresses but because of ground loading; without the ability to do large excavations and no steel reinforcements the pressure loading per unit footing area was limited.
And I don’t know how much of a difference this is, but the Romans (and others in the volcanically active regions of the Northern Mediterranean) used volcanic (pozzolan) ash and hydrate lime in their cement. This, combined with the slow, methodical compaction of the cement into concrete (instead of the mixing and quick pour methods we use, which virtually insure voids and fissures due to outgassing and contraction) meant that they experienced less cracking and spallation. Not having steel rod corroding within the concrete also contributes to the longevity.
We build to expand, so we build with methods that are quick and inexpensive. The Romans built to last used cheap slave labor, so the time and effort involved in construction was not as much of a factor. The ancient city capitol city of Rome, within the Aurelian Walls was only about 14 km[SUP]2[/SUP] and I think the maximum height of any building was about 30 m. The Island of Manhattan, New York City, is almost 90 km[SUP]2[/SUP], and has over a hundred buildings that are taller than 180 m, with all of the substructure and support that implies. If we were building Manhattan the way the Romes built up Rome, it would look nothing like modern the New York City skyline.
Stranger
Interesting, thanks!
I think it depends on the concrete & environment in question.
An old workplace of mine (a hospital) was built using concrete sourced from (I was told) Saudi Arabia. The concrete they made probably lasts fine in dry conditions but in England, it started crumbling after ~15 years and they had to replace the whole building.
I’m guessing you have to formulate the concrete based on the environment it’s going to be in, the Romans presumably had enough experience with other buildings to get the Pantheon right and didn’t have access to cheaper, differently formulated concrete from distant lands
They also, as I recall, had a rule that no apartment building should be higher than ??? 5 ??? levels? Because their repeated experience was that tall buildings fell down.
Another vote for rusty rebar. My anecdotal evidence is having seen that problem on many buildings from that time period. I hope nobody got hit by chunks of concrete falling to the street below…
Yes, rebar is the achilles heel of concrete structures in cold and/or wet locations, which is a lot of them. Of course, if you don’t use steel reinforcing, then you’re limited to very heavy arched construction like the ancient Romans and similar unreinforced masonry. That means you have very short spans between very thick columns, or domes. The Monadnock Building in Chicago for instance has solid masonry walls supporting a 16-story high rise. The walls are 6 feet thick at ground level, and while I think it has steel or cast iron floor framing, imagine how much less interior space there would be if you needed such thick columns every few feet. A giant dome is cool, but it’s a lot of volume without a lot of floor area. What do you then fill it with other than windowless interior rooms?
So pick your poison. The steel reinforcing allows for much longer spans, flat floor/ceiling slabs, smaller columns, integral beams, etc. Of course the more weight that can be eliminated from the structure, the less structure there has to be to carry it, making everything lighter. As everything gets thinner however, the more it relies on the rebar, and that rebar is more easily exposed to the elements. Stainless steel rebar is becoming more prevalent and can make for some truly long-lived structures compared to epoxy-coated rebar that has a knack for getting damaged and performing little better than bare metal. Of course stainless is quite a bit more expensive. I assume there’s people working on carbon fiber nanotube rebar which may someday trounce everything else.
Quite true. My next-door neighbor was an inspector, and often rejected loads of concrete that were substandard. It seemed to be fairly common for builders to try to ‘cheat’ by using less cement than specified in a concrete mix.
I once watched & listened as a construction company owner screamed & cursed & threatened him in his yard next door, because he had rejected some concrete, and they had to re-do a big section of runway. He told me later that the owner had first come to his home to offer him a large bribe, and his refusing it was what first made him so angry.
Concrete is strong under compression and weak under tension. A pure dome shape only contains compressive forces which makes it ideal to be build out of unreinforced concrete. Unfortunately, dome shapes are not very space efficient and so most modern structures are built into shapes that can’t be constructed out of pure concrete and require reinforcing. It’s generally the reinforcing that causes the problems, not the concrete.
The cheap apartments that are crumbling after 40 years may be particularly poor in terms of ventilation and drainage and suffer humidity problems. It just becomes too costly to repair every surface vs just starting new. The communist era apartments are hideous and uncomfortable anyway… ghetto effect kicks in and they destroy it on purpose.
As I recall Volcanic Ash, no embedded steel, and slow cure time. However it was years ago when I was in that class.