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For those who wanted the answer to the title in these comments, paraphrased it was: with proper maintenance, indefinitely. The "with proper maintenance" phrase

For those who wanted the answer to the title in these comments, paraphrased it was: with proper maintenance, indefinitely. The "with proper maintenance" phrase should be pointed out to management next time they think something we build should last forever; even these remarkable structures that appear formidably unchanging undergo continuous, hands-on, expert maintenance. There is a tangentially-related Straight Dope thread [1] asking "Is the Hoover Dam concrete still curing?", because if you take the tour (highly recommended for hackers with an affinity for industrial- and megastructure-scale engineering), you will be told "the concrete is still curing!" by the guides. This is apparently not technically precise; someone from the concrete industry please correct me if I'm wrong here. I gathered from a civil engineering page that Hoover Dam's concrete is considered cured, but it is still undergoing the hydration process as long as water is present in the concrete. [2] I think the Hoover Dam guides can be cut some slack for colloquially using the terminology "curing" in light of this technical distinction that most laypeople won't understand. [1] http://boards.straightdope.com/sdmb/showthread.php?t=258217 http://boards.straightdope.com/sdmb/showthread.php?t=258217 [2] http://www.engr.psu.edu/ce/courses/ce584/concrete/library/construction/curing/curing.html http://www.engr.psu.edu/ce/courses/ce584/concrete/library/co...

cmsmith 11y ago
As you probably gathered from your references, concrete curing is a continuous process - every time a stray water molecule binds with some cement the concrete will get a little bit stronger. We use 28 days to call the concrete 'cured' because it's a reasonable time on construction schedules (why it's in an even number of weeks) and hits a nice fat part of the exponential strength curve. It's a bit like asking when a pile of plutonium is done decaying. What will happen is that at some point, the strength gains are so marginal that various degradation processes will cause the concrete to start losing overall strength. But - the idea that the concrete is curing and will be finished in 50 years is fairly goofy. No one is doing high-temperature long-duration concrete curing research, but the idea that you can extrapolate the laws of heat transfer to figure out how long some bubble of superheated wet concrete in the middle of the dam will last isn't very reasonable.
- ethagknight 11y ago
  Fun fact on the topic of curing, the Hoover Dam was built with chilled water coolant lines running throughout the bulk of the dam in order to dissipate heat through the curing process. Without cooling, the sheer mass of the dam and concrete's exothermic curing process would have basically caused the dam to self destruct from expansion/contraction. http://www.usbr.gov/lc/hooverdam/history/essays/concrete.html http://www.usbr.gov/lc/hooverdam/history/essays/concrete.htm...

cmsmith 11y ago

As you probably gathered from your references, concrete curing is a continuous process - every time a stray water molecule binds with some cement the concrete will get a little bit stronger. We use 28 days to call the concrete 'cured' because it's a reasonable time on construction schedules (why it's in an even number of weeks) and hits a nice fat part of the exponential strength curve. It's a bit like asking when a pile of plutonium is done decaying. What will happen is that at some point, the strength gains are so marginal that various degradation processes will cause the concrete to start losing overall strength. But - the idea that the concrete is curing and will be finished in 50 years is fairly goofy. No one is doing high-temperature long-duration concrete curing research, but the idea that you can extrapolate the laws of heat transfer to figure out how long some bubble of superheated wet concrete in the middle of the dam will last isn't very reasonable.

ethagknight 11y ago
Fun fact on the topic of curing, the Hoover Dam was built with chilled water coolant lines running throughout the bulk of the dam in order to dissipate heat through the curing process. Without cooling, the sheer mass of the dam and concrete's exothermic curing process would have basically caused the dam to self destruct from expansion/contraction. http://www.usbr.gov/lc/hooverdam/history/essays/concrete.html http://www.usbr.gov/lc/hooverdam/history/essays/concrete.htm...