Dcal
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It wasn't meant to be a 'clever' answer just trying to illustrate the point that it's not easy (or impossible) to define a moment to call the curing done.
That Hoover Dam website is doing nothing more than putting out an impressive statistic to catch people's attention and it puts a mental image in reader's minds of a dam with a half-cured core because it hasn't dried out yet. It couldn't be further from the truth - all of the concrete had reached target strength many years ago and there's no going to be appreciable water content left (by %) because it's all consumed in the curing. Sure they had to get rid of a load of heat at the start because the reaction is slightly exothermic, but that's all done with by now and it also says that those pipes were later filled with concrete 'to increase strength'. That's another load of rubbish IMO, they filled the pipes to keep them from filling with water and rusting inside the pour. Concrete inside the pipe adds mass not strength and could only ever help stop it bending and if it's getting bending forces applied it's already time to start running (or swimming). It's typical visitor-information crap that sticks in the mind whether it's fact or not.
All of London's large buildings are standing on clay, or rather, concrete piles driven into it up to 60metres deep. They are all cured too (I've had to core drill one 22m deep to check it's integrity). No part of any of those piles are exposed to air for any time of the curing yet they cure perfectly well because air is not required for concrete to cure, it's all a chemical reaction. Many times too much exposure to air too soon will be detrimental, evaporating the water from the surface of the mix before it's had time to facilitate the cure. Then you end up with a weaker slab.
Concrete is a marvellous but much misunderstood material and as @Pete. has just shown it difficult to answer any questions about it without getting into far more detail than most people want.
On the Hover Dam the reason the cooling pipes were installed was not for cooling per se but to keep the temperature within the pours within limits to prevent thermal cracking of the concrete.
Another way of doing it could have been to insulate the outside faces of the concrete to keep the heat in, but that was impractical and it is better to have less heat and a slower more constant cure.
The reason they needed to do it is without measures the temperature across the pour would have varied wildly and the center would have heated and as a result expanded more than the outside.
As the concrete cures and the temperatures normalise, that expansion is locked in. As a result the center contracts more then the outside and you can / will get thermal cracking.
This can, to a degree, be controlled by the size of the pours, the type of cement and even the stone used in the concrete and by the design and installation of steel reinforcement but the Hover Dam was, by and large, a mass concrete (no rebar) structure and water was readily avaliable so was a good option.
Massive cracking in a water retaining structure is not ideal.
I'm guessing here but I assume the reason Pete had to core through the center of a concrete pile was to confirm the quality of the construction and concrete used in, probably a CFA (Continuously Flight Augered) pile.
These piles are cast in place and there can be issues including voidage, rebar cover and necking.
After installation the only way to check is dig it up ( not ideal if it's part of a building in Central London) or call on Pete and get him to take a core. (No small task)
There are other methods of checking for problems if you plan for it before construction and one. TIF (Temperature Integrity Profiling) uses the phenomenon the pipes in the Hover Dam was designed to counteract where the exothermic heat from the concete curing reaction is used to estimate the quality and amount of concrete.
Temperature sensors are cast into the concrete during construction and the readings are compared to control test samples of concrete.
If the temperature is lower than expected it could for example be because there is no concrete (voidage) or the wrong concrete mix (not enough cement, wrong cement type, too high water / cement ratio etc.)
Designers are a conservative bunch and a lot won't use these methods and if there is an issue it's time to call on Pete again.
The whole curing issue in the Hover Dam is a red herring, curing continues long after the concrete is cast but it's said to be cured after it has reached a certain value.
After that it's just a bonus and they wouldn't have flooded the Dam if the concrete (or most of it) hadn't reached it's design strength.
Sometimes you need to use massively overspecified concrete just to get early straight gain and I've used epoxy concrete just for that reason.
Sometimes you end up with 100N concrete when you only need 10N because you need that 10N in a few hours.