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Several sources state that if hydration is stopped during cement curing, is not possible to resume it, and final strength will be compromised. But so far, I haven't found a reliable explanation.

I wonder whether:

  1. Is it plainly wrong: cement hydration will continue as before, as soon as there is water or enough humidity available again.

  2. It is right, but it just applies to large chunks of cement/concrete (e.g 1m wide) , because water take too much time getting back to the interior, But this does not make much sense, because it got dry in a relatively short period of time, so water actually moved through.

  3. There is some other reason (chemical or related to microscopic structure) why water cannot resume hydrating the grains if the curing cement gets dry. I'm suspicious of this as well, as water does in fact penetrate cured cement/concrete so much that sealing compounds (silicone oils, TEOS) are needed in some environments.

Edit: the best source I got is this paragraph in a book by Kosmatka et al., that barely touches the subject and fails to provide an explanation :

When moist curing is interrupted, the development of strength continues for a short period and then stops after the concrete’s internal relative humidity drops to about 80%. However, if moist curing is resumed, strength development will be reactivated, but the original potential strength may not be achieved. (emphasis mine)

So, I guess, the answer is not 1) and it seems that hydration can be resumed but at an sluggish pace, or that something else prevents the full gain of strength. Any clue?

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I think the basic reason is that the hydrated curing essentially slows the overall cure rate, allowing for the equivalent of "annealing" to occur. Whenever you cease hydration, the material cures faster with less annealing. So long as the material doesn't reach terminal cure state, you can turn hydration on again and allow for additional annealing, but only from the current cure state.

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If I understand correctly, the argument is about whether the hydration of cement will resume after the process is stopped, the answer is "no".

  • Hydration of cement is a chemical process that is continuous as long as there is adequate water in the early stage of strength gain, and has optimum retained water/moisture/temperature thereafter. Once started, hydration will be stopped only after running out of the aforementioned means. When losing a significant amount of water required for complete hydration, partial hydration of cement will result. The partially hydrated cement will solidify and loses its original chemical/physical properties, which can't be recovered, in a very short duration. Should this occur, no amount of water can resume the original rate of hydration, which is required for the concrete to gain the full design strength.

Note that all of your reading sources are focused on the importance of curing during the early strength gain stage, which is imperative to prevent the rapid water losses from evaporation, especially in the hot arid regions, that subsequently could lead to inadequate hydration and compromise the strength of the concrete. As said above, once the hydration process has slowed to an extent due to drying, the addition of water has no effect on increasing the rate of hydration but to preserve and extend the chemical action of the cement has already (partially) hydrated and started to solidify.

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  • $\begingroup$ Hi, thanks for your prompt reply!. However, I don't understand part of this answer. What do you mean with "water has no effect on increasing the rate of hydration but to preserve and extend the chemical action of the cement has already (partially) hydrated and started to solidify"?. To the best of my knowledge, cement hydration of alite and belite (and ferrous phases, if present), is the whole curing process. The question here, is WHY this hydration reaction gets impaired once stopped, and why can't be restarted to its full extent again. Could you clarify? thanks! $\endgroup$ Mar 23, 2022 at 11:35
  • $\begingroup$ The hydration process is due to the water absorbed and retained at the mixing, after setting the cement starts to crytalize (harden), the retained water will continue to hydrate, but additional water has no effect but, similar to any chemical process, dilute the product. I am not a chemist, so my assertion could be wrong though. $\endgroup$
    – r13
    Mar 23, 2022 at 18:13

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