2
$\begingroup$

I'm writing a scene set on a construction site where the builders notice that the cement they pour is not setting: it just remains in its liquid state or it is taking a very long time to set. This is set in a world where there are mystical/magical/horrific anomalies of various kinds.

So magical things can happen but I'm interested in what they might look like to a scientist or engineer who does not believe in magic.

What scientific explanation could there be for this? I'm looking for some change in the world that would have the effect that cement would be prevented from setting. For example, if a particular chemical substance had its properties changed somehow or if the surrounding climatic conditions were altered somehow.

$\endgroup$
  • 3
    $\begingroup$ This is a civil engineering question which can be answered with a google search, not a worldbuilding question. civilblog.org/2016/09/22/… $\endgroup$ – L.Dutch Feb 25 '18 at 7:26
  • 1
    $\begingroup$ Now, had you asked the question, "how to I rationalize a lack of exothermic reactions on my world?" That's our kind of question. $\endgroup$ – JBH Feb 25 '18 at 19:02
  • $\begingroup$ This question has been nominated for reopening, but the OP hasn't done anything to improve the question and I agree that the question, a stated, is off-topic. I can't vote to reopen this Q in its present state. Frankly, the question should be asked on Chemistry.SE. $\endgroup$ – JBH Feb 26 '18 at 3:28
  • $\begingroup$ Thank you L.Dutch and others for your replies. L.Dutch's reply does help me but I'm interested in something slightly different that I think is of interest to worldbuilding.SE and not Chemistry.SE. I have changed my question to hopefully articulate that difference. $\endgroup$ – afilmforthefuture Feb 28 '18 at 15:01
  • 1
    $\begingroup$ Note that while there are many natural and artificial substances that can retard concrete setting: this is not an uncommon problem on construction sites, and they do check for it. On any project bigger than pouring a driveway, they will at least do slump testing. That means they will know something is going wrong within about 12 hours. If it matters enough to check (and it usually does), they will send it to a lab to identify the contaminant. Assuming current level of tech, they'll probably get results within two days, at a cost of a few hundred bucks. $\endgroup$ – Securiger Feb 10 at 10:22
10
$\begingroup$

Non-hydraulic cement will not set if it can't exchange water vapour and CO2 with the environment (or if water is replaced). Several oily and gelly substances exist that will form a thin film above or on the surface of a liquid and slow down evaporation and CO2 diffusion. "Slow down" is not the same thing as "prevent", though. To prevent it completely, you would need a film with the thickness and properties of clingy film, which would be really noticeable.

Hydraulic cement will not be hindered by this, since it is self-reacting. For it, you would need some substance capable of blocking calcium silicates from reacting with water. Perhaps some soaps could do that. Or some lubricants could make the sludge appear not to be setting; it would rather collapse in a sort of useless gritty gruel. I know of none that would be water-souble though, or survive in the alkaline environment. Also microencapsulation of cement particles with hydrophobic compounds would work, but here we'd be talking about high-tech sabotage; also, the powdered cement properties (color, weight, fluidity, texture) would likely change drastically. Same goes for "corning" and "glazing" the cement, if possible: it would slow penetration of water and the setting reaction.

ask the expert

I had forgotten this question, but by chance I've people pouring concrete just round the corner, and I asked them. It turns out that there are lots of substances that will do what you seek; they are called setting retardants, and they act by slowing down the calcium silicate hydration reaction. After a few Google enquiries I'd go for sodium glucoheptonate - on the usage directions it says that using an excessive quantity can "kill" the set of concrete. This is "commonly" done if for any reason it is impossible to empty the concrete drum on a mixer; killing the set wastes the concrete, but allows salvaging the mixer drum.

On a similar product (sodium gluconate), some producers claim that it can prolong "workable time" (which I assume means before setting) to a few days. The quantity needed is below one percent.

$\endgroup$
  • $\begingroup$ I've changed my question to including slowing down as well as preventing. High-tech sabotage is fine as long as it's possible in the known scientific world. Thank you for the very helpful answer. $\endgroup$ – afilmforthefuture Mar 1 '18 at 14:52
  • $\begingroup$ Wow, thanks for the #asktheexpert edit! This is great. $\endgroup$ – afilmforthefuture Mar 1 '18 at 16:04
3
$\begingroup$

Not sure about climactic changes, but you might want to look into plain table sugar. Adding sugar to wet concrete can delay or completely suspend hardening at high enough concentrations. Whether that sugar was provided by gumdrop rain or literal pixie sticks would be up to you.

$\endgroup$
  • 1
    $\begingroup$ Thank you, this would be a possible route for me I think. $\endgroup$ – afilmforthefuture Mar 1 '18 at 14:53
  • 1
    $\begingroup$ This seems indeed the simpler and most correct answer. The working guys cite sugar as an emergency set killer (see also: concreteconstruction.net/how-to/…) $\endgroup$ – LSerni Mar 1 '18 at 15:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.