The situation is that two magic users are fighting a concrete golem, their only way to defeat it is to destroy it, when this characters crack it they find that the golem is hollow so their strategy is to fill the golem with water and heat it until it explodes because of the pressure. How hard would it be in a cold climate with the last air bender type of fire bending?

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    $\begingroup$ Can the mages freeze the water? The golem might have a lot of problems moving with a frozen center. Also ice expands, bye byb golem. $\endgroup$ – NomadMaker Apr 11 '20 at 11:17

Not hard at all, provided that enough heat at a sufficiently high temperature can be supplied. Pressure will simply increase until it exceeds the concrete's limits. Note that while concrete is very resistant to compression, it is not resistant at all to expansion, which is why pre-stressed steel reinforcements are employed structurally. To be able to move, this golem cannot have much in the way of internal reinforcements.

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Saltwater exposed to lava temperatures (1200 °C, but may be as low as 800 - 900 °C) is known to cause explosions powerful enough to crack solid granite ("littoral explosions"). If the steam does not find a release, imprisoned water can hurl shrapnel up to 3 miles away.

Also, it is documented that the reinforced vessel of a nuclear reactor core cannot withstand a powerful enough steam explosion.

Thick concrete is a decent thermal insulator, so the cold outside won't be able to cool the water inside quickly enough.

So, I am confident that the golem won't stand a chance.

If the golem is thick enough to work a good head of steam, and they're too near the golem when it goes kaboom, neither will your heroes.

Kill a concrete golem. You have: water, heat.

If heat can be added magically, presumably it can also be removed magically. So, it might be possible to encase the golem in ice.

Otherwise, humid vapour can quickly enter microscopic cracks in the concrete, and can then freeze, expanding and causing spalling. This ought to be done several times to damage the golem, unless some points (e.g. the joints) are more vulnerable. Moving a joint while locked in frozen water should impart considerable surface damage, reducing mobility.

Also, adding a large quantity of water should alter the balance of the golem, and possibly even make it fall down.

  • $\begingroup$ That is another interesting question, how to have the heroes far enough so they wont die $\endgroup$ – Dawnstar watcher Apr 10 '20 at 22:40
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    $\begingroup$ Graph is wrong fwiw. At Pabs = 100 kP Pboil = 100 C. So graph should start at P = 10 x 10% = 2 minor divisions to right on X axis. Should anyone care :-). $\endgroup$ – Russell McMahon Apr 11 '20 at 7:30
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    $\begingroup$ Besides a wimpy Nuclear Power Plant, a steam explosion can destroy a mountain as well. So even a huge golem could be killed (if you have enough water and heat) en.wikipedia.org/wiki/Krakatoa $\endgroup$ – Nyos Apr 11 '20 at 16:16

Water has a very high specific heat, meaning that it takes a lot of energy transferred to water to increase its temperature. To rapidly heat water, it will take a large amount of energy, and in the case of heating through flame, a hot flame with long exposure will be required.

Concrete has the advantage of very a low thermal conductivity meaning heating the outside of the concrete Golem will not heat the inside very rapidly.

If the temperatures of the flames are hot enough to heat the water inside the Golem rapidly enough to cause an explosion (there's also the problem of pressure since any holes in the Golem would make this even more difficult), they would be hot enough to destroy the concrete on their own which would create cracks as the water is heating.

If possible it would seem to be a better strategy to first heat the Golem and damage the concrete, then fill it with water and freeze it. Water expands when frozen and this would be destroy the structural integrity of the concrete and be much more realistic than heating the water rapidly enough to cause an explosion.

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    $\begingroup$ You make a very good point that I had overlooked completely. What if the golem isn't airtight? $\endgroup$ – LSerni Apr 10 '20 at 22:44
  • $\begingroup$ I understand what youre saying but what about a slow build up instead of quickly making it explode? $\endgroup$ – Dawnstar watcher Apr 10 '20 at 22:48
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    $\begingroup$ It's all about scale. Water has a specific heat around 1000 J/(kg K). Lets consider 100 kg of water (Thats about 26 and a half gallons, which I'm guessing would fill a Golem, not sure how big this thing is but their usually depicted as pretty big from what I've seen). A big fire could output around 2,500,000 J/s, If we assumed that all of this energy was transmitted into the water (in actually it only a small fraction would be transmitted) it would only heat at about 6.25 C/s. This would still take over two minutes for all of the water to heat 900 degrees Centigrade. (part 1) $\endgroup$ – user110866 Apr 11 '20 at 0:16
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    $\begingroup$ Probably a better visualization would be to take a propane torch to the underside of a concrete bowl of filled water...its going to take a long time to boiling that water $\endgroup$ – user110866 Apr 11 '20 at 0:24

Why would a concrete golem be hollow? Use that against it!

It is tricky to cast a hollow thing out of concrete - much easier to make something solid. They don't really need to know exactly why it has to be hollow, but they want to find out. By making it not hollow.

Fill the golem with concrete, not water.

  1. Maybe non hollow golem does not work. Joints don't bend? Too heavy to move? Then you are done.

  2. Maybe solid concrete makes concrete golem not work. Then it will work less and less as concrete sets up.

  3. Concrete expands as it hardens. Maybe you will blow up golem after all?

  4. Golem is cracked already - that's how they know it is hollow. Water might drain out crack. But cement is thicker and hopefully will stay in crack.

How exactly you fill a hostile golem with water, concrete, Vegemite or anything else is left as an exercise for your characters.

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    $\begingroup$ Normal concrete shrinks while hardening. $\endgroup$ – D.J. Klomp Apr 11 '20 at 12:52
  • $\begingroup$ The main problem is the lack of concrete, the characters are in the wild and where attacked by the rouge golem, so they cant go with that plan, filling it with water would be easy with normal water manipulation taking enough water to make a stream that works as a distance control tool in combat. $\endgroup$ – Dawnstar watcher Apr 11 '20 at 18:45

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