What thickness of concrete to handle vacuum?

Question

I am working on a project and need to know if concrete can withstand vacuum, and what thickness is needed. For easier visualization, imagine a small bowl put inside a bigger bowl, sealed on top and the space between them evacuated. The difference is this time both bowls are concrete and huge, and they must not collapse when air is evacuated. A concrete hemisphere of diameter around 1 m will be placed in an external concrete hemisphere. The vacuum should be about 15 cm thick. 

What thickness should the concrete be (both the internal and external bowls), to 
prevent collapse?

I will place support concrete blocks between the bowls (in the vacuum), maybe four cylindrical blocks of radius 5 to 10 cm. What do you suggest?

Note that the bowls are expected to handle temperatures up to 1500 Celsius, So please, nobody suggests reinforcing with steel.

Answer

At 1500 C you are talking refractory recipes, and that means more fire clay than cement. It is difficult to find a reliable recipe for refractory insulation, and vacuum is not mentioned at all. I did some furnace work a few years ago and I had to reline my furnace three times because the insulation would burn out.

It is no great problem to obtain a vacuum chamber that big, made of convenient materials such as steel and borosilicate glass with mirrored inside surfaces (commonly called Dewar or Thermos bottle) and you can then heat your little whizbanger either with radio transmitting equipment or by direct contact to a resistance heater. Whatever you decide to do, it's going to have to be very clever. Bear in mind that a vacuum chamber one meter in diameter, made of glass, is about the power of a small bomb if it collapses. Also, you will need plenty of money to try this at all.

These people think they are hot stuff because their concrete holds up at 1000C: www.ceratechinc.com/products/firerok

Please enjoy these demonstrations: www.youtube.com/results?search_query=tank+collapse+vacuum

General info on producing high temperatures: www.backyardmetalcasting.com/

What thickness of concrete to handle vacuum?

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