Does concrete melt?

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qed

Senior Member
9-11 Debunker, Steven Dutch (Natural and Applied Sciences, of the University of Wisconsin), has this to say

  • Does concrete melt?
 

Landru

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9-11 Debunker, Steven Dutch (Natural and Applied Sciences, of the University of Wisconsin), has this to say

  • Does concrete melt?
Your premise is that the WTC fires were hot enough to melt steel and therefore should melt concrete. Please provide evidence to support this but before you do please read the 7 pages of this other thread. https://www.metabunk.org/threads/molten-and-glowing-metal.2029/
 
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qed

Senior Member
@Landru

All I am asking is if concrete can melt.

Please stay on topic. I had to post evidence and I got it from a debunking site. I have no premise.
 

Landru

Moderator
Staff member
@Landru

All I am asking is if concrete can melt.

Please stay on topic. I had to post evidence and I got it from a debunking site. I have no premise.
Does concrete melt? No.
http://www.newton.dep.anl.gov/askasci/mats05/mats05054.htm

Mr. Wilson's credentials

http://www.newton.dep.anl.gov/scicorps/wilson_r.htm

You could have done this with a Google search.
 

qed

Senior Member
I did do a Google search "does concrete melt" and that was what I got. Perhaps we should start a Debunked person thread on Steven Dutch.
 

qed

Senior Member
What is the melting point of concrete?

 

qed

Senior Member
Molten concrete is one of the indicators that is pointed out in the exotic accelerants section of the NFPA investigation guidelines.
Interesting. Can you give us the quote please because there appears to be doubt on this issue?
 

Jazzy

Closed Account
Any competent scientist knows that concrete could not possibly melt, because it is composed of interlocked silicate crystals with WATER as part of their structure. Plaster is another material using water of crystallization. That won't melt either.

If you heat concrete it will eventually explode, as the vibrational energy of the water molecules in the concrete becomes greater than the molecular binding energy in the concrete, and the water escapes as steam, leaving a dehydrated silicate powder. At this point you would know the concrete was destroyed.

Most of the remainder will eventually fuse, if you raise its temperature further, but this isn't any longer concrete, as we know it (Jim)...
 
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qed

Senior Member
@Jazzy

I still don't quite see why we don't get "lava"? (Not enough granites left to melt?)
 

Jazzy

Closed Account
I still don't quite see why we don't get "lava"? (Not enough granites left to melt?)
It is rare for granites to be present in concrete. They are strong and hard, and expensive to crush. Flint stones are another water-of-crystallization product (found in chalk beds) which make great concrete. That's the usual material. Where I am they use pumice, or slightly less-aerated, er, lava. But volcanic islands don't normally have chalk in their soils.
 

Mick West

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Yes. Molten concrete is one of the indicators that is pointed out in the exotic accelerants section of the NFPA investigation guidelines.
Seems like they are talking hypothetically though, rather than from experience. What does "melted concrete" look like?

 

Jazzy

Closed Account
It's easy enough to test. Take a piece of spalled-off concrete, and, wearing goggles and protective clothing, toast it with a propane burner. I've done it, and lived to tell the tale. Nice bang...

I have never managed to melt it.
 

Mick West

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It's easy enough to test. Take a piece of spalled-off concrete, and, wearing goggles and protective clothing, toast it with a propane burner. I've done it, and lived to tell the tale. Nice bang...

I have never managed to melt it.
Here's some concrete being heated until it fractures (spalls) off chips.

 

Mick West

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This video shows someone cutting concrete and stone with a thermal lance. There's clearly something molten there.

"thermal lance, 17mm diameter and 3 feet long, cutting a stone and refractory concrete blocks"
 
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Jazzy

Closed Account
This video shows someone cutting concrete and stone with a thermal lance. There's clearly something molten there.
A thermal lance is thermite-in-a-rod, so the "something molten" could be iron or metal slag. (Or anything else from which oxygen might be stripped by the burning aluminum).
Most likely, it's alumina, or an alumina-glass mix. Yessir, I keep forgetting it's pure oxygen going in, so only metallic and silicaceous oxides will be coming out.
 
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Tony Szamboti

Active Member
It's easy enough to test. Take a piece of spalled-off concrete, and, wearing goggles and protective clothing, toast it with a propane burner. I've done it, and lived to tell the tale. Nice bang...

I have never managed to melt it.
Oxyacetylene burns much hotter than propane and is likely the only easy to access thing needed to melt some of the ceramic/refractory constituents of concrete.
See http://en.wikipedia.org/wiki/Oxy-fuel_welding_and_cutting
 

Mick West

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@Mick West
  • Does concrete melt?
Yes, no, or I don't know.
Not really. Some of the components of concrete (like rocks, basically) will melt at a high enough temperature. But at that point it's no longer concrete.

Really high temperatures destroy concrete, and what's left over can melt. But there's really no such thing as molten concrete.
 

qed

Senior Member
Consider a block of concrete in a hypothetical oven at 800 degrees c. I leave it for a while.

  • Will I see a puddle of "lava" on the floor?
 

Mick West

Administrator
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Consider a block of concrete in a hypothetical oven at 800 degrees c. I leave it for a while.

  • Will I see a puddle of "lava" on the floor?
No.

800C is not going to do much for a start. If you continue to heat it then the concrete will break apart. You are then left with a mixture of type of minerals. If you heat that up enough you will get "lava", more like 1800C than 800C though. (Melting point of common sand is around 1720C)

The answers referenced earlier seem quite reasonable:
http://www.newton.dep.anl.gov/askasci/mats05/mats05054.htm
 

qed

Senior Member
While it is some time since I sat an exam in igneous petrology, pulling A. Hall from my bookshelf, I read
  • "The temperature range up to 1500 degree c encompasses all the igneous phenomena likely to occur near the Earth's surface".
Perhaps I misunderstand you?
 

Mick West

Administrator
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While it is some time since I sat an exam in igneous petrology, pulling A. Hall from my bookshelf, I read
  • "The temperature range up to 1500 degree c encompasses all the igneous phenomena likely to occur near the Earth's surface".
Perhaps I misunderstand you?
I'm just looking stuff up here. Sand is generally silicon dioxide which Wikipedia lists as melting at 1600C to 1725C. I believe it is plastic at a much lower temperature - like with glass blowing.
 

Josh Heuer

Active Member
I'm just looking stuff up here. Sand is generally silicon dioxide which Wikipedia lists as melting at 1600C to 1725C. I believe it is plastic at a much lower temperature - like with glass blowing.
It actually depends on the source. wolfram Alpha lists quartz/silicon dioxide at a melting point of 1427C. And sand varies with location, so it could be different depending on what the sand actually consists of.
 

qed

Senior Member
"Melting and crystallization temperatures of igneous rock in the laboratory vary between 950dC and 1250dC. Natural rocks have considerably lower melting temperatures than their constituent mineral..." A. Hall
 

qed

Senior Member
@Mick West [:sigh:]

I place 100kg of concrete in an oven at 1000C.

I return later.
  • What will I see inside the oven?
I then let the oven cool and determine the mass of the contents of the oven.
  • What will be the mass?
 

Mick West

Administrator
Staff member
@Mick West [:sigh:]

I place 100kg of concrete in an oven at 1000C.

I return later.
  • What will I see inside the oven?
I then let the oven cool and determine the mass of the contents of the oven.
  • What will be the mass?
Interesting questions, and I think largely dependent on the actual composition of the concrete. The key thing is that calcium hydroxide dehydrates at 1000F (538C) which basically means that well before the concrete gets to 1000C, it's going to easily crumble to powder, sand, and aggregate. The mass will be reduced because all the water will disassociate and evaporate (so around 16% reduction in mass from that). The aggregates themselves break down at different temps.

But the internet knows more than I do:

http://info.ornl.gov/sites/publications/files/Pub1043.pdf

http://www.concreteconstruction.net/images/Effect of High Temperature on Hardened Concrete_tcm45-345325.pdf
This is for high performance concrete, which remains solid at 1000C, but shows the weight loss from dehydration:
http://www.ipublishing.co.in/ijcserarticles/twelve/articles/voltwo/EIJCSE3035.pdf
 
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Mick West

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Staff member
@Mick West [:sigh:]

I place 100kg of concrete in an oven at 1000C.

I return later.
  • What will I see inside the oven?
I then let the oven cool and determine the mass of the contents of the oven.
  • What will be the mass?
Based on the previous, I'd say:
  • What will I see inside the oven? - A crumbling block or heap of very weak concrete
  • What will be the mass? - around 85-90kg
 

qed

Senior Member
I place 100kg of concrete in an oven at 1500C.

I return later.
  • What will I see inside the oven?
1000C = 1832F
1000F = 537C
 
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Mick West

Administrator
Staff member
I place 100kg of concrete in an oven at 1500C.

I return later.
  • What will I see inside the oven?
1000C = 1832F
1000F = 537C
What's with the helpful conversions? Did I get something wrong?

That's some fancy oven you've got there :)

You'd probably see a dirty glassy blob on the bottom of the oven, based on this from the above Oak Ridge National Labs paper:

Maybe you could explain the point you are trying to make?
 

Josh Heuer

Active Member
But it's not actually concrete at that point.

Iron melts. Concrete decomposes, some components of it evaporate, and some melt (at various temperatures).
It's hard to say really...we could get into a debate over what's considered melting.
When iron melts, the oxygen is released, obviously it doesn't melt. So can we say iron doesn't melt because one of its constituents doesn't?
 

Mick West

Administrator
Staff member
It's hard to say really...we could get into a debate over what's considered melting.
When iron melts, the oxygen is released, obviously it doesn't melt. So can we say iron doesn't melt because one of its constituents doesn't?
Oxygen is not a constituent of iron. Iron is an element.

I'd say a handy definition of if something can melt is if it can exist in molten form. Concrete cannot exist in molten form.
 
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