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Author Topic: Does Concrete Melt ?  (Read 52042 times)

Offline neilep

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Does Concrete Melt ?
« on: 20/08/2007 17:43:57 »
Whilst thinking about Pauls thread about volcanoes it got me thinking about Hawaii and the scenes we have all seen with the active volcano creating new land and stuff !


We've also all seen the scenes of the lava breaking the highway code and mounting the sidewalk !....does the concrete underneath the lava melt ?...in fact ..does concrete melt at all ?





Warning..this stuff does not give way to oncoming traffic and pedestrians !!


 

another_someone

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Does Concrete Melt ?
« Reply #1 on: 20/08/2007 19:05:05 »
Concrete is a composite material, so the different parts of it will react differently to temperature.

The core component is cement (mixed in with the cement you will have aggregates such as sand, gravel, waste glass, etc.).

I would expect that some constituents of concrete would decompose, while other would melt, but partial melting alone would allow the concrete to flow (roads do soften enough to partially melt even during extremely hot days, at least if the concrete mix had not allowed for the particular temperature).
 

Offline neilep

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« Reply #2 on: 20/08/2007 19:14:59 »
THANK YOU VERY MUCH GEORGE.

I have noticed when passing cement/comcrete mixers that cement/concrete is very gravelly...Are the gravelly bits there for reinforcement then ?

So, Concrete is really cement diluted with aggregates.

THANK YOU AGAIN George
 

another_someone

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« Reply #3 on: 20/08/2007 19:41:24 »
Aggregates don't reinforce in a simple way in the way the steel is used for reinforcement.

In part, the aggregates simply make the cement go further, but it will also increase the hardness, and will stop cracks from creeping across the cement.  I don't say I know enough about concrete to know which is the more important factor.
 

another_someone

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Does Concrete Melt ?
« Reply #4 on: 20/08/2007 19:45:21 »
http://en.wikipedia.org/wiki/Concrete#Fire
Quote
Due to its low thermal conductivity, a layer of concrete is frequently used for fireproofing of steel structures. However, concrete itself may be damaged by fire.

Up to about 300 °C, the concrete undergoes normal thermal expansion. Above that temperature, shrinkage occurs due to water loss; however, the aggregate continues expanding, which causes internal stresses. Up to about 500 °C, the major structural changes are carbonation and coarsening of pores. At 573 °C, quartz undergoes rapid expansion due to Phase transition, and at 900 °C calcite starts shrinking due to decomposition. At 450-550 °C the cement hydrate decomposes, yielding calcium oxide. Calcium carbonate decomposes at about 600 °C. Rehydration of the calcium oxide on cooling of the structure causes expansion, which can cause damage to material which withstood fire without falling apart. Concrete in buildings that experienced a fire and were left standing for several years shows extensive degree of carbonation.

Concrete exposed to up to 100 °C is normally considered as healthy. The parts of a concrete structure that is exposed to temperatures above approximately 300 °C (dependent of water/cement ratio) will most likely get a pink color. Over approximately 600 °C the concrete will turn light grey, and over approximately 1000 °C it turns yellow-brown[14] One rule of thumb is to consider all pink colored concrete as damaged, and to be removed.

Fire will expose the concrete to gasses and liquids that can be harmful to the concrete, among other salts and acids that occur when fire-gasses get in contact with water.
 

Offline neilep

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« Reply #5 on: 20/08/2007 20:03:37 »
FANTATSIC !..THANK YOU GEORGE !!
 

Offline Karen W.

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Does Concrete Melt ?
« Reply #6 on: 20/08/2007 20:19:35 »
I have a cement mixer siting in my yard and have made lots of cement. The cement is added in powder form then your gravel and water to mix.. the size of your gravel is optional for the texture you wish to achieve.. when sufficient water is added and mixed the cement is  a thick texture that still pours like slightly sloppy oatmeal.. HEE HEE! You pour it into forms spread it evenly level it up, I use a two by four! Contractors have whats called a screed. You put a two by four over the,lets say, a sidewalk form, and you pull it back and forth leveling and smoothing the mixture.. it is called screeding and it is easier if you have a partner opposite side of you to pull back and forth. After it has been screed, the walk is wet down screed again, and smoothed out with two by four screed. Allow to stand for several hours wetting down periodically as it sets and hardens.. The time to impress your child's hand print or yours is after the last screeding! LOL

Allow to dry over night should set up hard very quickly! LOL sorry I am sure you wanted a concrete lesson.. The gravel adds texture and makes it stronger and concrete pulls it all together and bonds it tightly!

HI Dave Frost..HEE HEE Thanks for the nudge! 0ct.14 2007
« Last Edit: 15/10/2007 07:22:28 by Karen W. »
 

Offline neilep

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« Reply #7 on: 20/08/2007 20:33:43 »
Yes..I did want a concrete lesson..THANKS KAREN !!

Just astonished that it's you giving the lesson.....but...knowing how great you are at DIY..I should not be so surprised really  !!

LOL...some of us have ponds or bird baths....ewe have a cement mixer !!  ;D

Your talents are well cemented !!.......*groan*..sorry !! ;D
 

Offline JimBob

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« Reply #8 on: 20/08/2007 20:53:28 »
Yes, concrete melts and flows. An oil tanker fire cause this to happen locally. I can't seem to find a picture in the news archives but the tanker was full of gasoline. A pillar buckled without any exfoliation of the concrete from the column. I also believe a beam also flowed.

 

Offline neilep

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« Reply #9 on: 20/08/2007 21:48:43 »
THANK YOU JIMMY BOY.

Does this mean concrete can combust ?...or is that another silly question because will anything combust if it's hot enough ?

Hmmmmm...this takes me back to a thread I started about water making a fire worse....I think i later discovered that if the fire was hot enough then the oxygen/hydrogen in the water would actually combust too.
 

Offline Bored chemist

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« Reply #10 on: 20/08/2007 21:56:15 »
Does this mean concrete can combust ?.
No
Combustion essentially means burning ie reacting exothermicly with air.Concreete won't do that (but steel will).
I believe that an arc welder and a couple of carbon rods will melt concrete very well but be careful. The water vapour and CO2 that get driven off as it heats will make the stuff shatter. I have a welder and lots of carbons but I have no desire to be showered with high-speed red-hot conctete shards so I have never tried the experiment.
 

Offline eric l

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« Reply #11 on: 21/08/2007 09:22:22 »
I remember from my schooldays (over 35 year ago) that cement like plaster gets its binding power by recrystalizing with more water.  Heating can make them loose this water, returning to smaller size crystals and lower binding power.  I think that rather than melting, most types of concrete will pulverize under influence of heat.
 

Offline Karen W.

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« Reply #12 on: 15/10/2007 07:30:26 »
Yes..I did want a concrete lesson..THANKS KAREN !!

Just astonished that it's you giving the lesson.....but...knowing how great you are at DIY..I should not be so surprised really  !!

LOL...some of us have ponds or bird baths....ewe have a cement mixer !!  ;D

Your talents are well cemented !!.......*groan*..sorry !! ;D
This post was brought to my attention by a kind fellow who read the post! Nice!

So You liked the lesson!! Neily your too much! LOL... Thanks Kindly Kind Sir!.
Thank you to D.F.
 

Offline diverjohn

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Does Concrete Melt ?
« Reply #13 on: 12/07/2011 15:37:05 »
Several years have passed since this thread was posted.
Concrete can be melted by using an "iron lance" which burns iron rods with oxygen to produce enough heat to melt concrete.
It consists of a cylinder holding iron rods or wire through which oxygen is pumped. An acetylene torch is used to ignite the open end so the iron combusts. Forced air blows the very hot flame outwards.
It was used in the late 1940s to help dismantle concrete bunkers used in the war.
I'm unable to find a wiki article on this device so I'm relying on memory for these facts.
 

Offline Bored chemist

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« Reply #14 on: 12/07/2011 19:33:23 »
Several years have passed since this thread was posted.
Concrete can be melted by using an "iron lance" which burns iron rods with oxygen to produce enough heat to melt concrete.
It consists of a cylinder holding iron rods or wire through which oxygen is pumped. An acetylene torch is used to ignite the open end so the iron combusts. Forced air blows the very hot flame outwards.
It was used in the late 1940s to help dismantle concrete bunkers used in the war.
I'm unable to find a wiki article on this device so I'm relying on memory for these facts.

http://en.wikipedia.org/wiki/Thermal_lance
 

Offline Aj

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« Reply #15 on: 18/08/2011 17:35:58 »
Hi,
I am in the process of doing some renovations in my house. As a result, I have got some building material such as, bricks, concrete chunks, wood pieces etc. I was thinking to use this material to make a rock which can be used in landscaping or to put it at the entrance of my drive way with the house # on it.  What I have in mind is this:

1. Make a one big mass first:
       - by either melting everything together (of course no wood)
           or by crushing it and then adding water to that and then let it dry
2. some how spray fibre or concrete on top of it
3. color it to give a look of rock.

Any ideas...........

Thanks.
 

Offline CliffordK

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« Reply #16 on: 19/08/2011 01:21:51 »
You haven't listed the quantities, and/or the resources you have available.

While you can make any rock into glass, or even molten lava, the temperatures required to do so are very extreme, and you would likely find it impractical for a large quantity of material.  And, containment may also be an issue.

If you have a way to crush your concrete/brick/stone/etc.  You can certainly use it as fill, or even as aggregate to  be bound with concrete.  It may be a lot of work to crush small quantities with a sledge hammer.  If you have a large construction project, you might get a rock crusher, but it is probably impractical for a residential project.  Some people have broken up and rounded corners on large pieces of concrete to give it a natural stone look.  Add some moss and it can look quite appealing.  If done right, you can also make an aesthetically appealing mix with multi-colored stones.

Dyes can be added to concrete mix if you desire.  It can also be washed to show off the aggregate inside.  Some people use moulds on walkways and driveways to create a stone-like or cobblestone appearance.
« Last Edit: 21/08/2011 08:12:06 by CliffordK »
 

Offline wolfekeeper

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« Reply #17 on: 20/08/2011 15:23:39 »
Actually, concrete kinda explodes when you heat it really strongly, or more accurately, spalls. If you go to Armadillo Aerospace's website, some of their videos are of them hovering a rocket over a concrete pad, if you look carefully you can see chunks of concrete flying off in all directions. This is mostly just the concrete getting heated by the jet and just popping and throwing bits everywhere.

If you can keep the bits together well enough to continue to heat it, then obviously it will melt; everthing melts if you get it hot enough.
 

Offline Bored chemist

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« Reply #18 on: 20/08/2011 16:05:32 »
"everthing melts if you get it hot enough."
unless it doesn't.
 

Offline wolfekeeper

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« Reply #19 on: 20/08/2011 16:22:02 »
Ok, a few things do sublime, but I don't think that concrete is one of them.
 

Offline Bored chemist

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« Reply #20 on: 20/08/2011 17:29:47 »
Quite a lot of things decompose, and concrete is one of them, that's why it spalls.
 

Offline Bass

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« Reply #21 on: 21/08/2011 05:42:42 »
A bit off-subject: but I see that Rossignol is melting basalt (the most abundant crustal volcanic rock) and manufacturing basalt fibers (which I assume are a glass fiber) which they use to manufacture skis.  Can melted concrete fibers be far behind? ::)
 

Offline Geezer

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Does Concrete Melt ?
« Reply #22 on: 21/08/2011 08:42:07 »
A bit off-subject: but I see that Rossignol is melting basalt (the most abundant crustal volcanic rock) and manufacturing basalt fibers (which I assume are a glass fiber) which they use to manufacture skis. 

Excellent! I will immediately contact them to see if they want to buy my "garden". It's nothing but a pile of basalt cobbles.
 

Offline Bored chemist

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« Reply #23 on: 21/08/2011 10:04:46 »
Having had a quick look at their website I think they would be more likely to buy your garden if it had been "fertilised" by a bull or two. They seem to sell more of that than they do basalt.
 

Offline Geezer

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« Reply #24 on: 21/08/2011 18:19:39 »
Interesting, although possibly more than anyone really wants to know;

http://www.compositesworld.com/articles/basalt-fibers-alternative-to-glass

(It might actually help if you ski so fast that your skis tend to catch fire)
 

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Does Concrete Melt ?
« Reply #24 on: 21/08/2011 18:19:39 »

 

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