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Saturday, 1 August 2009

Pharaoh Cement: Rediscovering Geopolymers

Pharaoh Cement
Rediscovering Geopolymers


Built to last an eternity, after [at least] 4,000 years the pyramids are still looking good...

Well, there's a new theory that the pyramids and other ancient splendours used an unusual concrete of extreme durability. Its secret formula, they say, died with the ancient Egyptians. 

Now a team in Melbourne have created a modern version of this forgotten building material. They call it a geopolymer. Not only is it uncommonly tough but it's made from industrial waste. 

In most cases those wastes also contain very large amounts of aluminium and silicon and we actually utilise those properties to, the reactive properties of those silicon, aluminium contained in the materials to manufacture geopolymers."

Worldwide, industry generates millions of tons of solid waste. One power station makes mountains of fly ash. Finding a use for it rather than dumping it has become high priority. Geopolymers might be just the ticket. 

Geoff Burchfield
How easy is it to make? 

Johan van Jaarsved
To make a basic geopolymer is really, really easy. You can basically do it in the kitchen if you've got the right ingredients. 

To a scoop of power-station ash, add some steelworks slag. Toss in caustic soda, a bit of waste-water and mix well. After ten minutes in a moderate oven a quick-setting geopolymer! 

Geoff Burchfield PTC
The neat thing about geopolymers is that you can make them from a wide range of waste materials. So long as the mixture contains reactive sources of silicon and aluminium it'll work. Then if you want to you can throw in anything from pulped newspapers to polystyrene, even toxic waste containing heavy metals. 

I was already impressed but wait, said Professor van Deventer, there's more. Cast into blocks of any shape, even a flat slab like this, he said, possesses amazing properties. This block even includes paper and polystyrene. 

Professor Jannie van Deventer
There's combustible material in this. That's why you'll see that it actually burns but it doesn't burn for a long time. If you look at that, the flame comes but then it disappears very quickly. 

Geoff Burchfield
But this is actually flame-proof though? 

Professor Jannie van Deventer
It is flame-proof. You can even put your hand underneath 

Geoff Burchfield
So I should trust you? 

Professor Jannie van Deventer
That's right. 

Geoff Burchfield
You're right. It's quite cold. 

Blast concrete with the same 2000 degrees and it'll explode. Then there's the acid test. Blocks of geopolymer have been soaking in hydrochloric acid for 3 months. 

Johan van Jaarsved
Little fine cracks forming but structurally it's pretty much intact. 

Concrete was put to the same test. All that's left is this slimey sludge. But after all these tests they had no idea why geopolymers are so resistant. Then, behold, they found this book. In it, a French research chemist claimed that the ancient Egyptians made geopolymers. He even suggested the biggest pyramids are built of geopolymer blocks. Cast on site from aluminium rich Nile silt, it certainly explains how they built them so fast but it still doesn't say how geopolymers work.
So with the power of an electron microscope, Johan zeroed in on their molecular "anatomy". What he found was a unique micro-structure - short interlocked chains of atoms strong enough to bind most waste materials. 

Johan van Jaarsved
The analogy to that would probably be a chocolate chip cookie - with chocolate chips which is bits of unreacted waste particles in like a dough of geopolymer paste. And this whole thing sets harder than concrete. 

So where to now? Will geopolymers soon be filling concrete's shoes? Well, expect to see them used in dangerous places where concrete fears to go. 

Professor Jannie van Deventer
It's not a competition between geopolymers and concrete. It's a question of complementing what concrete can do. 

Today there's no shortage of waste materials for making geopolymers. But maybe 4,000 years ago the Egyptians made something just as enduring, without a power station in sight. 

Further Information

  Johan van Jaarsved & Professor Jannie van Deventer
Department of Chemical Engineering
University of Melbourne
Parkville   VIC   3052
Email: jsj.van_deventer@chemeng.unimelb.edu.au

Web Links
  Geopolymer Institute in France, operated by Joseph Davidovits, the author of "The Pyramids: An Enigma Solved"
  Science Applied to Archaeology - more about the possible use of geopolymers by the ancient Egyptians.

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