A new type of concrete may improve the safety of buildings by making them more fire-resistant.
Credit: iStockphoto
SYDNEY: A by-product from coal-fired power stations can be made into a stronger and much safer concrete with far less carbon dioxide emissions, researchers have found.
They say this technology could "revolutionise the world's building and construction industries" and they hope to move the technology towards a large-scale trial and commercialisation.
Materials scientist William Rickard and his colleagues from Curtin University, in Perth, used waste materials called 'fly ash' to create the concrete.
Fireproof concrete may save lives
"The main benefit of using fly ash polymer cements is that they maintain their strength up to 1,200ºC whereas traditional cements start losing their strengths at about 600ºC … In the event of a fire, a building using traditional cement can lose its strength and collapse.
Buildings with fly ash concrete would have a much better chance of surviving a fire, Rickard says. Even coating exposed structural steel with it would reduce the heat that goes through the steel and prevent combustion.
Each year there are approximately 100 fatalities and about 3,000 injuries from structural fires in Australia alone.
Rickard says another application is full replacement with fly ash cement in the building of tunnels. "In Europe there have been cases of tunnels collapsing during a fire … this technology has the potential to save lives there."
Cutting the world's carbon
Over 600 million tonnes of fly ash are produced globally each year, according to Rickard, as a by-product from coal-fired power stations. He says his new cement will "turn a waste product into something useful, stopping it just being dumped."
As well recycling, the fly ash cement will be good for the environment because it releases up to 80% less carbon dioxide than standard cement.
It could make a big different on a global scale. "[Currently] 5–8% of the world's carbon emissions come from the manufacture of traditional cement," says Rickard.
Other cements
Manufacture of traditional cement known as Portland cement or OPC requires that limestone be burnt into lime. But this new cement is different: "It's an inorganic polymer with a different chemistry than traditional cements because it is not calcium based," says Rickard.
"Production of one tonne of Portland cement has been found to release approximately one tonne of carbon dioxide," says Rickard. Rickard's cement requires less energy and the chemical reaction doesn't release carbon dioxide.
Adding fly ash in concrete is not a new concept. Rickard says the use of fly ash in geopolymer cement is based on a different concept. "In Portland cement fly ash is purely there as a filler, whereas in geopolymer cement fly ash is a critical component because it's where the strength comes from," says Rickard.
Fireproof Concrete
Such a great idea. Excellent article.
what's the bigger picture?
Why aren't they talking about the extremely toxic nature of fly ash? It's considered such a hazardous waste in my state, it needs a special kind of landfill and none of the local governments want one built. We know fly ash, when exposed to water, leaches out all sorts of nasty heavy metals and toxins. Will a cement fly-ash building be able to release any of these when wet? Will students in a fly-ash cement building have to deal with poisoning?
This is NOT recycling. This is a way of making an extremely toxic substance "disappear", saving the coal power plants big money.
Better idea: stop burning coal!
Not new news!
Mate, Fly Ash has been used in concrete for years in Australia. Too late to panic about leaching, this is not a new feature of the concrete industry!
fly ash concrete toxicity
From what I have read over time, fly ash [aka "pozzolanic ash] has been used for thousands of years. It is my understanding that ancient builders of some impressive structures, like the Hagia Sophia cathedral, were built using pozzolanic ash [volcanic ash] in their concrete mixes.
The mortar used in the Hagia Sophia is still "curing" at its great age, and is strong enough to withstand the extreme seismic activity in that geographic area.
Using that ash became an almost lost art.
How or if Pozzolanic ash is same or different from fly ash, I do not know.
BUT, they are used interchangeably in concrete mix for same results.
Once a substance is entrained into something like concrete mix, I imagine that at least a certain amount of whatever components are made of would be trapped into the mix permanently.
Lime wash on buildings traps CO2 and some other nasty air pollution ingredients and holds them in place--it does not instantly wash into the stream of things again if rain or other water hits the walls it is on.
Lime is also in Concrete mixes.
Concrete stays in place far longer than Lime wash.
I think I would rather have all that ash locked into concrete, than having it used in lieu of gravel on roads as was done in Utah where I went to school [clinkers and coal ash were regularly spread on graveled roads and to fill potholes]
Chi
Fly ash...
... is _not_ "just a filler". It is used as a pozzolan, meaning it combines with free calcium hydroxide in the cement paste of the concrete which in time makes concrete stronger and more impervious to water (therefor more durable).
Fly ash is the waste product of burning coal and its toxicity depends greatly on the type of coal being burned. It is pozzolanic because it is high in alumina and silica. Volcanic ash pozzolan is the result of volcanic eruptions, i.e. silica and alumna (the predominate elements in the earth's crust) are super-heated by the eruption and then blast into the atmosphere. The ash that settles consists of highly amorphous silica (and alumina).