Concrete solution to gas problem

October 2005

Concrete is an essential element of building industries around the globe. Now, a Monash researcher has improved its formula, reducing greenhouse gas emissions and benefiting the environment.

Report: Robyn Anns
Photography: Greg Ford

Mountain of evidence: Associate Professor Jay Sanjayan stands on a pile of blast furnace slag at Independent Cement in Port Melbourne - the company that imports the raw material from Australian Steel Mill Services iron ore smelter in Port Kembla, New South Wales.

Each year, Australia's building industry uses about two billion tonnes of concrete in everything from suburban dwellings to freeways, bridges, shopping centres and city office blocks.

About 15 per cent of each tonne of concrete is cement. This poses problems for the environment, as one tonne of the greenhouse gas carbon dioxide is released into the atmosphere for every tonne of cement produced.

A decade ago, Associate Professor Jay Sanjayan of Monash's Department of Civil Engineering decided to find a concrete formula that did not include cement.

After years of work, he and his research team have developed a new mix that uses a by-product of steel manufacture, called slag, in place of cement.

Dr Sanjayan believes the environmental benefits of using slag concrete are huge.

"It takes one-and-a-half tonnes each of limestone and clay to produce one tonne of cement, and that process creates one tonne of carbon dioxide. That emission goes into the atmosphere and adds to our greenhouse gas problem," he says.

"On the other hand, we only get 0.14 tonnes of carbon dioxide for every tonne of slag produced."

Australia is not a signatory to the international Kyoto agreement to reduce greenhouse gases, but Dr Sanjayan believes if Australia changed its concrete manufacture to his new formula, the nation's greenhouse gas emissions would be reduced by 6.5 million tonnes of carbon dioxide each year.

"Australia would meet the Kyoto target that way," he says. "All four million tonnes of slag generated from Australia's steel industry each year could be effectively used in concrete production.

Mythbusters: PhD student Mr Tarek Aly (left), technician Mr Jeff Doddrell (centre) and Dr Sanjayan prepare a batch of concrete for testing. They are working to debunk the industry myth that concrete containing slag shrinks and cracks easily.

"This would prevent the discharge into the atmosphere of millions of tonnes of carbon dioxide each year."

Slag is created when iron ore is heated to a molten state. Impurities are skimmed off the top, and when this slurry is cooled quickly by water quenching, it forms an off-white, sand-like material called granulated blast furnace slag.

"Cement binds the other ingredients of concrete -- sand, stone and water -- but slag works equally well," Dr Sanjayan says. "Some people in the building industry believe you cannot replace cement at all, others believe you can replace up to 60 per cent. We believe it is possible to replace 100 per cent of the cement in the mix. In fact, we have produced concrete without any cement, and it stands up well to tests and is cheaper to produce and better for the environment."

In 1999, Monash's Department of Civil Engineering received an Award of Excellence from the Concrete Institute of Australia for its research contribution to the development of slag-based concrete.