09 June 2011

Block busters

Many of us are unaware that for such a ubiquitous building material, concrete is also damaging to our environment. The production of one tonne of its Portland cement component produces one tonne of carbon dioxide or CO2, and concrete accounts for 6 to 8 per cent of human-generated CO2.

Dr Indubhushan Patnaikuni and PhD student Mohamad Solikin

Dr Indubhushan Patnaikuni and PhD student Mohamad Solikin, who are investigating the viability of using high volume fly ash in concrete.

Positive result

The Docklands development was one of 16 Climate Positive real estate developments from across the world that was recognised by the Clinton Climate Initiative in 2009. Climate Positive real estate aims to reduce the amount of onsite CO2 emissions to below zero.

Andrew Staedler, construction manager for Bovis Lend Lease on its landmark Docklands building, The Gauge, says it was the first to achieve a "triple six" Green Star rating - on design, construction and fit-out.

One factor in this success was the use of more than 20 per cent fly ash in concrete. "This contributed to a great result for a commercially viable rate," Staedler says.

Portland cement is a key ingredient of concrete, and one way of making the material more environmentally friendly is to replace it with fly ash, a by-product of coal-powered electricity production. This has the added benefit of putting waste to good use.

The USA and European countries have been using fly ash in concrete for years, and the use of 20 per cent fly ash was a condition in the construction of Melbourne's Docklands development.

Now, RMIT researchers are working out just how much fly ash can be used to produce concrete that still retains its strength and construction integrity, while helping keep extra CO2 out of the atmosphere.

Dr Indubhushan Patnaikuni says he and colleagues are assessing cement mixes that include up to 70 per cent fly ash. "This gives the concrete high workability, good durability and high strength."

Other new concrete mixes using geopolymers that contain fly ash rather than cement may reduce CO2 emissions by as much as 80 per cent. The research will investigate the use of finely ground fly ash and how it combines with basalt, or volcanic rock, fibre.

Associate Professor Sujeeva Setunge says the use of geopolymers would eradicate the need to use cement in concrete. However, curing the geopolymers requires heat, while the fly ash compounds do not.

"Some work has been done on fly ash but much higher volume, ultra-fine fly ash with basalt fibre has not been explored," Setunge says. "Geopolymers are more useful for the precast industry, as production in a factory enables heat curing, while the new fly ash mixture should be suitable for use on site."

Similar strengths to traditional concrete have been achieved in the trial mixtures. Other potential benefits of these blends are the lower risk of thermal cracking and an overall reduced production cost.

Patnaikuni says China and India consume large amounts of cement and together produce more than 300 million tonnes of fly ash a year, making the outcome of the research of great interest to them. Australia has a capacity to produce eight million tonnes.

Even though Australia and most other countries have regulations to prevent fly ash being a pollutant, it is still a waste product that takes up valuable storage space. What could be more environmentally friendly, and economically sustainable, than to put this waste to use in something we all need?

This story was first published in RMIT's Making Cities Work magazine.

More news

Subscribe to RMIT news RSS feeds