Nothing lasts forever, even bricks, steel and concrete. Sometimes buildings are demolished, because they are no longer functional, are beyond repair, are in the way, or have simply gone out of style. But after being spectacularly reduced to a huge pile of rubbish, who's going to clean up the mess?

The trouble with this rubble is that it can't be compacted, and it doesn't decompose. So up till now most of the millions of tonnes of building and construction waste has been dumped as landfill.

In fact it makes up 40 per cent of all landfill. In the past, some has been recycled, but re use of the concrete has been limited. So one of the country's largest recyclers, Alex Fraser Pty. Ltd., with EcoRecycle Victoria enlisted the help of Kwesi Sagoe-Crentsil from the Australian Government's Science Agency, CSIRO to make a more reliable product.

During recycling, the concrete is crushed and the steel reinforcement removed, leaving the stones, known as aggregate, still coated with old cement.

"Because of the difference in properties, we have to check the quality, we have to look at all the foreign material that would be introduced in the recycling operation, to see how that would affect the performance of the concrete."

In the laboratory, the crushed concrete is remixed with new cement and chemical additives, before being set in a controlled environment. This is new concrete made with clean dark gray aggregate and here is the recycled concrete. The pale clumps are pieces of the old cement that held the concrete together in its former life.

It's this old cement that can weaken the recycled concrete. So it is rigorously tested by Kwesi and his team to make sure it is durable. Firstly in the lab, then in the field. This bike path is made from recycled concrete. It's regularly checked by CSIRO and so far, is showing no signs of strain.

"At the moment, after laying this concrete, we are looking at the durability. How long this concrete will perform in terms of the strength. To look at the strength, to look at the cracks. How the cracks will develop over a period of time."

Recycled concrete is also being used as a base in road works and for foundation floors in large buildings like the Melbourne Casino and the Sydney Olympic buildings.

"At this stage of our work, we are looking at only non structural types applications, but as we work we are still carrying out some tests so in the near future, we will see how the possibilities of using it for structural types of applications."

It means that while some buildings are no longer of any use, the materials they're made from can be given new life.

CSIRO Enquiries
Email: Enquiries@csiro.au
Phone: 1300 363 400
Locked Bag 10
Clayton South
VIC 3169

Kwesi.Sagoe-Crentsil@csiro.au