Turning coal dust into carbon credits

But, scientists from the University of New South Wales have converted the waste ash into a new range of lightweight, high strength building materials, which promise to slash greenhouse gas emissions in the carbon-hungry construction sector by at least 20 per cent.

The first 100% "made from waste" bricks, pavers and aggregates are coming off the production line in China, where hundreds of millions of tonnes of fly ash contaminates the air and clogs waterways.

UNSW’s commercial arm, NewSouth Innovations, is also negotiating to license the technology in Australia, India, Indonesia, the United States, and the Middle Eastern construction hubs of Dubai and Kuwait.

“The environmental consequences are enormous,” says inventor, Dr Obada Kayali, a senior lecturer in Civil Engineering at UNSW@ADFA (the Australian Defence Force Academy).

It’s taken him a decade in the lab, but Dr Kayali says he’s finally turned a global industrial waste burden into a commercially-viable, environmental asset.

The big savings in greenhouse gas emissions lie firstly in reducing the volume of cement needed to make high strength concrete.

Cement and concrete is one of the world's dirtiest industries, generating 10 to 12 per cent of all global emissions. Every tonne of cement manufactured, releases one tonne of carbon dioxide and for very person on earth one cubic metre of cement is produce every year.

The new lightweight fly-ash aggregate, known as Flashag ™, replaces quarried rocks such as blue metal and gravel which are usually mixed in with cement to make concrete. Flashag is the world’s first fly ash aggregate to drastically reduce the volume of cement needed to achieve high strength concrete structures.

“Cement is the culprit, in terms of greenhouse gas emissions. It is not sustainable any more to produce cement at current rates,” says Dr Obada.

China – where half the world’s construction is taking place – recently overtook the United States as the world’s single biggest polluter. The fly-ash products pilot plant opened in the Chinese city of Hebi earlier this year, in a special zone for sustainable industrial technologies and large scale industrial recycling.

“The amount of building going on in China -- and the pollution -- is unbelievable. If we can reduce the use of cement as much as possible there that is a very big gain, not only for China but for the global environment.”

The 100 per cent fly ash bricks and pavers, known as Flash Bricks TM, are about 20 per cent lighter and stronger than their clay counterparts. This means further emissions savings because less steel and shallower concrete foundations are needed for the same sized structures.

Globally, coal-fired power generation has produced billions of tonnes of fly ash waste over the past century, with annual production now at about 800 million tonnes. Uncontrolled it is a serious source of air pollution. In highly regulated environments, such as Australia, fly ash is trapped in super fine filters and pumped into special ash holding dams, or used to fill mining voids.

A small percentage of the world’s fly ash is already absorbed by the construction industry as an additive to cement, and is mixed-in with clay in bricks. However, earlier fly-ash aggregates have needed more cement, not less, to achieve the same strength, immediately losing much of the environmental advantage.

“My research was about finding a way to produce a lightweight aggregate from fly ash which used less cement -- this is the big difference,” says Kayali.

“You can imagine how good this is in terms of greenhouse gas emissions.”

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