Fly ash bricks to enter market

Materials World magazine
1 Aug 2009
The Vecor brick is made from 95-98% fly ash

A technology to manufacture bricks from waste fly ash will be put to the test in a new factory in Hebi, China.

Residue ash from coal power stations is sintered to form bricks or tiles whose complex crystal formations trap toxic chemicals within. The technique is said to be more environmentally friendly than clay or concrete brick production, as virgin materials are not included. The fly ash products also take less heat to form, and provide an end-use for the large quantities of waste produced annually.

The technology was invented by researchers at the Australian Defence Force Academy of the University of New South Wales (UNSW). It has been bought and patented by Australian manufacturer Vecor, who built a pilot plant in Hebi in 2008. It is now drawing up plans to convert the facility to a full-scale factory by 2011. The site is expected to produce at least 125 million bricks a year, using 250,000t of the waste.

‘Fly ash is abundantly available,’ explains Siegfried Konig, Executive Director of Vecor. ‘Over 800Mt is produced each year, with more than 70% dumped into landfill at a considerable cost to the producers (usually coal-fired power plants), and the environment. We have successfully produced products from Chinese and Australian ash.’

The company has modified the UNSW technology to enable mass-manufacture. Over the past 16 months, the pilot plant has investigated how to overcome problems related to cracking, bricks sticking together and the appearance of black spots. Vecor also looked at using retained carbon to reduce energy needs, and researched the effect of this on the kiln’s firing curve to find an optimal energy supply.

The plant has produced tiles, bricks, pavers and aggregates consisting of 95-98% fly ash. These have proved to be lighter than clay or concrete, and offer 33% less shrinkage, says Konig. Tests on thermal conductivities have also been favourable, he adds. ‘Clay brick has a thermal conductivity of around 1.8-2K, while cement brick is approximately 4K. The Vecor brick made from 98% fly ash is 0.17K.’

Lifecycle analysis by UK engineering consultants Arup has also shown that the Vecor process uses 30% less fossil fuel and, while its energy consumption is similar to clay brick, it offers a 45% increase in productivity per unit of energy. Konig adds that manufacturing costs are 20% lower than mainstream costs.

Vecor has received a Climate Ready grant of over AUS$900,000 from the Australian Government to develop the technology, and aims to begin construction of the Hebi plant at the end of 2009. It is hoping to license the technology worldwide.

Further information: Vecor