Disposing of waste products such as household waste is a perennial problem. It is excellent when a waste product can be recycled into a new and useful product.

Henry Liu of Missouri has done just that for the "fly ash", the fine waste removed from the smoke emitted by coal-fueled power stations. Only a third of the ash waste is at present re-used, meaning that in the USA alone 40 million tons annually is disposed of in slurry pits or in mine pits. Besides finding a use, they would reduce the use of conventional means of producing bricks, and of pollutants such as mercury from that activity. The USA makes 9 billion bricks annually.

Liu is a 70 year-old retired civil engineer (and professor). He used hydraulic presses in his career to enable space to be saved in transport, which enabled cheaper movement of goods. In 1999, while he was still at work, one of the companies he was working with gave him some fly ash.

He tried putting the white powder, mixed with water through an hydraulic press to see what would happen. 28 MPa of pressure, which is a lot. Within two weeks the mixture had set into blocks as strong as concrete. This makes sense, as concrete sticks together because of cement, the calcium oxide of which binds with surrounding materials like crushed rock when it reacts with water. Pure fly ash has calcium oxide levels of between 20 and 30 percent.

Liu spent eight years of work searching for the best solution, helped by $600,000 of grant money from the National Science Foundation. Much of the effort and money was needed to ensure that he met the American Society for Testing and Materials  standard for bricks, which is mandatory. Bricks are required to survive 50 cycles of freezing and thawing. Liu's cracked after just eight. He tried changing the shape and adding nylon fibres, but nothing seemed to work.
Then he tried adding a chemical which acts as an air-entrainment agent. It produces millions of microscopic bubbles in the hardened block, giving water less room to sneak in and extending the lifetime of fly-ash bricks to more than 100 freeze-thaw cycles. Another improvement was that his bricks are ready after one day in a 65°C steam bath. That's merely warm in comparison to conventional clay bricks, which are heated to over 1000°C.

As it is mainly pressure and not heat which is involved there is less energy involved. Each brick costs 20% less to make and is just as good as a conventional brick. They are also more uniform as they come out of a mould.  

In June 2005 Liu applied for WO 07/005065, my Patent of the Month. Its initial pages describe in considerable detail the problems involved in improving the product, and previous research.

The invention has won awards, and Liu is now trying to get manufacturers to take out licences to manufacture what he calls a green brick. "The people who buy bricks will definitely be interested," says Pat Schaefer, a sales manager for Jefferson City, Missouri, manufacturer Midwest Block & Brick. "But I don't see the brick companies liking it at all."


Our Patent of the Month is provided courtesy of Steve Van Dulken from the British Library.  Steve is a patent specialist at the British Library and has his own blog at http://britishlibrary.typepad.co.uk/patentsblog/

Steve has worked since 1987 as a patents librarian at the British Library. Author of Inventing the American Dream, Inventing the 19th century and Inventing the 20th century, both popular science, and of British patents of invention, 1617-1977: a guide for researchers and editor of Introduction to patents information.