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Since 70-year-old Henry Liu retired from his day job as a civil engineer a few years ago, he's been busier than ever. During his career, he worked with hydraulic presses-squashing cargo into compact bunches in order to transport them more efficiently.

Henry LiuOne of the companies he'd been working with was a coal company which gave him a gift only an engineer could appreciate: fly ash, which is a byproduct of coal-powered energy plants that normally ends up polluting the air and filling landfills.

Liu decided to run some of this fly ash through his hydraulic press, just to see what would happen.

He discovered that compressed fly ash, when mixed with water, is a lot like concrete. Fly ash consists of calcium oxide-the active ingredient in cement. So a waste product that researchers had tried to find a purpose for in vain finally found a use as a concrete brick.

The advantages of fly ash brick are multi-fold. For one, conventional bricks require costly mining and baking in kilns, while Liu's hydraulic press is comparably inexpensive.

The 9 million bricks manufactured every year in the U.S. also release poisonous mercury into the air. The fly ash brick, on the other hand, takes pollutants out of our landfills.

According to an article in Popular Science, Liu's invention did not just jump out at him, but required eight years of work searching for the strongest compounds, and $600,000 of grant money from the National Science Foundation.

But his work paid off, and he expects to sell his bricks to manufacturers in 2008. It seems that Liu has been more productive in his "retirement" than most of us are at our day jobs, and with that, he's an inspiration to an older generation of creative thinkers.

Lisa Zyga
Science Blogger
InventorSpot.com