INVENTION AWARDS【POPSCI】zt

John B. Carnett

Building Blocks: Henry Liu cures his fly-ash bricks in an enrgy-efficient steam bath.

The U.S. churns out nine billionclay bricks a year—every one of them an expensive environmentalnightmare. They require costly mining and bake in 2,000°F kilns thatguzzle fuel and spit out pollutants. And making cement for concretebricks spews thousands of pounds of poisonous mercury into the airannually.

So Henry Liu built a better brick,one that lasts just as long and puts to use a waste product ofcoal-power plants—fly ash—that would otherwise fester in a landfill.His bricks solidify under pressure, not extreme heat, so manufacturingthem saves energy and costs at least 20 percent less. And because thebricks are molded, they're smoother and more uniform, slashingbricklaying time and labor.

Liu, a 70-year-old retired civilengineer with a sober, matter-of-fact demeanor, spent most of hiscareer using hydraulic presses to make industrial freight easier andcheaper to move by squashing it into compact blocks. In 1999 a powerplant he was working with gave him some free fly ash, and Liu decidedto run it through his hydraulic rig "just to see what would come out."

Liu took the whitish powder, mixedit with water, and stamped it with 4,000 psi of pressure. Within twoweeks (or, he later discovered, one day in a 150°F steam bath), themixture set into blocks as strong as concrete. It's no coincidence:Concrete sticks together because of cement, the calcium oxide of whichbinds with surrounding materials like crushed rock when it reacts withwater. Liu's bricks can be pure fly ash, which has calcium oxide levelsof "between 20 and 30 percent," says David Goss of the American CoalAsh Association. "It's self-cementing in nature."

Meeting federal safety standards,however, took Liu another eight years and $600,000 from the NationalScience Foundation. Bricks are required to survive 50 cycles offreezing and thawing. Liu's cracked after just eight. He tried changingthe shape, adding nylon fiber—nothing worked. Finally, he blended in atype of chemical known as an air-entrainment agent. Sometimes used totoughen concrete bricks, it produces millions of microscopic bubbles inthe hardened block, giving water less room to sneak in and extendingthe lifetime of fly-ash bricks to more than 100 freeze-thaw cycles.