Making Better Concrete With Rice?

李武军

This is the VOA Special English Agriculture Report.

Rice hulls, or husks, are the protective coverings on grains of rice. Rice with just its hull removed is brown rice. Rice without its hull or bran is white rice.

Once rice is harvested, the hulls are out of a job. They may be taken to landfills or burned. Sometimes they are used to absorb waste in chicken houses. Other times they are used to amend soil.

But a chemist in Texas has another idea.

Rajan Vempati led a group that developed a new process to make rice hulls into ash. The idea is to replace some of the portland cement traditionally used in making concrete. Portland cement is a material that holds together the sand and crushed stone in concrete.

Rajan Vempati thinks rice hull ash could help the concrete industry produce less carbon dioxide. Carbon dioxide is released in cement manufacturing when fuel is burned and limestone is heated. The Portland Cement Association says the gas from the limestone is reabsorbed as concrete ages.

But cement manufacturing produces around five percent of the carbon dioxide released by human activity worldwide. Carbon dioxide is one of the gases that may affect the climate by trapping heat.

The process for making rice hull ash heats the hulls to eight hundred degrees centigrade. Carbon is driven out, and fine particles of almost pure silica remain. The process releases some carbon dioxide, but Rajan Vempati says it would be reabsorbed into the soil naturally.

Another inventor, Prasad Rangaraju, is an engineer at Clemson University in South Carolina. He tested the cement, and says less could be used because the rice hull ash makes it a stronger building material. Also, the inventors say the light-colored material better reflects sunlight, so buildings would cost less to cool.

The National Ready Mixed Concrete Association points out that using ash in cement is not a new idea. The ancient Romans discovered that volcanic ash made better cement.

But the modern inventors say rice hull ash works better than other materials. They developed the process with money from the National Science Foundation. They have not yet brought it to market.

Rice hull ash is already available, but the product is relatively costly.

Cost, including transportation, may decide the success of the new technology. Using it could make the most sense in areas where farmers grow lots of rice and the hulls might just go to waste.

And that's the VOA Special English Agriculture Report, written by Jerilyn Watson with Steve Baragona. I'm Bob Doughty.