听力首页 听力教程 VOA慢速 英语歌曲 外语下载 英语小说 英语词典 在线背单词 听力论坛 韩语学习
听力专题 英语教材 VOA标准 英语动画 英语考试 资源技巧 英语翻译 单词连连看 听力家园 德语学习
听力搜索 英语导读 BBC英语 英语视频 英语电台 英语QQ群 外语歌曲   英语游戏 英语网刊 日语学习
当前位置: 英语听力论坛 » 【VOA慢速教室】 » Making Better Concrete With Rice?
返回列表 发帖

Making Better Concrete With Rice?


       
       

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.

返回列表