Researchers: Recycled Concrete's Time Has Come

Researchers: Recycled Concrete's Time Has Come

SOUTH BEND, INDIANA — 

Recycling in the construction industry has become big business. It's easy to find new life for everything from old windows to wood beams. But until now, concrete — the most widely used building material on Earth — has been largely left behind.

That's a problem for the environment, says Notre Dame¹ engineering professor Yahya Kurama, because concrete has a huge carbon footprint. "It’s very intensive in terms of its demands on energy, water, land space, everything." Producing concrete accounts for 5 percent of the world’s annual human-generated CO2 emissions². In the U.S., it — along with other demolished³ building materials — takes up nearly half of all landfill space.

A second life for concrete

To reduce such harm, the industry has concentrated on things like reducing new concrete production and finding new uses for concrete byproducts.

In the United States, recycled concrete is used in sidewalks and roads, but not for load-bearing structures. Kurama and his team, along with scientists from the University of Texas at Tyler and New Mexico State University, set out to determine whether it was strong and durable⁴ enough to be used to construct buildings.

"Currently there’s a lot more supply of recycled concrete aggregates⁶ than demand," he pointed⁷ out. "What we’re trying to do is bring up the demand and at the same time generate the engineering background that these materials can be used in a higher-level application."

Kumara’s team is studying different recycled aggregate⁵ combinations in hopes of supplying that demand. Graduate student Michael Brandes says they’re interested in two sources for recycled concrete.

"The traditional RCA, or recycled concrete as we call it, is something that comes from a bridge that was demolished, a building that was demolished," he said. "Basically what that means is it has the opportunity to accumulate a lot of other materials — wood chips, asphalt, brick — from the construction site. We don’t want to have to sort that out, because it’s an added cost."

The other, cleaner source is rejected material from a precast concrete plant, which has no steel, wood or other construction debris⁸ mixed in. In both cases, the material is crushed down as aggregate and mixed with fresh cement to make a new product.

As strong as new

The team is testing both types of recycled concrete to determine durability⁹ and many other qualities: life-cycle costs, weight-bearing abilities, statistical¹⁰ variabilities and properties of the aggregates. Kurama says they are also working out how they might engineer around any differences between the recycled materials and traditional concrete. Currently, without that research, federal building codes bar its use in load-bearing structures, like walls and floors.

Kurama says using recycled material reduces concrete’s environmental impact by about half, from decreased water usage and less mining to decreased transportation costs, because materials are often on site or close by. His analysis also showed that in some instances recycled concrete is stronger than its natural counterpart.

"Nobody’s going to see an immediate¹¹ effect of this," he says of his work, "but if you think about the impact of built infrastructure¹² 20 years, 30 years, 40 years, 50 years down the road, this will have a big impact in terms of reducing concrete's impact on our environment."

That’s good news, because it’s expected the world will need 4.4 billion metric tons of concrete a year by 2050.

1 dame   

n.女士

参考例句：

• The dame tell of her experience as a wife and mother.这位年长妇女讲了她作妻子和母亲的经验。
• If you stick around,you'll have to marry that dame.如果再逗留多一会，你就要跟那个夫人结婚。

2 emissions   

排放物( emission的名词复数 )； 散发物（尤指气体）

参考例句：

• Most scientists accept that climate change is linked to carbon emissions. 大多数科学家都相信气候变化与排放的含碳气体有关。
• Dangerous emissions radiate from plutonium. 危险的辐射物从钚放散出来。

3 demolished   

v.摧毁( demolish的过去式和过去分词 )；推翻；拆毁（尤指大建筑物）；吃光

参考例句：

• The factory is due to be demolished next year. 这个工厂定于明年拆除。
• They have been fighting a rearguard action for two years to stop their house being demolished. 两年来，为了不让拆除他们的房子，他们一直在进行最后的努力。

4 durable   

adj.持久的，耐久的

参考例句：

• This raincoat is made of very durable material.这件雨衣是用非常耐用的料子做的。
• They frequently require more major durable purchases.他们经常需要购买耐用消费品。

5 aggregate   

adj.总计的，集合的；n.总数；v.合计；集合

参考例句：

• The football team had a low goal aggregate last season.这支足球队上个赛季的进球总数很少。
• The money collected will aggregate a thousand dollars.进帐总额将达一千美元。

6 aggregates   

数( aggregate的名词复数 )； 总计； 骨料； 集料（可成混凝土或修路等用的）

参考例句：

• Snowflakes are loose aggregates of ice crystals. 雪花是冰晶的松散凝结。
• Our airplanes based in Europe should be included in the aggregates. 我们驻欧飞机应包括在总数内。

7 pointed   

adj.尖的，直截了当的

参考例句：

• He gave me a very sharp pointed pencil.他给我一支削得非常尖的铅笔。
• She wished to show Mrs.John Dashwood by this pointed invitation to her brother.她想通过对达茨伍德夫人提出直截了当的邀请向她的哥哥表示出来。

8 debris   

n.瓦砾堆，废墟，碎片

参考例句：

• After the bombing there was a lot of debris everywhere.轰炸之后到处瓦砾成堆。
• Bacteria sticks to food debris in the teeth,causing decay.细菌附着在牙缝中的食物残渣上，导致蛀牙。

9 durability   

n.经久性，耐用性

参考例句：

• Nylons have the virtue of durability.尼龙丝袜有耐穿的优点。

10 statistical   

adj.统计的，统计学的

参考例句：

• He showed the price fluctuations in a statistical table.他用统计表显示价格的波动。
• They're making detailed statistical analysis.他们正在做具体的统计分析。

11 immediate   

adj.立即的；直接的，最接近的；紧靠的

参考例句：

• His immediate neighbours felt it their duty to call.他的近邻认为他们有责任去拜访。
• We declared ourselves for the immediate convocation of the meeting.我们主张立即召开这个会议。

12 infrastructure   

n.下部构造，下部组织，基础结构，基础设施

参考例句：

• We should step up the development of infrastructure for research.加强科学基础设施建设。
• We should strengthen cultural infrastructure and boost various types of popular culture.加强文化基础设施建设，发展各类群众文化。