Featured Research

from universities, journals, and other organizations

Could lightning strikes be used to break down rubble into useful components of cement and aggregate?

Date:
October 5, 2012
Source:
Fraunhofer-Gesellschaft
Summary:
Every year several millions of tons of building rubble are produced. An efficient way of recycling concrete – the building material of the 20th and 21st century – does not yet exist. Researchers are working on new recycling methods, and with the aid of lightning bolts, they can break down the mixture of cement and aggregate into its components.

Researchers have developed a method of breaking down concrete into its constituent parts.
Credit: Copyright Fraunhofer IBP

Every year several millions of tons of building rubble are produced. An efficient way of recycling concrete -- the building material of the 20th and 21st century -- does not yet exist. Researchers are working on new recycling methods, and with the aid of lightning bolts, they can break down the mixture of cement and aggregate into its components.

Related Articles


Whether the Pantheon in Rome or the German concrete canoe regatta, whether ultra-light or decorative: concrete is unbelievably versatile and is the world's most widely used material -- next to water. It is made of cement, water and aggregate, a mixture of stone particles such as gravel or limestone grit in various sizes. However, the CO2 emissions, which are mainly the result of cement production, are problematic: the production of one ton of burned cement clinker of limestone and clay releases 650 to 700 kilograms of carbon dioxide. This means that every year 8 to 15 percent of global CO2 production is attributable to concrete manufacturing. And when it comes to recycling waste concrete, there is no ideal solution for closing the materials loop. In Germany alone the quantity of construction waste amounted to almost 130 million tons in 2010.

"This is an enormous material flow, but at the moment there is no effective recycling method for concrete rubble" explains Volker Thome from the Fraunhofer Institute for Building Physics IBP from the Concrete Technology Group in Holzkirchen. The current method is to shred the concrete, which produces huge amounts of dust. At best, the stone fragments end up as sub-base for roads. "This is downcycling," explains Thome, in other words, simply the reutilization of raw materials, the quality of which deteriorates from process to process. On the other hand, if it were possible to separate the stone particles from the cement stone, the gravel could easily be reused as an aggregate in new cement -- a first decisive step in the direction of recycling waste concrete. "The recovery of valuable aggregate from waste concrete would multiply the recycling rate by a factor of around ten and thereby increase it to 80 percent," says Thome. If it were also possible to obtain a cement substitute from waste concrete, the cement industry's CO2 emissions would be considerably reduced. To achieve these goals Thome revived a method that Russian scientists already developed in the 1940s then put on ice: electrodynamic fragmentation. This method allows the concrete to be broken down into its individual components -- aggregate and cement stone.

Recycling valuable components

Using this approach, the researchers in Holzkirchen are unleashing a veritable storm of lightning bolts. "Normally, lightening prefers to travel through air or water, not through solids," says Thomas. To ensure the bolt strikes and penetrates the concrete, the expert uses the Russian scientists' expertise. More than 70 years ago they discovered that the dieletric strength, i.e. the resistance of every fluid or solid to an electrical impulse, is not a physical constant, but changes with the duration of the lightning. "With an extremely short flash of lightning -- less than 500 nanoseconds -- water suddenly attains a greater dielectric strength than most solids," explains Thome. In simple terms, this means that if the concrete is under water and researchers generate a 150 nanosecond bolt of lightning the discharge runs preferably through the solid and not through the water." That is the essence of the method," says Thome. In the concrete the lightning then runs along the path of least resistance which is the boundaries between the components, i.e. between the gravel and the cement stone. The initially generated impulses, the pre-discharges, first weaken the material mechanically. "The pre-discharge which reaches the counter-electrode in our fragmentation plant at first, then causes an electrical breakdown," explains Thome. At this instant a plasma channel is formed in the concrete which grows within a thousandth of a second, like a pressure wave from the inside outwards.

"The force of this pressure wave is comparable with a small explosion," says Thome. The concrete is torn apart and broken down into its basic components. With the laboratory fragmentation plant the researchers can currently process one ton of concrete waste per hour. "To work efficiently, our goal is a throughput rate of at least 20 tons per hour," says Thome. In as little as two years' time, an appropriate installation could be ready for market-launch.


Story Source:

The above story is based on materials provided by Fraunhofer-Gesellschaft. Note: Materials may be edited for content and length.


Cite This Page:

Fraunhofer-Gesellschaft. "Could lightning strikes be used to break down rubble into useful components of cement and aggregate?." ScienceDaily. ScienceDaily, 5 October 2012. <www.sciencedaily.com/releases/2012/10/121005123732.htm>.
Fraunhofer-Gesellschaft. (2012, October 5). Could lightning strikes be used to break down rubble into useful components of cement and aggregate?. ScienceDaily. Retrieved October 25, 2014 from www.sciencedaily.com/releases/2012/10/121005123732.htm
Fraunhofer-Gesellschaft. "Could lightning strikes be used to break down rubble into useful components of cement and aggregate?." ScienceDaily. www.sciencedaily.com/releases/2012/10/121005123732.htm (accessed October 25, 2014).

Share This



More Earth & Climate News

Saturday, October 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

EU Gets Climate Deal, UK PM Gets Knock

EU Gets Climate Deal, UK PM Gets Knock

Reuters - Business Video Online (Oct. 24, 2014) EU leaders achieve a show of unity by striking a compromise deal on carbon emissions. But David Cameron's bid to push back EU budget contributions gets a slap in the face as the European Commission demands an extra 2bn euros. David Pollard reports. Video provided by Reuters
Powered by NewsLook.com
Deep Sea 'mushroom' Could Be Early Branch on Tree of Life

Deep Sea 'mushroom' Could Be Early Branch on Tree of Life

Reuters - Innovations Video Online (Oct. 24, 2014) Miniature deep sea animals discovered off the Australian coast almost three decades ago are puzzling scientists, who say the organisms have proved impossible to categorise. Academics at the Natural History of Denmark have appealed to the world scientific community for help, saying that further information on Dendrogramma enigmatica and Dendrogramma discoides could answer key evolutionary questions. Jim Drury has more. Video provided by Reuters
Powered by NewsLook.com
Raw: Tornado Rips Roofs in Washington State

Raw: Tornado Rips Roofs in Washington State

AP (Oct. 24, 2014) A rare tornado ripped roofs off buildings, uprooted trees and shattered windows Thursday afternoon in the southwest Washington city of Longview, but there were no reports of injuries. (Oct. 24) Video provided by AP
Powered by NewsLook.com
Fast-Moving Lava Headed For Town On Hawaii's Big Island

Fast-Moving Lava Headed For Town On Hawaii's Big Island

Newsy (Oct. 24, 2014) Lava from the Kilauea volcano on Hawaii's Big Island has accelerated as it travels toward a town called Pahoa. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins