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Thursday, February 08, 2007

The Nano Secret to Concrete

Researchers aim to cut carbon-dioxide emissions by shedding light on the nanostructure of cement.

By Prachi Patel-Predd

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Probing a cement-based material with an ultrathin diamond needle makes an imprint on the order of nanometers. Researchers at MIT used this technique to study the nanostructure of cement, which governs the properties of concrete made with the cement. Through engineering cement on a nanoscale, they hope to reduce carbon-dioxide emissions from cement production.
Credit: Chris Bobko

Concrete is the most widely used man-made material, and the manufacture of cement--the main ingredient of concrete--accounts for 5 to 10 percent of all anthropogenic emissions of carbon dioxide, a leading greenhouse gas involved in global warming. But now, researchers at MIT studying the nanostructure of concrete have made a discovery that could lead to lower carbon-dioxide emissions during cement production.

The researchers found that the building blocks of concrete are particles just a few nanometers in size, and that these nanoparticles are arranged in two distinct manners. They also found that the nanoparticles' packing arrangement drives the properties of concrete, such as strength, stiffness, and durability. "The mineral [that makes the nanoparticle] is not the key to achieving those properties ... rather, it's the packing [of the particles]," says Franz-Josef Ulm, a civil- and environmental-engineering professor at MIT who led the work. "So can we not replace the original mineral with something else?" The goal is to formulate a replacement cement that maintains the nanoparticles' packing arrangement but can be manufactured with lower carbon-dioxide emissions.

Cement manufacture gives rise to carbon-dioxide emissions because it involves burning fuel to heat a powdered mixture of limestone and clay at temperatures of 1,500 ºC. When cement is mixed with water, a paste is formed; sand and gravel are added to the paste to make concrete. But scientists do not fully understand the structure of cement, Ulm says.

The biggest mystery is the structure and properties of the elementary building block of the cement-water paste, calcium silicate hydrate, which acts as the glue holding together all the ingredients of concrete. "All of the macroscopic properties of concrete in some way are related to what this phase is like at the nanometer level," says Jeffrey Thomas, a civil- and environmental-engineering professor at Northwestern University.

If this structure was better understood, researchers could then engineer cement on a nanoscale to tailor the properties of concrete, says Hamlin Jennings, a civil- and environmental-engineering and materials-science professor at Northwestern. Because researchers do not know the behavior of cement on a nanoscale, until now, "progress in concrete and cement research has largely been hit-and-miss," Jennings says.

Jennings had predicted that calcium silicate hydrate is a particle with a size of about five nanometers. Ulm and his postdoctoral researcher Georgios Constantinides have confirmed this structure using a technique called nanoindentation, which involves probing cement pastes with an ultrathin diamond needle.

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Comments

  • Technique vs Material
    Old Engineer on 02/08/2007 at 10:23 AM
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    5/5
    "Cement manufacture gives rise to carbon-dioxide emissions because it involves burning fuel to heat a powdered mixture of limestone and clay at temperatures of 1,500 ÂșC." Why not produce it with a non polluting fuel? Blaming the cement for the production technique seems bass akwards, but if you can produce a non sinstered cement, more power to you
    Rate this comment: 12345
  • Nano Secret Mega Use
    aluwu on 02/08/2007 at 5:15 PM
    Posts:
    5
    Great news! It is one of the best nano progress I have heard aside from the over hypes.  By taking advantage of nano level understanding (science/technology) many traditional building materials can be nano-producted or replaced by more green nano-made counterparts to save the earth from various pollutions
    Rate this comment: 12345
  • What is the proof that CO2 is responsible for global warming?
    neovask on 02/16/2007 at 12:22 AM
    Posts:
    6
    It is said that "Scientific community generally agrees that CO2 is responsible for global warming". Has science degenerated to such an extent that "generally agreed" hype has begun to pass off as "Scientific facts". Is there any incontrovertible, scientifically validated proof? Has a controlled scientific experiment been conducted ever, anywhere? I've been searching for it for quite some time, but haven't come across any. Can somebody help?

    Kulwant Sharma
    India
    Rate this comment: 12345
    • Re: What is the proof that CO2 is responsible for global warming?
      captainhu on 03/12/2007 at 1:48 PM
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      1
      http://www.aip.org/history/climate/co2.htm

      This will get you started.  No theory is incontrovertible, but the evidence is very strong.
      Rate this comment: 12345
    • Re: What is the proof that CO2 is responsible for global warming?
      GaryB on 03/15/2007 at 2:10 PM
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      42
      Avg Rating:
      3/5
      Re> has a controlled study ever been done ...

      Exactly what are you suggesting?  Duplicating Earth and it's civilizations and running shutting down CO2 emissions in one and measuring the difference in global temperature?

      Sorry, not all science falls neatly into controlled double blind experiments.  Rather, you can look at a number of interlocking measurements, models etc and come up with a mostly likely consensus but never never achieve definitive proof. The question comes down to rational risk assessment vs cost.
      Rate this comment: 12345
      • Re: What is the proof that CO2 is responsible for global warming?
        ccttn on 06/11/2007 at 6:06 PM
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        1
        The Earth is not warming from the outside in.  Oil exploration and extraction has decreased the Earths ability to regulate internal heat.  Simply put, the Earth is a heat engine and fluids found within the Earth such as salt water and oil deposits perform some degree of core radiated heat delay and consequentially some heat dissipation.  We have affected the Earth's internal heat regulating capacity.  The question is how do we compensate for the associated expansion of the Earth's crust? Not the condition of the atmosphere.
        Rate this comment: 12345
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