Thursday, June 18, 2009

The Last Time I Saw – Concrete

light-transmitting concrete Not much thought about by energy types, but exceptionally important in the construction of a nuclear power plant, concrete would seem an unchangeable item. After all, it’s been in use since Roman times. But that, as MIT demonstrates, is remarkably unimaginative thinking – the creation of cement, a component of concrete, accounts for 5 to 10 percent of the carbon emissions in the world (though that range is so broad, we think they should say, “If we had to guess.”) So how to make it more energy efficient?

In the January issue of the Journal of the Mechanics and Physics of Solids, the team reports that the source of concrete's strength and durability lies in the organization of its nanoparticles. The discovery could one day lead to a major reduction in carbon dioxide emissions during manufacturing.

It’s all about the nanoparticles.

He [Franz-Josef Ulm] and Georgios Constantinides, a postdoctoral researcher in materials science and engineering, studied the behavior of the nanostructure of cement. They found that at the nano level, cement particles organize naturally into the most densely packed structure possible for spherical objects, which is similar to a pyramid-shaped pile of oranges.

The guys poked various cements with nanoparticle needles to create a kind of taxonomy.

The C-S-H [calcium-silicate-hydrate] particles (each about five nanometers, or billionths of a meter, in diameter) have only two packing densities, one for particles placed randomly, say in a box, and another for those stacked symmetrically in a pyramid shape (like a grocer's pile of fruit). These correspond exactly to the mathematically proved highest packing densities allowed by nature for spherical objects: 63 and 74 percent, respectively. In other words, the MIT research shows that materials pack similarly even at the nano scale.

And?

If the researchers can find--or nanoengineer--a different mineral to use in cement paste, one that has the same packing density but does not require the high temperatures during production, they could conceivably cut world carbon dioxide emissions by up to 10 percent.

Yes, it’s pretty deep-dish. And creating that new mineral – ah, there’s the rub – may well prove as carbon intensive as creating cement. Nobody knows. But it’s fascinating that someone (Ulm and Constantinides being the someones) decided to do the deep-dish look at concrete and begin to ideate a replacement for it. Obviously, very early days, but enormous potential. Do read the whole thing.

Architect Aron Losonczi has developed a new type of concrete [this story is from 2006] that transmits light by adding "optical fibers" into the mix. The fibers are used to shift light at each end, producing a "see-through" effect. Called LiTraCon, "the blocks are a combination of 'optical fibers' and concrete, mixed so that the fibers create a fine glass aggregate within the concrete." The glass fibers then transfer light from one side of the block to the other, creating the effect of light transmission.

Perhaps Ulm and Constantinides need to have a chat with Mr. Losonczi.

1 comment:

Kelly L Taylor said...

The pictures remind me of the movie Star Trek IV: The Voyage Home where Scotty 'buys' the materials they need by offering a key to the chemical formula for transparent aluminum - a 'future technology' for the timeframe they're in. Who could suspect transparent *concrete* might come first?