September 14, 2007

NRC-IRC

The Joel JSPM5200 model Atomic Force Microscope used by the NRC-IRC to examine cement particles at the nano-scale.

Nanotechnology

National Research Council teaches old materials new tricks on a micro scale

PETER KENTER

CORRESPONDENT

The National Research Council’s Institute for Research in Construction (NRC-IRC) is studying how to improve the performance of ordinary Portland cement and the supplementary cementing materials that are added to the mix.

“People think of concrete mixtures as occurring on the macro scale,” says Dr. Laila Raki, Group Leader, Concrete Materials and Structural Technologies with the NRC-IRC. “We’re looking at what happens to these materials at the nano-scale — with particles measuring less than 100 nanometres across.”

At the NRC’s disposal is an arsenal of high-tech microscopes designed to investigate the interactions of materials at the nano-scale:
•The Transmission Electron-Microscope (TEM) which bounces electrons, instead of light waves, off its subject,
•The Scanning Electron Microscope with Field Emission Gun (FEG/SEM), and
•The Atomic Force Microscope, a device that “feels” the surface of nano-scale particles with a minuscule silicon tip.

“Over the years we’ve come to understand what happens when we change the mix design, add other materials and retard or accelerate the chemical processes that create concrete,” says Raki.

“But in many cases, we still don’t know why these things are happening. If we’re experimenting with a number of factors, such as different admixtures and the timing involved, we need to understand what is happening at the very lowest level of the structure so that we can retain positive results without undermining them at the next stage of research.”

One part of the study focuses on cement hydration — the chemical reaction in which cement compounds form bonds with water molecules. By controlling the hydration process, the researchers hope to create concrete that will be stronger, less porous and more durable than current mixes.

Using high-tech microscopes, the researchers examine the surfaces of individual cement grains to observe the effects of their experiments close-up.

By employing several techniques to view the same activity, the researchers gain greater understanding of the process than by looking at one set of results alone. Initial work has focused on tricalcium silicate hydration, and the effects of super-plasticizers and accelerators on the final product.

NRC-IRC

An image of calcium silicate hydrate gel as seen by a Scanning Electron Microscope at a magnification of 60,000.

“Super-plasticizers have shown great promise as an admixture,” says Raki. “But by observing the material at extreme magnification we’ve seen that they can also have adverse effects over time. We want to retain the positive effects while eliminating the negative ones.”

The researchers are also examining the addition of such industrial by-products as flyash from coal-fired furnaces and blast furnace slag to the concrete mix, a practice that mitigates carbon emissions by consuming less energy in mining new materials.

“Adding these products creates a denser concrete with greater durability,” says Raki. “We thought we would kill two birds with one stone and examine ways to improve the effects of these additives while reducing carbon dioxide emissions.”

Raki says that the research has already led to a patented method for mixing concrete that’s waiting for a business partner to distribute it.

“We’ve never really examined these hydraulic reactions at the nano-level before and this represents a huge ocean of opportunities for the material,” says Richard McGrath, director, codes & standards, engineered structures with the Cement Association of Canada.

McGrath says that the field of possibilities is wide open. “Imagine a chemical admixture that would allow concrete to set in minutes instead of hours,” he says.

“Think of the opportunities for paving — traffic lanes that could be ready for use within a matter of minutes. Right now we have no idea what possibilities lie ahead and that’s part of the allure of the research.”

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