DCN ARCHIVES

March 23, 2010

Hitachi S4800 Field Emission Gun Scanning Electron Microscope

NATIONAL RESEARCH COUNCIL

A Hitachi S4800 Field Emission Gun Scanning Electron Microscope (FEG-SEM) equipped with an Oxford Instruments Inca 200 EDS is used to characterize micro and nanostructural changes of cement systems.

Technology

No concrete detail too small for National Research Council

The National Research Council-Institute for Research in Construction (NRC-IRC) is looking for partners to help refine nano-tech research into marketable products that will most benefit the construction industry.

“It isn’t only about creating concrete with significantly improved strength, but about durability as well,” says Dr. Laila Raki, Group Leader, Concrete Materials and Structural Technologies with the NRC-IRC. “But the research is so painstaking and time- consuming that we prefer to see industry getting involved, joining the technical committees and funding research on concrete products that will be more acceptable to the market.”

It’s not as though all construction materials would benefit equally from the application of nanotechnology. The composite structure of concrete makes it an ideal candidate.

Research focuses on the main binder in concrete — calcium silicate hydrate — which is formed by a chemical reaction between cement and water and creates a structure that ranges in size from nanometres to millimetres.

Initial research concentrated on pure cement, not concrete, to help understand what occurs on the nano scale.

“We were minimizing parameters to understand what is taking place,” says Raki. “We needed to understand exactly what was happening when we added C3A [tricalcium aluminate] and C3S [tricalcium silicate], for example. We then built on this knowledge to make a more complex product.”

The research takes time because concrete is a dynamic material that may only achieve its maximum strength after years of hydration. But the technical teams examining the properties of novel concrete formulations don’t have to wait a decade to see whether the result of a particular experiment is encouraging.

“We’ll typically look at small samples over intervals,” says Raki. “Some samples are examined for up to 200 days. Using calorimetric testing, we can monitor the hydration process and examine the material’s structural features with the electron microscope. We can then nano-engineer a material that would perform over the long term using other complementary techniques such as thermal analysis, and X-ray diffraction.”

Much of the research concentrates on the use of chemical admixtures. Because concrete is made of simple ingredients, the relationship between certain admixtures and the resulting properties of the concrete is relatively straightforward. As the research team studies the chemical interactions of concrete on the nano scale, it becomes easier to determine exactly what happens when the formula becomes more complex.

“We know, for example, that we can add fly ash, silica fume or blast furnace slag to concrete to incorporate waste material,” says Raki. “But some of those materials may actually retard hydration and create a material that doesn’t set as quickly. Our research aims to show us not only how we can incorporate such materials, but also how we can fine-tune the mix and control the chemistry to both incorporate fly ash and improve the physical properties of the resulting material.

“We are adding nano-particles in an effort to accelerate hydration and offset the delay, while creating more binding phases that show promise in making the material stronger.”

The research heads into new ground, however, with the addition of synthetic nano-scale materials. “We are working with some calcium aluminate phases, commercial nano-calcium carbonates and calcium silicate hydrates,” says Raki.

“These are all synthetic nano-particles that can be used as seeds in the hydration process. The seeds fill the pores and spaces in the material and create an additional surface where the hydrates can grow.”

The NRC-IRC is working on both short- and long-term concrete research projects. While some research strives to provide solutions for the construction industry a decade or more into the future, other research has produced new formulations that are currently undergoing the patent process.

“We’re not trying to create only theoretical formulations,” says Raki. “Our aim is to create concrete products that will be used in roads, bridges, highways and buildings.”

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