ARCHIVED - Nanotechnology and Concrete: Small Science for Big Changes

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June 05, 2005— Ottawa, Ontario

Nanolayered calcium aluminate particles
Nanolayered calcium aluminate particles

Nanotechnology is usually associated with high-profile biomedical, telecommunications and military applications. But for most Canadians, one of the main ways this science at nanometer-level is revolutionizing our daily lives is right under our feet: concrete.

At the National Research Council Institute for Research in Construction (NRC-IRC) researchers are helping lead the way in understanding the nanoscale properties of concrete and using this knowledge to create stronger more durable concrete in a more sustainable manner.

A quick overview of the scope of the global concrete industry and its environmental impact makes it clear why nanotechnology R&D advances will have enormous economic, social and environmental impacts.

Concrete has the largest production of all man-made materials with an annual global production of about one cubic meter for every person on Earth. Canadian industry accounts for about $16 billion for concrete construction annually. Concrete materials alone account for about $5 billion per year.

Concrete is a composite mixture containing a binding phase (cement paste) and aggregates. The paste, composed of hydrated Portland cement and water, coats the surface of the fine and coarse aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete. Portland cement is manufactured by igniting (at 1300-1500°C) a mixture of raw materials, mainly composed of limestone (calcium carbonate) and other aluminium silicates such as clays and shale. The combination of energy use and carbon dioxide output makes cement production a leading contributor to green house gas production, accounting for about six per cent of the annual global total.

Nanoscience has a central role to play in producing innovative concretes for the 21st century. Nanoscience enables scientists to work at the molecular level – atom by atom – to develop new materials with fundamentally new physical and chemical properties.

Nanotechnology is already used in a variety of ways to produce innovative construction materials. Nanoparticulate additives are now widely used as fillers in protective paints, coatings, and clean-up systems for buildings and monuments exposed to radioactive materials. Other applications of nanotechnology in construction include its use in steel-reinforcement, fibre-reinforced plastics (FRP), nanofibre additives and nanoporous ceramics for environmental applications.

Cementitious nanoparticles synthesized by Chimie douce techniques
Cementitious nanoparticles synthesized by Chimie douce techniques

NRC-IRC's multi-disciplinary nanotechnology team is taking the lead in this field to provide cutting-edge nanotechnology-based materials for the construction industry. The NRC-IRC team's strength comes from combining researchers from the fields of chemistry, physics, and materials science, and includes Drs. J. Beaudoin, J. Makar, L. Mitchell, and L. Raki.

The team's interests lie primarily in developing new cements, concretes, admixtures (concrete performance-enhancing additives) and innovations based on these discoveries. Initial research has concentrated on such areas as low energy cements, nanocomposites, improved particle packing, and novel approaches for the controlled release of chemical admixtures.

Hydrated cement is porous with a pore size distribution that ranges from the nanometers to millimetres. However, the pores are also a core weakness: they are a pathway for chloride salts and other chemicals to seep into concrete causing cracking and deterioration that costs the Canadian economy billions of dollars annually.

Thus, a better understanding of the nanoscience of cement hydrates and cementitious materials will reveal new routes for tackling this problem. For example, the addition of nanoparticulates to concrete can improve its durability through physical and chemical interactions such as pore filling. The addition of nanoscale particles to concrete is expected to improve control of concrete porosity beyond what is presently possible with silica fume.

Carbon nanotubes bridging cracks in a cement composite
Carbon nanotubes bridging cracks in a cement composite

The performance of concrete can also be improved by adding nanofibres. Carbon nanotubes have the potential to enhance the strength, to effectively hinder crack propagation in cement composites, and to act as nucleating agents. Reinforcing concrete with nanofibres will produce tougher concretes by interrupting crack formation as soon as it is initiated.

Development of efficient nucleating agents and low energy cements will contribute to increased use of supplementary cementing materials, such as fly ash and slag while making concrete production more environmentally sustainable.

While the exploration for various applications of nanotechnology to develop innovative construction materials continues, it is already clear that the science of the very small is making big changes, with numerous economic benefits for the construction industry.

[The images in this article are SEM (Scanning Electron Microscopy) pictures.]

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