Nanotechnology in construction – part one

Nanotechnology is possibly the next big thing, but what does it have to do with construction? Michael Smith, NBS Information Specialist, investigates.

1 nanometre (nm) is a billionth of a metre; the smallest things visible to the naked human eye are around 10,000nm. Industry proponents say that nanotechnology will have a giant effect on building, gaining better performance from existing products at lower cost and creating new and novel applications, from self cleaning roads and fabrics to electricity generating coatings and other even more exotic products.

Market consumption of nanomaterials is accelerating. According to the Freedonia Group, there was $1bn in worldwide demand for nanomaterials in 2006, with 3 per cent of it in construction. Freedonia expects demand to grow to $4.2bn by 2011 and $100bn by 2025: Of this, construction is expected to claim around 7 per cent.

Seeing nanoparticles

Until scientists were able to view matter at the nanoscale it was impossible to effectively manipulate materials at that level, view the results of experiments, and measure their properties. Optical tools, along with tools for working with matter at the nanoscale such as electron-beam lithography, were only really developed during the 1980s and 90s.

Carbon nanotubes (CNT), possibly the first application of nanomaterials, look like a fine black powder to the human eye. Viewed through a microscope it's apparent that the tubes are hollow fibres that can be over a million times as long as they are thick. Their structure gives them a massive strength-to-weight ratio, which when blended with polymers can add strength to anything from car tyres to golf clubs. They are also good conductors, and are used at a much finer level in electronics.

However, it would seem nanotubes are not a new substance; Damascus swords apparently contain carbon nanotubes, which might contribute to the legendary sharpness and strength of this medieval steel.

Unique properties

As a large particle is divided into smaller and smaller pieces, the proportion of its surface area to its mass increases. This happens at an exponential rate when the particle size is 100nm or less. Since the magnitude of many chemical reactions is limited by the available surface area of the chemicals involved, nanotechnology can make far more efficient use of chemicals. This characteristic can have fairly predictable effects, as well as explosive ones; nanoparticles of aluminium, which is usually relatively inert, are explosive.

Controlled production of nanoparticles and the ability to shape materials at the nanoscale have opened up hitherto unimagined horizons. Instead of trying to create nanoscale machines, most nanotechnology in commercial use today simply uses the benefits of nanoparticles. For example, nanosilver has become a common antimicrobial treatment in everything from bandages to washing machines; while silver is antimicrobial in larger particles, using nanoparticles makes for more efficient use.

Nanotechnology in building materials

Nanomaterials still have a high cost relative to conventional materials, meaning that they are not likely to feature in high-volume building materials. The day when this technology slashes the consumption of structural steel is some way off. Nonetheless, the 'nano' tag is showing up more often in building products.

Two nanoparticles that stand out in their application to construction materials are titanium dioxide (TiO2 ) and carbon nanotubes. The former 's ability to break down dirt and pollution and allow it to be washed off by rain water is now being exploited on everything from concrete to glass. The latter is used to strengthen and monitor concrete. The following areas are those where nano-enhanced products are likely to be more widely available soon:

Surfaces and coatings

A number of companies are using nanotechnology to add special characteristics to product surfaces: anything from stain-resistance and colour durability to self-cleaning, improved hardness and scratch-resistance, corrosion and UV resistance, and improved thermal performance.

Nanotechnology also has the potential to bring antimicrobial properties to surfaces. In 2007, research from Yale University found that carbon nanotubes were effective at killing E. coli bacteria.

Thermal performance

By tweaking molecular properties affecting thermal performance, manufacturers have been able to significantly improve this quality in some materials, offering potential energy-efficiency benefits to buildings. Aerogels, very lightweight solids made from silica and carbon, are a high-performing thermal product benefiting from nanotechnology.

Structural materials

With the strength and lightness offered by materials like carbon nanotubes, structural materials would seem to offer a natural fit for nanotechnology in buildings. So far, however, improvement of major building materials is still at the research phase.

It is hoped that recent nanotechnology research in forest products, focusing on the nanoscale properties of wood, will help develop advanced nanomaterials. Wood densification, chemical modification, or impregnation by resins could improve hardness, wear and decay resistance.

An outline research agenda for nanotechnology in cement and concrete covering the next two decades has been enacted; however, practical applications have not yet emerged. Goals include improving mechanical and shrinkage properties, reducing energy consumption during cement production, developing self-powered sensors to monitor the performance of installations and developing innovative concrete materials.

Next issue: Part two – the health and environmental risks of nanotechnology, and its potential regulation

 

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