Construction is a massive global industry, with a very high environmental footprint - only the transportation and agricultural industries have higher annual greenhouse gas emissions. Many key players in the construction industry are pushing towards a more sustainable future, adopting new materials and new techniques.
There are clear opportunities for nanotechnology in this sustainable construction movement, and many companies are beginning to take advantage of the novel properties of nanomaterials to develop cleaner, more energy efficient construction. However, as of yet nanotechnology has not made a significant impact on the construction industry.
For quite some time, materials such as fly ash, slags and other waste materials from industry have been used as fillers in cement production. As well as providing a good way to reuse this high-volume waste, cements using these materials have often demonstrated improved mechanical properties, better abrasion resistance, and other benefits.
These properties are due in part to the nanoscale nature of the particles in the ash and slag - in particular, the dependence on particle size that comes into play with nanomaterials can have a big effect on the bulk properties of the material. Research has shown that controlling the composition and particle size of nanoadditives for cement can help produce materials with advantageous properties.
Silicon dioxide and iron oxide nanoparticles have bother been shown to have an advantageous effect on the compressive strength and flexural strength of cements, and also accelerate the hydration process. Making cement as strong as possible will reduce the amount needed in building, leading to a more efficient construction. Cement making is a highly energy-intensive process, so making the most of the cement which is produced is very important in sustainable construction.
Nanotechnology for Concrete
This video from Stevens Institute of Technology explains the use of silica nanoparticles to modify the properties of cement. Run time - 1:29 min
Nanomaterials designed for use as insulation in buildings are already commercially available. The unique properties of nanomaterials can offer enhanced performance coupled with additional useful properties not available from conventional materials.
Aerogels are nanoporous solids which are incredibly lightweight - around 95% of their volume is taken up by air. This makes them very good insulating materials (2-3 times more effective than conventional insulation materials), but also means they can be translucent. Aerogels are available with up to 75% transparency, for use as insulation in translucent walls, windows, or skylights. No other type of material can provide such a high level of insulation whilst remaining translucent.
Thin film coatings can add valuable functionality to on walls and windows which are traditionally purely structural. They can improve the energy footprint of the building, make the interior environment more comfortable, and even improve the appearance of the building.
Nanoscale coatings of stainless steel can absorb infrared light - when applied to curtains or blinds, these can block out heat as well as light from the sun, and help to lower room temperatures, reducing the need for expensive air conditioning.
Some companies, like Saflex and 3M, are manufacturing nanofilms for windows which absorb thermal energy, reducing the amount of heat which enters the building. The nanofilms also reduce the amount of damaging UV radiation which can pass through the glass.
Coatings of TiO2 nanoparticles and other materials on the exterior surfaces of a building can produce a self-cleaning effect. This can keep glass and concrete surfaces clean with minimal maintenance, and reduce corrosion of metals like stainless steel.
Energy Generation with BIPV
Going one step further than the reduction of energy usage, nanotechnology is enabling the development of thin film solar photovoltaic panels, which can actively generate electricity for use in a building without taking up any additional land through advanced building-integrated photovoltaics (BIPV).
Solar energy has the potential to be the main source of electricity in urban areas, if the surface area of large buildings can be exploited. The main barriers to this situation can be overcome by nanomaterials.
Silicon-based solar cells are too expensive and inefficient to be adopted on such a large scale. Nanomaterials would drive down the basic material cost of photovoltaics to make them more accessible, as well as allowing ultra-thin film photovoltaic coatings to be developed which can cover the walls and even windows of a building without affecting their appearance.
Nanotechnology in Lighting
Lighting contributes a great deal to the electricity used in buildings. Conventional lighting also produces heat, which can add significantly to the energy used in cooling a building.
Nanotechnology advances are producing lighting solutions which remove these issues. Highly efficient LEDs can save huge amounts of electricity, and nanostructured heat sinks can make sure they stay cool and run for the full extent of their lifetime.
OLED (Organic LED) technology is already used commercially, primarily in small scale displays. As the technology develops, however, it will become feasible to use OLEDs for lighting - this will result in huge energy savings, and completely change the way lighting is used as a design tool in construction.
OLEDs are constructed from layered nanoscale films of organic compounds which emit light when a current is passed through them. They can be applied to the surface of any material, and even made transparent. This could lead to any surface or object being used as a light source - even windows could contain a transparent OLED layer that could mimic the qualities of natural light at night.
Nanotechnology has much to offer the construction industry as it moves towards a more sustainable future.
Efficient and less carbon-intensive structures, coupled with smart, green design and building-integrated solar power generation will make a significant impact on the environmental impact of large buildings in particular, and improve the perception of the industry in the general public.
Sources and Further Reading