‘There’s plenty of room at the bottom.’
Those words from American physicist Richard Feynman in 1959 ushered in a new field, one focused on directly manipulating individual atoms. Since the 1980s, we’ve called the field nanotechnology.
Today, cosmetics, sporting goods, electronics, medical devices and, yes, construction materials all contain nanoparticles – and their use is expected to increase. ‘By 2025, more than 50% of building materials are expected to contain nanomaterials,’ said Bill Looney, environment director of multinational engineering firm AECOM, in the 2014 Blue Book Property and Construction Handbook.
That sounds promising – but it may also prove concerning, given that the human and environmental risks of nanomaterials in construction aren’t yet fully understood.
The benefits, however, are clearer. When used, nanomaterials in construction demonstrate some valuable and surprising properties. Here are some examples:
- Lighter and more resistant concrete for motorway construction
- Environmental paints that purify the air by absorbing greenhouse gases and producing oxygen
- Self-cleaning glass that repels water and dirt
- Thinner, lighter and stronger insulation
- Surfaces that kill COVID-19 – and other viruses – on contact
For a look at some of the latest products with nanoparticles, visit the Construction Nanomaterial Inventory, compiled by the Center for Construction Research and Training (CPWR). The CPWR designed the inventory to help construction workers and contractors better understand nanomaterial benefits and risks.
Before using nanomaterials in construction, it’s helpful for contractors to know exactly what they are.
The European Union definition is stringent compared with the one used in the United States, Japan or China, according to Denis Koltsov, director and consultant in nanotechnology at BREC Solutions and chair of ISO/TC229 on nanotechnology standards.
‘Nano’ could refer to particles, spaces, technology or other factors, according to ‘Nanomaterials in construction – what is being used, and where?’ a paper funded by the Institution of Occupational Safety and Health.
In the paper, Wendy Jones of Loughborough University in England and her co-authors mention several possibilities:
- Materials containing particles that are 1-100 nanometers in size (keeping in mind that 2.5 cm contain 25.4 million nanometers)
- Materials containing nano-sized spaces and enormous internal surface area, such as silica aerogel insulation
- Materials created intentionally using nanotechnology, known as engineered nanomaterials (ENMs), rather than those naturally occurring, such as fine beach sand or viruses
- Materials that are bound together, which opens up questions about what portion of the particles must be nanoscale
To regulate nanomaterials in the construction industry or make sense of manufacturers’ information requires agreeing on what they are, of course. But often labelling isn’t required, and manufacturers may not report including nanomaterials in the product information or safety data sheet.
Smaller but more bioreactive
The small scale of nanomaterials enables their benefits – and hazards. Compared to larger particles of the same material, the much greater surface area per unit of mass makes nanoparticles much more reactive.
For example, many ENMs can be inhaled into the lungs or absorbed through the skin. The National Institute of Occupational Safety and Health has issued Recommended Exposure Limits for carbon nanotubes (CNTs) and ultrafine titanium dioxide. Like asbestos, CNTs have been linked to inflammation and scarring in the lungs. Titanium dioxide may cause lung damage through inhalation, but can also pass through the blood-brain barrier, where the impacts are unknown.
Inherent or engineered protection
To prevent adverse effects from foreign particles, the body has natural protective mechanisms. But how well they work depends on the particle itself.
‘Normally in the lungs, there are macrophages or cells that get rid of foreign bodies’, Jones said. ‘They can wrap around small or very short particles or those tangled up in a ball and remove them. But macrophages can’t wrap all the way around long fibres. So those fibres can’t get out again.’
The question is not whether a nanomaterial has fibres, but what shape and size they are. Reducing the potential risk of nanomaterials like CNTs may be possible. For example, a manufacturer might use coatings or different processing methods, or substitute shorter or more ball-like forms for fibrous materials. The key is not to lose desirable properties.
‘With any nanomaterial, if you design it differently, the body might behave differently’, Jones said. ‘Theoretically, you could redesign them to make them less of a problem.’
Construction’s particular risks
‘You could put CNT in the handle of a tennis racket, and it will remain in a solid state and never be a problem’, Jones said. ‘But that doesn’t tell you what the problem is if you put it in concrete, leave it 20 years and then break it apart.’
More confounding is that even if you don’t add nanomaterials in concrete, it may release them when demolished. In fact, cutting, grinding, sanding or spraying may all produce dust or mist that could get inhaled, ingested or absorbed.
To evaluate the risk, you need to determine worker exposure and dose, but that research can be complex. In general, particles released from aerosols and powders present the greatest concern.
Still, construction worker exposure is likely to be low, Jones said, especially if it’s managed by protective measures. When dealing with powders or aerosols, for example, that means water suppression, dust extraction at the source and use of face-fitted N95 masks (FFP3 masks in the EU or KN95 filters in China).
Questions and answers
CPWR’s Toolbox Talks on nano-enabled materials cover exposure protection, as well as other useful topics, including basic principles, identification, nano-enabled cement with titanium, and wood coatings and stains.
Additionally, NIOSH created a poster to guide those who work with nanomaterials in construction on how to prevent exposures. The poster covers three categories of ENMs, with decreasing potential for exposure: dry powder with the highest potential; suspension in liquid; or physically bound or encapsulated nanoparticles. The poster then lists questions to ask as well as control and protective measures to take based on the nanomaterial.
If a new material offers advantages that are a remarkable leap forward, contractors may want to check with the supplier to see if it contains nanomaterials. If it does, then ask about the chemical composition, size, shape, electrical charge, solubility and structure. The possibilities are almost endless, but only some properties are linked to health issues.
Often the best advice about assessing and responding to risk goes back to an old adage: err on the side of caution. No matter how small the risks or how unlikely the possible consequences, protecting yourself and your workers from hazards always pays off.