Nanomaterials in the construction industry and resulting health and safety issues
(Nanowerk Spotlight) Tailing after emerging nanotechnology applications in biomedical and electronic industries, the construction industry recently started seeking out a way to advance conventional construction materials using a variety of manufactured nanomaterials. The use of nanotechnology materials and applications in the construction industry should be considered not only for enhancing material properties and functions but also in the context of energy conservation. This is a particularly important prospect since a high percentage of all energy used (e.g., 41% in the United States) is consumed by commercial buildings and residential houses by applications such as heating, lighting, and air conditioning. A recent review by scientists at Rice University has looked at the benefits of using nanomaterials in construction materials but also highlights the potentially harmful aspects of releasing nanomaterials into the environment.
Led by Pedro J. Alvarez, the the George R. Brown Professor of Engineering at Rice University, the team compiled a list of current use of nanomaterials in various building applications and also highlighted potential and promising future uses.
Use of nanomaterials in construction
Carbon nanotubes – Expected benefits are mechanical durability and crack prevention (in cement); enhanced mechanical and thermal properties (in ceramics); real-time structural health monitoring (NEMS/MEMS); and effective electron mediation (in solar cells).
Silicon dioxide nanoparticles (SiO2) – Expected benefits are reinforcement in mechanical strength (in concrete); coolant, light transmission, and fire resistance (in ceramics); flame-proofing and anti-reflection (in windows).
Titanium dioxide nanoparticles (TiO2) – Expected benefits are rapid hydration, increased degree of hydration, and self-cleaning (in concrete); superhydrophilicity, anti-fogging, and fouling-resistance (in windows); non-utility electricity generation (in solar cells).
Iron oxide nanoparticles (Fe2O3) – Expected benefits are increased compressive strength and abrasion-resistant in concrete.
Copper nanoparticles – Expected benefits are weldability, corrosion resistance, and formability in steel.
Silver nanoparticles – Expected benefits are biocidal activity in coatings and paints.
Quantum dots – Expected benefits are effective electron mediation in solar cells.
Potential risks and concerns
The authors point out that manufactured nanomaterials, in particular synthesized nanoparticles and carbon nanotubes, may be accidentally or incidentally released to the environment at different stages of their life cycle.
Possible exposure scenarios during the lifecycle of manufactured nanomaterials used in construction. (Reprinted with permission from American Chemical Society)
They write that "some manufactured nanomaterials could be considered as potential emerging pollutants because their environmental release is currently not regulated despite growing concerns about the associated risks to public and environmental health. Once in the environment, manufactured nanomaterials may undergo diverse physical, chemical, and biological transformations that change their properties, impact, and fate. Thus, a holistic manufactured nanomaterials
lifecycle exposure profiling is essential to evaluate potential impacts to human and ecosystem health, as well as to mitigate unnecessary risks."
Risk factors range from occupational exposure of workers during during coating, molding, compounding, and incorporation of nanomaterials into the finished building materials or components to community exposure to community exposure during construction, repair, renovation, and (mainly) demolition activities. At the end of the lifecycle, there is a risk of environmental release from solid nanomaterial wastes as they get disposed of in landfills and incinerators.
Aerosolization of manufactured nanomaterials, wastewater effluents from manufacturing processes, and construction-related work, as well as adhesive wear, abrasion, and corrosion of buildings/civil infrastructures could also result in manufactured nanomaterials' release to the environment
Mitigation of public and environmental health impacts
"Whether nanoenabled construction materials could be designed to be "safe" and still display the properties that make them useful is an outstanding question" the authors state.
Adopting principles of industrial ecology and pollution prevention should be a high priority to prevent environmental pollution and associated impacts by manufactured nanomaterials.
According to the authors, some substances can be re-engineered to create safer, greener, and yet effective products. Recent examples include the substitution of branched alkylbenzene sulfonate detergents, which caused excessive foaming in the environment, with biodegradable linear homologues, as well as the replacement of ozone-depleting chlorofluorocarbons by less harmful and less persistent hydrochlorofluorocarbons.
"Thus, it is important to discern the molecular structures and associated properties that make nanomaterials harmful and determine which receptors might be at higher risks. However, detoxification could result in loss of useful reactivity, and focusing on exposure control (e.g., by using appropriate durable coatings during manufacturing, improving matrix stability to minimize manufactured nanomaterials leaching, and adopting controlled construction and careful disposal practices) rather than suppressing intrinsic reactivity that contributes to toxicity might be appropriate in many cases."
In their concluding remarks, the authors emphasize the use of manufactured nanomaterials in the construction industry in the context of energy conservation.
"Opportunities for energy savings – other than using manufactured nanomaterials to harvest solar or other forms of renewable energy – include improved thermal management by using silica nanoparticles in insulating ceramics and paint/coating that enable energy conservation and solar-powered self-cleaning nano-TiO2-coated surfaces. Additional opportunities include the use of quantum dots and carbon nanotubes to improve the efficiency of energy transmission, lighting, and/or heating devices, as well as incorporation of fullerenes and graphene to enhance energy storage systems such as batteries and capacitors that harvest energy from intermittent, renewable sources (e.g., solar and wind)."
Furthermore, manufactured nanomaterials that extend the durability of structures (e.g., through enhanced resistance to corrosion, fatigue, wear, and abrasion) also contribute indirectly to saving energy that would otherwise be used to repair or replace deteriorated infrastructure.
As a final aspect, manufactured nanomaterials can also contribute to a greener construction industry when used as substitutes for materials that can become harmful environmental pollutants, such as lead and mercury (see EPA's brief on green nanotechnology manufacturing).