Carbon Nanotubes
We can now detect structural deficiencies in buildings - using embedded carbon nanotubes and electrical currents.
Carbon nanotubes are cylindrical molecules comprising rolled sheets of single-layer carbon atoms (graphene). Carbon nanotubes are referred to as either single-walled or multi-walled depending on their layers of graphene. Their diameters can range from 1 nanometre for single walled nanotubes to more than 100 nanometres for multi-walled nanotubes. They can conduct electricity and heat, though single walled carbon nanotubes can be altered at the atomic level to be non-conductive.
Nanosensor coatings can cover textiles and concrete to make a composite which senses deformations by sensing strain in the material. By charging the material with electrical current, any material strain changes their resistance. The resistance change signals the composite is experiencing a type of deformation. This can be measured remotely with computers.
Coatings composed of carbon nanotubes have the unique ability to be spray-applied to existing structures and sense strain. Structural sensing paint is a cementitious coating composed of fly ash, carbon nanotubes, binding agents, and wireless communication nodes. This coating can be applied to infrastructure works, building structures and envelopes.
Cement paste or concrete filled with conductive carbon nanotubes can also be embedded in structural elements of buildings. Inks containing dispersed carbon nanotubes can be printed on solar cells and light-emitting devices.
Carbon nanotubes can be categorized as single-walled or multi-walled carbon depending on their microscopic structure. Multi-walled carbon nanotubes comprise multiple layers of graphene, as seen in part of the image below.
If one needed their carbon nanotubes to be non-conductive, they would alter the atomic structure of the single-walled carbon nanotube pictured above. This allows it to not transfer heat readily, so the material can maintain its structural properties.Hydrogen sensors are better suited to single walled carbon-nanotubes for this purpose. The image below demonstrates a flexible hydrogen sensor:
Benefits and Drawbacks:
Nanosensor coatings are flexible, lightweight and can be applied to a variety of surfaces.
Structural sensing paint allows for the re-use of industrial waste material, since fly ash is a by-product of coal combustion. The paint is also able to monitor the structural stresses of large physical structures inexpensively.
Cement-based sensors with homogenously dispersed carbon nanotubes are promising for engineering applications. Other than the quality of dispersion, the amount of carbon nanotubes and aggregates are the primary factors that affect the strain-sensing properties.
Commercial Readiness
Carbon Nanotubes are expected to be used increasingly in the future. They have already been used in water-resistant,flame-retardant and electrically conductive textiles. Their applications in the automotive, industrial and aerospace industries demonstrate their potential for construction applications as light-weight, high-strength structural composites.
Various market research reports have predicted the carbon nanotube market will grow an estimated 16% from 2018 to 2023.
Cost Analysis
Carbon Nanotubes are available online at CTI materials for$1.50 to $15 USD per gram. Considering only a small amount are required, this makes them an affordable option for remote structural sensing.
