Concrete is such a necessary building material that people invented it twice, more than a thousand years apart. The credit for the concrete in filling our current infrastructure cannot be overestimated, but a group of researchers from MIT still found a way to spice things up.
Concrete is usually an electrical insulator. But researchers at MIT have managed to make it feasible by adding a concrete mix to nano-carbon black, a very cheap carbon-based material.
The addition of only 4% nano-carbon black to the mixture did the trick, experiments conducted by a team led by Nancy Soliman, who is a postdoc at the MIT Concrete Sustainability Hub (CSHub), showed. ‘Black concrete’ could prove useful for a range of new applications that are not traditionally associated with concrete, ranging from energy storage to self-heating.
One of the most important contributions of materials science in recent years has been the introduction of nanocarbon materials, such as fullerenes, graphene, and carbon nanotubes. The unique structures and new properties of nanocarbons – the main conductivity among them – have attracted attention not only in terms of their basic science, but also because of their potential application in many fields, for example, electronics, energy devices, nanocomposites and biomedical engineering.
But while graphene and carbon nanotubes bring much recognition for their amazing properties, they are also expensive to produce, at least for now. Soliman and colleagues have turned to nanosides or nanopowders, a cheap, environmentally friendly alternative already used in plastics, coatings, inks, fertilizers and electronics.
A pinch of nano-soot was enough to form a network of nanoparticles inside the concrete that allowed the circle to function. In other words, the added ingredient made the concrete electrically conductive. And because of a physical phenomenon known as the Joule effect, this concrete can also generate heat.
“Jol heating (or resistance heating) is caused by the interaction between electrons in motion and atoms in a conductor,” explains Nicolas Chanut, co-author at work and postdoc at MIT CSHub. “Accelerated electrons in an electric field exchange kinetic energy each time they collide with an atom, inducing vibrations of the atom in the lattice, which manifests as heat and a rise in temperature in the material.”
During one experiment, the researchers applied a small voltage (5 volts) to a 5 cm sample of nanocarbon concrete3. This demonstration showed that the voltage heated the concrete to 41 degrees Celsius (about 100 degrees Fahrenheit).
Instead of using water-based heaters, some residential and commercial buildings could use a form of radiant radiation based on electrically conductive concrete. According to researchers, the use of a concrete floor as a heart radiator would be cheaper to install and more reliable than conventional heating, which requires the installation of pipes and water heating systems.
Researchers from MIT are also predicting possible applications for external heating. For more than a hundred years, roads and pavements have been cleared of snow with saline solutions delivered by heavy trucks. They are expensive to work with, and salt can destroy concrete pavements in a timely manner.
“We see a lot of snow in North America. To remove this snow from our roads requires the use of de-icing salt, which can damage concrete and contaminate groundwater, ”Soliman said.
Nanocarbon concrete connected to a power source could defrost itself without the use of road salt. This could be a particularly attractive solution in those situations where navigation conditions are extremely important, such as an airport runway.
The findings appeared in the journal Materials for physical examination.