Tiny technology set to make a big difference in our buildings
2 June 2013
Concrete is everywhere. For every person, around two tons of concrete are produced every year, for buildings, roads, dams, bridges, walkways, parkways – all the infrastructure around us.
But while concrete is flexible in its applications, the material itself is very brittle. It can withstand amazing amounts of pressure, but when stretched or bent, it cracks and breaks. That rigidity makes it costly to use and maintain.
Reinforced steel bars (rebar) help, but at a high cost – and even then there is significant and costly wear and tear. Even in the UAE, where most of the buildings are relatively new, the concrete repair market is already worth around $50 million a year. As our roads, bridges and buildings age, that number is expected to balloon as weathering, foundation shifts and other phenomena take their toll.
If concrete could be made both more flexible and stronger, the savings could therefore be huge. A good deal of research is already focused on achieving that. But one area that has so far garnered little attention but has already shown significant promise is the combining of nanotechnology with materials science to create carbon nanotube-strengthened concrete.
Carbon nanotubes are carbon atoms arranged in the shape of tubes so small they are a one ten-thousandth of the diameter of a human hair. In this form, they are 100 times stronger than steel, lightweight, and able to transmit electricity and heat. Instead of running them through the concrete every few centimeters, as with rebar, the concrete can be made so it is chock-full of millions of these tiny stronger-than-steel rods.
My project at Masdar Institute, sponsored by the Qatar National Research Foundation, is investigating the properties of this nanotube-strengthened concrete. Our preliminary research has found that it can be not only stronger and more flexible, but also better able to withstand stretching and bending without cracking or breaking. Also, the nanotube’s thermal and electrical properties make it possible to construct smart concrete structures that can sense any damage or failure.
Our team is digging deep to design the ideal nanotube-strengthened concrete. To be able to model the behavior of millions of nanotubes packed into a section of concrete, we have created a specialized computational tool that can virtually generate random dispersals of the nanotubes.
We are also looking to include two other materials – carbon nanofibers and polymer microfibers, which are respectively each a scale of magnitude larger than carbon nanotubes, adding further dimensions of strength and flexibility to the material.
Preliminary studies have found that this can produce concrete that is five times as strong and durable as normal. Additionally, to reduce the its environmental footprint, our material will use industrial waste – such as fly ash produced from coal burning and “slug” powder from steel factories – in place of energy-intensive cement powder. Globally, reducing cement production even by just 1% would be equivalent to taking millions of cars off the road in carbon output.
One challenge is make concrete in which the carbon nanotubes are evenly dispersed, and properly bound in. If the nanotubes clump together in one area, it could lead to weaknesses in other parts, while if the carbon additives fail to properly bond with the rest of the concrete ingredients, it could result in structural weakness.
In order to mitigate these issues we are collaborating with American industrial giant Lockheed Martin to “grow” the nanotubes directly on the cement particles and the micro-fibers, thus ensuring a strong bond and even spread.
It is our hope that with this research, we can help make the UAE’s ongoing structural projects stronger, longer lasting and more sustainable.
This will not only help save massively on material and repair costs, but also make buildings better able to withstand earthquakes and other potential structural impacts. With this research, we can help make crack-free, steel-free concrete part of our near future.
Dr. Rashid Abu Al-Rub is associate professor of mechanical engineering at the Masdar Institute of Science and Technology.