There is a way of explaining how carbon nanotubes work by likening them to the rebar used to reinforce structural concrete. Interestingly enough, there’s also a newly emerging way to use carbon fiber rods as a replacement for rebar. Substituting rebar with carbon fiber rods is making one of the world’s most commonly used construction materials even better.
If you know anything about structural concrete, you know it is much too brittle to use as a building material by itself. A bridge made entirely of concrete without any reinforcing rebar would crumble under the weight of traffic. A concrete building without any rebar would not stand up to time, weather, or a variety of other forces. Without rebar, concrete is not a very good building material for large-scale projects.
At the same time, structural concrete reinforced with rebar has an inherent weakness: it is prone to a loss of integrity as the result of corrosion. Even though it’s wrapped in concrete, steel rebar is still exposed to moisture and, therefore, still corrodes. Carbon fiber rods solve that problem.
Carbon Fiber in Concrete in Russia
A traditionally-built structure using concrete reinforced with steel rebar is a lot stronger than concrete alone. But corrosion of the steel gradually destroys structural concrete from within. In Russia, they are overcoming this problem with a unique product made with a combination of carbon fiber rods and carbon nanotubes.
A solid carbon fiber rod is stronger and more rigid than steel. That can be a problem if you are looking at replacing rebar with it. Rebar is somewhat flexible, even though it is made from steel, so it allows concrete structures to flex somewhat. The question is, how do engineers use more rigid composites to create a similar material that is strong enough yet still flexible enough to replace rebar?
The answer is in carbon nanotubes. A carbon nanotube is essentially a sheet of bonded carbon molecules rolled together to create a tube. By creating composite rebar with just 0.05% carbon nanotubes by weight, Russian engineers have created a product with a tensile strength 32% better and a bending strength 29% better than standard rebar.
Using just a small volume of carbon nanotubes, it is now possible to create composite rebar that does what steel cannot. It gives structural concrete the extra reinforcement necessary without any risk of internal corrosion. That is a remarkable achievement.
There Is the Cost Issue
At Rock West Composites in Salt Lake City, Utah, composites professionals are very familiar with both carbon fiber rods and carbon nanotubes. They know full well the benefits of both materials, but they also know that cost is one of the problems that has prevented composites from being more widely adopted in many industries. All eyes are now on engineers to see if they can produce composite rebar as cost-effectively as its steel counterpart.
Rock West explains that a process known as pultrusion makes fabricating hollow tubing in mass quantities very cost-effective. Could the same process be used to create solid carbon fiber rods? More importantly, is there a process available for mass-producing a carbon fiber/carbon nanotube hybrid for making rebar?
No one knows the answer to those questions as yet. But just the fact that composite rebar is possible in a proof-of-concept build may be enough to lead the people who came up with it to work on a cost-effective manufacturing process. If they can do that, their composite rebar will have an enormous impact on building construction, infrastructure engineering, and a lot more. Let’s hope they succeed.