A new bridge will be built in California this summer. That’s hardly earth-shattering news. But this one will be different.
Thanks to the work of researchers at Purdue University, this bridge will use concrete that has been infused with microscopic-sized nanocrystals from wood. The idea is that the nanocrystals will make the concrete stronger so that less of it is needed.
The nanocrystals are a byproduct generated by the pulp and paper industries, among others.
Nanotechnology has grown by leaps and bounds in the last 30 years. Nanoparticles have always been with us, but because they are so small, we didn’t yet have the electron microscopes necessary to see them so that they can be manipulated.
They are, after all, as little as a billionth of a metre wide.
For perspective, a single strand of human hair is about 100,000 nanometres (nm) in diameter. A sheet of newspaper is about 160,000 nm thick.
The intriguing thing about nanoparticles is that nano-structured materials are often stronger or have different magnetic properties compared to other forms or sizes of the same material. Sometimes they’re better at conducting heat or electricity. They may be more chemically reactive or reflect light better, or change colour as their size or structure is altered. And they can add strength.
The research team at Purdue hopes the cellulosic nanocrystals — which are about 100 nm long and five nm wide — will yield stronger concrete through a chemical reaction that increases the hydration of the cement particles it contains.
Jeffrey Youngblood, a professor of materials engineering at Purdue, says “concrete scales with the degree of hydration. So the more hydrated it is, the stronger it is.
“So you’d think that if you add more water, the concrete would be stronger. The problem is water adds pores that make it weaker. But cellulose nanocrystals enhance hydration with less water, making the concrete stronger.”
Another benefit, he says, is that cellulose-infused concrete sets faster, which means less time waiting for it to cure.
Researchers say the cost of using cellulose nanocrystals may be offset since builders will be able to use less cement, but the exact cost hasn’t been determined. But even if only a small percentage of all the concrete produced used cellulose nanocrystals, it would have a big impact simply because concrete is the most common manmade material in the world.
If concrete is ubiquitous, so is cellulose, which is the most abundant organic compound on earth.
We never think of it, but it’s what makes plant stems, leaves and branches so strong.
If researchers pull this off, if the California bridge is a success, it could have a transforming effect on the concrete industry. Items made with concrete could be thinner and lighter while retaining the same strength.
And using less concrete means using less cement, which in turn means less carbon dioxide released into the atmosphere. The construction industry has long been aware that cement plants account for about eight per cent of global emissions of carbon dioxide, which is one of the main causes of climate change.
The Purdue researchers began looking into cellulose about a decade ago.
Youngblood, who works mostly with plastics, said the challenge at first was determining where the water-soluble cellulose nanocrystals could be used. The idea of using them in concrete came while he was digging a post hole and preparing concrete.
He says the team quickly found the cellulose nanocrystals made concrete stronger, but no one knew why. The nanocrystals shouldn’t have made the concrete stronger because they were too small.
“The fact that it did work was when we realized we had something,” he says.
So now it’s time to take the concrete out of the lab and use it to build a bridge in the real world. The size and location of the project should be announced soon.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org.