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By John Biggs
May 14, 2018
Concrete has been a focus of technological improvement in recent years, and some major innovations have come out of various research institutions and universities. Those innovations have ranged from self-healing concrete, which uses water to expand spores embedded within to automatically fix surface cracks, to carbon dioxide storing concrete, to porous concrete that allows water to rapidly seep through to the ground beneath.
Purdue University researchers have been studying ways to make concrete lighter and stronger by integrating microscopic wood nanocrystals into the mix, and the results could have wide-ranging implications on the construction world.
It’s not some far-flung concept out of science fiction, either. A bridge in California is set to begin construction this summer utilizing the nanocrystal-infused concrete that will serve as a real world proof of concept for the material. If all goes according to plan, there’s a good chance the material will start finding its way into the hands of civil engineers around the world.
Nanocrystals are small. Really, really small. Derived from byproducts from the paper, agriculture, pulp and other industries, the resulting cellulose nanocrystals are approximately 100 nanometers long and 5 nanometers wide. That’s 1/1000th of the width of a human hair. The reason such a tiny additive can boost the strength of concrete so dramatically can be explained at the chemical level.
“The strength of concrete scales with the degree of hydration. So the more hydrated it is, the stronger it is,” Jeffrey Youngblood, a materials engineering professor at Purdue University said in a news release. “So you’d think if you add more water it 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.”
The potential applications for nanocrystal-strengthened materials could lead to thinner, lighter concrete, requiring less of it to retain the same strength as a structure made entirely of concrete. Using less concrete would be a step in the right direction for “greening up” construction, particularly when it comes to concrete, which is well documented as a major source of greenhouse gas emissions. As much as 8% of emissions globally are produced from the manufacturing of concrete, according to ConstructConnect.
This isn’t researchers’ first foray into microscopic materials with potential applications in the construction industry. Scientists have been dabbling with ultra small, ultra strong nanofibers and carbon nanotubes in a variety of ways, but both are still too pricey for broad adoption as of now. Cellulose-derived nanocrystals come from abundant materials, costing a fraction of what carbon fiber costs, while at the same time being both stronger and lighter.
In their experimentation, the Purdue researchers discovered the tiny cellulose nanocrystals did indeed make concrete stronger, but were initially at a loss as to why.
“I walked down to the office of [head of the school of civil and construction engineering at Oregon State University and previously a professor at Purdue] Jason Weiss and showed him the data and he said it shouldn’t work because the cellulose nanocrystals are too small. That’s when we realized we had something, because if something based on how things normally work, based on theories or whatever, shouldn't work and it does, that's when you usually have found something important,” Youngblood said in a Purdue University news release. “That's how it all started.”
Nanocrystal-infused concrete also cures faster than traditional concrete, which means less idle time waiting for forms to set for building bridges or oil drilling, for example, which could have a direct impact on a company’s bottom line.
“Every day that a crew is out there not pumping oil is a day losing money,” Youngblood told Phys.org.
As the world’s most ubiquitous building material, improvements to concrete are something of a Holy Grail for researchers. Since its use is so widespread in construction worldwide, even a slight change to how the material can be produced or used more efficiently can have a significant impact.
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