Nanotube concrete: increased strength and durability
The use of carbon fibers to improve concrete pavement’s flexural strength and resistance to cracking is not a new concept, but the use of carbon nanotubes in concrete pavements is pushing the cutting edge of the approach. After his company developed its proprietary method of producing carbon nanotubes (CNTs), the next step was to identify where the technology adds the most value, said Robert Cavaliero, MCE, Vice President of EdenCrete® Admixtures at Eden Innovations.
“Conventional fibers provide crack-resistance, but CNTs are much stronger and more durable than conventional fibers, even stronger than carbon nanofibers,” said Cavaliero.
One of the early tests of CNTs in a pavement maintenance project was conducted by the Georgia Department of Transportation. Two 35-foot-long test sections were placed on I-20 near the border between South Carolina and Georgia. The “control” was poured with the standard 24-hour accelerated concrete mix formula used by the Georgia Department of Transportation.
“The CNT admixture significantly increased abrasion resistance and compressive strength of the concrete,” said Cavaliero. “Following the test, GDOT specified the product to be used for full-depth slab replacements using 24-hour accelerated concrete.”
The minuscule size of the carbon nanotubes—up to 50,000 times smaller than a hair—means they are respirable in a dry form. To overcome this challenge, the admixture was designed as a liquid suspension of CNTs able to be transported and added to concrete safely and easily, just like any standard concrete admixture.
“This alleviates the risk to workers,” said Cavaliero.
Adding nanotubes to a concrete mix causes lower permeability, resulting in pavements that are easier to place and finish and achieve higher ultimate tensile and compressive strengths in some cases. Pavements with nanotubes also have improved durability with greater resistance to wear and shrinkage-related cracking and curling, resistance to scaling from deicer chemicals, and a lower tendency of steel corrosion.
The future of concrete with CNTs is bright, with projects in Colorado, Georgia, Kansas, North and South Carolina, Texas, and Utah, at port authority terminals, and at several airports showing excellent results, said Cavaliero.
“The use of this admixture fits well with sustainability and resiliency goals as we all work to reduce cement content without sacrificing durability and long service life for concrete pavements,” he said.