Concrete: Evolved

“Smart concrete” has the potential to revolutionize the precast industry.

Nearly two decades ago, Deborah Chung, professor of mechanical and aerospace engineering at the University at Buffalo in New York, created smart concrete by adding carbon fiber admixtures to a standard concrete mix. Today, the material has evolved considerably, and is now on the cusp of becoming a major player in the world of concrete.

Structures built with smart concrete conduct electricity, altering conductivity and resistance values when deformed or damaged. They become more conductive when compressed and less conductive when tensioned.

In projects where the electrical or conductive properties of concrete are important, smart concrete is a great fit. For precasters, this equates to an opportunity for new business.

“Smart concrete widens the markets that precast manufacturers can participate in,” Chung said. “It allows them to participate in industries they may not have dreamed about.”

Well-suited for precasters

According to Chung, using carbon fibers to make smart concrete could be likened to using an admixture, a side of the industry with which precasters are familiar. Unlike conventional steel fibers, carbon fibers are microscopic. And because the fibers are so small, they clump. To help disperse the fibers, silica fume particles around 0.1 micrometer in diameter are added during mixing. Besides mechanically agitating the material to loosen the clumps, silica fume reduces the concrete’s pore size so that less water can enter the structure.

Chung explained that, though corrosion is generally of higher concern with conductive materials due to increased electron movement, silica fume actually provides better corrosion protection and reduces shrinking during drying. Additionally, carbon fibers and silica fume work together to produce concrete that not only has electrical conductivity, but also strong structural performance. Carbon fibers also improve ductility, strength and modulus, particularly under flexure.

“For all of these reasons, it may even be more convenient to make carbon fiber concrete from precast than in the field,” Chung said.

Making concrete smart

Although the cement used in smart concrete is the same as in conventional concrete, the mix designs are different. The electrical performance as well as mechanical properties must be kept in mind. Chung’s lab used mostly Type I portland cement, but she said any type can be used. Early strength cement also produced similar results.

“The procedure to make smart concrete is not special,” she said. “Dissolve a small amount of a water-soluble polymer in water, add carbon fibers, and then add that to the silica fume and cement. No special finishing is needed.”

Material costs are about 30% higher than standard concrete. She recommends precasters start with applications that not only benefit from the improved mechanical properties, but require the extra functionality of the conductivity.

“A whole bridge doesn’t need to be made of it, just certain regions,” Chung said.

New markets that could change the precast industry

Smart concrete’s electrical properties make it an ideal sensor for stress, weight and vibration. The following are different applications where it could be successfully incorporated to increase safety, alert communities of potential infrastructure hazards and more.

Protection from the elements

Conductive concrete may be required in tall buildings for lightning protection. It may help electrically ground buildings that currently rely on steel for grounding. It could also be used on roadways to prevent car accidents resulting from ice and snow, or on airport runways that need to be free of ice.

Electromagnetic shielding

Conductivity provides the electromagnetic shielding necessary to protect electrical components such as computers and transformers from radio frequency interference. Concrete with this shielding could be built into transformer vaults, under highways or in tall buildings that have their own transformers on various floors.

Weight monitoring

Smart concrete’s electromechanical behavior allows it to be used for weighing purposes. Outdoors, sidewalks or pavers could detect people walking, which is helpful for security monitoring. In addition, transportation departments, highway builders and those who maintain traffic flow may wish to use the technology to monitor trucks while they are in motion.

Smart concrete floors that weigh people indoors could serve as room occupancy sensors to save energy by controlling heating, cooling, ventilation and lighting. They could also help monitor security – a building’s weight could be zeroed when it is empty at night. Visitors or trespassers could then be detected when entering.

Vibration and damage control

Critical structures that require monitoring for vibration control could use smart concrete to replace vibration sensors. Monitoring dynamic strains on bridges, high-rise buildings or other structures that are subject to strong forces such as wind and ocean waves could make automatic active damping systems that suppress vibrations more effective.

Smart concrete also provides a non-destructive way to monitor damage. Instead of looking for cracks after they occur, smart concrete could send an alert before they are visible to the human eye or other sensors.

“Sensors attached to structures are fragile, fall off in a few years and need to be reattached,” Chung said. “Using the concrete as a sensor itself is inexpensive and durable compared to adding sensors. There is no loss of mechanical properties in the concrete.

“In fact, there can be a mechanical property gain from the carbon fibers.”

In architectural panels, where flexural properties are important, carbon fibers help improve strength so thinner, lighter slabs can be used.

“Thinner walls help in places where land is expensive, like in Japan where carbon fiber panels are currently used not so much to exploit their sensing properties, but for their mechanical gains,” Chung said.

What comes next

Chung and her research group have proven the concept; created, optimized and tested prototypes; collected data and performed lab testing. They monitored smart concrete’s sensing ability all the way to the end of fatigue life and found the electrical resistance change continued in every cycle until complete failure. The next step is field testing, and Chung wants to work with precasters to test preferred applications or help demonstrate the proof of concept.

“Although the electrical sensing functions haven’t yet been implemented, building and transportation industries have expressed interest in field tests,” she said. “The Smart Cities Initiative of the White House is expected to give additional impetus to this development.”

As our world becomes more connected, smart concrete has the potential to revolutionize the industry. Soon, sensing functions may be thought of as essential rather than as a “nice to have.” Should that occur, precasters will have the opportunity to shine, offering something that could impact many markets.

Debbie Sniderman is an engineer and CEO of VI Ventures LLC, an engineering consulting company.