The Vancouver Sun – Researchers Focus on Smart Materials

‘A dumb piece of concrete slab is not dumb anymore,’ says engineer

A concrete bench sits near Rishi Gupta’s lab at the University of Victoria.

Most people walking by the four-metre slab pay it little attention. They probably don’t know the seemingly incongruent structure is equipped with over 20 sensors which Gupta and his students at UVic’s Department of Mechanical Engineering (Civil Engineering Program) use to monitor the concrete’s health and durability.

The bench is an example of smart concrete, which can set off warnings when it begins to deteriorate and even heal itself in certain instances.

“A dumb piece of concrete slab is not dumb anymore,” said Gupta, an assistant professor. “There is so much technology to it.

“Concrete is the world’s most used construction material. Anything we do to make minor improvements affects millions of people.”

Concrete isn’t the only innovative material being developed for the B.C. construction industry. Dotted around the British Columbia Institute of Technology’s Burnaby campus are small houses.

Fitsum Tariku uses these for research on technologies that investigate the thermal and moisture performance of wall assemblies.

“There are new innovations on the market,” said Tariku, director of the Building Science Centre of Excellence and Building Science Graduate Program at BCIT. “We test their properties. We compare them to the existing ones.”

The B.C. Construction Association says 190,000 people are employed in the province’s construction industry. The association pegs the value of current construction projects in the province at $83.6 billion.

Manley McLachlan, the association’s president, said provincial government policies on climate change have pushed the B.C. construction industry to the forefront when it comes to innovation.

“I think B.C. leads the country in sustainable building, that kind of thing,” he said.

“We’re just about to enter into some really interesting times in the industrial sector with the LNG developments, the mining and resource extraction developments. There is going to be all kinds of new technologies required … to put those things together.”

McLachlan said some of the biggest changes on job sites include the use of cordless tools and laser technology for measurements and design.

“The most important tool in the tool box is the laptop computer,” he said.

Nemy Banthia, a professor of civil engineering at the faculty of applied science at the University of B.C., said the use of smart concrete would help reduce the estimated $125 billion currently needed to maintain Canada’s infrastructure of bridges, roads and parking lots.

“These are highly innovative things that are slowly getting into our structures,” said Banthia.

Banthia foresees a time when shape memory alloys are perfected to the point where bridges and buildings can repair themselves. This also has applications for pipelines and even tanker ships.

“At the moment we are not quite there in terms of allowing the structure to actually fix the problem,” he said.

What is currently possible is structural health monitoring using fibre optic sensors integrated into a structure. A bridge near Duncan already uses this technology, but it is prohibitively expensive, said Banthia.

So Banthia is designing smart concrete with sensors built in. They are based on nano-technology. On a bridge, the sensors would be monitored by a computer which could detect and sound an alarm if traffic on the bridge exceeds the allowable load limit or if the structure is close to a collapse.

“The sensors would also allow us to interact with the structure and take corrective measures,” said Banthia. “For example, the sensors can warn about corrosion and deterioration. This would allow for earlier and less costly repairs.

Sensors which indicate where deterioration is happening could also be installed on bridge decks.

“What they do is sense the chemical environment,” said Banthia. “They sense cracking and they can sense changes in the physical characteristics of the material, such as deterioration and loss of strength. Then you would have enough time to create a repair solution.”

The sensors can also be used to turn on heaters that can de-ice the bridge.

Several structures at UBC have been built with the new concrete. UBC students are monitoring the information gathered from the sensors to refine and improve the process.

At UVic, Gupta is working on the already existing technology which allows concrete to heal itself of cracks. Gupta, along with his industry partners, has developed an innovative method to quantify this healing ability of concrete.

Currently, chemical admixtures are added to concrete — materials in the form of powder or fluids that give it certain characteristics. Some develop microscopic crystals when they come into contact with moisture invading the concrete though cracks.

“Whenever you have voids or cracks, you have water or moisture ingressing in the structure,” said Gupta. “These admixtures have a chemical reaction with the moisture and start converting into crystals, blocking all these voids.”

The concrete is more expensive initially, but saves money because it lasts longer. The self-healing concrete can be used for homes, office buildings, parking lots and dams.

Banthia said similar technology can be used for combating bacteria growth and corrosion in sewer lines.

“UBC is also close to realizing concrete materials that carry capsules of anti-bacterial biocides that are released when bacteria are sensed,” he said. “Worldwide, bacterial decomposition of concrete in sewers is a multi-billion dollar problem.”

The topic of shape memory alloys offers a world of “very exciting materials,” said Banthia.

“These are special materials which remember the shape that they were at and then they slowly go back to essentially the same shape after an event.”

Banthia envisions a day when a building that suffers structural damage during an earthquake can begin to repair itself, or an oil pipeline could repair a leak.

Gupta agreed the technology is achievable but anticipates hurdles.

“The challenge they are facing at the moment, like any of the technologies, is the expense,” he said. “I think we are a little bit away from doing that … it certainly is a possibility.”

An innovation closer to reality is a lightweight concrete Gupta is developing.

“The idea behind that is we have small, tiny air bubbles induced in the structure of concrete,” he said.

The final product would be precast panels about half the weight of normal concrete.