All urban infrastructure is essential for properly functioning communities, but there’s something about a bridge that really puts the issue into perspective — perhaps because all that separates you from a likely fatal splash below are impossibly huge concrete structures built on towering stilts. Keeping these structures in good working order demands ongoing maintenance of old bridges and, maybe more important, effective monitoring systems to catch deterioration before it’s too late.
Nemkumar Banthia, a professor of civil engineering at the University of British Columbia, has developed a new method for doing both of the above simultaneously. Banthia’s synthetic mixture of high-performance fibres (glass, carbon and other durable polymers) can be sprayed through a high-pressure hose directly onto the concrete surface of older bridges and overpasses, increasing their strength and durability. Tests show that structures treated with the strengthening spray are able to withstand twice the load of cars and trucks as they could before and can absorb three times more energy from an earthquake.
Even better, the spray is designed to detect the early warning signs of deterioration. The spray coating is embedded with fibre optic sensors that can send digital signals back to engineers via the internet so that bridges can be monitored in real time from afar. “The sensors offer us continuous assessment of a structure,” says Banthia. “It’s analogous to health monitoring online, sort of like a pacemaker in a body.” The sensors integrate seamlessly with concrete structures and can detect anything amiss, including any moisture buildup or changes in chemical composition, as well as interior cracking or symptoms of steel corrosion in a structure’s support beams.
Banthia and his team are also developing carbon-nanotube-enabled cement-based sensors for structural health monitoring that are far less expensive than most fibre optic sensors thus far employed in smart infrastructure. Their technique has been tested successfully on a 46-year-old bridge near the town of Duncan, B.C. In addition to the spray coating and embedded sensors, the bridge also received a few repair patches in the form of fibre-reinforced mortar — essentially a carbon and polypropylene mix that bonds to the concrete structure, enhancing its durability while providing water-resistant properties. The spray was applied quickly, so costly traffic disruptions were kept at a minimum. It is surely just one of countless future applications.