Crumbling asets. Rusting pipes. Leaking watermains. Musings about the state of our civil infrastructure usually come around to this type of talk. It may seem overwhelming to consider the thousands of kilometres of pipe that need replacing—or at least serious upgrading.
But any asset manager will tell you that prioritizing which pipes to fix first is a relatively simple numbers game. It all comes down to risk assessment: determining the projected life cycle of any asset and, based on its expiry date, deciding when to take action. But with the massive asset bases cities have—in Montreal alone, there are more than 100,000 sewer and water pipes—a simple numbers game can quickly get complicated.
Add to that another layer of complexity: there’s no way to pinpoint exactly when an asset will fail. Not all assets will deteriorate at the same rate. Two pipes may have the same estimated life cycle, and for any number of reasons, one may fail early, while the other may last years beyond its projected replacement year.
The decision becomes whether to gamble on an asset lasting longer than the average, and leave it for a few years beyond its projected service life, or be cautious and replace an asset before it has a chance to fail. It’s less of a gamble if public works staff can find ways to monitor the state of these assets. That’s becoming easier to do thanks to technological advancements. Sensor networks within civil infrastructure have become ubiquitous. Sensors that can be placed virtually anywhere can send information about the state of a pipe or a bridge. These networks can measure everything from corrosion, movement in joints caused by temperature change, strain, material strength.
Of course, as you install sensors in civil infrastructure, you may lower the risk, but you increase the cost. The extra money spent on implementing and maintaining these measurement systems must be weighed against the cost of replacing an aging piece of infrastructure. There may be new ways to reduce the cost of running these automated systems, making them an easier sell.
Despite improvements in sensor electronics and wireless communications, sensor networks still require conventional sources of power. Most of these sensors are currently run off a city’s electricity grid or batteries. Vainatey Kulkarni with University of Toronto’s Mechatronics and Microsystems Design Lab is working on a solution to that problem. At the Ecocity World Summit in Montreal this August, Kulkarni said. “You can install sensors in every bridge, but if they’re battery powered you have to send someone out to replace the batteries every six months. Why not just send him to take measurements himself?”
Kulkarni said the large-scale implementation and maintenance required with batteries also prevents sensors from being installed in inaccessible locations, though that’s typically where they are most useful. His proposed solution? Piezoelectric energy harvesting. Energy harvesting is the process of capturing ambient energy from a device’s surroundings and converting it into electrical energy.
Piezoelectric energy harvesting is one of several methods of harvesting energy. In this process, energy harvesters convert mechanical vibrations to electricity. It’s best suited for low power applications in enclosed, high-vibration/high-force environments, making it ideal for embedded applications in civil infrastructure. It can feed off the vibrations created from a moving car on a bridge—or water flowing through a pipe.
But it’s still early days for this solution. The five-year-old technology is still not viable. Considering photovoltaics (another form of energy harvesting) have been around for over 50 years and scientists are still working out the kinks (in particular, how to make the economics work), will this invention be ready for practical use any time soon?
Kulkarni is confident issues of power output and reliability will be solved sooner rather than later. The real challenge is finding a material that works as well as lead. The best piezoelectric materials contain lead oxide, a material about which many are leery as it may soon be banned.
In the meantime, the thousands of sensors being installed (as many as 20,000 in one bridge) will continue to draw power from either the grid or good old double A batteries. WC
Mira Shenker is Water Canada’s associate editor and editor of ReNew Canada magazine.