It’s an increasingly familiar story for Torontonians: road closures due to pieces of concrete falling from the city’s elevated highway, the Gardiner Expressway. The cause, explain professors from the Department of Civil Engineering, is a combination of porous concrete, road salt and a lack of maintenance.

“Back in those days, they used a lot of water to mix concrete,” explained Professor Paul Gauvreau to CBC reporter Charlsie Agro.

The porous concrete allows salt, used in winter to guard against ice, to seep into the concrete and corrode the metal that supports it. The result is a weakened roadway.

To stave off the crumbling concrete, regular maintenance is needed. However, as Professor Shamim Sheikh recently told Toronto Star reporter Liam Casey, “we tend to only pay attention when it becomes critical.”

To learn more, you can read The Toronto Star article or view  CBC News’ report.