Montreal Gazette - Looks can be deceiving

Stuck in traffic in the St. Pierre Interchange, the motorist was so startled he pulled out a camera and recorded video of what he saw: steel wires, which were supposed to be providing structural support to a concrete beam, were dangling under the elevated highway. Minutes later, nearing the Mercier Bridge, he drove over another unnerving roadway -- an overpass that appears to be held up by scaffolding, steel beams and blocks of wood…

A key reason for the disintegration is the permeability of the poor-quality concrete used when they were built in the 1960s during Quebec's highway building boom, said Saeed Mirza, a McGill University civil engineering professor.

"Our problem is when we built in the 1960s and 1970s, all these bridges and highways, including the Turcot Interchange, the concrete was very permeable," he said. "The result was the chlorides from de-icing salt got in and caused all kinds of damage." Later, Quebec cut back on maintenance of infrastructure, allowing it to deteriorate. These days, better-quality concrete is used, Mirza said.