Let’s try to crack that great Montreal mystery: Why do we build self-destructing roads?

When it comes to durability, all roads lead to Rome. While our roads barely last 50 years, some ancient paved Roman roads still survive. A metre thick, they were built on compacted soil in four layers: crushed rock, mortared crushed rock, concrete, and stone pavers.

Two millennia later, in 1816, roads of compacted gravel called macadam were developed by John McAdam — not, however, the John Macadam whose name graces the rather more digestible macadamia nut. Macadam was far inferior to its Roman equivalent, without even a concrete layer because “modern” concrete was first used for paving in 1865. By 1904, macadam had tar added to it as a binder and dubbed “tarmac.” We call it asphalt.

Roadbuilding techniques have essentially remained unchanged ever since,........

© Montreal Gazette