The chip grows into a fissure, the fissure yawns into a crack that crumbles away into a pothole. Another break in the highway becomes another break in the prairie transportation system.
In Saskatchewan, six percent of the roads carry 70 percent of the traffic -that’s beyond the load they were intended to carry.
“This puts a great deal of stress on that six percent and much of that six percent was not designed for the job it does today,” said George King, manager of highway preservation for Saskatchewan.
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King said there are three major classes of prairie roads:
Pavement surfaced roads
Designed to last 15 years, these are major highways built of many compacted clay and gravel base layers with a hot tar and gravel mix forming the surface.
Seal coated roads
Built to last from five to 15 years, depending on the design, these roads are made from a built-up base over a compacted sub-base, topped with a sprayed-on seal coat of hot tar over a gravel and clay base.
Thin-membrane paved roads
A thin layer of hot pavement is applied over a base and sub-base. This road is designed to last 15 years and be dust and mud free, but is not built for heavy truck traffic. Saskatchewan has 8,700 kilometres of this design, more than either Alberta or Manitoba.
Roads break down either because of environmental damage or load stress – caused by weight or too much traffic.
Environmental factors usually involve moisture seeping below the road surface and through freeze and thaw cycles breaks the pavement as the water expands and contracts. Moisture then builds up under the surface until it is forced out through pressure or drainage, and carries road materials with it, causing holes in the surface.
Load-associated failure causes much of the damage on thin-membrane roads.
Shear failure, as it is known, occurs when heavy loads flex the pavement up and down. The flexing, like the bending of a thin wire, eventually snaps the surface, which breaks up in chunks. Heavy vehicle weights, high speeds and hard braking combine to create pressures on the pavement.
Treatments for the problem vary in cost and effectiveness.
Filling cracks quickly can delay moisture invasion, but these repairs will not last forever and water will eventually make its way through the surface. Asphalt is sprayed into the cracks at a cost of $200 to $300 per km.
Other options
Spot sealing with aggregate and tar will fill surface imperfections on larger areas. This technique comes with a price tag of $1,000 to $2,000 per km.
Seal coats made of aggregate with a sprayed-on layer of tar can cover minor repairs, preventing water damage and sealing shear repairs. The cost of seal coats ranges from $4,000 to $6,000 per km.
Resurfacing involves the removal of damaged pavement and replacement of base and sub-base. A new layer of pavement is applied to the surface.
It costs from $40,000 per km for a simple resurfacing to $110,000 for a structural overlay that involves the base layer.
The most expensive repair is complete reconstruction with a price tag of $150,000 per km.
