Surface Treatment Technology Across Canada

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Surface Treatment Technology Across Canada

• Dr. Donaldson MacLeod
• Manager Highways and Bridges
• PWGSC
• P.Eng.

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Outline

• Introduction
• Bituminous Surface Treatments (BSTs)
• BST Distresses
• BST Performance
• Maintenance
• Summary and Conclusions

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BST CLASSES

• Class 1 - on unimproved subgrade
• Class 2 - nominal (100-150 mm) of base course
• Class 3 - full pavement structures with base and
  subbase, BST surface instead of asphalt concrete
  surface

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Class 1 BST
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Class 2 BST
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Class 3 BST
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Inventory PWGSC Yukon
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Comparison of Two Systems
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Why are Low Volume NORTHERN Roads Different?

• They tend
• To cover long distances in isolated areas where
  drivers want to travel at high speeds.
• To have low overall traffic volumes but with
  significant amounts of truck traffic related to
  primary resource industries.
• To be problematic for construction and
  maintenance due to isolation and severe climatic
  conditions.
• To cover difficult terrain conditions, muskegs,
  permafrost and mountainous topography.

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Bituminous Surface Treatments

• Thin surfaces.
• Also known as chip seals.
• Originally used as a dust palliative.
• Widely used in Northern Canada.

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Why BST

• 25 the cost of conventional pavement.
• If there is settlement (muskeg or permafrost, in
  particular) in the short term and there has to be
  a major patch or rehabilitation whether it is a
  pavement or BST, the BST was the cheaper surface.
• Mobilization of BST crew for patching less of a
  problem than mobilizing a hot-mix plant.

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Differences Between Pavements and BSTs

• BST performance changes rapidly often within a
  year.
• No structural strength.
• Asset preservation is less of a issue.
• Maintenance is an absolute must.

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BST is not without its problems too
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Distortions
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Raveling
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Bleeding
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Rutting
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Cracking
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Joints
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Subgrade failures
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Potholes
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Intervention Levels

• Class 1 BCI 60
• Class 2 BCI 60
• Class 3 BCI 65
• Higher level for Class 3 indicative of higher
  level of service expected by the highway user for
  Class 3 highways

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Estimated BST Life - years
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How do BSTs Fail

• 1. Structural Failure (Class 1 and 2).
• 2. Permafrost related (specific sections).
• 3.Construction Related (potholes on joints).
• 4. Rough ride due to a combination of factors.
• 5. Rutting.
• Vast majority are 4 and 5 which require rip-up,
  reshape and re-BST.

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Summary and Conclusions

• BSTs provide an alternative to pavement on low
  volume northern roads
• BSTs are particularly suited even at higher
  traffic volumes when distortions are anticipated
  from permafrost or muskeg zones
• Maintenance is critical factor in the success of
  BSTs
• Rehabilitation is often rip-up and reshape rather
  than an overlay.

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QUESTIONS ?
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Cumulative Distribution Field Recommendations BST
Class 1 2
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Cumulative Distribution Field Recommendations BST
Class 3