The Future is Thin: Surface Mix Experience and Performance in the City of Ottawa

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The Future is ThinSurface Mix Experience and
Performance in the City of Ottawa
Canadian User/Producer Group for Asphalt

• Steve Goodman, M.Eng., P.Eng.
• Senior Pavement Engineer, City of Ottawa
• November 5, 2006

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Topics of Discussion

• Microsurfacing
• Safety Improvement Program
• Surface over Cold-In-Place Recycling
• Edge and Centreline Alligator Cracking
• 4.75mm Superpave and SMA
• Tack and overlay
• Surface over CIP/Expanded Asphalt/CRM
• Urban Shave and Pave

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Afternoon Quiz

• Most skids are caused by
• Worn tires,
• Polished pavement surface,
• Excessive speed,
• Wet pavement surface

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In simplistic terms, it may be said that most
automobile accidents involving skidding are due
to the unfortunate, but common, combination of a
wet pavement and an attempt by the driver to
perform a manoeuvre such as braking, cornering or
accelerating at a speed too high for the
conditions Dearinger and Hutchinson 1970
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Why Not an Issue at Municipal Level?

• Lack of consistent standards
• Friction data not collected routinely as part of
  management system
• Reactive wait until after accidents occur
• Different branches deal with highway maintenance
  and safety
• New Municipal Act (2001)
• Section 44 Duty to Repair
• Ontario Reg 239/02 Minimum Maintenance
  Standards
• Treating icy roadways

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Practicalities of Urban Friction Measurement

• Erratic traffic flow and speed
• Intersections
• Compact geometric design
• High capital, operating and maintenance cost for
  high speed friction devices
• High cost of traffic control
• Staff safety

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Safety Improvement Program

• Accident data analyzed by Traffic and Parking
  Operations
• Countermeasures recommended for high collision
  areas such as geometric modification, speed
  reduction and/or high friction asphalt

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• Minimum BPN of 45 recommended (55 for critical
  areas)

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Restoring Pavement Friction

• Past practice has been to remove and replace with
  high friction asphalt
• particularly if pavement otherwise good
• New tools allow less expensive correction
• Thin surfacings (10 to 25 mm)
• Installed rapidly
• May not require adjustment of appurtenances
• Cost effective and prolong life of pavement
• Precision milling
• Removal of 15 mm of surface to expose new
  aggregate

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Microsurfacing
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After Microsurfacing
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Microsurfacing for Edge and Centreline Alligator
Crack Repair
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Microsurfacing for Edge and Centreline Alligator
Crack Repair
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Microsurfacing for Edge and Centreline Alligator
Crack Repair

• Dont go too far from edge!
• Differential friction scenario
• Should cover entire surface or stay out of
  wheelpaths

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Microsurfacing over CIP

• Low volume truck route with severely depressed
  transverse cracking
• CIP to address cracking but wanted to reduce cost
  of overlay
• Decided to try microsurfacing directly over
  (tacked) CIP
• Profile control of CIP train critical to ensure
  smooth ride

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Microsurfacing over CIP
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Microsurfacing over CIP
January 2006
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Microsurfacing over CIP
January 2006
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Microsurfacing over CIP
October 2006
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Microsurfacing over CIP
October 2006
October 2006
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4.75mm Superpave and SMA

• Many roads have good grade/profile and display
  only raveling and moderate cracking
• Why mill and replace with 50mm of HMA?
• Its going to crack anyway!
• Thin HMA layers can restore surface properties at
  lower cost
• 25mm layer thickness
• Use existing aggregate products
• No shouldering required
• Increased friction

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4.75mm Superpave Tack and Overlay
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4.75mm Superpave Tack and Overlay
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4.75mm Superpave over CRM

• Will 25mm of HMA perform better than
  microsurfacing over recycled base?
• Parkway Road project

600m
1400m
Existing Asphalt
Base
Solid Granular Structure
Weak Sandy Silt Structure
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Thank You
Any Questions, contact Steve Goodman, M.Eng.,
P.Eng. Senior Pavement Engineer City of
Ottawa Tel [phone], Ext. 28583 Email
Steve.Goodman_at_ottawa.ca