the future is thin: surface mix experience and performance in the city of ottawa steve goodman,...
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The Future is Thin:Surface Mix Experience and Performance in the City of
Ottawa
Steve Goodman, M.Eng., P.Eng.Senior Pavement Engineer, City of Ottawa
November 5, 2006
Canadian User/Producer Group for Asphalt
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
Afternoon QuizMost skids are caused by:
a) Worn tires,
b) Polished pavement surface,
c) Excessive speed,
d) Wet pavement surface
“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]
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
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
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”
Minimum BPN of 45 recommended (55 for critical areas)
Location Average BPN
(corrected to 20C)
Mean Texture Depth (mm)
50m south of Radius Centre
32 0.41
Centre of Radius 33 0.33
35m North of Radius Centre
32 0.42
Comments BPN very low Texture Depth OK
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
Microsurfacing
Location Average BPN
(corrected to 20C)
Mean Texture Depth (mm)
50m south of Radius Centre
6332
0.220.41
Centre of Radius6633
0.330.33
35m North of Radius Centre
5732
0.420.42
Comments BPN goodTexture Depth OK but
reduced slightly in some areas
After Microsurfacing
Microsurfacing for Edge and Centreline Alligator Crack Repair
Microsurfacing for Edge and Centreline Alligator Crack Repair
Microsurfacing for Edge and Centreline Alligator Crack Repair
Don’t go too far from edge!
Differential friction scenario
Should cover entire surface or stay out of wheelpaths
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
Microsurfacing over CIP
Microsurfacing over CIP
January 2006
Microsurfacing over CIP
January 2006
Microsurfacing over CIP
October 2006
Microsurfacing over CIP
October 2006October 2006
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? It’s 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
4.75mm Superpave – Tack and Overlay
4.75mm Superpave – Tack and Overlay
4.75mm Superpave over CRM Will 25mm of HMA perform better than
microsurfacing over recycled base? Parkway Road project
600m 1400m
Existing Asphalt
Base
75mm Cold Recycled Mix25mm Superpave 4.75
Solid Granular Structure Weak Sandy Silt Structure
Thank You
Any Questions, contact:
Steve Goodman, M.Eng., P.Eng.
Senior Pavement Engineer
City of Ottawa
Tel: 613-580-2424, Ext. 28583
Email: [email protected]