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: Steve.Goodman@ottawa.ca