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 Quiz Most 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) LocationAverage BPN (corrected to 20C) Mean Texture Depth (mm) 50m south of Radius Centre Centre of Radius m North of Radius Centre CommentsBPN very lowTexture 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

LocationAverage BPN (corrected to 20C) Mean Texture Depth (mm) 50m south of Radius Centre Centre of Radius m North of Radius Centre CommentsBPN good Texture Depth OK but reduced slightly in some areas After Microsurfacing

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

January 2006

Microsurfacing over CIP January 2006

Microsurfacing over CIP October 2006

Microsurfacing over CIP October 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 over CRM Will 25mm of HMA perform better than microsurfacing over recycled base? Parkway Road project 600m1400m Existing Asphalt Base 75mm Cold Recycled Mix 25mm Superpave 4.75 Solid Granular StructureWeak Sandy Silt Structure

Thank You Any Questions, contact: Steve Goodman, M.Eng., P.Eng. Senior Pavement Engineer City of Ottawa Tel: , Ext