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

1. The Future is Thin:Surface 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

2. 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

3. Afternoon Quiz Most skids are caused by: • Worn tires, • Polished pavement surface, • Excessive speed, • Wet pavement surface

4. “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]

5. 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

6. 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

7. 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”

13. Minimum BPN of 45 recommended (55 for critical areas)

14. 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

15. Microsurfacing

16. After Microsurfacing

17. Microsurfacing for Edge and Centreline Alligator Crack Repair

18. Microsurfacing for Edge and Centreline Alligator Crack Repair

19. 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

20. 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

21. Microsurfacing over CIP

22. Microsurfacing over CIP January 2006

23. Microsurfacing over CIP January 2006

24. Microsurfacing over CIP October 2006

25. Microsurfacing over CIP October 2006 October 2006

26. 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

29. 4.75mm Superpave – Tack and Overlay

30. 4.75mm Superpave – Tack and Overlay

31. 25mm Superpave 4.75 75mm Cold Recycled Mix 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

32. 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