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Chapter 10 Thin Maintenance Overlays

Chapter 10 Thin Maintenance Overlays. From… Maintenance Technical Advisory Guide (MTAG). Manager’s Overview. From… Maintenance Technical Advisory Guide (MTAG). Introduction to Thin Maintenance Overlays. What are thin maintenance overlays ? Why use thin maintenance overlays ?

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Chapter 10 Thin Maintenance Overlays

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  1. Chapter 10Thin Maintenance Overlays From… Maintenance Technical Advisory Guide (MTAG)

  2. Manager’s Overview From… Maintenance Technical Advisory Guide (MTAG)

  3. Introduction to Thin Maintenance Overlays • What are thin maintenance overlays ? • Why use thin maintenance overlays ? • When to use thin maintenance overlays ? • Where to use thin maintenance overlays ?

  4. What Are Thin Maintenance Overlays? • Defined as thin treatment using a hot mix system • Non-structural layer • Applied as a maintenance treatment (corrective or preventive) • Thickness: • Caltrans: 1.2 in (30 mm) • Nationally: less than 1½ in (37.5mm)

  5. What Are Thin Maintenance Overlays?

  6. Why Use Thin Overlays? • Restores the surface conditions (smoothness, noise, and skid) • Improves the appearance of the roadway • Extends the life of the pavement

  7. I-77 Columbia, SC Dry, Oxidized, Slightly Rutted Pavement, 60,000 ADT When to Use? • Structurally sound pavement • Rut depth < 1/2” • Minor cracking cracking • Minor to moderate bleeding • Raveled surface

  8. High Severity Block Cracking When NOT to use!Poor Candidates High Severity Alligator Cracking Rutting >1/2” High Severity “D” Cracking

  9. Where to Use? • As a surface treatment over asphalt concrete pavements and on portland cement concrete pavements • Over structurally sound pavements • Oxidation Reduction: Successfully used as a protection layer to prevent asphalt aging in the main structural layers. • Mitigation of Cracking: Thin Overlays can be used to mitigate cracking. Dense-graded overlays required a SAMI or fabric interlayer. • Skid Resistance: Use in sections with poor frictional properties. A skid test should be conducted to determine the existing coefficient of friction of the pavement surface (CT 342).

  10. Where to Use? Open- and Gap-Graded Overlays • Wet Weather Accidents: Use in sections with high frequency of wet weather accidents or when recommended to minimize wet weather accident occurrences.

  11. End OverviewBegin Project Design, Materials & Specifications

  12. Module 10-1 Design, Materials & Specifications From… Maintenance Technical Advisory Guide (MTAG)

  13. Topics to be covered • Project Selection • Distress and Other Application Considerations • Performance • Cost • Design Considerations • Mobilization • Typical Materials Items • Quantity Calculations • Production Rates • Roadway Widths • Roadway Geometry • Traffic Control • Miscellaneous Items • Sample Project • Materials and Specifications (including SSP’s) • Summary

  14. Project Selection • Distress and Application Considerations • Performance • Traffic loading • Existing pavement conditions • Environment

  15. Factors to Consider When Choosing a Maintenance Treatment • Will the treatment address the distresses present? (i.e., Will it work?) • Can the required preparation for the treatment be carried out? • Is the treatment affordable and cost effective? • Will the treatment be performed before the situation being addressed changes?

  16. Three Basic Steps In The Selection Process • Assess the existing conditions. • Determine the feasible treatment options. • Analyze and compare the feasible options with each other.

  17. Initial Site Assessment – Distress Identification • Types of Distresses and Definitions • Definitions from Caltrans Pavement condition survey manual or the FHWA“DISTRESS IDENTIFICATION MANUAL for the Long-Term Pavement Performance Program” PUBLICATION NO. FHWA-RD-03-031 JUNE 2003

  18. Caltrans Maintenance Treatment Matrix MTAG Chapter 3 Figure 3-3

  19. Distress Types and Levels that can be addressed by Thin Overlays • Perform Visual Site Inspection. • Identify types, quantity and levels of distress • For example on a 2 lane highway (Route xxx from PM 0.0 to PM 10.8)with <30,000 ADT: • 10% Alligator B Cracking • Minor Transverse Cracking • An area of isolated base failure 1000 ft x 4 ft • Heavy raveling and oxidation • Rutting < ½”

  20. DISTRESS AND APPLICATION CONSIDERATIONS TMO is a viable application for treating structurally sound, worn pavements

  21. Other Application Considerations • Traffic Control • Safety • Night Work • Returns/Hand Work • Turn Pockets • Milling • Job Quantities • Prep Work Required • Quick return to traffic- Reduced Work Zone Time (Workers’ Safety) • Noise Reduction- Open/Gap Graded Mix • Night Work- Min Temp 45º F (More working days) • Reduced Backspray- Open/Gap Graded Mix • High Volume Roadways- Faster Paving Process (Get In- Get Out)

  22. Performance Expectations • Life and Costing • Improved skid resistance • Reduced traffic noise (Open-Graded) • Spray Reduction (Open Graded) • Improved ride quality (Smoothness) • Preventive Maintenance Activities Recommended

  23. Application Cost and Life Cycle Data (from Handout) • Expected Life and Cost Data from Strategy Selection Group

  24. Improved Ride Quality -(Smoothness) • Minor ruts and depressions can be filled with Thin Maintenance Overlays to improve ride quality

  25. Future Maintenance Activities Recommended • Crack Sealing • Patching • Re-Striping

  26. Design Considerations • Mobilization • Typical Materials Items • Quantity Calculations • Production Rates • Roadway Widths • Roadway Geometry • Traffic Control • Miscellaneous Items • Sample Project

  27. Mobilization • Typical Asphalt Paving • Rubberized Asphalt Binder will require additional equipment for its production • On-site Staging Required – • Area for Tanker and Distributor exchange

  28. Typical Materials Items • Asphalt Concrete Tons • Use maximum lbs/SY for selected aggregate size • 3/8” PMA OG or GG (9.5mm) = 85 lbs/SY • ½” PMA OG or GG (12.5mm) = 100 lbs/SY • 3/8” AR OG of GG (9.5mm) = 85 lbs/SY • Emulsion Tons • Use 0.2 gallons/SY for emulsion application

  29. Quantity Calculations • Lane Mile (LM) (Centerline to Fog Line) • 5280 ft x 12 ft = 63,360 SF = 7040 SY • When calculating quantities, application should extend beyond fog line • Shoulder quantities need to be calculated independently • Shoulder application may vary from mainline application • Typical Shoulder calculation: • 3 ft wide x 5280 ft length = 15,840 SF = 1760 SY • Typical 2 Lane Roadway Calculation • (2 x 7040) + (2 x 1760) = 17,600 SY

  30. Quantity Calculations • When calculating quantities for each application use highest application rate per SY for estimate purposes • Example: • Specification 37-1.06 Spreading of screenings for chip seal application. Range is 12-20 lb per SY. Use 20 lb for estimating quantities

  31. Production Rates andPaving Days • Production Rate • Mainline Paving - 125 tons per hour • Returns/Turnpockets - 40-50 tons per hour • (# of Paving Days) • Minimum 5 days to make cost effective

  32. Roadway Geometry and Widths • Urban • Milling • contour edge grind required to match curb and gutter and existing pavement • Drainage • Minimal water trapped against curb due to emulsion filling void structure and thin lift • Less water intrusion to pavement interface due to emulsion membrane • Rural • Cross-slopes • Shoulder • Generally best used for Travel Lane with 1 foot beyond fog line • For Grade differential greater than 2% from Mainline to Shoulder, the shoulder must be paved separately in order to maintain the grade • Edge drop-off will be less than ¾” (consider bicycle traffic material can not be feather down lower then top size agg.) • Varying Width • Typical Paving machine width 8-14 feet variable

  33. Traffic Control • Typical release to traffic 10-20 minutes behind paver • Multi-lane highways, consider moving lane closure • Two-lane roadways ½ to ¾ mile closure • Thinner lift allows faster production

  34. Miscellaneous Items • Edge grinding • Crack seal hot applied min one month prior • Patching - hot mix only, cold mix continues to rut • Utilities – Adjustments most likely necessary • Loops may need to be replaced if doing edge grinding • Dig Outs – Prior to paving • Signing and Striping

  35. Material Specifications • Binders • PG Grade spec • Polymer modified asphalt spec • Rubberized Asphalt spec • Aggregates • Gradations • Physical Properties • Mix Design • Asphalt Emulsion • Application • Specifications

  36. PG Grade Specs

  37. Polymer Modified Binders Maintenance Technical Advisory Guide Chapter 8 Page 2

  38. Polymer Modified Binder Testing Maintenance Technical Advisory Guide Chapter 8 Page 3

  39. Rubberized Binders • A paving asphalt blended with a crumb rubber modifier • Shall conform to : • SSP 39-400 (Type G) • SSP 39-403 (Type D-MD) • SSP 39-405 (Type G-MB) • SSP 39-450 (Type D) • SSP 39-480 (Type O)

  40. Aggregate Gradations with PMA • Aggregate Gradations • Dense Graded: • ¾” Maximum, Coarse and Medium • ½” Maximum, Coarse and Medium • 3/8” Maximum • No. 4 Maximum • Open Graded • ½” Maximum • 3/8” Maximum

  41. Aggregate Gradations with PMA • Aggregate Gradations • Gap Graded: • ¾” Maximum • ½” Maximum

  42. ¾” Gradation Table for Gap Graded Overlays

  43. Aggregate Physical Properties Polymer Modified Asphalt

  44. Aggregate for use with Rubberized Asphalt Concrete • The aggregate for rubberized asphalt concrete (Type O) shall conform to the 9.5 mm maximum grading conforming to the provisions in Section 39‑2.02, "Aggregate," of the Standard Specifications. • The aggregate for rubberized asphalt concrete (Type O) shall be lime treated in conformance with the specifications.

  45. Gap Graded AR

  46. Aggregate Physical Properties For Rubberized Gap Graded Mix • AGGREGATE • The aggregate for Type G rubberized asphalt concrete shall conform to the following grading and shall meet the quality provisions specified for Type A asphalt concrete in Section 39‑2.02, "Aggregate," of the Standard Specifications, except as follows: • A. California Test 211, Los Angeles Rattler loss at 500 revolutions shall be 40 percent maximum. • B.California Test 205, Section D, definition of a crushed particle is revised as follows: "A particle having 2 or more fresh mechanically fractured faces shall be considered a crushed particle." • C.The swell and moisture vapor susceptibility requirements shall not apply. • The symbol "X" in the following table is the gradation which the Contractor proposes to furnish for the specific sieve.

  47. Open Graded Aggregate Gradations with AR or PMA Ref: Caltrans Standard Specifications 2006 Section 39 Page 282

  48. Open Graded Aggregate Gradations with AR or PMA Ref: Caltrans Standard Specifications 2006 Section 39 Page 282

  49. Mix Design for Polymer Modified HMA • The performance of a bonded wearing course depends on the quality of the materials and how they interact during application, rolling and after opening to traffic. The amount of polymer modified asphalt binder to be mixed with the aggregate for gap-graded polymer modified asphalt concrete shall be determined by the Contractor using Asphalt Institute MS 2 Table 6.1.

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