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Chapter 6 Dowel Bar Retrofit

Chapter 6 Dowel Bar Retrofit. From… Maintenance Technical Advisory Guide (MTAG). Load Transfer Restoration Through Dowel Bar Retrofit. Learning Objectives. List benefits of load transfer restoration Describe recommended materials and mixtures Describe recommended construction procedures

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Chapter 6 Dowel Bar Retrofit

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  1. Chapter 6Dowel Bar Retrofit From… Maintenance Technical Advisory Guide (MTAG)

  2. Load Transfer Restoration Through Dowel Bar Retrofit

  3. Learning Objectives • List benefits of load transfer restoration • Describe recommended materials and mixtures • Describe recommended construction procedures • List important quality control activities • Describe potential construction and performance problems • Identify associated solutions

  4. Presentation Outline • Introduction • Material selection • Construction • Quality control • Troubleshooting 3-5.4

  5. Load Transfer • Definition Mechanism of transferring wheel loads across a joint or crack • Accomplished through: • Mechanical devices (dowel bars) • Aggregate interlock • Foundation support • Load transfer efficiency (LTE)

  6. 100% Load Transfer Wheel Load Direction of Traffic Approach Slab Leave Slab Load Transfer (continued) 0% Load Transfer Wheel Load Direction of Traffic Approach Slab Leave Slab

  7. Causes of Poor Load Transfer • Absence of load transfer devices • Failed load transfer device • Excessive crack/joint opening • Poor pavement drainage • Erodible base

  8. Results of Poor Load TransferPumping

  9. Results of Poor Load TransferTransverse Joint Faulting

  10. Results of Poor Load TransferCorner Breaks

  11. Results of Poor Load TransferDeteriorated Mid-Panel Cracking

  12. Load Transfer Restoration • Definition Installation of mechanical devices in an existing pavement to restore load transfer • Suitable for transverse joints or cracks

  13. 65 mm (2.5 in) min. 100 mm (6 in) max. Retrofitted Dowel Bar Temporary joint insert for sealant reservoir End view As required Mill or Saw cut 350* mm + 5 mm (14 in + 0.2 in) Full depth joint forming medium & dowel support T/2 T Dowel bar cap (at least one side) 6 mm (0.25 in) expansion 40 mm (1.5 in) *460 mm (18 in) max. Side view 3-5.13

  14. Load Transfer RestorationBenefits • Reduced probability of pumping, faulting, and corner breaks • Improved long-term rideability • Increased service life

  15. Good Candidate Projects • Relatively good condition but with: • Poor load transfer • Faulting between 3 and 13 mm (0.125 and 0.5 in) • <10% slabs with multiple cracks • Pavements expecting overlays • Medium to heavy truck traffic

  16. Typical Item Codes http://i80.dot.ca.gov/hq/esc/oe/awards/#item_code

  17. Module 6-1 Design, Materials & Specifications From… Maintenance Technical Advisory Guide (MTAG)

  18. Presentation Outline  • Introduction • Material selection • Construction • Quality control • Troubleshooting 3-5.18

  19. Material Selection • Load transfer devices • Retrofitted dowel bars • Other devices • Repair (filler) materials • Portland cement concrete (PCC) • Rapid-setting proprietary materials • Polymer concretes • Epoxy-resin adhesives

  20. Load-Transfer DevicesDowel Bars

  21. Dowel Design and Layout 457 mm (18 in) 610 mm (24 in) 38-mm (1.5-in) dia. dowels 3 to 5 dowels @305 mm (12 in) 3 to 5 dowels @305 mm (12 in) Truck Lane Truck Lane 3.7 m (12 ft) 305 mm (12 in) 457 mm (18 in) AC Shoulder PCC Shoulder

  22. Repair Material Requirements • Little or no shrinkage • Good ultimate strength • Thermal compatibility • Freeze-thaw durability • Good bond to existing concrete

  23. Selecting Repair Materials • Partial-depth repair materials work well • Required time until opening to traffic • Laboratory testing

  24. Module 6-2 Construction and Inspection From… Maintenance Technical Advisory Guide (MTAG)

  25. Presentation Outline  • Introduction • Material selection • Construction • Quality control • Troubleshooting  3-5.25

  26. Construction • Slot creation • Slot preparation • Dowel bar placement • Repair material placement • Material consolidation and finishing

  27. Slot Creation • Parallel to centerline • Diamond saw cutters vs. modified milling machines • Slot dimensions • Length: 1 m (3 ft) on surface • Width:65 and 100 mm (2.5 and 4 in) • Depth:13 mm (0.5 in) below dowel

  28. Slot CreationSlot Cutting Machine

  29. Slot CreationClose-Up of Sawblades

  30. Slot CreationSlot Sawcuts

  31. Slot CreationSlot Cutting with Milling Machine

  32. Slot CreationMilled Slots

  33. Slot PreparationMaterial Removal

  34. Slot PreparationMaterial Removal

  35. Slot PreparationMaterial Removal

  36. Slot PreparationSandblasting Slots

  37. Slot PreparationCleaning Slots after Sandblasting

  38. Slot PreparationCaulking of the Joint or Crack

  39. Dowel Bar Placement • Apply bondbreaker to dowels • Attach expansion caps • Place dowel on chair at slab mid-depth • Filler board placed at mid-point of dowel bar to maintain joint • Proper alignment is critical

  40. Dowel Bar Placement

  41. Dowel Bar Placement

  42. Repair Material Placement • Mix material in small quantities • Generally 10 mm (3/8 in) top size aggregate • Totally encase dowel bar • Consolidate with small 25 mm (1 in) spud vibrator • Apply curing compound

  43. Repair Material PlacementBackfilling

  44. Repair Material PlacementConsolidation and Finishing

  45. Review of Process

  46. Diamond Grinding after LTR

  47. Retrofitted Dowel Project

  48. Retrofitted Dowels at Cracks

  49. Presentation Outline  • Introduction • Material selection • Construction • Quality control • Troubleshooting   3-5.49

  50. Quality Control • Preliminary responsibilities • Inspection of equipment • Weather requirements • Traffic control • Construction inspection

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