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

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Presentation on theme: "From… Maintenance Technical Advisory Guide (MTAG) Chapter 6 Dowel Bar Retrofit."— Presentation transcript:

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

2 Load Transfer Restoration Through Dowel Bar Retrofit Load Transfer Restoration Through Dowel Bar Retrofit

3 Learning Objectives 1.List benefits of load transfer restoration 2.Describe recommended materials and mixtures 3.Describe recommended construction procedures 4.List important quality control activities 5.Describe potential construction and performance problems 6.Identify associated solutions

4 3-5.4 II ntroduction MM aterial selection CC onstruction QQ uality control TT roubleshooting Presentation Outline

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

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

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 Transfer Pumping

9 Results of Poor Load Transfer Transverse Joint Faulting

10 Results of Poor Load Transfer Corner Breaks

11 Results of Poor Load Transfer Deteriorated Mid-Panel Cracking

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

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

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

15 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 Good Candidate Projects

16 Typical Item Codes Item CodeDescription Prepare water pollution control program Prepare storm water pollution prevention plan Water pollution control Temporary concrete washout (portable) Construction area signs Traffic control system Portable changeable message sign Dowel bar retrofit Repair spalled joints Seal transverse joint Grind existing concrete pavement

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

18 II ntroduction MM aterial selection CC onstruction QQ uality control TT roubleshooting Presentation Outline

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 Devices Dowel Bars

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

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

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

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

25 II ntroduction MM aterial selection CC onstruction QQ uality control TT roubleshooting Presentation Outline

26 Construction 1.Slot creation 2.Slot preparation 3.Dowel bar placement 4.Repair material placement 5.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 Creation Slot Cutting Machine

29 Slot Creation Close-Up of Sawblades

30 Slot Creation Slot Sawcuts

31 Slot Creation Slot Cutting with Milling Machine

32 Slot Creation Milled Slots

33 Slot Preparation Material Removal

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36 Slot Preparation Sandblasting Slots

37 Slot Preparation Cleaning Slots after Sandblasting

38 Slot Preparation Caulking of the Joint or Crack

39 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 Dowel Bar Placement

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42 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 Repair Material Placement

43 Repair Material Placement Backfilling

44 Repair Material Placement Consolidation and Finishing

45 Review of Process

46 Diamond Grinding after LTR

47 Retrofitted Dowel Project

48 Retrofitted Dowels at Cracks

49 II ntroduction MM aterial selection CC onstruction QQ uality control TT roubleshooting Presentation Outline

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

51 Quality Control Class Exercise Break into three groups Preliminary responsibilities Equipment inspection, weather requirements, and traffic control Construction inspection considerations Identify importance of each item Use Reference Manual and your experience

52 II ntroduction MM aterial selection CC onstruction QQ uality control TT roubleshooting Presentation Outline

53 Project Checklist Preliminary Responsibilities Project Review Document Review Materials Checks Cementing grout Dowel bars Joint/crack materials Other materials General

54 Project Checklist Equipment Inspections Slot Cutting Equipment Slot Cleaning and Preparation Mixing and Testing Equipment Other Equipment Others Weather Requirements Traffic Control

55 Project Checklist Project Inspection Responsibilities Slot Cutting and Removal Slot Cleaning and Preparation Placement of Dowel Bars Mixing, Placing, Finishing, and Curing Backfill Material Cleanup Diamond Grinding Resealing Joints and Cracks

56 Troubleshooting Identify Problem Determine Cause Identify Solution Construction and performance problems Approach:

57 Troubleshooting What is wrong here? Misaligned joint forming material

58 Sawcuts are not cut parallel to the centerline Troubleshooting Construction Problems Solution? Problem

59 Dowel bar slots are cut too shallow Troubleshooting Construction Problems Solution? Problem

60 Dowel bar slots are cut too deep Troubleshooting Construction Problems Solution? Problem

61 Concrete fin is not easily removed Troubleshooting Construction Problems Solution? Problem

62 Jackhammer punching through slot Troubleshooting Construction Problems Solution? Problem

63 Cracking of in place patch material Troubleshooting Performance Problems Causes? Problem

64 Patch material pops out Troubleshooting Performance Problems Causes? Problem

65 Wearing off of patch material Troubleshooting Performance Problems Causes? Problem

66 Troubleshooting Guide – Causes and Solutions Slots are not parallel to pavement edge or longitudinal joint Dowel bar slots are too shallow Dowel bar slots are too deep Concrete fin not easily removed Jackhammer punches through bottom of slot Epoxy coating on dowel bar is chipped or missing

67 Troubleshooting Guide – Causes and Solutions Joint/crack sealant does not fully seal joint/crack along entire length expose in slot Joint/crack sealant extends more than 0.5 in. (13 mm) into slot Backfill material cracks in place Backfill material pops out of slot Backfill material wears faster than adjacent pavement

68  Introduction  Material selection  Construction  Quality control  Troubleshooting Presentation Outline

69 Learning Objectives 1.List benefits of load transfer restoration 2.Describe recommended materials and mixtures 3.Describe recommended construction procedures 4.List important quality control activities 5.Describe potential construction and performance problems 6.Identify associated solutions


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