Chapter 6 Dowel Bar Retrofit - California Department of ... · PDF filePresentation Outline...

Chapter 6Dowel Bar Retrofit

From… Maintenance TechnicalAdvisory Guide (MTAG)

Load Transfer RestorationThrough Dowel Bar RetrofitLoad Transfer RestorationThrough Dowel Bar Retrofit

Learning Objectives

1. List benefits of load transfer restoration2. Describe recommended materials and

mixtures3. Describe recommended construction

procedures4. List important quality control activities5. Describe potential construction and

performance problems6. Identify associated solutions

Chapter 6 – Dowel Bar Retrofit

Presentation Outline

IntroductionMaterial selectionConstructionQuality controlTroubleshooting

Chapter 6 – Dowel Bar Retrofit 3-5.4

Load Transfer

Mechanism of transferring wheel loads across a joint or crackAccomplished through:• Mechanical devices (dowel bars)• Aggregate interlock• Foundation support

Load transfer efficiency (LTE)

Definition


Load Transfer (continued)

Wheel Load

Slab 2Slab 1

0% Load Transfer

Direction of Traffic

Direction of Traffic

Wheel Load

Slab 2Slab 1

100% Load Transfer

Causes of Poor Load Transfer

Absence of load transfer devicesFailed load transfer deviceExcessive crack/joint openingPoor pavement drainageEroded base


Results of Poor Load TransferPumping

Results of Poor Load TransferTransverse Joint Faulting

Results of Poor Load TransferCorner Breaks

Results of Poor Load TransferDeteriorated Mid-Panel Cracking

Load Transfer Restoration

DefinitionInstallation of mechanical devices in an existing pavement to restore load transferSuitable for transverse joints or cracks


2.5 in min.6 in max.Retrofitted

Dowel Bar Temporary joint insert for sealant

reservoir

End view

Dowel bar cap(at least one side) 0.25 in expansion

As required

Full depth joint forming medium & dowel support

Side view

18 in + 0.2 in

TT/2

*18 in max. 1.5 in

3-5.13

Load Transfer RestorationBenefits

Reduced probability of pumping, faulting, and corner breaksImproved long-term rideabilityIncreased service life


Good Candidate Projects

Relatively good condition but with:• Poor load transfer• Faulting between 0.125 and 0.5 in• <10% slabs with multiple cracks

Medium to heavy truck traffic


Examplel Item CodesItem Code Description

074017 Prepare water pollution control program074019 Prepare storm water pollution prevention plan074020 Water pollution control074042 Temporary concrete washout (portable)120090 Construction area signs120100 Traffic control system128650 Portable changeable message sign406100 Dowel bar retrofit413111 Repair spalled joints414101 Seal transverse joint420201 Grind existing concrete pavement

http://i80.dot.ca.gov/hq/esc/oe/awards/#item_code

http://i80.dot.ca.gov/hq/esc/oe/awards/#item_code

Module 6-1

Design, Materials & Specifications


3-5.18




Material Selection

Load transfer devices• Retrofitted dowel bars • Other devices not recommended

Repair (filler) materials• Portland cement concrete (PCC)• Rapid strength materials• Polymer concretes• Epoxy-resin adhesives


Load-Transfer DevicesDowel Bars

Dowel Design and LayoutExisting longitudinal joint Existing longitudinal joint

18 in

12 ft

18 in

18 in

3 dowels @12 in centers

Truck Lane

18 in

4 dowels @12 in centers

Truck Lane

1.5-india. dowels

Existing Shoulder Existing Shoulder

Repair Material Requirements

Little or no shrinkageGood ultimate strengthThermal compatibilityFreeze-thaw durabilityGood bond to existing concreteNon shrink


Selecting Repair Materials

Partial-depth repair materials work wellRequired time until opening to trafficLaboratory testing


Module 6-2

Construction and Inspection


3-5.25




Construction

1. Slot construction2. Slot preparation3. Dowel bar placement4. Repair material placement5. Material consolidation and finishing


Slot Construction

Parallel to longitudinal jointsDiamond saw cutters vs. modified milling machinesSlot dimensions• Length: 3 ft on surface• Width: 2.5 and 4 in• Depth: 0.5 in below dowel (mid-panel depth +

half diameter of dowel + 0.5 inch)


Slot ConstructionSlot Cutting Machine

Slot ConstructionClose-Up of SawbladesSlot ConstructionClose-Up of Sawblades

Slot ConstructionSlot Cutting with Milling Machine

Slot ConstructionMilled SlotsSlot ConstructionMilled Slots

Slot PreparationMaterial Removal

Slot PreparationSandblasting Slots

Slot PreparationCleaning Slots after Sandblasting

Slot PreparationCaulking of the Joint or Crack

Dowel Bar Placement

Apply bondbreaker to dowelsAttach expansion capsPlace dowel on chair at slab mid-depthFiller board placed at mid-point of dowel bar to maintain jointProper alignment is critical


Dowel Bar Placement

Repair Material Placement

Mix material in small quantitiesGenerally 3/8 in top size aggregateTotally encase dowel barConsolidate with small 1 in pencil vibratorApply curing compound


Repair Material PlacementBackfilling

Repair Material PlacementConsolidation and Finishing

Diamond Grinding after LTR

Retrofitted Dowel Project

Retrofitted Dowels at Cracks

3-5.47




Quality Control

Preliminary responsibilitiesInspection of equipmentWeather requirementsTraffic controlConstruction inspection


3-5.49




Project Checklist

Preliminary Responsibilities • Project Review • Document Review

Materials Checks • Cementing grout • Dowel bars • Joint/crack materials • Other materials • General


Project Checklist

Equipment Inspections • Slot Cutting Equipment • Slot Cleaning and Preparation • Mixing and Testing Equipment• Other Equipment

Others • Weather Requirements • Traffic Control


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


Troubleshooting

Construction and performance problemsApproach:

IdentifyProblem

DetermineCause

IdentifySolution


TroubleshootingWhat is wrong here?

Misaligned joint forming materialMisaligned joint forming material


TroubleshootingConstruction Problems

Sawcuts are not cut parallel to the longitudinal joints

Solution?

Problem



Dowel bar slots are cut too shallow

Solution?

Problem



Dowel bar slots are cut too deep

Solution?

Problem



Concrete fin is not easily removed

Solution?

Problem



Jackhammer punching through slot

Solution?

Problem


TroubleshootingPerformance Problems

Cracking of in-place patch material

Causes?

Problem



Patch material pops out

Causes?

Problem



Wearing off of patch material

Causes?

Problem


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


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. into slot Backfill material cracks in place Backfill material pops out of slot Backfill material wears faster than adjacent pavement


3-5.65




Learning Objectives

1. List benefits of load transfer restoration2. Describe recommended materials and

mixtures3. Describe recommended construction

procedures4. List important quality control activities5. Describe potential construction and

performance problems6. Identify associated solutions


Thank You

Questions?


Chapter 6 Dowel Bar Retrofit - California Department of ... · PDF filePresentation Outline...

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