Long Joint Presentation -- Short Version
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Transcript of Long Joint Presentation -- Short Version
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Longitudinal Joints in Asphalt Pavements
37th Annual Utah Asphalt ConferenceMarch 27, 2012
Howard Anderson, PE.
UDOT Central Materials
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Acknowledgements
• FHWA and Asphalt Institute Partner to Identity Best Practices for Longitudinal Joints. Training Class, February 23, 2012. Mark Buncher, Ph.D., P.E.
• NCAT Report No. 97-4 Longitudinal Joint Construction Techniques for Asphalt Pavements.
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Best Practices forSpecifying and Constructing
HMA Longitudinal Joints
A Cooperative Effort betweenAsphalt Institute & FHWA
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Definitions
• Longitudinal Joint – HMA placed adjacent to existing lane, Interface between two existing HMA mats.
• Hot Joint – Adjacent lanes paved in echelon.
• Cold Joint – first pass cooled to ambient temperature with next HMA pass.
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Longitudinal Joint
Performance equals
Mat Performance
Goal LJP = MP
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Is It a Problem?
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LCC Alternate Bid Competitiveness DOT Program Costs HMA Industry’s Livelihood the Travelling Public
An Agency and Industry Concern
Longevity matters, it impacts:
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Project Team– Asphalt Institute
• Mark Buncher• Carlos Rosenberger• AI Regional Engineers
– FHWA• Thomas Harman• Michael Arasteh• Stephen Cooper
– PA State Asphalt Paving Association• Gary Hoffman
National Asphalt Pavement Association• David Newcomb
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How many State Agencies have a longitudinal joint specification?
•About thirdA
•About halfB
•About two-thirdsC
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Takeaways from FHWA Survey to 52 Division Offices
• ½ States are not satisfied with overall performance of L-Joints
• 2/3rds of States have a “L-Joint spec”– Half of those (17) require a minimum density
• Range from 89% - 92% min Gmm (Rice)
– Other half are method specs• From Joint Adhesive to very prescriptive
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312
Trucking Compaction
Paving Plant
Dump Person MTV
GETTING STARTED OFF RIGHT
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Managing Material in the Hopper
Conveyor area is exposed and augers are starved!
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Tack Coat
Full width of mat to minimize movement of unsupported edge
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Dump Person
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First Pass Must Be Straight!Unanimous that a string-line should be used to assure first
pass is straight
String-line Skip Paint Reference
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Great Results
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Paver operator using the curb as his reference
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Tough to get proper overlap (1”) with next pass
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Contact Grade Sensor
Ultrasonic Grade Sensor
Use Automatic Control
Systems
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Vibratory Screed Should Always Be On
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Department, Name, Security Class 23Date
Forward Motion
Screed Weight
Screed HeatingVibration
Angle of Attack
Achieving Pre-Compaction
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END GATE
Seated on the Existing Surface
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Uniform Head of MaterialAcross the Entire Screed
Auger
Carry Material Within12 – 18-inches of
the End Gate
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Another example of uniform head of material
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Controlling material flow at outer edges of screed and
delivering homogenous HMA
Hydraulic Extending Tunnels
Tunnels
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Result of uniform head of HMA and auger/tunnel within 12 to 18-inches of end gate: non-segregated HMA at the joint
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Auger Overload…these are unacceptable
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Auger not extended towithin 12 to 18-inches of the end gate.
The result -SEGREGATION at joint
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Rollers Need to Be Kept Close to the PaverCritical in cool and cold weather!
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Our Recommendation:1st Roller Pass Hangs Over 4-6 inches
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Alternative: Stay Back 4-6 inches on 1st pass, then roll 2nd pass w/
slight overhang
• Concern:–developing
stress crack?
• Merit:–minimize
lateral movement?
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What We Don’t Want
Edge of drum inside unsupported edge
can cause cracking near the edge
Rolling Unsupported Edge
(First Paver Pass)
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Compacting Notched Wedge
add-on vibratory compactorplate compactor
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Quality Control, Monitor Joint Density
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Tack the Joint! (Butt or Wedge)
Emulsion, or
PG asphalt or Proprietary Joint Adhesive (JA)
Good, Better, Best
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Paver Automation Using Joint Matcher (versus Ski) to Always Achieve Exact
Thickness of Mat Needed
If the joint (hot-side) is starved of material, the roller drum will “bridge” onto the cold mat and no further density will occur at joint. To ensure this never occurs, target height difference after compaction is 0.1”
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Destined for Failure Hot side of joint
starved of material.Bridging?
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Types of Joint Matchers
G. Bridenbaugh photo
Frank Colella photo
Non-contact sensor
Contact sensor
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Ski best for smoothness
Arm
Averages optimum HMA thickness over entire length of ski.
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Proper Overlap: 1.0 + 0.5 inches.
Exception: Milled or sawed joint should be 0.5 inches
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Bridenbaugh & Colella
Top Photos Show Voids at Bottom of Lift (no overlap)
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Bumping the joint?
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Don’t broadcast material across the mat
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Lute the Longitudinal Joint
This lute person isdoing a great job
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No lute person
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1st pass off the jointapprox 6-8 inches
2nd pass overlap onto the cold mat
Rolling the Supported Edge
Our Recommendation:
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Roller
Make a roller pass in the vibratory mode overhanging 2 to 4-inches on the cold side.
versus an Alternate Method of1st Pass over the Supported Edge
Concern is bridging (roller being supported by cold mat)
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• Plant tons/hour• # of trucks• Plant to project (time)• Type of project
(rural/urban)• Ambient / Surface temps• Paver speed• # of rollers
On this day goal was 35 ft/min
Contractor Prior Planning
Consideration given to mix selection
Plan joint offsets when multiple lifts
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Tack Full Width to Minimize Lateral Movement
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Paver on Automatic
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Vibratory Screed “ON”
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End Gate Tight to the Existing Surface
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First Pass Must be Straight
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Uniform head of materialacross entire screed to joint…Do Not Overload Auger
Extend auger and tunnel within 12 to 18-inches of the end gate
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Rolling Unsupported Edge: Overlap 6-inches on the First Pass
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Tack / Paint the Vertical Face
1. Joint Adhesive2. PG Binder3. Double Tack
with Emulsion
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Overlap the cold lane by 1-inch +/-(unless milled or cutback joint, then 0.5-inch) Use a Joint Matcher
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Do Not Push Overlap Back
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Rolling Supported Edge: Stay off the Joint 6 to 12 inches on the first pass
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Making sure everythingis just right
Attention to Detail
Monitor density with gauge, on both sides of the joint, as part of QC program
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Less permeable mixes• Smallest NMAS that will do the job• Consider using a “fine” gradation• Lower gyration levels
Min lift thickness is NMAS x 4, exception: for “fine” gradation NMAS x 3 Warm Mix Asphalt may serve as compaction aid Pay for tack as a separate bid item to facilitate proper
application rate
Consider use of the notch wedge joint (versus butt) for lift thicknesses > 1.5 inches and < 3 inches
Mix Selection and Design Considerations
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Offset longitudinal joints between layers by at least 6-inches
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Innovative Techniques / Materials
• Infrared Joint Heaters– In cold weather
• Evaluate Project and Traffic Control Requirements for:– Echelon Paving– Mill / Fill One Lane at a Time– Cutting Back the Joint
• Consider Joint Enrichment – Overbanding with PG Binder – Use of Surface Sealers
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I-68 project 5+ years old
GOAL
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I-68 project 5+ years old
( same project, same location as previous slide )
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Industry Help Needed HMA
• Concrete getting more competitive due to HMA cost increase.
• Concrete has worked out many of its problems with smoothness.
• HMA problems with Longitudinal Joints, durability, dry mixes.
• UAPA can bring one voice to UDOT to represent best interest of the industry, not just one contractor.
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We Know Unsupported Edge Will Have Lower Density
Proper Overlap Sufficient Materialfor Roll-Down
Low Density Area