Long Joint Presentation -- Short VersionPresentation Transcript
Longitudinal Joints in Asphalt Pavements 37th Annual Utah Asphalt Conference March 27, 2012 Howard Anderson, PE. UDOT Central Materials
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.
Best Practices forSpecifying and Constructing HMA Longitudinal JointsA Cooperative Effort between Asphalt Institute & FHWA
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.
Is It a Problem?
An Agency and Industry ConcernLongevity matters, it impacts: LCC Alternate Bid Competitiveness DOT Program Costs HMA Industry’s Livelihood the Travelling Public
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
How many State Agencies havea longitudinal joint specification? A •About third B •About half C •About two-thirds
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
GETTING STARTED OFF RIGHT Plant Paving 3 2 1Trucking Compaction Dump Person MTV
Managing Material in the HopperConveyor area is exposed and augers are starved!
Tack CoatFull width of mat tominimize movement ofunsupported edge
First Pass Must Be Straight!Unanimous that a string-line should be used to assure first pass is straight String-line Skip Paint Reference
Paver operator usingthe curb as his reference
Tough to get proper overlap (1”) with next pass
Use Automatic Control SystemsContact Grade Sensor Ultrasonic Grade Sensor
Vibratory Screed Should Always Be On
Achieving Pre-Compaction Screed Weight Forward Motion Vibration Screed Heating Angle of AttackDepartment, Name, 23 DateSecurity Class
END GATESeated on the ExistingSurface
Auger Uniform Head of Material Across the Entire ScreedCarry Material Within 12 – 18-inches of the End Gate
Another example ofuniform head ofmaterial
Hydraulic Extending Tunnels Controlling material flow at outer edges of screed and delivering homogenous HMA Tunnels
Result of uniform head of HMAand auger/tunnel within 12 to18-inches of end gate: non-segregated HMA at the joint
Auger Overload…these areunacceptable
Auger not extended towithin 12 to 18-inchesof the end gate.The result -SEGREGATION at joint
Rollers Need to Be Kept Close to the Paver Critical in cool and cold weather!
Our Recommendation:1st Roller Pass Hangs Over 4-6 inches
Alternative: Stay Back 4-6 incheson 1st pass, then roll 2nd pass w/ slight overhang • Concern: –developing stress crack? • Merit: –minimize lateral movement?
What We Don’t Want Rolling Unsupported Edge (First Paver Pass) Edge of drum inside unsupported edge can cause cracking near the edge
Tack the Joint! (Butt or Wedge) Emulsion, orGood, Better, Best PG asphalt or Proprietary Joint Adhesive (JA)
Paver Automation Using Joint Matcher(versus Ski) to Always Achieve Exact Thickness of Mat NeededIf the joint (hot-side) isstarved of material, the rollerdrum will “bridge” onto thecold mat and no furtherdensity will occur at joint. Toensure this never occurs,target height difference aftercompaction is 0.1”
Destined for Hot side of jointFailure starved of material. Bridging?
Types of Joint Matchers Non-contact sensorG. Bridenbaugh photo Contact sensor Frank Colella photo
ArmSki best for smoothnessAverages optimum HMA thicknessover entire length of ski.
Proper Overlap:1.0 + 0.5 inches.Exception: Milledor sawed jointshould be 0.5inches
Top Photos Show Voids at Bottom of Lift (no overlap) Bridenbaugh & Colella
Bumping the joint?
Don’t broadcast material across the mat
Lute the Longitudinal Joint This lute person is doing a great job
No lute person
Rolling the Supported Edge Our Recommendation:1st pass off the joint 2nd pass overlapapprox 6-8 inches onto the cold mat
versus an Alternate Method of1st Pass over the Supported Edge Roller Make a roller pass in the vibratory mode overhanging 2 to 4-inches on the cold side. Concern is bridging (roller being supported by cold mat)
Contractor Prior PlanningConsideration given to mix selectionPlan joint offsets when multiple liftsOn this day goal was 35 ft/min •Plant tons/hour •# of trucks •Plant to project (time) •Type of project (rural/urban) •Ambient / Surface temps •Paver speed •# of rollers
Tack Full Width to Minimize Lateral Movement
Paver on Automatic
Vibratory Screed “ON”
End Gate Tightto the ExistingSurface
First Pass Must be Straight
Uniform head of material across entire screed to joint…Do Not Overload AugerExtend auger andtunnel within 12 to 18-inches of the end gate
Rolling UnsupportedEdge: Overlap 6-incheson the First Pass
Tack / Paint the Vertical Face1. Joint Adhesive2. PG Binder3. Double Tack with Emulsion
Overlap the cold lane by1-inch +/-(unless milled or cutbackjoint, then 0.5-inch) Use a Joint Matcher
Do Not Push Overlap Back
Rolling Supported Edge: Stay off the Joint6 to 12 inches on the first pass
Attention to Detail Making sure everything is just rightMonitor density withgauge, on both sides ofthe joint, as part of QCprogram
Mix Selection and Design Considerations 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 properapplication rate Consider use of the notch wedge joint (versus butt) forlift thicknesses > 1.5 inches and < 3 inches
Offsetlongitudinaljoints betweenlayers by at least6-inches
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
GOALI-68 project 5+ years old
I-68 project 5+ years old( same project, same location as previous slide )
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.
We Know Unsupported Edge Will Have Lower Density Proper Overlap Sufficient Material for Roll-Down Low Density Area