Everything You Need to Know About Constructing Long-Lasting Longitudinal Joints in Asphalt Pavements
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Everything You Need to Know About Constructing Long-Lasting Longitudinal Joints in Asphalt Pavements
- 1. Longitudinal Joints in Asphalt Pavements 37th Annual Utah Asphalt Conference March 27, 2012 Howard Anderson, PE. UDOT Central Materials
- 2. 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.
- 3. Best Practices for Specifying and Constructing HMA Longitudinal Joints A Cooperative Effort between Asphalt Institute & FHWA
- 4. 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.
- 6. Is It a Problem?
- 7. An Agency and Industry Concern Longevity matters, it impacts: LCC Alternate Bid Competitiveness DOT Program Costs HMA Industry’s Livelihood the Travelling Public
- 8. 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
- 9. How many State Agencies have a longitudinal joint specification? A •About third B •About half C •About two-thirds
- 10. 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
- 11. GETTING STARTED OFF RIGHT Plant Paving 3 2 1 Trucking Compaction Dump Person MTV
- 12. Managing Material in the Hopper Conveyor area is exposed and augers are starved!
- 13. Tack Coat Full width of mat to minimize movement of unsupported edge
- 14. Dump Person
- 15. First Pass Must Be Straight! Unanimous that a string-line should be used to assure first pass is straight String-line Skip Paint Reference
- 16. Great Results
- 17. Paver operator using the curb as his reference
- 18. Tough to get proper overlap (1”) with next pass
- 19. Use Automatic Control Systems Contact Grade Sensor Ultrasonic Grade Sensor
- 20. Vibratory Screed Should Always Be On
- 21. Achieving Pre-Compaction Screed Weight Forward Motion Vibration Screed Heating Angle of Attack Department, Name, 23 Date Security Class
- 22. END GATE Seated on the Existing Surface
- 23. Auger Uniform Head of Material Across the Entire Screed Carry Material Within 12 – 18-inches of the End Gate
- 24. Another example of uniform head of material
- 25. Hydraulic Extending Tunnels Controlling material flow at outer edges of screed and delivering homogenous HMA Tunnels
- 26. Result of uniform head of HMA and auger/tunnel within 12 to 18-inches of end gate: non- segregated HMA at the joint
- 28. Auger not extended to within 12 to 18-inches of the end gate. The result - SEGREGATION at joint
- 29. Rollers Need to Be Kept Close to the Paver Critical in cool and cold weather!
- 30. Our Recommendation: 1st Roller Pass Hangs Over 4-6 inches
- 31. Alternative: Stay Back 4-6 inches on 1st pass, then roll 2nd pass w/ slight overhang • Concern: –developing stress crack? • Merit: –minimize lateral movement?
- 32. What We Don’t Want Rolling Unsupported Edge (First Paver Pass) Edge of drum inside unsupported edge can cause cracking near the edge
- 33. Compacting Notched Wedge add-on vibratory compactor plate compactor
- 34. Quality Control, Monitor Joint Density
- 35. Tack the Joint! (Butt or Wedge) Emulsion, or Good, Better, Best PG asphalt or Proprietary Joint Adhesive (JA)
- 36. 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”
- 37. Destined for Hot side of joint Failure starved of material. Bridging?
- 38. Types of Joint Matchers Non-contact sensor G. Bridenbaugh photo Contact sensor Frank Colella photo
- 39. Arm Ski best for smoothness Averages optimum HMA thickness over entire length of ski.
- 40. Proper Overlap: 1.0 + 0.5 inches. Exception: Milled or sawed joint should be 0.5 inches
- 41. Top Photos Show Voids at Bottom of Lift (no overlap) Bridenbaugh & Colella
- 43. Don’t broadcast material across the mat
- 44. Lute the Longitudinal Joint This lute person is doing a great job
- 45. No lute person
- 46. Rolling the Supported Edge Our Recommendation: 1st pass off the joint 2nd pass overlap approx 6-8 inches onto the cold mat
- 47. versus an Alternate Method of 1st 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)
- 48. Contractor Prior Planning Consideration given to mix selection Plan joint offsets when multiple lifts On 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
- 49. Tack Full Width to Minimize Lateral Movement
- 52. End Gate Tight to the Existing Surface
- 53. First Pass Must be Straight
- 54. Uniform head of material across entire screed to joint…Do Not Overload Auger Extend auger and tunnel within 12 to 18- inches of the end gate
- 55. Rolling Unsupported Edge: Overlap 6-inches on the First Pass
- 56. Tack / Paint the Vertical Face 1. Joint Adhesive 2. PG Binder 3. Double Tack with Emulsion
- 57. Overlap the cold lane by 1-inch +/- (unless milled or cutback joint, then 0.5-inch) Use a Joint Matcher
- 58. Do Not Push Overlap Back
- 59. Rolling Supported Edge: Stay off the Joint 6 to 12 inches on the first pass
- 60. Attention to Detail Making sure everything is just right Monitor density with gauge, on both sides of the joint, as part of QC program
- 61. 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 proper application rate Consider use of the notch wedge joint (versus butt) for lift thicknesses > 1.5 inches and < 3 inches
- 62. Offset longitudinal joints between layers by at least 6-inches
- 63. 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
- 64. GOAL I-68 project 5+ years old
- 65. I-68 project 5+ years old ( same project, same location as previous slide )
- 66. 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.
- 67. We Know Unsupported Edge Will Have Lower Density Proper Overlap Sufficient Material for Roll-Down Low Density Area
Editor's Notes
- This co-op study (partnership between AI and FHWA) was limited in scope, funding and time. Focus not on doing additional research on LJs, but rather to examining what has been done over last 50 years in this area and search for consensus and make recommendations on how to construct and specify LJs.Workshop will cover our findings in terms of LJ specifications, and density requirements as they relate to permeability. Workshop will also cover key steps (best practices) that give contractor best chance of building a LJ that will last as well as interior mat.
- Premature failure should be a concern to both industry and agencies. Initial performance has been shown to be the most critical factor (after initial construction cost) in a life cycle analysis. Increasing the performance period from 10 years to 15 yearswill have a significant impact on the life cycle analysis and ultimately the pavement selection process. The difference in Net Present Worth will probably be in the 8 to 10-percent range (depending on prices; 8.5-percent in the next hidden slide).
- Partners on this project.
- Antidotal comments of longitudinal joint performance similar to the previous photos and reports with findings that paralleled the Kentucky report prompted the FHWA to survey their Field Offices regarding the performance of the longitudinal joints in their states.That initial survey provided a great starting point, it gave insight into the specifications and practices being used in the U.S. Specifically it noted:-1/2 of the states were not satisfied with their longitudinal joint performance-2/3 of the states reported that they have a longitudinal joint specification (in some cases an addendum or special provision), but only ½ of those states accepted based on a minimum density. The other ½ were using “method specifications”-some states reported use of longitudinal joint adhesives, but only New Jersey required it on all projects(Note: This may be a good spot to ask the audience what type of LJ spec or requirements their state has.)While the initial survey got the project off in the right direction, it did not provide the necessary data to recommend a specification or “best practices”.
- Permeability at the joint is a joint destined for premature failure
- A good joint requires getting started off right.That means having a balanced paving operation; plant production, number of trucks (time to / from the project), paver speed and roller speed coordinated to match tonnage arriving on the project. Trucks loaded to avoid segregation, MTV helps to minimize segregation and allows paver to maintain consistent speed, without getting bumped by trucks. Without a MTV, “dump person” is critical to get truck lined up properly to avoid paver deviating from a straight line.
- Example of “Basics” don’t starve hopper for material; leads to possible segregation
- The application of a properly cured tack coat (PG grade or emulsion) is critical to minimizing the lateral movement of the unsupported edge. It is important the tack coat cover the full width of the lane being placed. In the photo above, the tack was placed beyond the edge of the mat, which is OK too.
- Whether the material is supplied to the paver by windrow, dumping directly from the truck, or using a material transfer device, the dump person is the initial paving crew member responsible for successful longitudinal joint construction.
- It was unanimious, the first pass must be straight. A straight first pass allows the paver operator to consistently and uniformly overlap the existing lane. The examples show here are a stringline and a stringline that has been skip painted. (Circumstances may negate the need for a stringline, one example being urban paving where there is a curb that can be used as a reference.) It is equally important the paver operator have a clearly visible reference that can be used in conjunction with the stringline. Several of the Shedon Hayes winners commented on the importance of a straight first pass and one sends a survey team out to set the line.
- Great results. This is the stringline project in the previous slideAlso note that the longitudinal joint from the underlying mat is staggered what looks like about 8 inches.
- In this case the stringline is not necessary as the paver operator is able to use the curb as his reference. Note the drop down chain is clearly marked and easily visible to the operator. (This project is just outside Baltimore, MD. Contractor P. Flanigan & Sons, a Sheldon Hayes winner)
- The inability to get a consistent overlap is obvious in these photos; they highlight the need for a straight first pass. These projects will result in some areas having excess material at the joint and insufficient material in other areas. In all likelihood, the areas with excessive material will see the lute person push that material back and spread it across the mat.Chuckle: (Orange sign on right “uneven pavement” has dual meaning).
- There is overwhelming agreement that the paver must be run with the automation rather than manually.
- Like the paver automatics, the vibratory screed should always be on, it increases the mat and the joint density. When conducting the interviews it was estimated that the vibratory screed is not turned on 50% of the time. (Project visits confirmed that estimate. Paver operators cited being very uncomfortable when having it turned on for any length of time.)
- The end gate should be seated on the existing lane to prevent material from leaking out from underneath; unless removed that material can lead to air voids at the interface of the two lanes.
- There should be a uniform head of material across the entire screed and the auger should carry the material to within 12 to 18-inches of the end gate. Augers that fail to carry the material to the end gate are a source of segregation and the resulting low density, high permeability found in many longitudinal joints.
- Another good example with a uniform head of material across the auger, and the auger carrying the material to within 12 to 18-inches of the end gate
- When there is a proper head of material and the auger carries the material to within 12 to 18-inches of the endgate; the result a uniform, not-segregated joint
- This is unacceptable. The auger is buried, 3+ feet from the end gate, and material is being pushed, rather than carried. The result is a high probability for segregation at the longitudinal joint.
- Segregation at the longitudinal joint, most likely the result of improper head of material and the augers not extended to within 12 to 18-inches of the endgate
- Keeping the rollers close to the paver is always important, it is critical when the weather turn cool / cold. (This project is just outside Baltimore, MD. Contractor P. Flanigan & Sons, a Sheldon Hayes winner)
- These two pictures show the 1st pass overhanging 6”Those suggesting staying back 6-inches +/- on the first pass did so saying it resulted in less lateral movement of the unsupported edge. Those who supporting overhanging the edge on first pass shared a concern with the method of staying back 6-inches in that a shear crack could develop along the edge of the roller drum as the material move laterally. Ultimately this report chose to recommend the overhang method.Very Important: The joint must be compacted while the mat is hot!
- Illustration shows 1st pass staying back 6” with 1st pass, then 2nd pass has slight overhang.There is some support in the paving community for staying back from the unsupported edge and then overlapping on the second pass. It is recommended contractors choosing this method of rolling the joint review their projects paved over the last 5 +/- years to see if a crack has developed. It may well be that certain mixtures are stable enough to roll using this method, however there will also be mixtures susceptible to the stress crack. Only after assuring themselves that their mixtures placed over the past 5 +/- years have not developed a stress crack along the unsupported edge should a contractor use this method.
- Connecticut noted that their early wedge joints raveled when left open to traffic, prior to placing the adjacent lane. Consequently, their specification now requires the wedge be compacted. They do not specify the method of compacting the joint, just that it be compacted.In picture on the right, a plate compactor was used for about an hour because the wedge compactor broke down.
- Regardless of the type of joint or the rolling pattern, it is important that the joint density be monitored. This wedge joint in Connecticut achieved 91% of maximum theoretical density at this location. Both the unsupported side and the supported side of the joint should be monitored. Lateral support from wedge offers some confinement for rolling “unconfined” edge. Note 91 density there%.
- Painting the longitudinal joint (butt or notched wedge) is recommended. Emulsions, PG-graded asphalts and proprietary joint adhesives have all been used successfully. Contractors prefer to use the same material specified for the roadway, consultants tended to prefer the joint adhesives. Work done by Kandhal found the best performing joints were notched wedge joints using joint adhesives. (New Jersey requires joint adhesives on their longitudinal joints. New Hampshire has used it on specific projects, Mississippi uses on Interstates). Use of an emulsion to paint the joint is considered “Good”, use of a PG asphalt (typically 64-22) is “Better”, and use of the Joint Adhesive (JA) is “Best.” When emulsions are used, double tacking the joint is encouraged for extra residual asphalt. The cost of the JA is around $0.30 per linear foot. A discussion and slide is provided later in this workshop on doing an economic analysis to determine if using a Joint Adhesive is beneficial from a cost/benefit perspective. Emulsion pic was on Lindy Paving Job just north of Pittsburgh, PA.Proprietary Joint Adhesive pic on I-295 in New Jersey
- You saw this photo earlier. Could this be the result of a ski rather than a joint matcher? Random retained moisture along the longitudinal joint may be result of the ski averaging adjacent joint thickness. Some places just right; some places too low, and some places too high.
- Joint matcher is critical to getting proper amount of material at the joint! There was complete agreement that the best longitudinal joint will be constructed using the “joint matcher”. The joint matcher does the best job at making sure there is sufficient material at the joint. Non-contact sensor on left and contact sensor on right. Non-contact sensor accuracy can be affected by heat while contact sensor accuracy can be affected by debris and may require a person brooming the pavement in front of it.
- This photo shows a ski setup with stringline. A ski is typically preferred when the focus is on smoothness, versus a joint matcher when the focus is on the joint . The ski averages the thickness of HMA required over the length of the ski (30-40 ft) and may not always provide the optimum amount of HMA for the joint. On the other hand, the joint matcher placed immediately ahead of the auger does the best job of getting sufficient material at the joint because it measures the HMA thickness required at that precise location. Those choosing the ski typically do so because the project has a ride spec whose bonus/penalty outweigh that of the joint spec (if there is one). Projects with multiple lifts offer the opportunity to use a ski on the intermediate lift(s) to get smoothness and a joint matcher on the surface lift to get a good joint.
- There is general agreement the overlap of material onto the existing lane should be 1-inch + / - one-half inch. In a break from the traditional recommendation to lute the material back the consensus is the material should not be luted back. If the material could always be properly luted back it would probably be the recommended method, but too often the material is luted across the mat; the result is a joint starved for material and one destined for premature failure (see next several slide).It is important to remember the roll down of a typical hot-mix asphalt pavement is approximately 0.25-inch / 1-inch and make sure that the second lane lift thickness is sufficient to allow for that roll down. When done properly the overlap material will be above the cold lane by roughly 0.1-inch. We are not looking for a pretty joint (one that is smooth measured transversely). One inch wide band of crushed aggregate is OK.
- These photos, taken by Garth Bridenbaugh (Pa DOT) illustrate interface voids and attributes the voids in Core #2 & #7 to not overlapping the hot lane mat over the cold lane mat.Conversely, Core #9 & #10 appear to be tight, both cores were taken from a joint constructed with the hot lane overlapping onto the cold lane.These photos show “bottom of lift”, so the void would not be observed without taking a core.
- You would expect a core taken on the joint (1/2 core from cold lane & ½ from hot lane) to be the average of the density on each side of the joint. However, as seen in this graph from the Texas Transportation Institute Research Report the value is much lower. This has to be caused by voids at the interface of the two lanes. The photo of the core in the lower right hand corner was taken by CazBognacki, NY / NJ Port Authority and shows what can happen at the interface. (Comment: I expect contractors given the option of a butt joint or a notched wedge joint would choose to build a wedge joint, it should be less likely to have the interface voids included in the test results. Cores from a notched wedge will normally be centered on the wedge.
- If the material would always be properly luted back it would probably be the recommended method, but too often the material is pushed across the mat; the result is a joint starved for material and one destined for premature failure.Picture on right is starving the joint.
- All too common event; overlapped material being broadcast across the mat. The result is a joint starved for material and a non-uniform mat.Really starving the joint and mat segregation.
- All too common event; overlapped material being broadcast across the mat. The result is a joint starved for material and a non-uniform mat.Really starving the joint and mat segregation.
- In a break from the traditional method oflutingthe material back to the joint; the consensus is the material should not be luted back. Not luting the joint provides the highest probability of good joint performance. It also increases the safety of the paving operation as the lute person no longer has to contend with luting the joint and having the lute handle out in the passing traffic.(Note use the following sentence only if not using slide with title: “Bump the Joint”. If the material could always be properly luted back it would may well be the recommended method, but too often the material is luted across the mat; the result is a joint starved for material and one destined for premature failure.)
- On this paving operation there is not a lute person.Note the crushed material in the 1-inch overlap
- Recommended method of compacting the supported edge is to stay off the joint on the first pass overlapping onto the cold lane on the succeeding pass. This method was chosen to minimize the bridging effect of the roller being supported by the cold lane. This recommend rolling pattern is opposite of what we recommend for the unconfined joint.
- The alternate method of rolling the supported edge is to overlap onto the cold lane on the first pass. This method was not chosen due to concern of a bridging that would result in low density just off the joint on hot side.
- Consider all the factors: Initial thoughts must include proper mix selection (NMAS & coarse vs fine graded). When placement begins each day requires planning the: Plant tons/hour, # of trucks, haul time to / from the job, temperatures and number of rollers it was decided the proper paving speed for that day was 35 ft/min
- The application of a properly cured tack coat (PG grade or emulsion) is critical to minimizing the lateral movement of the unsupported edge. It is important the tack coat cover the full width of the lane being placed
- There is overwhelming support that the paver must be run with the automation rather than manually. There is also complete agreement that the best longitudinal joint will be constructed using the “joint matcher”. The joint matcher does the best job at making sure there is sufficient material at the joint. Using a ski averages the depth of material required over the length of the ski (30 to 40-ft) and may not always provide the correct amount of material. Some times it will be too low, other times too high and sometimes just right. Multiple lifts provide the opportunity to use the ski to get a smooth ride and then using the joint matcher on the final lift to get a good joint.
- Like the paver automatics, the vibratory screed should always be on, it increases the mat and the joint density.
- The end gate should be seated on the existing lane to prevent material from leaking out from underneath; unless removed that material can lead to air voids at the interface of the two lanes.
- The first pass must be straight. A straight first pass allows the paver operator to consistently and uniformly overlap the existing lane. The examples show here are a stringline and a stringline that has been skip painted. (Circumstances may negate the need for a stringline, one example being urban paving where there is a curb that can be used as a reference.) It is equally important the paver operator have a clearly visible reference that can be used in conjunction with the stringline. Several of the Shedon Hayes winners commented on the importance of a straight firs pass and one sends a survey team out to set the line.
- There should be a uniform head of material across the entire screed and the auger should carry the material to within 12 to 18-inches of the end gate. Augers that fail to carry the material to the end gate are a source of segregation and the resulting low density, high permeability found in many longitudinal joints
- The joint must be compacted while the mat is hot! Ultimately this report chose to recommend the overhang method to avoid the concern that a shear crack would develop along the edge of the roller drum as the material move laterally
- Tack / Paint the vertical face
- Overlap the existing mat by 1-inch + / -. There is also complete agreement that the best longitudinal joint will be constructed using the “joint matcher”. The joint matcher does the best job at making sure there is sufficient material at the joint. Using a ski averages the depth of material required over the length of the ski (30 to 40-ft) and may not always provide the correct amount of material. Some times it will be too low, other times too high and sometimes just right. Multiple lifts provide the opportunity to use the ski to get a smooth ride and then using the joint matcher on the final lift to get a good joint.
- Not luting the joint provides the highest probability of good joint performance. It also increases the safety of the paving operation as the lute person no longer has to contend with luting the joint and having the lute handle out in the passing traffic.
- Compact the supported edge bystay off the joint on the first pass overlapping onto the cold lane on the succeeding pass. This method was chosen to minimize the bridging effect of the roller being supported by the cold lane.
- A quality joint requires attention to detail, making sure everything is just right.
- Prior planning is a key factor in constructing a successful longitudinal joint. As noted in the previous slide there are advantages to each type of joint; choose the joint best suited for your particular project.Permeability is related to the nominal maximum aggregate size (NMAS); the smaller the NMAS mixture the less likely it is to be permeable. Consider the type of traffic and choose the smallest NMAS with which you are comfortablePermeability is also a factor of gradation selection; fine mixtures (those below the maximum density line) are less likely to be permeable. Again, consider the type of traffic and choose the gradation understanding that fine gradations offer a greater probability of being impermeable Higher binder contents will improve compactability resulting in reduced in-place air voids and less permeability. Compaction, whether it is the mat or the longitudinal joint requires sufficient lift thickness to allow the rollers to do their job. National recommendations currently recommend a minimum of 4 x NMAS for coarse graded mixtures and 3 x NMAS for fine graded mixtures.
- Offset longitudinal joint between layers by at least 6-inches to minimize intrusion of water down through various HMA layers at the joint.
- The goal is to build high quality ( good density, impermeable) longitudinal joint whose performance is equal to the mat performance. This longitudinal joint is 5+ years old and has not opened up. The longitudinal line you see is the overlapped material (it was not luted). See next photo
- This photo was taken at the same location only shooting down with the camera ($0.25 for reference) and you are unable to tell where the longitudinal joint is. I believe the line represents the joint, but regardless it illustrates the goal (joint remained closed)