Longitudinal Joints in Asphalt Pavements

37th Annual Utah Asphalt ConferenceMarch 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 Joints

A Cooperative Effort betweenAsphalt 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.

Longitudinal Joint

Performance equals

Mat Performance

Goal LJP = MP

Is It a Problem?

LCC Alternate Bid Competitiveness DOT Program Costs HMA Industry’s Livelihood the Travelling Public

An Agency and Industry Concern

Longevity matters, it impacts:

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 have a longitudinal joint specification?

•About thirdA

•About halfB

•About two-thirdsC

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

312

Trucking Compaction

Paving Plant

Dump Person MTV

GETTING STARTED OFF RIGHT

Managing Material in the Hopper

Conveyor area is exposed and augers are starved!

Tack Coat

Full width of mat to minimize movement of unsupported edge

Dump Person

First Pass Must Be Straight!Unanimous that a string-line should be used to assure first

pass is straight

String-line Skip Paint Reference

Great Results

Paver operator using the curb as his reference

Tough to get proper overlap (1”) with next pass

Contact Grade Sensor

Ultrasonic Grade Sensor

Use Automatic Control

Systems

Vibratory Screed Should Always Be On

Department, Name, Security Class 23Date

Forward Motion

Screed Weight

Screed HeatingVibration

Angle of Attack

Achieving Pre-Compaction

END GATE

Seated on the Existing Surface

Uniform Head of MaterialAcross the Entire Screed

Auger

Carry Material Within12 – 18-inches of

the End Gate

Another example of uniform head of material

Controlling material flow at outer edges of screed and

delivering homogenous HMA

Hydraulic Extending Tunnels

Tunnels

Result of uniform head of HMA and auger/tunnel within 12 to 18-inches of end gate: non-segregated HMA at the joint

Auger Overload…these are unacceptable

Auger not extended towithin 12 to 18-inches of the end gate.

The result -SEGREGATION at joint

Rollers Need to Be Kept Close to the PaverCritical in cool and cold weather!

Our Recommendation:1st Roller Pass Hangs Over 4-6 inches

Alternative: Stay Back 4-6 inches on 1st pass, then roll 2nd pass w/

slight overhang

• Concern:–developing

stress crack?

• Merit:–minimize

lateral movement?

What We Don’t Want

Edge of drum inside unsupported edge

can cause cracking near the edge

Rolling Unsupported Edge

(First Paver Pass)

Compacting Notched Wedge

add-on vibratory compactorplate compactor

Quality Control, Monitor Joint Density

Tack the Joint! (Butt or Wedge)

Emulsion, or

PG asphalt or Proprietary Joint Adhesive (JA)

Good, Better, Best

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”

Destined for Failure Hot side of joint

starved of material.Bridging?

Types of Joint Matchers

G. Bridenbaugh photo

Frank Colella photo

Non-contact sensor

Contact sensor

Ski best for smoothness

Arm

Averages optimum HMA thickness over entire length of ski.

Proper Overlap: 1.0 + 0.5 inches.

Exception: Milled or sawed joint should be 0.5 inches

Bridenbaugh & Colella

Top Photos Show Voids at Bottom of Lift (no overlap)

Bumping the joint?

Don’t broadcast material across the mat

Lute the Longitudinal Joint

This lute person isdoing a great job

No lute person

1st pass off the jointapprox 6-8 inches

2nd pass overlap onto the cold mat

Rolling the Supported Edge

Our Recommendation:

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)

• 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

Tack Full Width to Minimize Lateral Movement

Paver on Automatic

Vibratory Screed “ON”

End Gate Tight to the Existing Surface

First Pass Must be Straight

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

Rolling Unsupported Edge: Overlap 6-inches on the First Pass

Tack / Paint the Vertical Face

1. Joint Adhesive2. PG Binder3. Double Tack

with Emulsion

Overlap the cold lane by 1-inch +/-(unless milled or cutback joint, then 0.5-inch) Use a Joint Matcher

Do Not Push Overlap Back

Rolling Supported Edge: Stay off the Joint 6 to 12 inches on the first pass

Making sure everythingis just right

Attention to Detail

Monitor density with gauge, on both sides of the joint, as part of QC program

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

Offset longitudinal joints between layers by at least 6-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

I-68 project 5+ years old

GOAL

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 Materialfor Roll-Down

Low Density Area