what’s known and what’s new -...
TRANSCRIPT
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Timothy R. Murphy, P.E.President
Whats Known and Whats New
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Transportation Research Boards Report 202 (1984)
TRB declared that "asphalt, more than any other single product, sustains the nation's highway system and facilitates the flow of commerce."
Mr. Allan WoodUS Army, 82nd AirborneParachuted into Holland 9/17/1944Operation Market Garden &The Battle of the BulgePurple HeartBronze Star for combat valorE-mail: [email protected]'
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Trucking Compaction
PavingHMA Facility
Balancing Production
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Permeability reduction,
Public satisfaction,
Performance enhancement.
Density,
Smoothness,
Strength.
Why do we care about compaction?
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Improve Mechanical Stability Improve Resistance to Permanent
Deformation
Reduce Moisture/Air Penetration Improve Fatigue Resistance Reduce Low-Temperature Cracking Potential
Importance of VMA
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Permeability and rutting
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Reference Density ComparisonIn-PlaceAir Voids
0
1
2
3
4
5
6
7
8
991
92
93
94
95
96
97
98
99
100
% of MaximumTheoretical Density
100
99
98
97
96
95
% ofLaboratory
Density
100
99
% ofControl Strip
Density
For 4.0% VoidsMix Design
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Mat during Compaction
Courtesy of Caterpillar Paving Products
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Types of rollers
1. Vibratory (aka Breakdown)
2. Pneumatic (aka Rubber tire)
3. Static Steel Wheel (aka Finish)
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Den
sity
Incr
easi
ngHigh
Low
DensityPassing
1 2 43 5 6
Roller Passes
Marshall Mixes
Superpave Mixes
7 8
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Vibratory roller
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Method of expressing a vibratory rollers impact force on the asphalt pavement.
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Increase with lift thickness. Vary with mix characteristics.
Unit Total Applied Force (UTAF)
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UTAF (lb. / in.)
1 Surface Course 290 - 370
1 Binder Course 330 - 420
3 Base Course 400 - 500
4 plus Base Course 440 - 600
Desirable UTAF Ranges
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Amplitude
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DIRECTION OF TRAVEL
Impact Spacing
High FrequencyLow Frequency
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Reed tachometer; vibrations per minute (vpm)
35(x100)
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Typical Data for Vibratory Tandem Rollers
Vibratory Steel Tandem
(ton)
Oper.Wt.(lb.)
DrumDiam.(ft.)
Drum Width
(ft.)
Static Drum(pli)
Dynamic Drum(pli)
VPMNom. Amp. (in.)
6.0-8.0 14,700 3.6 4.6 130 260 2,900 0.0259.5-11.0 20,500 3.9 5.6 158 384 2,600 0.03> 13.0 30,000 4.9 6.9 186 423 2,400 0.03
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Lack of smoothness
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Do not vibrate thin lifts of Asphalt
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Do not vibrate thin lifts of Asphalt
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Roller vs. paving widths
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Roller in training
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Skirted pneumatic roller
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Tire inflation pressure vs. ground contact pressure
Courtesy of Caterpillar Paving Products
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Inflation Pressure and Ground Contact Pressure at Various Wheel Loads and Ply Ratings
Ply Rating
Wheel Loadlb
Tire Pressure
psi
Contact Areain2
Ground Contact Pressure
psi
* 14 1,250 130 16 7814 2,800 130 30 92* 14 2,300 35 41 5614 2,300 130 26 88* 10 2,800 90 38 7314 2,800 130 30 92
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Finish rolling removes marks and gets a touch more density with pounds per lineal inch (PLI) ~ 280
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Ballasting finish roller to get PLI > 300
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Properties of the Materials Environmental Variables Laydown Site Conditions
Factors Affecting Compaction
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Can mix type and base support cause compaction difficulties?
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Compaction compromised
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Forces must be equal and opposite Sub-grade, Sub-base, Existing pavement structure.
How do we ensure adequate compaction?
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Sub-grade
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Sub-base
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Sub-base density checks
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Hot Mix Asphalt, Concrete, Oil & chip.
Existing pavement structure
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Is it
con
cret
e?
Yes;
Rubbilize
See Process
See Photos
No;
No ProblemOverlay
Engineering Flowchart for Concrete Pavement
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Process
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Rubblization Photos
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Rubblization Photos
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Courteous Contractor
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Placement Equipment
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Augers
SensorsSlat feeders
Hopper
Screed Tractor
Courtesy of Caterpillar Paving Products
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Pre-Pave Meeting
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Watch out for moisture
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How worn flights affect temperatures
TEMPERATURES ACROSS THE INTAKE BREECHING SHOULD BE CONSTANT.
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Evaluation of Asphalt Absorption by Mineral Aggregate AAPT 1991, p. 207-229.
Asphalt Absorption vs . Aging
0 1 2 3 4 5 6 7 8 Time, hr.
Abso
rptio
n, %
Wt.
Aggr
egat
e In
crea
sing
PG58-28
PG64-22 Curves vary from aggregate to aggregate.
Absorption, % Wt. Aggregate
Increasing
Evaluation of Asphalt Absorption by Mineral Aggregate
AAPT 1991, p. 207-229.
Curves vary from aggregate to aggregate.
PG64-22
PG58-28
Time, hr.
8
7
6
5
4
3
2
1
0
. Aging
vs
Asphalt Absorption
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Silo & Truck loading: Recognize the evil spirit
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Night paving
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Truck Tarping
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Side Insulation
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262.0
164.8
*>270.0F
*
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Pre-Pave Adjustments
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Screed Unit
Courtesy of Blaw-Knox Ingersoll Rand Paving Products
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Screed temperature
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Lift Thickness
General rule of thumb is 3-times the maximum particle size; compacted lift thickness.
Variable thickness yields variable density.
Low Density = 88.9High Density = 94.4Avg. Density = 91.8Std Deviation= 1.7
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Straight Longitudinal Lines
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Construction
Longitudinal Joints Start with a Straight Line
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Opportunity
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Not so excellent joint construction
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Wheres the Raker?
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Compaction problems along the longitudinal joint
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We are headed to hanging out at the joint
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Longitudinal joint solution
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Echelon Paving, Part II
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Paver Operation
GOOD!!!
BAD!!!
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End of truck load / dumping hopper wings [from afar]
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151.0
212.2
163.1
228.1
*>237.6F
*
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Ingenuity
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Longitudinal Segregation & Cracking
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Auger hold point
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Bearing / hanger
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Tools of the trade
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Special Thanks to the
TxDOT Mr. Dale Rand, P.E.
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Why is Thermal Segregation Important?
Cold spots typically become low density Density is the primary contributor to
performance
Contractor and agency risk are impactedAcceptance and pay schedules are based on densitySegregated locations may deteriorate prematurely
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Research conducted by University of Connecticut, Connecticut Advanced Pavement Laboratory
Example of a Density Profile
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End of truckload segregation
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Fatigue Life Substantially Reduced
Source: NCAT (2000)
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Sampling Distributions of Segregated and Non-Segregated HMA
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Common Methods of Measuring Thermal Segregation
Infrared Thermometers less than $200 Infrared Cameras less than $5K Pave-IR System less than $30K
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Test Method Tex-244-F Handheld IR thermometer Thermal camera Pave-IR
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End dump operation shows cyclic paving speed decrease with cyclic thermal segregation
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Background, Use, and Advanced Techniques
Dale Rand (TxDOT)
Richard Izzo (TxDOT)
Stephen Sebesta (TTI)
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PAVE IR Conclusions
TxDOT is implementing better specifications & better techniques to address the problem
Excellent Passive Inspection device that allows end result versus method specifications
Contractors to see what they are doing and improve their operations
Contractors can focus on causes & cures
What Gets Measured Gets Done
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PAVE-IR COMPONENTS
INFRARED SENSOR
PAVE-IR COMPUTER
(OPERAND)
GPS ANTENNA
DISTANCE ENCODER
MOUNTING HARDWARE
SIGNAL CONDITIONER
2010 Hot Mix Asphalt Center - All Rights Reserved
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Questions?
Compaction of AsphaltTransportation Research Boards Report 202 (1984)Balancing ProductionWhy do we care about compaction?Hot Mix Asphalt (HMA)Importance of VMAPermeability and ruttingReference Density ComparisonMat during CompactionTypes of rollersSlide Number 11Vibratory rollerUnit Total Applied Force (UTAF)Unit Total Applied Force (UTAF)Desirable UTAF RangesSlide Number 16Slide Number 17Reed tachometer; vibrations per minute (vpm)Typical Data for Vibratory Tandem RollersLack of smoothnessDo not vibrate thin lifts of AsphaltDo not vibrate thin lifts of AsphaltRoller vs. paving widthsRoller in trainingSkirted pneumatic rollerTire inflation pressure vs. ground contact pressureInflation Pressure and Ground Contact Pressure at Various Wheel Loads and Ply RatingsFinish rolling removes marks and gets a touch more density with pounds per lineal inch (PLI) ~ 280Ballasting finish roller to get PLI > 300Factors Affecting CompactionCan mix type and base support cause compaction difficulties?Compaction compromisedHow do we ensure adequate compaction?Sub-gradeSub-baseSub-base density checksExisting pavement structureEngineering Flowchart for Concrete PavementSlide Number 39Slide Number 40Slide Number 41Courteous ContractorPlacement EquipmentSlide Number 44Pre-Pave MeetingWatch out for moistureHow worn flights affect temperaturesSlide Number 48Slide Number 49Silo & Truck loading: Recognize the evil spiritSlide Number 51Night pavingTruck TarpingSide InsulationInfrared Photo of End DumpPre-Pave AdjustmentsScreed UnitScreed temperatureLift ThicknessStraight Longitudinal LinesSlide Number 61OpportunityNot so excellent joint constructionWheres the Raker?Compaction problems along the longitudinal jointWe are headed to hanging out at the jointLongitudinal joint solutionEchelon Paving, Part IISlide Number 69End of truck load / dumping hopper wings [from afar]Infrared Photo(End Dump Mix Behind Paver)IngenuitySlide Number 73Slide Number 74Slide Number 75Auger hold pointBearing / hangerTools of the tradePAVE - IRWhy is Thermal Segregation Important?Slide Number 81End of truckload segregationFatigue Life Substantially ReducedSampling Distributions of Segregated and Non-Segregated HMACommon Methods of Measuring Thermal SegregationMeasuring Thermal SegregationEnd dump operation shows cyclic paving speed decrease with cyclic thermal segregationSlide Number 88PAVE IR ConclusionsPAVE-IR COMPONENTSQuestions?