segregation in asphalt paving identification, causes & prevention pennsylvania asphalt pavement...
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Segregation in Asphalt PavingIdentification, causes & prevention
Pennsylvania Asphalt Pavement Association Conference
January 30, 2014
Sam GregoryMunicipal Transportation SpecialistState and Local Road Consultant
What Is Segregation?
Webster defines Segregation as: “to separate from the main mass and collect together in a new body.”
What Is The Effect Of Segregation On Pavement?
• Premature Distress– Raveling– Frost Damage– Potholes
Why Do Premature Failures Occur Due To Segregation?
•Weaker Aggregate Structure and Gradation
•Weaker Mix
•Higher Voids
Sources of Segregation• Stockpiling• Cold Feed Bins• Hot Bins• Truck Loading
Plant Responsibility
• Truck Hauling• Truck Unloading• Paver – Hopper, Slat
Conveyers, Hopper gates, Auger, Screed
• Paving Operation Continuity (Balance)
Field Responsibility
Stockpile Segregation – how does it happen?
• Large Stockpiles
• Single Aggregate Blends
Stockpile Segregation – how is it prevented?
• Well-trained Operators
Stockpile Segregation – how is it prevented?
• Different-sized material
• Separate piles
Stockpile Segregation – how is it prevented?
• Build Horizontal Layers
• Build Sloped Layers
• Bridging
Cold Feed Bin Segregation – how does it happen?
• Reconfigure Opening – uniform feeding
Cold Feed Bin Segregation – how is it prevented?
• Range of Materials
• Size of Bin
• Shape of Bin
• No. 1 Bin
Hot Bin Segregation – how does it happen?
• Install Baffle – dust slides to center
Hot Bin Segregation – how is it prevented?
• Dribbling the material
• Single drop
Truck Loading Segregation – how does it happen?
• No dribbling, no topping off• Multiple Drops
Truck Loading Segregation – how is it prevented?
Truck Hauling Segregation – how does it happen?
• Temperature variations causing:– Crusting – Lumps in mix
due to:– Long hauls– Delays – No tarps– No Insulation
Temperature Segregation in
truck!
Temperature Variation• 1% increase in air voids
over 7% results in a minimum 10% reduction in pavement life
Raveling and Moisture Damage
Fatigue Cracking
Aggregate Segregation
Truck Hauling Segregation – how is it prevented?
• Proper planning
• Proper tarp
• Proper insulation
• Proper Planning /Scheduling– Proper Coordination with Plant– Proper Number of Trucks– Coordination with Paver Speed– Avoid Bunching of Trucks
at Paver or Clean-out Area– Use Material Transfer
Vehicle
Truck Hauling Segregation – how is it prevented?
“Strive for Continuous Paving”
How Does It Happen?In Unloading the Truck•Dribbling the material•Poor Bed Condition•No Truck Release Agent
• Discharge in Mass• Flood Hopper• Truck Release Agent• Modify Dump Enclosure
Truck Unloading Segregation – how is it prevented?
Baffles
Paver Segregation – how does it happen?
• Hopper Wings
• Slat Conveyer
• Hopper Gates
• Auger
• Screed
Proportional Feed Control
Hopper Gates
Slat Conveyors
Hopper Wings
Augers
In the operation of the Auger
Feed Sensor
Gear Box
Material to the midpoint (or just covering) the Shaft
Install Kickback Paddles
Paver Segregation – how is it prevented?
Paver Segregation – how is it prevented?
In the Hopper
Fillet Corners
Caution in Cycling Hopper Wings
Cycle Wings onto full slat conveyors
Paver Segregation – how is it prevented?
In the Slat Conveyer
Never Run the Hopper empty
Preventing Segregation at Slats
• Truck dumper must communicate with paver operator
• MTV operator is responsible to not let hopper insert run “dry”
• Smooth and effective truck exchange when working without an MTV
In setting the Hopper Gates
Gates too HIGH - augers overloaded
Gates too LOW - insufficient material supply
Correct adjustment - uniform material volume/flow
Paver Segregation – how is it prevented?
In the operation of the Screed
Hydraulic Extension
Manual Extension Hydraulic Auger & Tunnel Extension
Auger & Tunnel Extensions missing
Paver Segregation – how is it prevented?
In the Operation of the Paver
• Proper Starting & Stopping
• Continual & Constant Paver Speed
Paver Segregation – how is it prevented?
Goal: Non-Stop Paving
Industry’s Answer
• Material Elevator
• Mobile Conveyors
• Material Transfer Vehicle
Segregation can still occur!
Problem:
Dropping Materials
Solution:
Limit drop
Keep hopper insert full
How to Prevent Segregation
Key Points in Prevention of Segregation
1. Proper Stockpiling2. Proper Plant Operation3. Proper Truck Loading4. Proper Truck Unloading5. Continuity of Paving Operation
Is this Pavement Segregated?
Does Every One Agree?
Segregation can be difficult to identifyAvailable tools to assist in this determination
If Pattern Segregation Is Suspected
• Notify Department and contractor
• Contractor continues work at his own risk
• The Department will initiate an investigation
• Surface texture depth (PTM 751) can be used to determine if segregation is present
PennDOT Specs Section 409.3(h)3.a
P.T.M. 751
P.T.M. 751 PROCEDURES• Perform the test at 3
locations in the suspected segregated area
• Calculate the average radius of these 3 locations
• Obtain the texture depth from Table 1 on page 7 of PTM 751
P.T.M. 751 PROCEDURES• Perform the test at 3
locations in a non- segregated area
• Calculate the average radius of these 3 locations
• Obtain the texture depth from Table 1 on page 7 of PTM 751
P.T.M. 751 PROCEDURES
• If average texture depth between areas exceeds 0.024 inches, suspected area is considered:
“Unacceptable Pattern Segregation”
If Unacceptable Pattern Segregation Is Evident
• [PennDOT Specs Section 409.3(h)3.b]:• Stop Paving• Department will evaluate segregation to
determine corrective work– DO NOT resume paving until Department reviews
corrective actions & authorizes paving to continue
• Test section then placed, <200 tons• Resume normal paving after successful test
section
If Unacceptable Pattern Segregation Is Evident
• Evaluating Segregation [PennDOT Specs Section 409.3(h)3.c]:– Take 6” Cores– Remove & Replace Segregated Areas if
sum of any 2 sieves vary 20% or more from the JMF or core Density is less then 90%
– Remove full lane width of segregated area plus 5 feet minimum beyond each end
SegregationTrouble Shooting
• Begin/end of load segregation
• Material segregated in truck
• Running conveyor deck dry.
• Cycling hopper wings too soon .
SegregationSource & cause
Begin/end of load segregation
• Center line segregation (single)
SegregationTrouble Shooting
• Missing or damaged baffle plates
• Overloaded material feed system
• Worn reversing augers
• Low auger RPM
• Warped or improperly set screed
SegregationSource & cause
Center line segregation (single)
• Stripe in line with outer auger bearing support
SegregationTrouble Shooting
• Excessively slow auger RPM
SegregationSource & cause
Stripe in line with outer auger bearing support
• Stripe in line with conveyors
SegregationTrouble Shooting
• Overloaded feeder system
• Low auger RPM
• Maintain proper head of material
SegregationSource & cause
Stripe in line with conveyors
• Stripe at outboard edge of mat
SegregationTrouble Shooting
• Insufficient material
• Not enough auger extensions
• Cold material dragging at extension
SegregationSource & cause
Stripe at outboard edge of mat
• What is Wrong?
SegregationTrouble Shooting
• Nothing!
• This is one beautiful mat.
SegregationSource & cause
Questions?
Did I go too fast?