Segregation in Asphalt Paving
Identification, causes & prevention
Pennsylvania Asphalt Pavement
Association Conference
January 30, 2014
Sam Gregory
Municipal Transportation Specialist
State 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
• Truck Hauling
• Truck Unloading
• Paver – Hopper, Slat
Conveyers, Hopper gates, Auger, Screed
• Paving Operation
Continuity (Balance)
Plant Responsibility
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

Cold Feed Bin Segregation – how does it happen?
•
Bridging

Cold Feed Bin Segregation
– how is it prevented?
•
Reconfigure Opening – uniform feeding

Hot Bin Segregation – how does it
•
Range of Materials happen?
•
Size of Bin
•
Shape of Bin
•
No. 1 Bin

Hot Bin Segregation – how is it prevented?
•
Install Baffle – dust slides to center

Truck Loading Segregation – how does it happen?
•
Dribbling the material
•
Single drop

Truck Loading Segregation – how is it prevented?
•
No dribbling, no topping off
•
Multiple Drops

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
Aggregate Segregation
Fatigue Cracking

Truck Hauling Segregation – how is it prevented?
• Proper planning
• Proper tarp
• Proper insulation

Truck Hauling Segregation – how is it prevented?
“Strive for Continuous Paving”
• 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

How Does It Happen?
In Unloading the Truck
•
Dribbling the material
•
Poor Bed Condition
•
No Truck Release Agent

Truck Unloading Segregation – how is it prevented?
•
Discharge in Mass
•
Flood Hopper
•
Truck Release Agent
•
Modify Dump Enclosure
Baffles

Paver Segregation – how does it happen?
•
Hopper Wings
•
Slat Conveyer
•
Hopper Gates
•
Auger
•
Screed
Hopper Wings
Slat Conveyors
Hopper Gates
Proportional
Feed Control
Augers

Paver Segregation – how is it prevented?
In the operation of the Auger
Material to the midpoint
(or just covering) the Shaft
Gear Box
Install
Kickback
Paddles
Feed Sensor

Paver Segregation – how is it prevented?
Caution in Cycling
In the Hopper
Hopper Wings
Fillet
Corners
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

Paver Segregation – how is it prevented?
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
Manual Extension Hydraulic Auger &
Tunnel Extension
Hydraulic
Extension
Auger & Tunnel
Extensions missing

Paver Segregation – how is it prevented?
In the Operation of the Paver
•
Proper Starting & Stopping
•
Continual & Constant Paver Speed

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 Stockpiling
2. Proper Plant Operation
3. Proper Truck Loading
4. Proper Truck Unloading
5. Continuity of Paving Operation

Is this Pavement
Segregated?
Does Every One Agree?
Segregation can be difficult to identify
Available tools to assist in this determination

If Pattern Segregation Is
Suspected
PennDOT Specs
Section 409.3(h)3.a
• 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

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

Segregation
Trouble Shooting
• Begin/end of load segregation

Segregation
Source & cause
Begin/end of load segregation
• Material segregated in truck
• Running conveyor deck dry.
• Cycling hopper wings too soon .

Segregation
Trouble Shooting
• Center line segregation
(single)

Segregation
Source & cause
Center line segregation
(single)
• Missing or damaged baffle plates
• Overloaded material feed system
• Worn reversing augers
• Low auger RPM
• Warped or improperly set screed

Segregation
Trouble Shooting
• Stripe in line with outer auger bearing support

Segregation
Source & cause
Stripe in line with outer auger bearing support
• Excessively slow auger RPM

Segregation
Trouble Shooting
• Stripe in line with conveyors

Segregation
Source & cause
Stripe in line with conveyors
• Overloaded feeder system
• Low auger RPM
• Maintain proper head of material

Segregation
Trouble Shooting
• Stripe at outboard edge of mat

Segregation
Source & cause
Stripe at outboard edge of mat
• Insufficient material
• Not enough auger extensions
• Cold material dragging at extension

Segregation
Trouble Shooting
• What is
Wrong
?

Segregation
Source & cause
• Nothing!
• This is one beautiful mat.

Questions?
Did I go too fast?