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Segregation in Asphalt Paving Identification, causes & prevention Pennsylvania Asphalt Pavement Association Conference January 30, 2014 Sam Gregory Municipal.

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Presentation on theme: "Segregation in Asphalt Paving Identification, causes & prevention Pennsylvania Asphalt Pavement Association Conference January 30, 2014 Sam Gregory Municipal."— Presentation transcript:

1 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

2 What Is Segregation?

3 Webster defines Segregation as: “to separate from the main mass and collect together in a new body.”

4 What Is The Effect Of Segregation On Pavement? Premature Distress –Raveling –Frost Damage –Potholes

5 Why Do Premature Failures Occur Due To Segregation? Weaker Aggregate Structure and Gradation Weaker Mix Higher Voids

6 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

7 Stockpile Segregation – how does it happen? Large Stockpiles Single Aggregate Blends

8 Stockpile Segregation – how is it prevented? Well-trained Operators

9 Stockpile Segregation – how is it prevented? Different-sized material Separate piles

10 Stockpile Segregation – how is it prevented? Build Horizontal Layers Build Sloped Layers

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

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

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

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

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

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

17 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!

18 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

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

20 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”

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

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

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

24 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?

25 In the Hopper Fillet Corners Caution in Cycling Hopper Wings Cycle Wings onto full slat conveyors

26 Paver Segregation – how is it prevented? In the Slat Conveyer Never Run the Hopper empty

27 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

28 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?

29 In the operation of the Screed Hydraulic Extension Manual Extension Hydraulic Auger & Tunnel Extension Auger & Tunnel Extensions missing Paver Segregation – how is it prevented?

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

31 Goal: Non-Stop Paving Industry’s Answer Material Elevator Mobile Conveyors Material Transfer Vehicle

32 Segregation can still occur! Problem: Dropping Materials Solution: Limit drop Keep hopper insert full

33 How to Prevent Segregation

34 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

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

36 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

37 P.T.M. 751

38 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

39 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

40 P.T.M. 751 PROCEDURES If average texture depth between areas exceeds inches, suspected area is considered: “Unacceptable Pattern Segregation”

41 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

42 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

43 Segregation Trouble Shooting Begin/end of load segregation

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

45 Center line segregation (single) Segregation Trouble Shooting

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

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

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

49 Stripe in line with conveyors Segregation Trouble Shooting

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

51 Stripe at outboard edge of mat Segregation Trouble Shooting

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

53 What is Wrong ? Segregation Trouble Shooting

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

55 Questions? Did I go too fast?


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