1. Principles of Paving rev 8-2009 Principles of Paving

2. Principles of Paving rev 8-2009 Paver System Five Smoothtrac Sonic Averaging System Slope Control Control Sensors Sonic Control Laser Control = The answer for perfect, smooth paving? Grade Control Systems Tremendous benefits to the paving contractor: Increase efficiency and productivity Control Material Quantities Improve smoothness and rideability Increase jobsite safety

3. Principles of Paving rev 8-2009 Paver System Five Control Sensors Grade Control Good Paving Practice = + Control Sensors = + = + Decent paving Fair paving Great paving!

4. Principles of Paving rev 8-2009 Principles of Paving Good principles of paving must come BEFORE Grade Control Paving is a TEAM project Grade control is a great tool to help the paving team:  be more efficient  control material quantities  provide a smoother surface Train the entire TEAM!

5. Principles of Paving rev 8-2009 Paver Components Asphalt Paver The paver has two primary components: Tractor Screed

6. Principles of Paving rev 8-2009 Paver Tractor Tractor has two primary functions Material Handling Forward Movement

7. Principles of Paving rev 8-2009 Paver Tractor Asphalt distribution The paver typically receives the asphalt: directly from a truck by a pickup machine (windrow elevator)

8. Principles of Paving rev 8-2009 Paver Tractor Asphalt distribution The asphalt is received into the paver’s hopper Hopper is a holding station for the asphalt The operator tilts the hopper to deliver material into the feeder conveyor

9. Principles of Paving rev 8-2009 Paver Tractor Asphalt distribution Feeder conveyors distribute the asphalt to the augers The augers spread the asphalt in front of the screed End gates contain the material at the outer edge of the screed

10. Principles of Paving rev 8-2009 Screed Components Paver Screed Function of the screed is mat laydown Screed has several components

11. Principles of Paving rev 8-2009 Floating, Self-Leveling Screed The screed floats on the asphalt as it passes under the screed plate The screed will “self-level” and maintain a thickness based on the forces acting on the screed. Screed concept

12. Principles of Paving rev 8-2009 …controls mat thickness … Screed angle of attack… Screed Concept The desired thickness is controlled by the screed angle of attack As the angle of attack is increased or decreased, the screed will float up or down changing the thickness

13. Principles of Paving rev 8-2009 Changing Angle of Attack The angle of attack can be changed by: The manual crank The hydraulic cylinder at the tow point

14. Principles of Paving rev 8-2009 increased, Mat thickness increases decreased, Mat thickness decreases Screed Concept If the angle of attack is…

15. Principles of Paving rev 8-2009 Floating, Self-Leveling Screed The paver tractor, and therefore the screed tow point, travel over the existing “rough” surface The floating screed doesn’t react immediately to the variations in the tow point path The floating screed seeks it’s own level, smoothing out small humps and bumps.

16. Principles of Paving rev 8-2009 Fills in low spots Cuts off high spots Floating, self-leveling screed The floating screed naturally cuts off high spots and fill in low spots.

17. Principles of Paving rev 8-2009 Screed Reaction Tow point “step disturbance” and screed reaction Two point is changed by a unit of one (1) Net effect = the angle of attack has been changed

18. Principles of Paving rev 8-2009 Screed Reaction Example of tow point “step disturbance” and screed reaction Two point is changed by a unit of one (1)

19. Principles of Paving rev 8-2009 Screed Reaction Example of change in angle of attach by turning manual crank and screed reaction.

20. Principles of Paving rev 8-2009 Checking Mat Depth Goal is to “average” a particular paving thickness Always check several places, horizontally and laterally

21. Principles of Paving rev 8-2009 Adjusting Mat Depth Once an adjustment is made – GIVE THE SCREED TIME TO REACT!

22. Principles of Paving rev 8-2009 Determine average depth by measuring tons/mile Make small adjustments based on calculation Adjusting Mat Depth Goal – Provide smoothness and compaction, while hitting target tonnage for entire project!

23. Principles of Paving rev 8-2009 Left alone, the screed will self-level and assume a thickness based on forces that are acting on the screed. What are these forces? Floating, Self-Leveling Screed

24. Principles of Paving rev 8-2009 Forces Acting on the Screed There are four major forces acting on the screed

25. Principles of Paving rev 8-2009 Forces Acting on the Screed If any one of these forces change, the mat thickness will change.  But in “real life” job applications, these forces cannot always remain constant.

26. Principles of Paving rev 8-2009 Goal - Non-stop, continuous paving! decreases; mat thickness will increase increases; mat thickness will decrease Tow Point Force If the forward speed…

27. Principles of Paving rev 8-2009 Determine paving speed based on plant supply in tons/hour Regulate trucks to the paving supply and operation, not the paving operation to the trucks Tow Point Force Goal - Non-stop, continuous paving! Plant supply = 210 tons/hour Paving speed = 25’/minute

28. Principles of Paving rev 8-2009 Bump in mat at every truck exchange (probably “caused by faulty grade control!”) Tow Point Force Maintain smooth truck exchange!

29. Principles of Paving rev 8-2009 While stopped waiting for trucks, the screed will settle slightly Screed goes down, the tracker will also go down slightly In Motion Switches

30. Principles of Paving rev 8-2009 Grade control would want to drive the tow cylinder up to compensate The paver’s In-Motion switch stops the valve electrical signal A timer initiates the electrical signal after the paver is in-motion In Motion Switches X

31. Principles of Paving rev 8-2009 Maintain a CONSISTANT head of material Head of Material Force

32. Principles of Paving rev 8-2009 Head of Material Force Maintain a CONSISTANT head of material

33. Principles of Paving rev 8-2009 Head of Material Force Maintain a CONSISTANT head of material

34. Principles of Paving rev 8-2009 Mix Characteristics Gradation Segregation Mix Temperature Reaction of Material Force

35. Principles of Paving rev 8-2009 Compaction Force = Pounds per square inch Weight of the Screed Force

36. Principles of Paving rev 8-2009 Weight of the Screed Force Compaction Force = Pounds per square inch How can the weight force change? (lbs per square inch) People climbing on and off the screed can have a small effect on overall screed weight

37. Principles of Paving rev 8-2009 Weight of the Screed Force Screed extension Changing screed width changes the compaction force - Lbs per square inch

38. Principles of Paving rev 8-2009 Roller Compaction Good rolling practice is critical to the quality of the mat

39. Principles of Paving rev 8-2009 Roller Compaction A freshly laid, smooth mat will reflect some of the original surface after rolling Quality of the base being paved affects smoothness Multiple lifts help to minimize these effects

40. Principles of Paving rev 8-2009 Mechanical condition of the Paver The paving machine itself needs to be in good shape and adjusted correctly Feeder system Hopper, flight chain operation and adjustment, augers, etc. Operation and adjustment of feeder controls No excessive wear on screed components Screed plates Thickness control screws, bearings, and bushings Screed pivot point bushings Screed adjustment Strike off plates Screed flatness Screed extensions adjusted properly, elevation and slope

41. Principles of Paving rev 8-2009 Paver System Five Control Sensors Grade Control Good Paving Practice = + Control Sensors = + = + Decent paving Fair paving Great paving!

42. Principles of Paving rev 8-2009 Paver System Five Tow point is smoothly controlled to a desired path: Curb Stringline SAS smoothing out existing surface Then let the floating, self-leveling screed do it’s job!

43. Principles of Paving rev 8-2009 Best Paving Practices Good mechanical condition of the paver Minimize changes in the natural forces on the screed Non-stop, continuous paving Good, smooth truck exchange Constant paving speed Constant head of material Consistent mix characteristics Good rolling techniques Good quality of sub-base  Understand proper setup and operation of Grade Control

44. Principles of Paving rev 8-2009 Principles of Paving