Principles of Paving

1. Principles of Paving

2. Paver System Five • Grade Control Systems • Tremendous benefits to the paving contractor: • Increase efficiency and productivity • Control Material Quantities • Improve smoothness and rideability • Increase jobsite safety Control Sensors Slope Control Laser Control = Theanswer for perfect, smooth paving? Sonic Control Smoothtrac Sonic Averaging System

3. Paver System Five Good Paving Practice Grade Control Decent paving Control Sensors Control Sensors Control Sensors = + Fair paving = + Great paving! = +

4. 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. Paver Components • Asphalt Paver • The paver has two primary components: • Tractor • Screed

6. Paver Tractor • Tractor has two primary functions • Material Handling • Forward Movement

7. Paver Tractor • Asphalt distribution • The paver typically receives the asphalt: • directly from a truck • by a pickup machine (windrow elevator)

8. 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. 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. Screed Components • Paver Screed • Function of the screed is mat laydown • Screed has several components

11. Screed concept • 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. Floating, Self-Leveling Screed

12. 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 Screed angle of attack… …controls mat thickness …

13. Changing Angle of Attack • The angle of attack can be changed by: • The manual crank • The hydraulic cylinder at the tow point

14. Screed Concept If the angle of attack is… increased, decreased, Mat thickness decreases Mat thickness increases

15. 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. Floating, self-leveling screed • The floating screed naturally cuts off high spots and fill in low spots. Cuts off high spots Fills in low spots

17. 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. Screed Reaction • Example of tow point “step disturbance” and screed reaction • Two point is changed by a unit of one (1)

19. Screed Reaction Example of change in angle of attach by turning manual crank and screed reaction.

20. Checking Mat Depth • Goal is to “average” a particular paving thickness • Always check several places, horizontally and laterally

21. Adjusting Mat Depth • Once an adjustment is made – GIVE THE SCREED TIME TO REACT!

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

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

24. Forces Acting on the Screed There are four major forces acting on the screed

25. 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. Tow Point Force If the forward speed… increases; mat thickness will decrease decreases; mat thickness will increase Goal - Non-stop, continuous paving!

27. Tow Point Force Goal - Non-stop, continuous paving! • 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 Plant supply = 210 tons/hour Paving speed = 25’/minute

28. Tow Point Force Maintain smooth truck exchange! Bump in matat every truck exchange (probably “caused by faulty grade control!”)

29. In Motion Switches • While stopped waiting for trucks, the screed will settle slightly • Screed goes down, the tracker will also go down slightly

30. In Motion Switches • 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 X

31. Head of Material Force Maintain a CONSISTANT head of material

32. Head of Material Force Maintain a CONSISTANT head of material

33. Head of Material Force Maintain a CONSISTANT head of material

34. Reaction of Material Force • Mix Characteristics • Gradation • Segregation • Mix Temperature

35. Weight of the Screed Force Compaction Force = Pounds per square inch

36. 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. Weight of the Screed Force • Screed extension • Changing screed width changes the compaction force - Lbs per square inch

38. Roller Compaction • Good rolling practice is critical to the quality of the mat

39. 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. 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. Paver System Five Good Paving Practice Grade Control Decent paving Control Sensors Control Sensors Control Sensors = + Fair paving = + Great paving! = +

42. 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. 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