1. Asphalt Pavement Laydown and Compaction
Picture of plant

2. Compaction of the asphalt mat, typically, has more affect on the life of the pavement than any other item in asphalt construction.

3. Adequate Compaction Helps Reduce or Retard….
Fatigue Cracking
Rutting
Binder Oxidation
Moisture Damage
Thermal Cracking

4. Fatigue Cracking

5. Rutting

6. Asphalt Binder Oxidation - Hardening

7. Moisture Damage
Adequate compaction will help minimize the infiltration of water.

8. Thermal Cracking

9. Mixture Items that Affect Compaction
Aggregate texture, hardness and shape
Asphalt Binder Grade
Mixture Properties
Voids
Asphalt Binder Content
Mixture Temperature and Cooling Rate

10. Field Operations that Affect the Compaction of the Bituminous Mixture
Number of Roller Passes
Types of Rollers and Order they are used
Mode of the Steel Rollers
Vibratory mode on or off
High/Low Amplitude
High/Low Frequency
in most cases the roller should be set to high frequency and low amplitude
Speed of Rollers

11. Number of Roller Passes1 3 5 7 9 2 4
Number Passes to Cover Paver Width
Minimum Passes on Critical Longitudinal Section

12. Roller Speed Example Given: Plant & Paver Specifics - 12 feet wide
- 500 tons per hour
- 1.5 inch lift
Roller Specifics
- minimum 3 passes coverage
- roller width is 54 inch
Required
What is the minimum roller speed you need to compact the mat?

13. Roller Speed Answer The speed of the paver is:
500 tons per hour = 500*2000/145 = 6900 cuft per hour
Pavement Cross section = 12 feet * 1.5 inch/12 = 1.5 sqft
Paver speed = (6900 cuft/hr) / 1.5 sqft = 4600 ft/hour
The required roller speed is:
Roller Speed = 4600 ft/hour * 9 passes /5280 ft/mi = 7.8 mph

14. What are the Recommended Roller Speeds ?
Range of Roller Speeds (mph)
Operating Position
Type of Roller Breakdown Intermediate Finish
Static Steel Wheel
2 – 3.5
3 - 5
Pneumatic
4 - 7
Vibratory
2 - 3
2.5 – 3.5 --
From Chapter 18 of Hot Mix Paving Handbook

15. You Need More Than 1 Roller !!!

16. Roller Settings and Roller Patterns
Typical Rolling Pattern:
Vibratory Steel Roller as break down
Pneumatic Roller as intermediate
Static Steel Roller as finish roller
Vibratory Steel Roller generally works best in the high frequency and low amplitude mode
Only Pneumatic rollers should be used when the temperature of the mat is within the bituminous mixtures “tender zone”

17. Vibratory Breakdown

18. Pneumatic Breakdown

19. Amplitude (A) Time (T) For Full CycleUp
Amplitude
(A)
Movement
Time
Down
Time (T) For
Full Cycle
The elements of comparison for the dynamic component of a vibratory roller are the magnitude of the centrifugal force, its vibrating frequency, the nominal amplitude, and the ratio of the vibrating and non-vibrating masses acting on the drum.
Amplitude: How high does the drum jump?
Frequency, f = the number of hertz (cycles/s)--a single cycle
is one full rotation of the eccentric weight. Frequency = 1/T
Amplitude, A = the maximum deviation from position at
rest -- one-half the total movement.

20. Amplitude
Normal values of nominal amplitude range from 0.25 to 1 mm (1/100 to 1/32 in).
Some rollers can operate at only one fixed amplitude, while others have “high” and “low” amplitude positions.
Typically as the layer thickness increases, it is often advantageous to increase the nominal amplitude applied to the asphalt mix.
Unless ‘high’ amplitude is needed to achieve a particular density level, the vibratory roller should be operated in ‘low’ amplitude.
Ask: Does changing frequency change the compaction effort? (Yes vibrations/ft. Never less than 10.)

21. Frequency Low Frequency High Frequency Impact Spacing
The frequency of vibration is the number of complete cycles that the eccentrics rotate per minute.
The faster the rotation of the eccentrics, the greater the frequency of vibration.
Some vibratory rollers can operate at only one frequency or have a very limited selection of frequencies.
Other vibratory rollers can alter the frequency of the applied load between 1600 and 4000 vibrations per minute.
Frequencies below 2000 vibrations per minute are not normally acceptable to compact asphalt mixtures.
DIRECTION OF TRAVEL

22. Joint Compaction
Compaction of the Longitudinal Joint is the Weak Link in the Paving Process
Compaction of the Both the Confined and Unconfined Edges is a Challenge
The Unconfined Edge Needs to be Compacted with the Edge of the Steel Roller Over-hanging the Mat by 6 Inches
If a Pneumatic Roller is used in the Break Down Position, it Should not be Closer than 6 Inches to the Joint

23. Joint Compaction
Compaction of the Confined Joint is Best Achieved by Rolling on the Hot Mat and Overlapping the Cold Mat by 6 Inches
Rolling from the Cold Side is No Longer Recommended
Steel Rollers may Tend to Bridge from the Cold Mat and this May Impede Compaction Right at the Joint. A Pneumatic Roller will be More Effective in Reducing this Bridging.
Raking of the Joint is Not Recommended

24. Factors Affecting Rolling Time
allows MORE time
allows LESS time
FACTORS
Mat Thickness
THICK
THIN
Layer thickness is the thickness of an asphalt pavement layer, and it is the most important variable in the rate of cooling of asphalt mixtures.
It is very difficult to obtain the desired density on thin lifts of mix in cool weather because of the rapid loss in temperature in the mix.
A portion of the heat in the asphalt layer is lost to the air as well as the base as it is placed.
Depending on the air and base temperature as well as moisture content, the loss of temperature could be large or small.
Mix Temperature
HIGH
LOW
Base Temperature
HIGH
LOW

25. Time for Compaction Exercise

26. Paver Operations

27. Paver Operations
The primary objective of the paver is to place a bituminous mixture on the roadway, in a manner that results in mat that has an even distribution of temperature, thickness and pre-compaction, in both the longitudinal and transverse directions.

28. Mix Placement Concerns
Even and steady flow of mixture to the paver
Even and steady flow of mixture into the paver hopper
Even and steady flow of mixture through the paver and in front of the paver screed
The appropriate angle of attack of the screed needs to be set and frequent adjustments minimized

29. Flow of Mixture to the Paver

30. Flow of Mixture into the Paver Hopper

31. Paver Hopper and Flow Gates

32. Flow Gates set to Allow Uniform Material Flow to the Auger

33. Operating the Screed

34. What Affects the Thickness of the Bituminous Being Paved
If the paver speed, the height of material behind the screed, and tow point height are held constant, there is only one screed angle of attack that will give you the desired mat thickness.

37. Paver Schematic

42. TOW POINT

43. Automatics Screed Controls
Primary purpose of automatic screed control is to produce a smooth asphalt pavement layer.
Smoother than a screed operator can accomplish by continually changing the setting of the thickness control cranks.

44. Automatics Screed Controls
Automatic Screed Functions by:
maintaining the elevation of the screed tow points in relation to a reference other than that of the wheelbase of the paver itself.
Elevation of the tow point is kept at a constant elevation in relation to a given grade reference.
The automatics don’t allow the relative position of the tow point to change even though the tractor unit is moving up and down.

47. Automatics of the Paver
The paver operator controls the angle of attack of the screed.
The automatic controls on the paver control the tow point height.

48. Checking the Mat Thickness

49. Adjusting the Thickness

50. Screed Reaction Time
The screed reacts to change in angle of attack over 5 tow arm lengths.
65% of change occurs in the first tow arm length.
35% of change occurs in the last 4 tow arm lengths.

51. How Long Does it Take the Screed to React to an Adjustment of the Thickness Control Screw

52. What do the Automatics on a Paver do?

53. Contract Special Provisions

57. Bituminous Web Page

65. Common Errors When Using Spread Sheets
Most common error happens when the macros are disabled due to the security setting being set to high
Set the security level to “low”
Move cursor to the menu on top and under the “Tools” menu, pick Tools: Macro: Security
In the security dialog box, set the security level to “low” and press “OK”

68. Common Errors When Using Spread Sheets
Problems with creating random numbers
The two versions of the core locations spread sheets use random number functions to pick the core locations. The program must make a decision whether or not be make new random numbers. Read the instructions for the spread sheet to be sure that the random numbers are being treated properly.

71. Questions ?