Free Floating Screed. Screed Weight Forward Motion. Head of Material. Material Stability. Angle of Attack

Transcription

1 Free Floating Screed Screed Weight Forward Motion Material Stability Head of Material Angle of Attack

2 Stability of the Mix Stability of Mix is Critical. Temperature Changes in Mix Can Effect Mat Being Laid. Consistent Temperature = Smooth Mat

3 Free Floating Screed Screed Weight Forward Motion Material Stability Head of Material Angle of Attack

4 Screed Weight Surface Area of Screed in Contact With Mat (PSI)

5 Screed Weight Watch When Extending & Retracting Screed Changes PSI When Extending and Retracting Variable Width Screed

6 Screed Adjustments Lead Crown Correct v Even texture across full width v Zero crown for most mixes

7 Screed Adjustments Lead Crown Low v Open texture in center v Tight on sides v Put in crown

8 Screed Adjustments Lead Crown High v Tight, shiny strip in center v Open texture on sides v Reduce lead crown

9 Paving Speed v Maintaining a consistent paver speed is key l material feed system is set by paver speed

10 Paver - Segregation v Stopping & starting paver v Paving speed

11 Paver - Segregation v Truck v Keep End drag slats covered

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13 Paver - Segregation v Cycling hopper wings

14 Don t Run the Hopper Empty! Don t Expose Conveyor Chains

15 Don t Allow HMA to Dribble When Raising the Bed! Segregation

16 Don t Bump the Paver!

17 Don t Disturb the Paver Steering

18 Don t Clean & Leave Piles of HMA on the Grade!

19 Don t Dump Material on Grade!

20 Alabama Fire Alarm

21 Texas Horseshoes

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24 v Compaction basics v Asphalt compaction

25 Importance of Compaction v Improve Mechanical Stability v Improve Resistance to Permanent Deformation v Reduce Moisture Penetration v Improve Fatigue Resistance v Reduce Low-Temperature Cracking Potential

26 Hot Mix Compaction v Asphalt binder holds particles together l Provides lubrication at high temperatures l Provides cohesion at in-service temperatures v Prevents air and water intrusion into mat

27 Factors Affecting Compaction v Properties of the Materials v Environmental Variables v Laydown Site Conditions

28 Properties of the Materials v Aggregate v Asphalt Cement v Mix Properties

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30 Environmental Variables v Layer thickness v Air and base temperature v Mix laydown temperature v Wind velocity v Effect of sun

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33 Laydown Site Conditions v Lift thickness versus aggregate size v Lift thickness uniformity v Base Conditions

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35 Compaction Forces Static Pressure Manipulation Impact Vibration

36 Static Pressure Weight at Drum Ground Contact Area Drum Width

37 Manipulation

38 Vibration v Eccentric weights cause drum to move up and down v Vibration increases compactive effort

39 Frequency & Impact Spacing

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41 Drum Impacts per foot (10/ft min.) Frequency 2 MPH 3 MPH 4 MPH 5 MPH 2000 vpm vpm vpm vpm vpm vpm vpm vpm vpm vpm

42 Compaction Rules Compaction must be achieved while viscosity of binder and stiffness of mix are low enough to allow reorientation of aggregate particles under action of rollers

43 Compaction Rules Initial compaction should occur directly behind paver in order to reach required density quickest

44 Drum Movement Large Amplitude Small Amplitude At same frequency large amplitude generates greater force

45 Amplitude vs Centrifugal Force Machine 1 Machine " Amplitude (lift height) 0.078" 3,000 vpm Frequency 1,500 vpm (number of hits) 40,000 lb Centrifugal Force 40,000 lb

46 Asphalt Compaction

47 Keys to Compaction v Roll mix as hot as possible l Keeps asphalt viscosity low l Able to re-orient aggregate particles v Keep rollers close to paver

48 Density Growth n Primary compaction n Aggregate movement v Some additional compaction v Binder movement n Minimal additional compaction n Smooth surface

49 Amplitude *For very thin lifts, vibration is not recommended, especially on rigid base supports

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51 Double Drum Vibratory v Keep close behind paver v Breakdown should be completed before mix falls below 250 o F v Operated at highest frequency level v Amplitude dependent on thickness of HMA being placed

52 Pneumatic Compaction

53 Pneumatic Roller v Keep tires at same temperature as mat being compacted v Don t let rollers sit v Difficult to avoid pickup with some PMA s v Compaction should be completed before mix temperature drops to about 210 o F

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56 Asphalt Sticking Possible causes: v Tires too cool v Modifiers in asphalt v Nonstick emulsion ineffective

57 Static Compaction

58 Static Compaction v Get last little bit of density v Remove any roller marks v Complete before about 175 o F

59 Time Available for Compaction (TAC)

60 TAC Example # Mix Temp, o F Air/Base Temp, o F Mat Thk, in / / / /40 3 THE Answer, minutes

61 TAC Example # Mix Temp, o F Air/Base Temp, o F Mat Thk, in THE Answer, minutes / / / /

62 TAC Example # Mix Temp, o F Air/Base Temp, o F Mat Thk, in / / / /40 2 THE Answer, minutes

63 TAC Example # Mix Temp, o F Air/Base Temp, o F Mat Thk, in THE Answer, minutes / / / /

64 Time Available for Compaction Search for MultiCool

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