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Top 10 Listfor

More Durable HMA Pavements

November 29, 2018

Dave Newcomb

Texas A&M Transportation Institute

Ontario Asphalt Pavement Council

The List1. Do your homework.

2. Use mixes with higher AC content.

3. Use a finer gradation.

4. Use the right mixing temperature.

5. Include the right surface preparation.

6. Make sure you get bonding between layers.

7. Aim for higher density.

8. Ensure uniformity and consistency in mix.

9. Use RAP appropriately.

10. Use QA and inspection for improvement.

November 29, 2018 OAPC Meeting

DO YOUR HOMEWORK


Coach wouldn’t let me finish it!

Homework

• Use preconstruction evaluation for effective design– Surface defects

– Subsurface conditions• Water

• Depth of cracking

• Weak base

• Subgrade condition

• Previous widening

– Material integrity

– Current and future traffic

– Constructability review


Surface Defects



Avg. Surface Thickness = 62 mmAvg. Base Thickness = 150 mmGPR

LiDAR

USE HIGHER ASPHALT CONTENT


Don’t be dense!

Increasing Asphalt Content

• Lower number of gyrations

• Regressing to 3% air voids

– Compact mix to 4% air voids

– Regress the asphalt content from the 4% air void level to the 3% air void level – Design asphalt content

• Use performance tests to define asphalt content

• Use finer gradations


Lower Number of Gyrations

• High gyrations may lead to damaging aggregate structure and lowering VMA

• States with fixed number of gyrations (between 50 and 80)– Texas

– Alabama

– Iowa

– Virginia

– Minnesota

• SPG compactor is very harsh on mixtures


Regress to 3% Air Voids


log Gyrations

Gm

m, %

96

97

60

5.5%

5.0%

4.5%4.7% AC

5.4% Design AC

Asp

halt C

on

tent

Performance Testing for Balanced Mix Design


DCT IDEAL

IDEAL Test Results – Mix 2

12/5/2018 MNAAPT

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

4.5 4.7 4.9 5.1 5.3 5.5 5.7 5.9

CT

Ind

ex

% Binder Content

IDEAL Test Results for Mix 2

4.9+0.4 = 5.3

DCT Test Results – Mix 2

12/5/2018 MNAAPT

300.0

400.0

500.0

600.0

700.0

800.0

900.0

1000.0

1100.0

4.7 4.9 5.1 5.3 5.5 5.7 5.9 6.1

Ener

gy

% of Binder Content

DCT Test Results for Mix 2

HV

LV

4.9+0.4 = 5.3

Too Dense!


Lots of Room!


USE FINER GRADATIONS


Be a rebel, strive for uniformity!

Advantages of Finer Gradations

• Avoid segregation

– Physical

– Thermal

• Easier to work

• Easier to compact

• Greater cracking resistance

• Quieter


Finer Gradations


94.6%

201.2

89.8%

154.392.7%

176.693.7%

194.992.4%

204.387.8%

206.0

*>237 . 6 °F

*<68 . 0°F

80. 0

100. 0

120 . 0

140. 0

160 . 0

180 . 0

200. 0

220. 0

Workability (NCAT)


DCT Results

300

350

400

450

500

550

600

4 4.5 5 5.5 6 6.5 7

Frac

ture

En

ergy

, J/m

2

Asphalt Content, %


OAC @ 4% AV

12.5 mm

9.5 mm

Finer = Quieter


DON’T OVERHEAT


Save the heat for the beach!

Aging

• Stiffening of asphalt binders and mixtures

• Key factor affecting mixture properties and pavement performance

Stif

fne

ss

Temp X Time

Colder

Hotter

Warm Mix Asphalt

• WMA Technologies –proven benefits

– Longer haul times

– Lower initial aging

– Improved workability -higher density

– Lower emissions


Control

Temp = 320oF

WMA

Temp = 270oF

SURFACE PREPARATION


Smoothness is not an accident!

IT’S IMPORTANT TO BONDStrong bonds are not shear luck!

Don’t let it slip!

Surface Preparation

• Advantages of Milling– Gets rid of surface defects

– Create a rough interface –less slippage

– Produce RAP

– Create a level pavement

– Reduced impact on profile

• Plans– Mill to bottom of cracks

– Or use interlayer

– Accommodate multiple lifts


Bonding

• Shear Stress Cracking

– Weak or thin surface

– Need pavement to act as a system, not individual layers


DENSITY IS THE GOAL


Rutting vs. Air Voids

0

5

10

15

20

25

30

35

40

Rutting,

mm

Low Medium High

Relative Air Voids

Ref: WesTrack

Fatigue vs. Air Voids

0

0.5

1

1.5

2

2.5

3

4 5 6 7 8

Avg. Air Voids, %

Esti

mate

d F

ati

gu

e L

ife

0.60%

1.20%

1.80%

Ref: WesTrack

Permeability

NCHRP Report 531

Relationships of HMA In-Place Air Voids, Lift Thickness, and Permeability (NCHRP 9- 27)

• Recommended minimum lift thicknesses:

– 3 X NMAS for fine-graded mixes

– 4 X NMAS for coarse-graded mixes

• Thin lifts cool faster

– less time available for compaction

http://trb.org/news/blurb_detail.asp?id=4377

150

175

200

225

250

275

300

0 5 10 15 20 25 30 35 40 45 50 55 60

Time, minutes

Tem

pera

ture

, F

1.5" 2" 3"

80OF Surface & Air Temperature, 5 mph wind

150

175

200

225

250

275

300

0 5 10 15 20 25 30 35 40 45 50 55 60

Time, minutes

Tem

pera

ture

, F

1.5" 2" 3"

30OF Surface, 40OF Air Temperature, 15 mph wind

UNIFORMITY AND CONSISTENCY


Construction is not the time or place forREBELLION!

Good Control


91

93

95

97

99

101

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43

Den

sity

%

Sublot Number

Average Density Readings %

Lower Limits Upper Limits QC Readings QA Readings

4.6

4.8

5

5.2

5.4

5.6

5.8

6

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43

Asp

hal

t C

on

ten

t %

Sublot Number

Asphalt Content Readings


Less Control


4.8

5

5.2

5.4

5.6

5.8

6

6.2

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101

105

109

113

Asp

hal

t C

on

ten

t %

Sublot Number

Asphalt Content


86

88

90

92

94

96

98

100

102

1 4 7

10

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55

58

61

64

67

70

73

76

79

82

85

88

91

94

97

10

0

10

3

10

6

10

9

11

2

Den

sity

%

Sublot Number

Density Readings


USE RAP RESPONSIBLY


RAP/RAS and PG

RAP/RAS binder too stiff?

February 1, 2017 Ohio Paving Conference

QC/QA AND INSPECTION


Avoid 5-minute screw-ups!

It’s a Target, not a Limbo Bar!


5-minute Screw Up

Inspect Items that Can’t Be Measured


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