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T I M A SCHE N B RE N E R, P . E .S E N I O R A S P H A L T P A V E M E N T E N G I N E E R
P A V E M E N T M A T E R I A L S T E A M
O F F I C E O F P R E C O N S T R U C T I O N , C O N S T R U C T I O N A N D P A V E M E N T S
F H W A
FHWA’s Demonstration Project for Enhanced Durability Through Increased Density
Courtesy Asphalt Institute
Achieving Increased In-place Density2
1• Density is Important
2• Gold Medal Examples
3• Density Demonstration Projects
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Density Is Important
From an FHWA document
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Cracking• To improve fatigue cracking resistance
• To improve thermal cracking resistance
Rutting• To minimize/prevent further consolidation
• To provide shear strength and resistance to rutting
Moisture Damage• To ensure the mixture is waterproof (impermeable)
Aging• To minimize oxidation of the asphalt binder
Density is important, but not a cure-all
Reasons for Obtaining Density4
FHWA photo
“A 1% decrease in air voids was estimated to:• improve fatigue
performance by 8.2 and 43.8%• improve the rutting
resistance by 7.3 to 66.3%• extend the service life by
conservatively 10%”
National Center for Asphalt Technology (NCAT) Report 16-02 (2016) (Funded by FHWA)
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http://eng.auburn.edu/research/centers/ncat/files/technical-reports/rep16-02.pdf
How Much Density (%Gmm) is Enough?Loss of Pavement Service Life
0
10
20
30
40
50
60
70
80
90
100
93 92 91 90 89
Per
cen
t Ser
vice
of L
ife
Density (%Gmm)
Washington State DOT Study
0
10
20
30
40
50
60
70
80
90
100
93 - 95 92 - 90 89 - 87 < 87
Per
cen
t Ser
vice
of L
ife
Density (%Gmm)
Colorado DOT Study
TRR 1217, 1989 CDOT 2013-4, 2013Thicker Pavements Typical Pavements
Reduced in-place density at the time of construction results in significant loss of service life!
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How Much Density (%Gmm) is Enough?NCAT Permeability Study
From NCAT Report 03‐02
Finer NMAS mixes generally less permeable at equivalent air void levels!
≤ 125x10‐5 cm/sec
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Achieving Increased In-place Density8
1• Density is Important
2• Gold Medal Examples
3• Density Demonstration Projects
Some “Gold Medal” Density (% Gmm) SpecificationsPurpose
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Identify density (% Gmm) specifications that are success stories.
Since this is an Olympic year, these success stories are considered “gold medal” examples.
Image Pixabay
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Some “Gold Medal” Density (%Gmm) Specifications
Alaska DOT&PF Connecticut DOT Maine DOT Maryland DOT SHA Michigan DOT Montana DOT New York State DOT Pennsylvania DOT Tennessee DOT
Note: There are likely more. Contact me if you think you have one.
WA
OR
ID
MT
CA
AK
HI
NV
UT
AZ
WY
ND
SD
NE
CO
NM
KS
OK
TX
MN
WI
IA
MO
AR
LA
IL IN
MI
OH
KY
WV
TN
MS AL GA
FL
SC
NC
PA
NY
ME
VA
VTNH
MA
CT
DE NJ
MD DC
PR
EFL
RI
CFL
WFL
Enhanced Durability of Asphalt Pavements through Increased In‐Place
Pavement Density
“Gold Medal”Density (%Gmm) Specifications
Gold Medal Density (% Gmm) SpecificationsProject Information
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StateD
AK ME MD MI MT NY PA TN
Year(s) of Data Analyzed
2016 20152013 to
20172017 2015
2007 to 2018
2017 20172015 to
2017
Mix Type Type C
Type II 19mm &
Superpave 12.5 mm
9.5, 12.5and 19
mm
Dense Graded
9.5, 12.5and 19
mm
9.5, 12.5 and 19
mm
Series 509.5, 12.5 and 19
mm
High level
wearing surface
9.5, 12.5 & 19mm
D-mix(3/8”
NMAS)
Type of Projects
N/A
Interstateand
principal arterial
All mainline projects
All projects>
5,000 tons
All projects
Full or partially
controlled roadways
Interstate and SR
Freeways
Acceptance Testing
Agencyonly
Agencyonly
Agencyonly
Contractorvalidated by agency
Agency only
Agency only
Agency only
Agency only
Agency only
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Maine DOTStatewide Results 2013 to 2017
0 8 1259
194
517
894
1163 1130
571
151
110
200
400
600
800
1000
1200
1400
87.5 88.5 89.5 90.5 91.5 92.5 93.5 94.5 95.5 96.5 97.5 98.5
Number of Records
Density (% Gmm)
Avg.=94.5%
5.8% below 92%
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Michigan DOTStatewide Results from 2015
0
20
40
60
80
100
120
140
160
Number of Records
Density (% Gmm)
Avg.=94.4%
5.5% below 92%
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State DStatewide Results from 2016
2
99
22
31
4445
52
57
29
2219
16
6
000
10
20
30
40
50
60
96.095.595.094.594.093.593.092.592.091.591.090.590.089.589.088.5
Number of Records
Density (% Gmm)
25.3% below 92%
Avg.=92.6%
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State DStatewide Results from 2016
2
99
22
31
4445
5257
29
2219
16
6
000
10
20
30
40
50
60
96.095.595.094.594.093.593.092.592.091.591.090.590.089.589.088.5
Number of Records
Density (% Gmm)
Avg.=92.6%41.0% below 92.4%
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Arizona DOTStatewide Results from 2017
17
7 20 64 163
479
1144
1997
2434
1937
862
22137 3
0
500
1000
1500
2000
2500
3000
Number of Records
Density (% Gmm)
Avg.=93.2%
20.0% below 92%
Arizona DOTTwo Demonstration Projects in 2018
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533
93
264
383
275
109
261
0
50
100
150
200
250
300
350
400
450
86.5 87.5 88.5 89.5 90.5 91.5 92.5 93.5 94.5 95.5 96.5 97.5 98.5
Nu
mb
er o
f R
eco
rds
Density (% Gmm)
Avg.=94.0%
5.7% below 92%
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2017 Standard2017 Standard 2018 Demonstration Projects2018 Demonstration Projects
PWL
USL = 9.0 %
Average Air Voids = 6.8%
Lot Standard Deviation = 1.36
> 8% Air Voids = 20.0%
PWL
USL = 8.0 %
Average Air Voids = 6.0%
Lot Standard Deviation = 0.86
> 8% Air Voids = 5.7%
Specification Comparison
“Gold Medal” Density (%Gmm) SpecificationsSpecification / Criteria / Results
StateD
CT MD MT TN
Type of Specification
Lot Avg.
Lot Avg.
Lot Avg. &Ind. Sublot
Lot Avg. & Range
Lot Avg.
Limits(% Gmm)
91.5 to 95.0
92.0 to 97.0
92.0 to 97.0
93.0 to 100.0
92.0 to 97.0
Incentive for Only Density
1.5% 2.5% 5.0%8.0%
(AC sep.)2.0%
Max. Incent. (% Gmm)
92.75 94.5 94.094.0 to
95.094.0
Avg. (% Gmm) 92.6 93.7 94.0 94.3 93.9
Std. Dev. of Lots
N/A N/A 1.03 N/A N/A
< 92% Gmm 25.3% 19.0% 5.3% 6.6% 11.0%
“Gold Medal” Density (%Gmm) SpecificationsSpecification / Criteria / Results
StateD
AK ME MI NY PA
Type of Specification
Lot Avg.
PWL PWL PWL PWL PWL
Limits(% Gmm)
91.5 to 95.0
93.0 to 100.0
92.5 to97.5
92.5 to 100.0
92.0 to 97.0
92.0 to 98.0
Incentive for Only Density
1.5% 5.0% 2.5% 2.0% 5.0% 2.0%
Max. Incent. (% Gmm)
92.75 ≈96.0 ≈93.5 ≈94.5 ≈94.0 ≈94.0
Avg. (% Gmm) 92.6 94.9 94.5 94.4 94.2 94.4
Std. Dev. of Lots
N/A 1.76 1.20 1.03 1.01 1.46
< 92% Gmm 25.3% 5.6% 5.8% 5.5% 5.0% 3.1%
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“Gold Medal” Density (%Gmm) SpecificationsTesting and Frequency
State D CT MD MT TN
Lot Size (tons)
2,000 2,000 Day’s production
3,000 1,000
Sublots per Lot
8 4 5 min. 5 5
Frequency(tons)
250 500 500 max. 600 200
Measuring Gmb
6-in. cores1 per
sublot
6-in. cores1 per
sublot
4 or 6-in. cores2 per sublot
4 or 6-in cores2 per sublot
4 or 6-in. cores1 per
sublot
Measuring Gmm
Avg. of 5 tests:
every 500 tons
Avg. of 2 tests:Daily
Ind. test:Daily value
Avg. of 5 tests:every
1000 tons
DailyAvg.:
2 tests per day
“Gold Medal” Density (%Gmm) SpecificationsTesting and Frequency
State D AK ME MI NY PA
Lot Size (tons)
2,000 5,000 4,500 5,000 1,000 2,500
Sublots per Lot
8 10 6 5 4 5
Frequency(tons)
250 500 750 1000 250 500
Measuring Gmb
6-in. cores1 per
sublot
6-in. cores1 per
sublot
6-in. cores1 per
sublot
6-in. cores1 per
sublot
6-in cores1 per
sublot
6-in cores1 per
sublot
Measuring Gmm
Avg. of 5 tests:
every 500 tons
Ind. test:1 per lot
Ind. test:1 per
sublot
Ind. test: 1 per
sublot
Ind. test: 1 per
lot
Ind. test:Daily value
Gold Medal Density (% Gmm) SpecificationsSpecification/Criteria/Results
StateD
AK ME MD MI NY PA TN
Type of Specification
None Lot Avg. PWL None Lot Avg. Under Development PWL Lot Avg.
Limits(% Gmm)
--- >91.0 >91.0 --- >90.5 --- >90.0 >91.0
Incentive for Only Joint Density
---$1.50 per
L.F.(≈6.25%)
2.0% ---$1.00 per
L.F.(≈4.0%)
---$5000 per
Lot(≈2.5%)
1.25%
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Longitudinal Joint
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Achieving Increased In-place Density25
1• Density is Important
2• Gold Medal Examples
3• Density Demonstration Projects
WA
OR
ID
MT
CA
AK
NV
UT
AZ
WY
ND
SD
NE
CO
NM
KS
OK
TX
MN
WI
IA
MO
AR
LA
IL IN
MI
OH
KY
WV
TN
MS AL GA
FL
SC
NC
PA
NY
ME
VA
VTNH
MA
CT
DE NJ
MD DC
RI
CFL
WFL
Workshops
EFL
AK
HI PR
28 States
Enhanced Durability of Asphalt Pavements through Increased In‐Place
Pavement Density
WA
OR
ID
MT
CA
AK
HI
NV
UT
AZ
WY
ND
SD
NE
CO
NM
KS
OK
TX
MN
WI
IA
MO
AR
LA
IL IN
MI
OH
KY
WV
TN
MS AL GA
FL
SC
NC
PA
NY
ME
VA
VTNH
MA
CT
DE NJ
MD DC
EFL
RI
CFL
WFL
Enhanced Durability of Asphalt Pavements through Increased In‐Place
Pavement Density
Demonstration Projects
Phase 1 (10 states)
PRMobile Asphalt Testing Trailer (2)
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WA
OR
ID
MT
CA
AK
HI
NV
UT
AZ
WY
ND
SD
NE
CO
NM
KS
OK
TX
MN
WI
IA
MO
AR
LA
IL IN
MI
OH
KY
WV
TN
MS AL GA
FL
SC
NC
PA
NY
MEVT
NH
MA
CT
DE NJ
MD DC
EFL
RI
CFL
WFL
Enhanced Durability of Asphalt Pavements through Increased In‐Place
Pavement Density
Demonstration Projects
Phase 1 (10 states)Phase 2 (9 states)
PRMobile Asphalt Testing Trailer (3)
VA
WA
OR
ID
MT
CA
AK
HI
NV
UT
AZ
WY
ND
SD
NE
CO
NM
KS
OK
TX
MN
WI
IA
MO
AR
LA
IL IN
MI
OH
KY
WV
TN
MS AL GA
FL
SC
NC
PA
NY
MEVT
NH
MA
CT
DE NJ
MD DC
PR
EFL
RI
CFL
WFL
Enhanced Durability of Asphalt Pavements through Increased In‐Place
Pavement Density Phase 1 (10 states)Phase 2 (9 states)Phase 3 (10 states)
Demonstration Projects
Mobile Asphalt Testing Trailer (3)
VA
Demonstration Project Status
Phase Year States ConstructedState
ReportsSummary
Report
1 2016 10 10 10 July 2017
22017-2018
9 8(2 re-do’s)
4
3 2018 10 10 4
30
Updated: Jan. 15, 2019
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Colorado DOT
Location Mode Passes Equipment
Delivery Belly DumpBOMAG Cedarapids
MS-2
Control (July)
Breakdown Vibratory 5 CAT CB64
Intermediate Pneumatic 7 CAT CW34
Photos Courtesy NCAT
Colorado DOT
Experiment Contractor’s Compactive EffortTest Section 1 (July) Added 1 roller – Hypac C784A (3 rollers)
Test Section 2 (Aug) Added 1 roller (3 rollers) with 7 more passes
Test Section 3 (Aug) Added 1 roller (3 rollers) with 9 more passes
Colorado DOTExperiment Density
Results (% Gmm)
Std.Dev.
Change
Control 92.9 1.6 ---
Test Section #1 92.5 1.8 Not Significant
Test Section #2 94.0 -- + 1.1
Test Section #3 94.7 1.1 + 1.8
• Density (%Gmm) values are averages of a minimum 12 nuclear gauge readings correlated to cores
• Higher density obtained with additional roller and more passes (Aug)
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Field Compactive EffortControl Sections
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State ID
Total Vibratory Pneumatic Echelon FocusAreaRollers Passes Rollers Passes Rollers Passes Brkdn. Inter.
2 1 7 1 7 0 0 No No More passes
9 2 16 1 3 0 0 No No Oscillation
6 2 14 2 10 0 0 Yes No More AC
7 3 15 3 12 0* 0 Yes No Std. Dev.
5 3 15 2 10 1 5 Yes No More AC
10 2 18 2 18 0* 0 No No New Tech.
1 2 18 0 0 0* 0 Yes No Pneumatic
4 3 21 2 10 1 11 Yes No More AC
3 4 24 2 10 2 14 Yes YesMore AC and
New Tech.
8 2 24 1 8 1 15 No No Std. Dev.
* Polymer Modified Asphalt
Density (%Gmm) Test Sections35
State ID
TotalBreakdown
Roller
Field Density (% Gmm)
∆ from control
SpecificationRequire-
mentIncentive/
DisincentiveRollers Passes
2 1 9 No echelon 91.8 + 0.8 Min. Sublot 92.0 D
9 2 12 No echelon 92.0 - 0.2% Control
Strip98.0 D
6 2 14 Echelon 95.4 + 2.1 PWL 91.0 I/D
5 3 15 Echelon 95.2 + 2.7 PWL 92.0 I/D
7 3 15 Echelon 96.1 + 1.7 PWL 92.0 I/D
10 2 18 No echelon 95.7 + 0.1 PWL 92.0 I/D
8 2 24 No echelon 93.0 + 1.0 PWL 91.0 I/D
4 4 26 Echelon 95.4 + 1.9 Min. Lot Avg. 91.5 D
1 3 27Echelon /
No vibratory95.4 + 1.9 PWL 91.8 I/D
3 5 29 Echelon 94.1 + 1.2 Min. Lot Avg. 92.0 I/D
Can We Achieve Increased In-place Density?36
Test sections had increased density (% Gmm):
8 of 10 States achieved > 1.0% increase
7 of 10 States achieved > 94.0% Gmm
6 of 10 States achieved > 95.0% Gmm
Will there be changes?
8 of 10 States are changing specifications
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Agency Changes (1 of 2)37
Measuring density (1) Reference density (1) Density of pavement to meet requirements (4) Some at 90 to 91% Gmm Others at 94% Gmm
Type of specification (2) 22 states use minimum lot average 25 states use PWL
Impacts contractors’ target and consistency
Consistency (2) Standard deviations <1.00 were achievable
(#) – Number of States making changes or in the process
Agency Changes (2 of 2)38
Incentives (3) 37 states have incentives: range from 1 to 10%; average 2.9%
Mixture design changes (5) Many states changing Superpave to get more asphalt
Must also look at density specification
New technologies (2) Did not help improve density, but were a good trouble-shooting tool
(#) – Number of States making changes or in the process
Contractor Changes39
More passes “Roll until you meet density requirements”
More rollers Some were using 1 roller
Type of rollers Pneumatic / Oscillation
Location of rollers Echelon
General best practices Temperature / spacing / screed Courtesy Miguel Montoya
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State 4: Cost / Benefit of Best Practices
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Benefit of 1% Density Increase10 percent of $60 / ton mix = $$$$$$
Cost of 1 Percent Density IncreaseAdditional rollers ≤ $AVR to 3% W/binder ≤ $$WMA Additive ≤ $9.5mm vs. 12.5mm ≈ $$
Benefits Costs
Image: Pixabay; text added
Summary Document Phase 141
NCAT Report 17-05:
“Demonstration Project for Enhanced Durability of Asphalt Pavements through Increased In-place Pavement Density”
July 2017
http://eng.auburn.edu/research/centers/ncat/files/technical-reports/rep17-05.pdf
Next Steps42
Field experiment – Phase 2 8 of 9 states completed construction 4 of 9 states completed reports
Field experiment – Phase 3 10 of 10 states completed construction 4 of 10 states completed reports
FHWA’s best practices communication Summary documents: Phases 2 and 3 Tech Brief Additional workshops
Funding dependent
Image: Pixabay
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Thank youQ U E S T I O N S / C O M M E N T S :
T I M A S C H E N B R E N E R , P . E .
F H WAS E N I O R A S P H A L T P A V E M E N T E N G I N E E R
P A V E M E N T M A T E R I A L S T E A M
O F F I C E O F P R E C O N S T R U C T I O N , C O N S T R U C T I O N A N D P A V E M E N T S
L A K E W O O D , C O L O R A D O
( 7 2 0 ) 9 6 3 - 3 2 4 7
T I M O T H Y . A S C H E N B R E N E R @ D O T . G O V
Image Pixabay
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