Verification of Gyration Verification of Gyration Levels in the SuperpaveLevels in the Superpave
NNdesigndesign TableTable
Brian D. Prowell, P.E.Brian D. Prowell, P.E.
NEAUPGNewport, Rhode Island
The compaction effort used in a The compaction effort used in a volumetric mix design should volumetric mix design should produce laboratory samples produce laboratory samples
which approximate the ultimate which approximate the ultimate density of the pavement density of the pavement
The goal of this project is to verify the The goal of this project is to verify the laboratory compaction efforts laboratory compaction efforts
established in 1999 for the Superpave established in 1999 for the Superpave gyratory compactorgyratory compactor
OverviewOverview
•• Background of Background of NNdesigndesign
•• NCAT Test TrackNCAT Test Track•• NCHRP 9NCHRP 9--9(1) Field Test Sections9(1) Field Test Sections•• Affect of Internal Angle of GyrationAffect of Internal Angle of Gyration•• ConclusionsConclusions
SHRP SHRP NNdesigndesign ExperimentExperiment•• Looked at three traffic levels and three Looked at three traffic levels and three
climates, two replicates for each except climates, two replicates for each except “hot” climate (nine cells)“hot” climate (nine cells)
•• Sites selected from LTPP GPS Sites selected from LTPP GPS pavement sites 12 years old or older pavement sites 12 years old or older --reached “design” air voids of 3% reached “design” air voids of 3% -- 5%5%
•• Construction air voids assumed to be Construction air voids assumed to be 8%8%
SHRPSHRP NNdesigndesign Experiment Cont.Experiment Cont.
•• Fifteen 12 inch diameter cores were Fifteen 12 inch diameter cores were taken, one from each project.taken, one from each project.–– Asphalt was extracted Asphalt was extracted –– Recovered aggregate reRecovered aggregate re--mixed with virgin mixed with virgin
ACAC--20 20 –– Aged for four hours Aged for four hours –– Compacted to 230 gyrations (design levels Compacted to 230 gyrations (design levels
were back calculated).were back calculated).
Original SGC Compaction EffortOriginal SGC Compaction Effort
DesignDesign Average Design High Air TemperatureAverage Design High Air Temperature
ESALsESALs <39 ºC<39 ºC 39 39 -- 40 ºC40 ºC 41 41 -- 42 ºC42 ºC 43 43 -- 44 ºC44 ºC(millions)(millions) NN
iniiniNN
desdesNN
maxmaxNNiniini NNdesdes NNmaxmax NNiniini NNdesdes NNmaxmax NNiniini NNdesdes NNmaxmax
?? 0.30.3 77 6868 104104 77 7474 114114 77 7878 121121 77 8282 127127
0.3 0.3 -- 11 77 7676 117117 77 8383 129129 77 8888 138138 88 9393 1461461 1 -- 33 77 8686 134134 88 9595 150150 88 100100 158158 88 105105 167167
3 3 -- 1010 88 9696 152152 88 106106 169169 88 113113 181181 99 119119 192192
10 10 -- 3030 88 109109 174174 99 121121 195195 99 128128 208208 99 135135 220220
30 30 -- 100100 99 126126 204204 99 139139 228228 99 146146 240240 1010 153153 253253
?? 100100 99 143143 233233 1010 158158 262262 1010 165165 275275 1010 172172 288288
National Efforts to Address National Efforts to Address NNdesigndesign
•• Asphalt Institute Asphalt Institute -- NNdesigndesignII II ExperimentExperiment–– Examined field densification of SPSExamined field densification of SPS--9 pavements9 pavements–– Looked at mixture stiffness (G*) with SSTLooked at mixture stiffness (G*) with SST
•• NCAT NCAT -- NCHRP 9NCHRP 9--9 Evaluation of the SGC 9 Evaluation of the SGC ProcedureProcedure–– Looked at sensitivity of mix Looked at sensitivity of mix volumetrics volumetrics to changes to changes
in in NNdesigndesign
•• A new A new NNdesigndesign Table was developed from each Table was developed from each efforteffort
SGC Compaction Effort 1999SGC Compaction Effort 1999ESAL’s N ini N des N max App
< 0.3 6 50 75 Light
0.3 to < 3 7 75 115 Medium
3 to < 30 8 100* 160 High
10 to <30 8 100 160 High
> 30 9 125 205 Heavy
Base mix (< 100 mm) option to drop one level, unless the mix will be exposed to traffic during construction.
Thoughts on Thoughts on NNdesigndesign
•• Laboratory compaction effort should produce Laboratory compaction effort should produce sample density approximately equal to sample density approximately equal to ultimate pavement densityultimate pavement density
•• Ultimate pavement density believed to be Ultimate pavement density believed to be reached after 2reached after 2--3 years of traffic3 years of traffic
•• Typically, select laboratory density of 96% of Typically, select laboratory density of 96% of Theoretical maximum density or 4% air voidsTheoretical maximum density or 4% air voids–– Too little air voids (<2%) results in ruttingToo little air voids (<2%) results in rutting–– Too many air voids tend to cause durability Too many air voids tend to cause durability
problems problems
NCAT Test Track near Auburn, Alabama U.S.A.
Asphalt PlantLaboratory
North
Lee County Road 151
• 2.74 km Oval Test Track on 309 acres• 46 Cooperatively Sponsored 61 m Test Sections• 437 sq m Testing Laboratory• 242 sq m Truck Maintenance Facility
SECTION LAYOUTSECTION LAYOUT
NN
ONSITE LABONSITE LAB
AND TRUCKAND TRUCK
MAINTENANCEMAINTENANCE
HMA PLANTHMA PLANT
N13 N12 N13 N12 N11 N10 N9 N8 N7 N6 N5 N4 N3 N2 N11 N10 N9 N8 N7 N6 N5 N4 N3 N2 N1N1
S1 S2 S3 S4 S5 S6 S7 S8 S9 SS1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S1310 S11 S12 S13
W1W2
W3
W4
W5
W6
W7
W8W9
W10
E1E2
E3
E4
E5
E6
E7
E8E9
E10
NCAT Test Track Average Densification
PG 67-22 Upper Lift R2 = 0.98 PG 67-22 Lower Lift R2 = 0.96
PG 76-22 Lower Lift R2 = 0.99
PG 76-22 Upper Lift R2 = 0.98
90.00
91.00
92.00
93.00
94.00
95.00
96.00
97.00
98.00
0 1000000 2000000 3000000 4000000 5000000 6000000 7000000 8000000 9000000
ESALs
Pav
emen
t D
ensi
ty, %
Gm
m
PG 67-22 Lower LiftPG 76-22 Lower LiftPG 67-22 Upper Lift
PG 76-22 Upper Lift
Winter 2001-2002
Estimation of Density at a Estimation of Density at a Given Gyration LevelGiven Gyration Level
XGyrationatHeightNDesignatHeight
DesignNatDensity
XGyrationatDensity
?
?
NCAT Test Track - Design Gyrations to Meet Pavement Density
PG 67-22 Upper Lift R2 = 0.97PG 67-22 Lower Lift R2 = 0.87
PG 76-22 Lower Lift R2 = 0.95
PG 76-22 Upper Lift R2 = 0.94
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
110.00
120.00
130.00
0 1000000 2000000 3000000 4000000 5000000 6000000 7000000 8000000 9000000
ESALs
Des
ign
Gyr
atio
ns
PG 67-22 Lower Lift
PG 76-22 Lower Lift
PG 67-22 Upper Lift
PG 76-22 Upper LiftNote: Samples compacted on Troxler Compactor
Winter 2001-2002
The Whole Truth The Whole Truth –– Predicted Gyrations Predicted Gyrations to Match Test Track Densityto Match Test Track Density
Test Track Modified AC, R2 = 0.11
Test Track Unmodified AC, R2 = 0.29
0
20
40
60
80
100
120
140
0 500000 1000000 1500000 2000000 2500000 3000000 3500000
ESALs
Pre
dic
ted
Gyr
atio
ns
to M
eet
Pav
emen
t D
ensi
ty
Test Track Unmodified AC
Test Track Modified AC
What Factors Cause this Variability?What Factors Cause this Variability?
NANANANA177177ErrorError
YesYes0.0170.01722NMASNMAS
YesYes0.0000.00022GradationGradation
YesYes0.0000.00077Aggregate TypeAggregate Type
YesYes0.0000.00022BinderBinder
YesYes0.0180.01811LiftLift
SignificantSignificantPP--ValueValueDFDFSourceSource
Based on Analysis of Variance
NCHRP 9NCHRP 9--9(1)9(1)Field ProjectsField Projects
Verification of Verification of NNdesigndesign TableTable
Experimental PlanExperimental Plan•• Sample 40 pavements at the time of Sample 40 pavements at the time of
construction with a range of:construction with a range of:–– Lift Thickness to NMAS (2Lift Thickness to NMAS (2--4)4)–– Design Gyration Level (50Design Gyration Level (50--125)125)–– Binder Grade (Normal to +2 bumps)Binder Grade (Normal to +2 bumps)–– Gradation (Fine or Coarse)Gradation (Fine or Coarse)
Experimental PlanExperimental Plan•• Plant mix taken at time of construction, Plant mix taken at time of construction,
compacted to 100 and 160 gyrations in compacted to 100 and 160 gyrations in three three SGCsSGCs::–– Baby Pine (AFG1A)Baby Pine (AFG1A)–– Small Small Troxler Troxler (4141)(4141)–– BrovoldBrovold/Test Quip/Test Quip
•• Used in 2001 onlyUsed in 2001 only•• Data not yet reducedData not yet reduced
Experimental PlanExperimental Plan
•• Roadway cores taken at construction, 3 Roadway cores taken at construction, 3 months, 6 months, 1 year and 2 years months, 6 months, 1 year and 2 years after construction from right wheel pathafter construction from right wheel path
•• Goal: predict gyrations to match field Goal: predict gyrations to match field densitydensity
NCHRP 9-9 (1): Field Project Locations
Legend
: Project Site
General ObservationsGeneral Observations
•• Gradation, coarse or fine, was related to Gradation, coarse or fine, was related to compaction level:compaction level:–– Almost all 75 gyration mixes were fine gradedAlmost all 75 gyration mixes were fine graded–– TwoTwo--thirds of 100 gyration mixes were coarse thirds of 100 gyration mixes were coarse
gradedgraded–– All 125 gyration mixes were coarse gradedAll 125 gyration mixes were coarse graded
•• Binder Grade Bumps:Binder Grade Bumps:–– 15 of 17, 100 gyration mixes included at least one 15 of 17, 100 gyration mixes included at least one
binder grade bumpbinder grade bump–– All 125 gyration mixes included at least a one All 125 gyration mixes included at least a one
grade bumpgrade bump
Cumulative Frequency of Construction Densities
0102030405060708090
100
84 85 86 87 88 89 90 91 92 93 94 95 96
Percent Maximum Density, %
Cum
ulat
ive
Freq
uenc
y, %
55%
78%
Summary of Projects with Two Summary of Projects with Two Years of TrafficYears of Traffic
Pavement DensificationPavement Densification
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
84 86 88 90 92 94 96 98 100
Density, Percent Theoretical Maximum
No
rmal
ized
Fre
qu
ency
, Per
cen
t
One Year, N=382 Year, N=14One Year, N=14Construction N=40
Design Vs Predicted GyrationsDesign Vs Predicted Gyrations
R2 = 0.2269
R2 = 0.1911
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
0 20 40 60 80 100 120 140 160
Design Gyrations
Pre
dic
ted
Gyr
atio
ns
to M
atch
Fie
ld D
ensi
ty a
t 2
Yea
rs Brand 1 SGCBrand 2 SGCLinear (Brand 1 SGC)Linear (Brand 2 SGC)
Line of Equality
Design Gyrations Vs Two Year TrafficDesign Gyrations Vs Two Year Traffic
R2 = 0.366
R2 = 0.3446
0
20
40
60
80
100
120
140
160
0 500000 1000000 1500000 2000000 2500000 3000000 3500000 4000000 4500000 5000000
ESALs
Pre
dic
ted
Gyr
atio
ns
to M
atch
Fie
ld D
ensi
ty
Brand 1 SGC
Brand 2 SGC
Power (Brand 1 SGC)
Power (Brand 2 SGC)
Comparison of Modified and Comparison of Modified and Unmodified Sections After Two YearsUnmodified Sections After Two Years
0
20
40
60
80
100
120
140
160
0 1000000 2000000 3000000 4000000 5000000
ESALs
Pre
dic
ted
Gyr
atio
ns
to M
atch
Fie
ld D
ensi
ty a
t T
wo
Y
ears Brand 1 Modified
Brand 2 ModifiedBrand 1 NeatBrand 2 Neat
Comparison of Coarse and Fine Comparison of Coarse and Fine Mixes Mixes -- Two YearsTwo Years
R2 = 0.5075
R2 = 0.502
0
20
40
60
80
100
120
140
160
0 1000000 2000000 3000000 4000000 5000000
ESALs
Des
ign
Gyr
atio
ns
to M
eet
Den
sity
at
Tw
o Y
ears
Brand 1 CoarseBrand 2 CoarseBrand 1 FineBrand 2 Fine
Comparison of Nominal Maximum Comparison of Nominal Maximum Aggregate Size Aggregate Size –– Two YearsTwo Years
Brand 1 12.5 mm R2 = 0.23
Brand 2 12.5 mm R2 = 0.32Brand 1 9.5 mm R2 = 0.70
Brand 2 9.5 mm R2 = 0.81
0
20
40
60
80
100
120
140
160
180
0 500000 1E+06 2E+06 2E+06 3E+06 3E+06 4E+06 4E+06 5E+06 5E+06
ESALs
Pre
dic
ted
Gyr
atio
ns
to M
atch
Fie
ld D
ensi
ty a
t 2
Yea
rs
9.5 mm NMAS Brand 19.5 mm NMAS Brand 212.5 mm NMAS Brand 112.5 mm NMAS Brand 2
y = 1.3832x1.0041
R2 = 0.9584
0.0
20.0
40.0
60.0
80.0
100.0
120.0
0.0 20.0 40.0 60.0 80.0 100.0 120.0
Brand 1 SGC
Bra
nd
2 S
GC
Line of Equality
Comparison of Number of Gyrations to Comparison of Number of Gyrations to Match Field Density for Two CompactorsMatch Field Density for Two Compactors
Brand 1 angle = 1.24Brand 2 angle = 1.15
Summary of TwoSummary of Two--Year Performance Year Performance of NCHRP 9of NCHRP 9--9(1) Projects9(1) Projects
•• Rutting generally nonRutting generally non--existent. One project existent. One project with approximately 0.25 inchwith approximately 0.25 inch
•• Minor Minor ravelling ravelling commoncommon•• Several overlays over PCC evidence Several overlays over PCC evidence
reflective cracking, even when total (new) reflective cracking, even when total (new) overlay 3.5 inches or moreoverlay 3.5 inches or more
•• Joints vary from fair to very goodJoints vary from fair to very good•• Some permeability evidenced by wet spotsSome permeability evidenced by wet spots
SummarySummary•• Test Track Data Indicates:Test Track Data Indicates:
–– Modified binders Modified binders densify densify less than less than unmodified bindersunmodified binders
–– This may mean that mixes containing This may mean that mixes containing modified binders maybe designed at lower modified binders maybe designed at lower gyrations or higher asphalt contents to gyrations or higher asphalt contents to enhance durabilityenhance durability
–– Aggregate type, binder grade, nominal Aggregate type, binder grade, nominal maximum aggregate size and gradation all maximum aggregate size and gradation all affect predicted affect predicted Ndesign Ndesign valuesvalues
Summary Summary -- ContinuedContinued
•• Data from Test Track and NCHRP 9Data from Test Track and NCHRP 9--9 seem 9 seem to confirm current compaction level 0.3 to 3 to confirm current compaction level 0.3 to 3 million ESALsmillion ESALs
•• Results indicate that different compactors Results indicate that different compactors provide differentprovide different compactivecompactive effortsefforts
•• Scatter in 9Scatter in 9--9(1) data decreases with 9(1) data decreases with additional trafficadditional traffic
•• Trends developing, should be well founded Trends developing, should be well founded once 2once 2--year core data collectedyear core data collected
Thank You!Thank You!
AcknowledgementsAcknowledgementsThe Authors thank the National The Authors thank the National Cooperative Highway Research Cooperative Highway Research
Program for their support of NCHRP 9Program for their support of NCHRP 9--9(1), the U.S. state pooled fund 9(1), the U.S. state pooled fund participants and FHWA for their participants and FHWA for their support of the NCAT Test Tracksupport of the NCAT Test Track
