“Understanding the “Understanding the Performance of Modifiers in Performance of Modifiers in Asphalt Mixtures” Asphalt Mixtures” – – 67 67 - - 80 Binder Study 80 Binder Study Revised T.T.S. + Revised T.T.S. + Statistical Analysis Statistical Analysis Materials & Construction Team Materials & Construction Team Federal Highway Administration Federal Highway Administration www.TFHRC.gov www.TFHRC.gov
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“Understanding the “Understanding the Performance of Modifiers in Performance of Modifiers in
Asphalt Mixtures” Asphalt Mixtures” ––6767--80 Binder Study80 Binder Study
Materials & Construction TeamMaterials & Construction Team
Federal Highway AdministrationFederal Highway Administrationwww.TFHRC.govwww.TFHRC.gov
AcknowledgementsAcknowledgements
Thanks toThanks to•• Mr. Scott Parobeck Mr. Scott Parobeck •• Mr. Frank Davis Mr. Frank Davis •• Ms. Susan Needham Ms. Susan Needham •• Dr. Ghazi AlDr. Ghazi Al--Khateeb Khateeb •• Dr. Aroon Dr. Aroon ShenoyShenoy•• Mr. Nelson GibsonMr. Nelson Gibson
Two FHWA ALFs with Two FHWA ALFs with 12 Pavement Lanes Constructed in 12 Pavement Lanes Constructed in
the Summer and Fall of 2002the Summer and Fall of 2002
2001 ALF Pavement Facility2001 ALF Pavement FacilityTarget Grade, AB cTarget Grade, AB c--PG 74PG 74--2828
Binder IDBinder ID cc--PG HTPG HT cc--PG LTPG LT UTIUTI
1: AZ CR1: AZ CR2/8: Control2/8: Control3/10: Air3/10: Air--blownblown4/11: SBS4/11: SBS--lglg5: TBCR5: TBCR6/12: Terpolymer6/12: Terpolymer9: SBS 649: SBS 64--4040
n/an/a727274747474797974747171
n/an/a--2323--2828--2828--2828--3131--3838
n/an/a9595102102102102103103105105109109
UTI – Useful Temperature Index
In situ ALF BindersIn situ ALF Binders
-40
-34
-28
-2258 64 70 76 82
Continous High Temperature Grade, (c-HT) °C
c-LT
, °C
ControlAirblownSBS-lgTBCRTerpolySBS
ETG Concern
6767--80 Binders80 Binders
-40
-34
-28
-2258 64 70 76 82 88
Continous High Temperature Grade, (c-HT) °C
c-LT
, °C
EFEF + SBSTerpolyTBCRSBS lg
58 64 70 76 82 88
Mixture Test at HT cMixture Test at HT c--PGPG
•• Superpave Shear Tester (SST)Superpave Shear Tester (SST)–– Repeated Shear at Constant Height (RSCH)Repeated Shear at Constant Height (RSCH)
Cycles to 2% Strain FailureCycles to 2% Strain Failure•• Strain at 5,000 cyclesStrain at 5,000 cycles•• Strain at 1,000 cyclesStrain at 1,000 cycles
Mixture Test at HT cMixture Test at HT c--PGPG
•• Cycles to 2% Strain FailureCycles to 2% Strain Failure•• Best connection to Full Scale Rutting (ALF)Best connection to Full Scale Rutting (ALF)
RD = - 0.004 NRSCH Failure + 19.0
0.0
5.0
10.0
15.0
20.0
0 1000 2000 3000 4000 5000
RSCH Cycles to Failure at 74°C
150m
m Pa
veme
nt Ru
t Dep
th at
64°C
(mm)
RD = - 0.003 NRSCH Failure + 15.8
0.0
5.0
10.0
15.0
20.0
0 1000 2000 3000 4000 5000
RSCH Cycles to Failure at 74°C
100m
m P
avem
ent R
ut D
epth
at
64°C
(mm
)
Outlier = Terpolymer
R2 = 0.77
R2 = 0.99
150mm
100mm
Summary of 67Summary of 67--80 Mixture Testing80 Mixture TestingCV for Trimmed Mean CV for Trimmed Mean (5(5--2=3)2=3)
Working Data Set after Trimmed Working Data Set after Trimmed Mean AnalysisMean Analysis
•• Typical ExampleTypical Example
0
250
500
750
1000
1250
1500
68 70 72 74 76 78 80 82 84
SST RSCH Test Temperature, °C
Cyc
les
to 2
% S
trai
n
Trimmed Mean Variability
Much care was taken in this experiment, however, results do not always follow expected decreasing trend
– THIS IS A FACT OF LIFE WITH HT SST.
RR22 Approach…Approach…Understanding R2 behavior as linear slope approaches zero for various qualities of data.
0
0.2
0.4
0.6
0.8
1
0.0001 0.001 0.01 0.1 1 10 100 1000
Data Quality = Standard Deviation about Underlying Linear Function
R2
Slope 100
Slope 10
Slope 1
Slope 0.1
RR22 ApproachApproachUnderstanding R2 behavior as linear slope approaches zero for various qualities of data.
0
0.2
0.4
0.6
0.8
1
0.0001 0.001 0.01 0.1 1 10 100 1000
Data Quality = Standard Deviation about Underlying Linear Function
R2
Slope 100
Slope 10
Slope 1
Slope 0.1
Slope 0.000005
Conclusion – R2 is not the most appropriate method. Essentially R2=1 for a perfect horizontal Model, but HYPERSENSITIVE. Smallest deviation from perfect horizontal causes poor R2 with moderate variability.
Pivotal Question…Pivotal Question…
•• Can we perform SST tests at cooler temperature Can we perform SST tests at cooler temperature where variability is smaller ?where variability is smaller ?
•• Then……relate test data to warmer conditions Then……relate test data to warmer conditions where ETG suggests mixture tests be where ETG suggests mixture tests be performed.performed.
•• WHAT TOOLS ARE AVAILABLE TO DO WHAT TOOLS ARE AVAILABLE TO DO SOMETHING LIKE THIS WITH EXISTING DATA ?SOMETHING LIKE THIS WITH EXISTING DATA ?
•• Utilization of Utilization of TIME TEMPERATURE TIME TEMPERATURE SUPERPOSTIONSUPERPOSTION–– Creep & Permanent Deformation at Multiple Creep & Permanent Deformation at Multiple
Temperatures…Neat 64Temperatures…Neat 64--22 Dense Graded22 Dense Graded–– It is Feasible to “Shift” Permanent Strains like |G*|It is Feasible to “Shift” Permanent Strains like |G*|
Calibrate a SST RSCH Model with integrated Calibrate a SST RSCH Model with integrated Time Temperature SuperpositionTime Temperature Superposition
0
500
1000
1500
2000
2500
3000
3500
68 70 72 74 76 78 80 82 84
SST RSCH Test Temperature, oC
# S
ST
RS
CH
Cycle
s to
2%
Pe
rma
ne
nt S
tra
in
High Calib
Measured
( ) ( ) ( ) 213
223
212
23311
23322
22211 666 τττσσσσσσσ +++−+−+−=eq
212
211 3τσσ +=eq
( )( )qvp
peq
R
vp
B
Adtd
12
12
γ
σγ=
From Binder |G*|Trimmed Mean Variability
)(TattR =
Each Binder Parameter for Each Binder Has a Distinct Temperature
Calibrate a SST RSCH Model with integrated Calibrate a SST RSCH Model with integrated Time Temperature SuperpositionTime Temperature Superposition
0
500
1000
1500
2000
2500
3000
3500
68 70 72 74 76 78 80 82 84
SST RSCH Test Temperature, oC
# S
ST
RS
CH
Cycle
s to
2%
Pe
rma
ne
nt S
tra
in
High Calib
Int. Calib
Measured
( ) ( ) ( ) 213
223
212
23311
23322
22211 666 τττσσσσσσσ +++−+−+−=eq
212
211 3τσσ +=eq
( )( )qvp
peq
R
vp
B
Adtd
12
12
γ
σγ=
From Binder |G*|Trimmed Mean Variability
)(TattR =
Each Binder Parameter for Each Binder Has a Distinct Temperature
Calibrate a SST RSCH Model with integrated Calibrate a SST RSCH Model with integrated Time Temperature SuperpositionTime Temperature Superposition
0
500
1000
1500
2000
2500
3000
3500
68 70 72 74 76 78 80 82 84
SST RSCH Test Temperature, oC
# S
ST
RS
CH
Cycle
s to
2%
Pe
rma
ne
nt S
tra
in
High Calib
Int. Calib
Low Calib
Measured
( ) ( ) ( ) 213
223
212
23311
23322
22211 666 τττσσσσσσσ +++−+−+−=eq
212
211 3τσσ +=eq
( )( )qvp
peq
R
vp
B
Adtd
12
12
γ
σγ=
From Binder |G*|Trimmed Mean Variability
)(TattR =
Each Binder Parameter for Each Binder Has a Distinct Temperature
High Spec. Temperature, THigh Spec. Temperature, THSHS
•• |G*|/sin |G*|/sin δ = 2200 Paδ = 2200 Pa at 10 rads/sat 10 rads/s (Superpave)(Superpave)
•• |G*|/(1|G*|/(1--(1/tan(1/tanδδ sinsinδ)) = 50 Paδ)) = 50 Pa at 0.25 rads/sat 0.25 rads/sCriterion 1 Criterion 1 (FHWA)(FHWA)
•• TTE E /(1/(1--(1/tan(1/tanδδ sinsinδ)) where Tδ)) where TEE is when |G*|= 50 is when |G*|= 50 PaPa at 0.25 rads/sat 0.25 rads/sCriterion 2 Criterion 2 (FHWA)(FHWA)
High Spec. Temperature, THigh Spec. Temperature, THSHS
Calibration at Higher SST TemperatureBinder\Parameter
ObservationsObservations•• Utilization of the Lower and Intermediate T.T.S. Utilization of the Lower and Intermediate T.T.S.
Calibrations is desired…Calibrations is desired…–– Higher Temp Calibration has strongest potential for Higher Temp Calibration has strongest potential for
variabilityvariability–– Lower and Intermediate compare with each otherLower and Intermediate compare with each other
•• Lower Calibration (7 of 9)Lower Calibration (7 of 9)11--(1/(1/tantanδ δ sinsinδδ) methods and ZSV capture more ) methods and ZSV capture more behaviorbehavior
•• Intermediate Calibration (4~ or 9)Intermediate Calibration (4~ or 9)11--(1/(1/tantanδ δ sinsinδδ) methods and LSV capture more ) methods and LSV capture more behaviorbehavior
Next Steps… Next Steps… High Temperature ParametersHigh Temperature Parameters