Incorporating Impact of Aging on Cracking Performance of Mixtures during Design Principle Investigator: Jo E. Sias, Co-Principle Investigator: Eshan V. Dave, Ph.D. Researcher: Runhua Zhang Department of Civil and Environmental Engineering, University of New Hampshire 19 Introduction Hot mix asphalt pavements undergo aging during mixing and compaction, and over the service life. Aging results in more cracking susceptibility and shortening the service lives and lowered serviceability of pavement. Objectives Develop a screening tool (including aging protocol) to identify crack susceptible binders/mixtures during material selection and mix design. Quantitatively evaluate how the cracking potential of typical NHDOT mixtures change with different aging levels for future maintenance and rehabilitation planning. Materials 11 plant produced mixtures; Field cores are available for four of the mixtures. Binder samples are extracted and recovered from the mixtures and field cores. Dynamic Modulus (AASHTO T342) Characterize stiffness and relaxation capability of mixture. Test Output: Dynamic Modulus mastercurve Phase angle mastercurve Mixture Glover-Rowe Parameter S-VECD Fatigue (AASHTO TP107) Semi-circular Bend (SCB) (AASHTO TP124) Characterize fatigue behavior of asphalt mixture Test Output Parameters: D R N f @ G R =100 Evaluate intermediate temperature cracking performance of mixture Test Output Parameters: Fracture Energy (G f ) Flexibility Index (FI) Evaluate low temperature/thermal cracking performance of mixture Test Output Parameters: Fracture Energy (G f ) Fracture Strain Tolerance (FST) Disk-shaped Compact Tension (DCT) (ASTM D7313) Selected Mixture Results Guidance for Material Selection and Design Future Work Acknowledgement The authors would like to acknowledge New Hampshire Department of Transportation (NHDOT) for sponsoring this study and the University of New Hampshire Center for Infrastructure Resilience to Climate (UCIRC). Asphalt Binder Evaluation: Appropriate binder aging/conditioning protocols to simulate long term field performance need to be further explored; Additional tests that evaluate the binders beyond the linear viscoelastic response should be investigated for inclusion in material selection, design, and quality assurance. Asphalt Mixture Evaluation: Continued collection of field performance data and periodic sampling of field cores for study mixtures and additional projects to calibrate the threshold values for different performance indices, refine the aging model and better define the aging gradient with depth. It is important to have an understanding of how the cracking resistance of the binders and mixtures will change over time at the time materials are selected and pavements are constructed. The results of this study will help NHDOT to improve the selection of asphalt mixtures to resist cracking, resulting in long term cost savings and better ride quality. The experimental study will provide the NHDOT and industry with information on cracking characteristics of mixtures including different mix variables. Performance Tests Mixture Aging Model Aging Protocol: An extended protocol (e.g. 40hr.PAV) is suggested to capture the aging and long-term cracking susceptibility of asphalt binder. Testing Method: 4mm DSR test is suggested to measure the multiple rheological indices to evaluate the different properties of asphalt binder; However, mixture fatigue testing should be included to specifically evaluate the fatigue performance of the designed mixtures since 4mm DSR cannot capture the fatigue behavior of asphalt binder. STA: Short term aging during production. LTOA: Long term aging condition 95ºC, loose mix (NCHRP project) for 1-12 days (5 and 12 days are the primary conditions) 24-hour, 135ºC, loose mix (Asphalt Institute) Aging Methods 4mm Dynamic Shear Rheometer (DSR) (MTE) Characterize stiffness and relaxation capability of binder. Test Output: Complex Modulus mastercurve Phase angle mastercurve Rheological Indices: Glover-Rowe Parameter; R-value; ΔTc; PGLT 0 10000 20000 30000 40000 50000 5234LM 5234LL 5834LM 5828SM 5828LM 5828LL 6428SV 6428SM 6428LM 7034LV 7628SM G-R m (MPa) STA Field Cores 5d@95°C 12d@95°C 24hr.@135°C Treshold for STA Threshold for LTOA (a) 100 1000 10000 100000 0.0001 0.01 1 100 10000 Dynamic Modulus (MPa) Reduced Frequency (Hz) 24 hr., 135°C 12 days, 95°C 5 days, 95°C STA Field Cores 5234LL 0 10 20 30 40 50 0.0001 0.01 1 100 10000 Phase Angle (Degrees) Reduced Frequency (Hz) 24 hr., 135°C 12 days, 95°C 5 days, 95°C STA Field Cores 5234LL 0 2 4 6 8 10 12 5234LM 5234LL 5834LM 5828SM 5828LM 5828LL 6428SV 6428SM 6428LM 7034LV 7628SM G-R m Ratio Field Cores/STA 5d@95°C/STA 12d@95°C/STA 24hr.@135°C/STA 3 mixture aging levels are compared with RTFO/PAV binder aging method. 20 hr. PAV binder aging condition simulates less than 4 years’ field aging, thus cannot represent the long-term performance of the asphalt material. Selected Binder Results 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E-06 1.E-03 1.E+00 1.E+03 1.E+06 1.E+09 Complex Modulus (Pa) Frequency (Hz) 12d@95°C 5d@95°C 20hr. PAV STA 6428SV Field cores overlap with 5 days at 95ºC laboratory aging condition. Considering the lower air void content of the field cores, the 5 days aging condition likely simulates more than four years of field aging. 12 days at 95ºC laboratory aging condition simulates more than 10 years of field aging in NH based on Climatic Aging Index (CAI) proposed by NCHRP 09-54 project. Two virgin mixtures show good cracking performance after each aging condition. Mixtures with softer binder (5234LM, 5234LL, 5834LM, 5828LM), and those with large difference between PGHT and PGLT (7034LV and 7628SM) show higher aging susceptibility. Other performance indices (FI; FST; D R ) show the similar trend. 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E-06 1.E-03 1.E+00 1.E+03 1.E+06 1.E+09 Complex Modulus (Pa) Frequency (Hz) 12d@95°C 5d@95°C 20hr. PAV STA 7034LV Layer 1; 1/2" Layer 2; 1/2" Layer 3; 1/2" 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 0.0 60.0 120.0 180.0 240.0 300.0 Depth (mm) G-R (kPa) 5234LM 5234LL 5828LM 5828LL Binder samples are extracted and recovered from the three layers of field cores; Binder G-R parameter is calculated, showing the aging gradient within the pavement structure. The middle point of each layer is selected as the representative depth to reflect the performance of each layer (60mm represents the pavement below the surface layer that doesn’t age significantly). The rate of field aging within the first inch of the pavement is much faster than the layers below it. The mixture Glover-Rowe (G-R m ) parameter is selected and used to model the change of mixture properties with aging. The advantage of using the G-R m parameter for modelling is that it incorporates both stiffness and relaxation capacity (phase angle) to evaluate the cracking performance of asphalt mixtures. The mixture aging model can be used to quantitatively evaluate and predict the change of mixture cracking performance, as well as aging susceptibility over pavement service life. Guidance for Binder Selection Guidance for Mixture Selection and Design Rheological Indices Cracking Warning Cracking Limit Glover-Rowe (G-R) 180kPa 600kPa ΔTc -2.5ºC -5.0ºC Aging Protocol: 135ºC can be used for the fabrication of complex modulus test specimens; 95ºC conditioning temperature is recommended for the evaluation of fatigue and fracture properties of mixtures; Appropriate conditioning time is determined based on the desired equivalent field aging duration. Field Aging Duration (year) 4 6 8 10 12 14 16 18 20 Lab Aging Duration (hr.@95ºC） 120 180 235 295 360 420 475 535 600 Testing Method: Mixture aging model is suggested as the screening tool; Only complex modulus test is needed; Only three aging conditions (selected from table above) are required to calibrate the aging model. Cracking Limit STA LTOA Mixture G-R m Parameter 8,000MPa 19,000MPa Mixture ID Virgin Binder Grade Design Gyration Levels NMAS (mm) Total Binder Content (%) Recycled Binder Content (%) 5234LM PG 52-34 50 12.5 5.3 18.9 5234LL 28.3 5834LM PG 58-34 5.4 18.5 5828SM PG 58-28 9.5 5.9 16.9 5828LM 12.5 5.3 18.9 5828LL 75 28.3 6428SV PG 64-28 9.5 6.4 0 6428SM 6.3 18.5 6428LM 12.5 5.8 7034LV PG 70-34 0 7628SM PG 76-28 9.5 6.1 14.8 Field Core 100 1000 10000 100000 0 2 4 6 8 10 12 14 G-R m (MPa) Lab Aging Duration (Days) 5834LM R2=0.942 6428SV R2=0.975 6428SM R2=0.995 6428LM R2=0.991 7034LV R2=0.996 7628SM R2=0.995 Fast Reaction Period Constant Reaction Period
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Incorporating Impact of Aging on Cracking Performance of Mixtures during DesignPrinciple Investigator: Jo E. Sias, Co-Principle Investigator: Eshan V. Dave, Ph.D. Researcher: Runhua Zhang
Department of Civil and Environmental Engineering, University of New Hampshire
19
Introduction
Hot mix asphalt pavements undergo aging during mixingand compaction, and over the service life. Aging resultsin more cracking susceptibility and shortening theservice lives and lowered serviceability of pavement.
Objectives
Develop a screening tool (including aging protocol) toidentify crack susceptible binders/mixtures duringmaterial selection and mix design.
Quantitatively evaluate how the cracking potential oftypical NHDOT mixtures change with different aginglevels for future maintenance and rehabilitation planning.
Materials
11 plant produced mixtures; Field cores are available forfour of the mixtures.
Binder samples are extracted and recovered from themixtures and field cores.
Dynamic Modulus (AASHTO T342) Characterize stiffness and relaxation
capability of mixture. Test Output:
Dynamic Modulus mastercurvePhase angle mastercurveMixture Glover-Rowe Parameter
S-VECD Fatigue (AASHTO TP107)Semi-circular Bend (SCB) (AASHTO TP124)
Characterize fatigue behavior of asphalt mixture
Test Output Parameters: DR
Nf @ GR =100
Evaluate intermediate temperature cracking performance of mixture
Test Output Parameters: Fracture Energy (Gf) Flexibility Index (FI)
Evaluate low temperature/thermal cracking performance of mixture
Test Output Parameters: Fracture Energy (Gf) Fracture Strain Tolerance
(FST)
Disk-shaped Compact Tension (DCT) (ASTM D7313)
Selected Mixture Results
Guidance for Material Selection and Design
Future Work
Acknowledgement
The authors would like to acknowledge New HampshireDepartment of Transportation (NHDOT) for sponsoring thisstudy and the University of New Hampshire Center forInfrastructure Resilience to Climate (UCIRC).
Asphalt Binder Evaluation: Appropriate binderaging/conditioning protocols to simulate long term fieldperformance need to be further explored; Additionaltests that evaluate the binders beyond the linearviscoelastic response should be investigated forinclusion in material selection, design, and qualityassurance.
Asphalt Mixture Evaluation: Continued collection offield performance data and periodic sampling of fieldcores for study mixtures and additional projects tocalibrate the threshold values for different performanceindices, refine the aging model and better define theaging gradient with depth.
It is important to have an understanding of how thecracking resistance of the binders and mixtures willchange over time at the time materials are selected andpavements are constructed.
The results of this study will help NHDOT to improve theselection of asphalt mixtures to resist cracking, resultingin long term cost savings and better ride quality. Theexperimental study will provide the NHDOT and industrywith information on cracking characteristics of mixturesincluding different mix variables.
Performance Tests
Mixture Aging Model
Aging Protocol: An extended protocol (e.g. 40hr.PAV)is suggested to capture the aging and long-termcracking susceptibility of asphalt binder.
Testing Method: 4mm DSR test is suggested tomeasure the multiple rheological indices to evaluate thedifferent properties of asphalt binder; However, mixturefatigue testing should be included to specificallyevaluate the fatigue performance of the designedmixtures since 4mm DSR cannot capture the fatiguebehavior of asphalt binder.
STA: Short term aging during production. LTOA: Long term aging condition
95ºC, loose mix (NCHRP project) for 1-12 days(5 and 12 days are the primary conditions)
24-hour, 135ºC, loose mix (Asphalt Institute)
Aging Methods
4mm Dynamic Shear Rheometer (DSR) (MTE) Characterize stiffness and relaxation capability of
binder. Test Output:
Complex Modulus mastercurvePhase angle mastercurveRheological Indices: Glover-Rowe Parameter; R-value; ΔTc; PGLT
0
10000
20000
30000
40000
50000
5234LM 5234LL 5834LM 5828SM 5828LM 5828LL 6428SV 6428SM 6428LM 7034LV 7628SM
G-R
m(M
Pa)
STAField Cores5d@95°C12d@95°C24hr.@135°CTreshold for STAThreshold for LTOA
(a)
100
1000
10000
100000
0.0001 0.01 1 100 10000
Dyn
amic
Mod
ulus
(MPa
)
Reduced Frequency (Hz)
24 hr., 135°C12 days, 95°C5 days, 95°CSTAField Cores
5234LL
0
10
20
30
40
50
0.0001 0.01 1 100 10000
Phas
e An
gle
(Deg
rees
)
Reduced Frequency (Hz)
24 hr., 135°C12 days, 95°C5 days, 95°CSTAField Cores
5234LL
0
2
4
6
8
10
12
5234LM 5234LL 5834LM 5828SM 5828LM 5828LL 6428SV 6428SM 6428LM 7034LV 7628SM
G-R
mR
atio
Field Cores/STA5d@95°C/STA12d@95°C/STA24hr.@135°C/STA
3 mixture aging levels are compared with RTFO/PAVbinder aging method.
20 hr. PAV binder aging condition simulates less than 4years’ field aging, thus cannot represent the long-termperformance of the asphalt material.
Selected Binder Results
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E-06 1.E-03 1.E+00 1.E+03 1.E+06 1.E+09
Com
plex
Mod
ulus
(Pa)
Frequency (Hz)
12d@95°C5d@95°C20hr. PAVSTA
6428SV
Field cores overlap with 5 days at 95ºC laboratory agingcondition.
Considering the lower air void content of the field cores,the 5 days aging condition likely simulates more than fouryears of field aging.
12 days at 95ºC laboratory aging condition simulates morethan 10 years of field aging in NH based on Climatic AgingIndex (CAI) proposed by NCHRP 09-54 project.
Two virgin mixtures show good cracking performance aftereach aging condition.
Mixtures with softer binder (5234LM, 5234LL, 5834LM,5828LM), and those with large difference between PGHTand PGLT (7034LV and 7628SM) show higher agingsusceptibility.
Other performance indices (FI; FST; DR) show thesimilar trend.
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E-06 1.E-03 1.E+00 1.E+03 1.E+06 1.E+09
Com
plex
Mod
ulus
(Pa)
Frequency (Hz)
12d@95°C5d@95°C20hr. PAVSTA
7034LV
Layer 1; 1/2"
Layer 2; 1/2"
Layer 3; 1/2"
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
0.0 60.0 120.0 180.0 240.0 300.0
Dept
h (m
m)
G-R (kPa)
5234LM5234LL5828LM5828LL
Binder samples are extracted and recovered from thethree layers of field cores;
Binder G-R parameter is calculated, showing the aginggradient within the pavement structure.
The middle point of each layer is selected as therepresentative depth to reflect the performance of eachlayer (60mm represents the pavement below the surfacelayer that doesn’t age significantly).
The rate of field aging within the first inch of the pavementis much faster than the layers below it.
The mixture Glover-Rowe (G-Rm) parameter is selected and used tomodel the change of mixture properties with aging.
The advantage of using the G-Rm parameter for modelling is that itincorporates both stiffness and relaxation capacity (phase angle) toevaluate the cracking performance of asphalt mixtures.
The mixture aging model can be used to quantitatively evaluate andpredict the change of mixture cracking performance, as well as agingsusceptibility over pavement service life.
Guidance for Binder Selection
Guidance for Mixture Selection and Design
Rheological Indices Cracking Warning Cracking LimitGlover-Rowe (G-R) 180kPa 600kPa
ΔTc -2.5ºC -5.0ºC
Aging Protocol: 135ºC can be used for the fabricationof complex modulus test specimens; 95ºC conditioningtemperature is recommended for the evaluation offatigue and fracture properties of mixtures; Appropriateconditioning time is determined based on the desiredequivalent field aging duration.
Field Aging Duration (year) 4 6 8 10 12 14 16 18 20
Lab Aging Duration
(hr.@95ºC）120 180 235 295 360 420 475 535 600
Testing Method: Mixture aging model is suggested asthe screening tool; Only complex modulus test isneeded; Only three aging conditions (selected fromtable above) are required to calibrate the aging model.
Cracking Limit STA LTOA
Mixture G-Rm Parameter 8,000MPa 19,000MPa
Mixture IDVirgin Binder Grade
Design Gyration Levels
NMAS (mm) Total Binder Content (%)
Recycled Binder
Content (%)5234LM
PG 52-34
5012.5
5.318.9
5234LL 28.35834LM PG 58-34 5.4 18.55828SM
PG 58-289.5 5.9 16.9
5828LM12.5 5.3
18.95828LL
75
28.36428SV
PG 64-289.5
6.4 06428SM 6.3
18.56428LM
12.5 5.87034LV PG 70-34 07628SM PG 76-28 9.5 6.1 14.8
Field Core
100
1000
10000
100000
0 2 4 6 8 10 12 14
G-R
m(M
Pa)
Lab Aging Duration (Days)
5834LM R2=0.9426428SV R2=0.9756428SM R2=0.9956428LM R2=0.9917034LV R2=0.9967628SM R2=0.995
FastReaction Period
Constant Reaction Period
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