1. Nanomechanistic Investigation of RAP-Modified Asphalt
Binders by Using an Atomic Force Microscope (AFM)
Feroze Rashid1 and Zahid Hossain2
1M.Sc. Candidate at Arkansas State University and 2Assistant Professor of Civil Engineering
MOTIVATION & CHALLENGES
Addition of Reclaimed Asphalt Pavement (RAP) with virgin asphalts
alters the properties of base binders, resulting in different in-service
performance. However, Superpave tests are reported to have limitations in
characterizing modified asphalts. Hence, alternative tools such as Atomic
Force Microscope (AFM) have been utilized by pavement researchers and
professionals. In this study, binders from two field RAP samples were blended
at the rate of 25%, 40%, and 60% with a PG 64-22 binder and tested by
following conventional Superpave test protocols and an AFM technique. As
expected, the addition of RAP binder with the base binder increased the
stiffness, thereby increasing the high PG temperature up to 85oC for 60% RAP.
The elastic modulus of 60% RAP was over 70% higher than that of the base
binder, as found from the AFM tests. The modulus was found to be correlated
with the morphology. The nanoscale properties were in agreement with
microscale properties of the tested binders with more detailed results.
ABSTRACT
Understand atomic level properties of RAP
 Waste into construction materials => Material sustainability
 Facilitate constructing more durable and longer lasting pavements
 Huge cost savings for taxpayers with low environmental impact
 The FHWA promotes using RAP in new pavement construction
Overcome the limitations of Superpave Test Methods
 Developed based on unmodified asphalts only
 Does not consider molecular level properties event though asphalt is a
highly complex chemical with long chains of hydrocarbons
 Reported to have limitations, specially in cases of modified asphalts
 Recover asphalt binders from field RAP samples
 Observe the micro-level changes of properties from the Superpave tests
 Observe nano-level properties from AFM
 Compare virgin versus RAP-modified binder properties
 Correlate micro- and nano-level properties
OBJECTIVES
What is an AFM ?
• Atomic Force Microscope
• An advanced technology, nano-scale measurement
• Can get morphology and mechanistic properties at atomic level
AFM system Construction of Force-Distance Curve
Why AFM ?
• Can detect changes of nano-structures and phase differences
• Find correlations between mechanical properties and morphology
• Can visualize changes structure and properties
INTRODUCTION
Material collection (Field Core Samples and Virgin Binders)
Extraction and Recovery from RAP
Blending of RAP
Testing
Superpave
• Viscosity
• Complex
modulus
AFM
• Morphology
• Elastic Modulus
• Adhesion
• Deformation
AASHTO T 319-08
Aging
25%, 40%, and 60% RAP
RTFO and PAV Aging
TEST SETUP
Sample
Sample
Description
Source of
Materials
Remarks
Control PG 64-22
Ergon, Memphis,
TN
Unmodified
RAP-A
25%, 40%, and
60% by weight
I-30, Arkadelphia,
AR
Field performance
GOOD
RAP-B
25%, 40%, and
60% by weight
I-40, Russellville,
AR
Field performance
POOR
EQUIPMENTS AND MATERIALS
• Rotational Viscometer (RV)
• Rotational Thin Film Oven
• Pressure Aging Vessel
• Dynamic Shear Rheometer (DSR)
• Dimension Icon AFM
• PFQNMTM Mode
• RTESPA Probe
(25 N/m stiffness)
RESULTS AND DISCUSSION
0
500
1000
1500
2000
2500
135°C 150°C 165°C 180°C
Viscosity(mPa-s)
Temperature (0C)
Control
PG64-22+RAP-A(25)U
PG64-22+RAP-A(40)U
PG64-22+RAP-A(60)U
PG64-22+RAP-B(25)U
PG64-22+RAP-B(40)U
PG64-22+RAP-B(60)U
58
64
70
76
82
88
Control 25% 40% 60%
HighPGTemperature(oC)
Blend type (% RAP)
RAP-A
RAP-B
Change of Viscosity with the Amount of RAP
High Temperature (Rutting) Resistance
RESULTS AND DISCUSSIONS
• RAPs increased the high PG temperatures of blends
• 60% RAP-B increased the high PG up to180C
• Both RAPs improved the rutting resistance
• Addition of RAP-A produced 2.7 times extra
viscosity, which is 4 times for RAP-B
• RAP-B is stiffer than RAP-A
Control Binder
• Three distinct phases (Dispersed, Interstitial, and
Matrix; also called as Catana, Peri and Perpetua phase)
• Dispersed phase has lower area coverage DMT
(Derjaguin, Muller, Toporov) modulus ranged from
360 to 450 MPa
• Modulus of any specific aged blend
increases with the amount of RAP-A
• Modulus of any specific RAP-A blend
increases with aging
• RAP-A increases the modulus from
511 MPa (25%, unaged) to 803 MPa
(60%, PAV-aged)
Modulus of RAP-A BlendsMorphology of RAP-A Blends
• Changes in bees is an amplified
view of changes in the bulk (Ramm
et al. 2016)
• Bees change in size and number
with blend age and amount of RAP
• PAV aged binders have fewer bee
• Surface roughness varied from 50
nm to 70 nm
• The modification by RAP-B has
similar impact on the modulus as
RAP-A
• 60% unaged RAP-B blend showed
maximum increase (70%) in
modulus out of all unaged samples
• The maximum modulus for RAP-B
blend is 824 MPa (60%, PAV-aged)
Modulus of RAP-B Blends
Blend ratio and aging condition
DMT Modulus (MPa)
Average Adhesion
(nN)
Average
Deformation (nm)
Average of entire
specimen
Dispersed and
Interstitial
Matrix
Control Unaged 367 380 – 450 367 – 390 35.39 11.00
RAP-A
25%
Unaged 511 520 – 570 370 – 430 42.20 3.21
RTFO 580 610 – 680 450 – 510 41.30 4.97
PAV 583 570 – 700 380 – 530 32.70 3.70
40%
Unaged 590 520 – 730 425 – 500 36.75 3.84
RTFO 624 570 – 690 450 – 510 39.50 3.81
PAV 667 625 – 755 370 – 570 31.60 6.74
60%
Unaged 633 600 – 710 460 – 590 44.00 2.92
RTFO 675 594 – 765 380 – 550 34.00 5.96
PAV 803 820 – 970 620 – 670 22.60 3.26
RAP-B
25%
Unaged 536 570 - 605 420-460 37.40 5.82
RTFO 525 560 - 650 360 - 500 34.82 6.87
PAV 564 690 - 870 291 - 506 18.60 2.00
40%
Unaged 582 630 - 680 450 - 590 38.70 4.05
RTFO 616 685 - 720 475 - 600 28.25 7.07
PAV 757 875 - 1065 524 - 680 28.60 3.58
60%
Unaged 631 640 - 821 473 - 591 49.80 6.84
RTFO 632 612 - 863 492 - 611 37.50 3.60
PAV 824 744 - 985 495 - 690 28.00 5.65
• DMT modulus varied from 500 to 800 MPa for both RAPs
• RAP introduced extra adhesion while aging reduced it
• Increased adhesion after aging is due to the introduction of additional polar
molecules (Ramm et al. 2016), which is not true for all cases and could be
due to the result of reorganization of polar molecules
• RAP-blended binders had lower deformation than the control
• No specific trend of changes in the deformation values with respect to RAP
content or aging condition
• Stiff probe (spring constant 25 N/m) could be a reason behind not getting a
trend of change
• Effects of Rejuvenator: reduced average modulus values; increased
adhesion; reduced the stiffness; most of the “bee” structures disappeared
• Southern Plains Transportation Center (SPTC)
• Arkansas State Highway and Transportation Department
• Arkansas State University, University of Texas at Austin (Dr. Bhasin)
• National Science Foundation for the Major Research Instrument Award
• Suppliers of test materials
ACKNOWLEDGEMENTS
• Both of the RAPs increased the high PG temperatures of the blend
• Sixty percent (60%) RAP-B showed maximum 180C increment
• Control and RAP-A had three phases in the morphology while additional
small protrusions were noticed in RAP-B blends
• The control showed average modulus of about 350 MPa, which was 650
MPa in case of 60% RAP-modified binder
• Aging of asphalt further increases the modulus (around 800 MPa)
• Catana and Peri-phases showed higher modulus than Perpetua
• RAP modification and aging stiffen the binder
• Rejuvenator changed the structure and morphologies of the blend
• Rejuvenated blends showed lower modulus and stiffness, higher adhesion.
• Both of test methods showed consistent test results
• The AFM is a viable tool to characterize asphalt binder in a detailed
fashion
CONCLUSIONS
RejuvenatedRAP
40% RAP1
Unaged
702 610-800 700-780 10.2 1.56
Rej. RAP1 584 630 - 750 150-530 32 9.12
40% RAP2
Unaged
550 560-575 550-575 15.00 3.00
Rej. RAP2 410 420-500 90-350 23 3.00
40% RAP3
Unaged
637 635-660 570-630 15.57 3.65
Rej. RAP3 429 410-530 250-320 16 3.38
40% RAP4
Unaged
611 600-650 520-590 16.40 3.14
Rej. RAP4 304 300-340 170-245 20.6 1.52
• Observed small protrusions in
addition to three phases
• The dispersed phase diminishes as the
binders age for 25% and 40% blends
• For 60% RAP-B blends, bees were
almost absent
• The changes in RAP-B blends are
different than RAP-A blends
Morphology of RAP-B Blends