characterizing pma performance with pg plus tests · characterizing polymer modified asphalt...
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Characterizing Polymer Modified Asphalt Performance with PG Plus Tests
2020 OAPC Asphalt Symposium
Presented by: Mike Aurilio
June 16, 2020
1
2
Physical Properties of PMA
Stiffness
▪ Increases▪ Improves rutting resistance▪ Can improve fatigue cracking resistance
Response to Loading
▪ More elastomeric▪ No longer purely ductile/brittle▪ Improves cracking resistance
Coil- speedwaymotors.comPavement Distresses- pavementinteractive.com
3
Styrene-Butadiene-Styrene
SBS Structure- polymerdatabase.com
Linear Radial
▪ Thermoplastic- Rubber▪ Good solubility in asphalt (Hildebrand
parameters are similar)▪ Glass Transition Temperature (Tg) of -90˚C
Butadiene Styrene
4
PMA Compatibility
▪ Good compatibility causes swelling of SBS chains (increase in volume fraction)▪ Good compatibility causes increase in stiffness and elastomeric properties
Asphalt Cement Chemistry
▪ Different crude sources result in asphalt with different chemistries
▪ Increase in aromatic fraction can improve compatibility
SBS Microstructure
▪ Molecular weight can effect dispersion in asphalt
▪ Styrene content can effect level of swelling
Cross-linking Agents
▪ Generally improve SBS stability
▪ Can improve quality of polymer network
Images- Planche, Elwardany, Adams, Rovani, Boysen, “Compatibility in Asphalt – A moving Target with Sources, Modifications and Aging”, TRB Annual Meeting, January 13, 2020
Increasing Compatibility
5
How much SBS do we need?
0 – 2%
▪ Small increase in stiffness
▪ Not enough to improve elastomeric properties
2 - 4%
▪ Asphalt continuous phase
▪ Noticeable improvement to elastomeric properties
4 - 6%
▪ Co-continuous phases
▪ Possibility of instability?
6 - 8%
▪ Polymer continuous phase
▪ Great performance but expensive
Perf
orm
ance
incr
ease
s as
co
nce
ntr
atio
n in
crea
ses
Images- Planche, Elwardany, Adams, Rovani, Boysen, “Compatibility in Asphalt – A moving Target with Sources, Modifications and Aging”, TRB Annual Meeting, January 13, 2020
PMA Master Curve
6
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1.0E+07
1.0E+08
1.0E+09
1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05
Co
mp
lex
Mo
du
lus
(Pa)
Reduced Frequency (Hz)
58-28 0% SBS
58-28 2% SBS A
58-28 4% SBS A
58-28 2% SBS B
58-28 4% SBS B
Low TemperatureHigher Frequency
High TemperatureLower Frequency
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1.0E+07
1.0E+08
1.0E+09
1.0E-07 1.0E-05 1.0E-03 1.0E-01 1.0E+01 1.0E+03 1.0E+05
Co
mp
lex
Mo
du
lus
(Pa)
Reduced Frequency (Hz)
Self-Healing Asphalt Cement Unaged Self-Healing Asphalt Cement PAV 58-28 0% SBS Unaged 58-28 0% SBS PAV
Aging Master Curve
7
PMA Black Space Diagram
8
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1.0E+07
1.0E+08
0 20 40 60 80 100
Co
mp
lex
Mo
du
lus
(Pa)
Phase Angle (˚)
58-28 0% SBS58-28 2% SBS A58-28 4% SBS A58-28 2% SBS B58-28 4% SBS B
High TemperatureLower Stiffness
Intermediate TemperatureHigher Stiffness
Experimental Design
9
5 Asphalt Cements:
▪ PG 58-28▪ PG 64-28▪ PG 52-34▪ PG 58-28B▪ PG 52-34B
2 SBS Sources:
▪ SBS A▪ SBS B
Concentrations:
0, 1, 2, 3 and 4%
Low Strain Amplitude Cracking Tests:
▪ DENT▪ ΔTc / ExBBR▪ Glover-Rowe Parameter▪ Cross-Over Temperature
Large Strain Amplitude Cracking Tests:
▪ Linear Amplitude Sweep (LAS)▪ Asphalt Binder Cracking Device
(ABCD)
20 Hour PAVRTFO
Large Strain Amplitude Rutting Test:
▪ MSCR
0
10
20
30
40
50
60
70
80
90
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Pe
rce
nt R
eco
ve
ry (
%)
Percent Polymer (%)
58-28 SBS A 58-28 SBS B
64-28 SBS A 64-28 SBS B
52-34 SBS A 52-34 SBS B
Percent Recovery vs Percent Polymer
-10
0
10
20
30
40
50
60
70
80
90
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Perc
en
t R
ecovery
(%
)
Percent Polymer (%)
PG 58-28 SBS A PG 58-28 SBS B
PG 52-34 SBS A PG 52-34 SBS B
58-28B SBS A 58-28B SBS B
52-34B SBS A 52-34B SBS B
Percent Recovery vs Percent Polymer
11
0.0
5.0
10.0
15.0
20.0
25.0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
CT
OD
(m
m)
Percent Polymer (%)
Average CTOD 58-28 SBS A Average CTOD 58-28 SBS B
Average CTOD 64-28 SBS A Average CTOD 64-28 SBS B
Average CTOD 52-34 SBS A Average CTOD 52-34 SBS B
DENT (Average CTOD) vs Percent Polymer
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
CT
OD
(m
m)
Percent Polymer (%)
Average CTOD PG 58-28 SBS A Average CTOD PG 58-28 SBS B
Average CTOD 58-28B SBS A Average CTOD 58-28B SBS B
58-28 DENT (CTOD) vs Percent Polymer
13
-28 MTO PMA Minimum
-28 MTO Unmodified Minimum
0.0
5.0
10.0
15.0
20.0
25.0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
CT
OD
(m
m)
Percent Polymer (%)
Average CTOD PG 52-34 SBS A Average CTOD PG 52-34 SBS B
Average CTOD 52-34B SBS A Average CTOD 52-34B SBS B
52-34 DENT (CTOD) vs Percent Polymer
14
-34 MTO Minimum
Fatigue Indicator (ε6 ) vs Percent Polymer and Recovery
15
0
100
200
300
400
500
600
700
800
900
0 2 4
Str
ain
Am
plit
ude (
µm
/m)
Percent Polymer (%)
PG 58-28 SBS A
PG 64-28 SBS A0
100
200
300
400
500
600
700
800
900
1000
0 25 50 75
Str
ain
Am
plit
ude (
µm
/m)
Percent Recovery (%)
Logarithmic!64-28 500 µm/m: 2,500,00064-28 700 µm/m: 200,000Results of individual tests
Fatigue Indicator (ε6 ) vs DENT (CTOD)
16
0
200
400
600
800
1000
0 1 2 3 4 5 6 7 8 9 10
Str
ain
Am
plit
ude (
µm
/m)
CTOD (mm)
PG 58-28 SBS A
PG 64-28 SBS A
CTOD: 2.3 mmΕ6: 621.2 µm/m
CTOD: 3.2 mmΕ6: 798.7 µm/m
CTOD: 3.5 mmΕ6: 314.2 µm/m
CTOD: 9.2 mmΕ6: 620.9 µm/m
Bending Beam Rheometer
17
▪ Used to determine Low Temperature Grade, ΔTc, Low Temperature Limiting Grade and Grade Loss▪ Does not characterize SBS modified asphalt very well▪ Extended conditioning times does not change shortcomings with measurement
0.29
0.3
0.31
0.32
0.33
0.34
0.35
0.36
0.37
0.38
0 1 2 3 4 5
M-V
alu
e
Percent Polymer (%)
58-28 SBS A
58-28 SBS B
64-28 SBS A
64-28 SBS B
52-34 SBS A
52-34 SBS B
ΔTc = Tc,S - Tc,m
Tc,S – Stiffness Critical TemperatureTc,m – m-Value Critical Temperature
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0% 1% 2% 3% 4%
ΔTc
Percent Polymer (%)
58-28 SBS A 58-28 SBS B 64-28 SBS A 64-28 SBS B 52-34 SBS A
52-34 SBS B 52-34B SBS A 52-34B SBS B 58-28B SBS A 58-28B SBS B
ΔTc vs Percent Polymer
18
Dynamic Shear Rheometer
19
▪ Measures phase angle, modulus (stiffness) with constant shear strain and single frequency• High temperature grade does not predict rutting resistance well• Intermediate temperature grade does not predict cracking resistance well
Glover-Rowe Parameter
▪ Taken from master curve data at reference temperature of 15˚C and frequency of 0.005 rad/s
▪ Damage zone calculated using:
G∗ (cosδ)2/sinδ = 180 kPa
G∗ (cosδ)2/sinδ = 600 kPa or 450 kPa
Cross-Over Temperature
▪ Temperature at which the phase angle of PAV aged material reaches 45°
▪ Phase Angle:• 0˚ = purely elastic• 45˚ = transition between more viscous and
more elastic behaviour• 90˚ = purely viscous
Black Space Diagrams- Close Ups!
20
58-28 64-28 58-28B
52-34 52-34B
Phase Angle Decreases
Phase Angle Increases
Black: 0% SBSGreen: 2% SBSPurple: 4% SBS
Y-Axis: Complex ModulusX-Axis: Phase Angle
Glover-Rowe Parameter vs Percent Polymer
21
10
12
14
16
18
20
22
24
0% 1% 2% 3% 4%
Cro
ss-O
ver
Tem
pe
ratu
re (
°C)
Polymer Concentration
58-28 SBS A 58-28 SBS B
64-28 SBS A 64-28 SBS B
58-28B SBS A 58-28B SBS B
Cross-Over Temperature vs Percent Polymer
22
0
2
4
6
8
10
12
14
16
0% 1% 2% 3% 4%
Cro
ss-O
ver
Tem
pe
ratu
re (
°C)
Polymer Concentration
52-34 SBS A 52-34 SBS B52-34B SBS A 52-34B SBS B
Cross-Over Temperature vs Percent Polymer
23
Linear Amplitude Sweep
24
𝑁𝑓 = 𝐴 𝛾𝑚𝑎𝑥𝐵
Viscoelastic Continuum Damage Model (VECD)
• Number of Cycles to Failure
Fracture Mechanics Approach
• Fatigue Resistance Energy Index (FREI)
▪ Part 1: Frequency Sweep- gives initial binder properties▪ Part 2: Amplitude Sweep- cyclic loading ramps up from 0.1% to 30% applied strain
• Binder begins to crack at edge of sample▪ AASHTO TP 101
▪ Two approaches to data analysis:
𝐹𝑅𝐸𝐼 =𝐽𝑓−𝜏𝑚𝑎𝑥
𝐺0.5𝜏𝑚𝑎𝑥
⋅ 𝛾0.5𝜏𝑚𝑎𝑥
2
LAS (Number of Cycles to Failure) vs Percent Polymer
25
y = 98563x + 504358-28 SBS A R² = 0.99
y = 94293x + 504358-28 SBS B R² = 0.9827
y = 66997x + 382858-28B SBS B R² = 0.9877
y = 72473x + 382858-28B B SBS A R² = 0.9393
y = 69443x + 398064-28 SBS A R² = 0.9829
y = 68867x + 398064-28 SBS B R² = 0.8612
3000
4000
5000
6000
7000
8000
9000
10000
0% 1% 2% 3% 4% 5%
Nu
mb
er o
f C
ycle
s to
Fai
lure
Percent Polymer (%)
58-28 SBS A 58-28 SBS B 58-28B SBS A
58-28B SBS B 64-28 SBS A 64-28 SBS B
LAS (Number of Cycles to Failure) vs Percent Polymer
26
y = 143557x + 508752-34 SBS A R² = 0.9816
y = 140060x + 508752-34 SBS B R² = 0.9893
y = 130663x + 454552-34B SBS A R² = 0.9831
y = 108590x + 454552-34B SBS B R² = 0.9451
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
0% 1% 2% 3% 4% 5%
Nu
mb
er o
f C
ycle
s to
Fai
lure
Percent Polymer (%)
52-34 SBS A 52-34 SBS B
52-34B SBS A 52-34B SBS B
LAS (FREI) vs Percent Polymer
27
y = 71.333x + 3.258-28 SBS A R² = 0.7907
y = 70x + 3.258-28 SBS B R² = 0.717
y = 16.333x + 1.264-28 SBS A R² = 0.8038
y = 22.333x + 1.264-28 SBS B R² = 0.9212
y = 29x + 1.7658-28B SBS A R² = 0.7994
y = 45x + 1.6558-28B SBS B R² = 0.931
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0% 1% 2% 3% 4% 5%
Fati
gue
Res
ista
nce
En
erg
y In
dex
Percent Polymer (%)
58-28 SBS A 58-28 SBS B 64-28 SBS A
64-28 SBS B 58-28B SBS A 58-28B SBS B
LAS (FREI) vs Percent Polymer
28
y = 66x + 5.952-34 SBS A R² = 0.4594
y = 49.333x + 5.952-34 SBS B R² = 0.3635
y = 28.333x + 4.752-34B SBS A R² = 0.3229
y = 12x + 4.752-34B SBS B R² = 0.0916
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0% 1% 2% 3% 4% 5%
Fati
gue
Res
ista
nce
En
erg
y In
dex
Percent Polymer (%)
52-34 SBS A 52-34 SBS B52-34B SBS A 52-34B SBS B
Asphalt Binder Cracking Device
29
▪ ABCD critical temperature based on modulus, phase angle, thermal coefficient of contraction and failure strength of binder
▪ Proposed to replace Direct Tension Test▪ Sample is cooled at constant rate of -10˚C until cracking occurs
▪ AASHTO TP 92
Elwardany, Planche and King, “A Tale of Two Deltas: Toward a Universal “Blind” Framework for Asphalt Durability”, TRB Annual Meeting, January 13, 2020
Tf = Tc,S - Tcr(BBR) (ABCD)
y = -127.5x - 34.11758-28 SBS B R² = 0.9643
y = -90x - 31.73364-28 SBS B R² = 0.999
y = -95x - 39.16752-34 SBS B R² = 0.9991
y = -127.5x - 32.48358-28B SBS B R² = 0.9938
y = -90x - 38.53352-34B SBS BR² = 0.9838
-46
-44
-42
-40
-38
-36
-34
-32
-30
0% 1% 2% 3% 4% 5%
AB
CD
Cra
ckin
g Te
mp
erat
ure
(°C
)
Polymer Concentration (%)
58-28 SBS B 64-28 SBS B 52-34 SBS B 58-28B SBS B 52-34B SBS B
ABCD (Tcr )vs Percent Polymer
30
2.5
3.5
4.5
5.5
6.5
0% 1% 2% 3% 4% 5%
ΔTf
(°C
)
Polymer Concentration (%)
58-28 SBS B
64-28 SBS B
52-34 SBS B
58-28B SBS B
52-34B SBS B
ABCD (ΔTf )vs Percent Polymer
31
Unmodified Asphalt Rankings
32
52-3452-34B58-2858-28B ≈ 64-28
ΔTc Cracking Resistance MoreLess
Cross-Over Temperature Cracking Resistance MoreLess
52-3452-34B58-2858-28B64-28
LAS Cracking Resistance MoreLess
52-3452-34B58-2858-28B ≈ 64-28
ABCD Cracking Resistance MoreLess
52-3452-34B58-2858-28B64-28
Rankings are relative to each other, not definitive measures of performance
Conclusions
33
▪ SBS polymer modified asphalt has a fundamentally different behaviour than unmodified asphalt• It is more elastomeric than purely ductile
▪ Low strain tests and parameters which operate in the linear viscoelastic region seem to be unable to characterize SBS modified asphalt well
• High temperature grade, low temperature grade, DENT, ΔTc / Extended BBR, Cross-Over temperature
▪ Large strain tests produce conditions more comparable to the strains observed in pavements and seem to improve characterization of SBS polymer modified asphalt• MSCR, LAS (VECD or fracture mechanics approach) and ABCD
Recommendations
34
Simpler Binder Characterization
▪ Single specification across Ontario would be optimal
▪ AASHTO M 332 would increase simplicity of rutting characterization
▪ MSCR is suitable for evaluating SBS concentration▪ Ash content is suitable for limiting REOB
▪ More frequent?• Increasing simplicity could allow for
resources to be reallocated to more frequent testing if desired
Mixture Characterization
▪ Best form of characterization▪ Will require multiple years of coordinated work
from industry and owners▪ Gives understanding of final product performance▪ Has been shown to be sensitive to mix and binder
properties
Improved Binder Cracking Characterization?
▪ If necessary, a large strain amplitude cracking test would likely be better suited to characterizing cracking performance for all types of asphalt
