Sarnia Technology Applications & Research
Asphalt Re-Recycling Impact on Rheology & Chemistry Pavel Kriz
Expert Task Group Meeting, Salt Lake City April 28, 2016
2016.1375
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Continuously Recycled Asphalt Pavement = Industry Sustainability
Average Percent Recycled Asphalt Pavement (RAP) Used in the USA* *http://www.asphaltpavement.org/PDFs/IS138/IS138-2014_RAP-RAS-WMA_Survey_Final.pdf
15%
18%
21%
2009 2010 2011 2012 2013 2014
• Rate of recycling is growing
• Re-Recycling is occurring
• Do we understand the implications?
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How Much Re-Recycling is Viable?
+ 60-90% Virgin material (aggregate + softer binder)
Service
Construction Removal
Stockpiling Grading
Production
Life-end
• Aging Stiffening/Embrittlement Road failure
• Irreversible changes in chemistry Is this sustainable long term?
• Softeners? Asphalts, REOB, bio-oils, refinery oils – paraffinic, aromatic etc.
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Test Plan Simulated Binder Re-Recycling
Softened Asphalt
Simulated In-Service Aging
Testing
Softening 4× +75% Virgin Asphalt:
1. PG 58-28 or
2. PG 64-22 or
3. PG 64-22+Mohawk oil to meet PG 58-28
60 °C UV, H2O,
Freeze
Rheology & Chemistry (Aged 1-4)
Rheology & Chemistry (Softened 1-4)
New Aging Method
RTFO
3× 24h
• Artificial aging of asphalt binder in Weather-o-Meter (WoM) to better mimic in-service aging
~80+ years of service
Weather-o-Meter
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Ratio of Binders in Re-Recycled Materials
0
0.2
0.4
0.6
0.8
1
0 1 2
w/w
No. of Recycling Cycles
RAP 2
RAP 1
Virgin
Virgin
Virgin
Virgin
…
6
3 Weather-O-Meter Cycles Match RAP Rheology
• Three virgin binders subjected to weather-o-meter aging method
• 3×24 h cycle found suitable to obtain similar rheology to particular RAP
0
10
20
30
40
50
60
70
80
90
100
DSRo T, °C R&B, °C Pen. at 25 °C,dmm
T, °
C o
r P
en
, dm
m
RAPPG 64-22PG 58-28PG 64-22 + Mohawk 1.9 1.0 2.1
4.3
-24
-18
-12
-6
0
6
12
T S, °C T m, °C m-S
BB
R T
est
T, °
C
RAPPG 64-22PG 58-28PG 64-22 + Mohawk
High Temperature Properties (field RAP vs virgin PG after 3×24h in WoM)
Low Temperature Properties (field RAP vs virgin PG after 3×24h in WoM)
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• C & O bonds (Carbonyl/Carboxyl/Alcohol/Ether…) more prevalent in RAP
• Baseline drift (presence of condensed aromatic rings) only observed in RAP
• RAP & weather-o-meter aged binders not compositionally equivalent
Field Aging Differs From WoM aging in FTIR
0
0.2
0.4
0.6
0.8
1
5001000150020002500300035004000
Re
lati
ve A
bso
rba
nce
Wavenumber, cm-1
RAP
PG 64-22
PG 58-28
PG 64-22+Mohawk
C=O C-O
Baseline drift
FTIR Spectra of Field RAP and WoM Aged Virgin PG Binders
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• Re-recycling at 25 %wt. recycling rate showed minimal impact
• Minor increase in m-value temperature noted with each cycle
Re-recycling No Change to PG at 25% Rate
46
52
58
64
70
76
82
88
DS
Ro
T, °
C
-30.0
-24.0
-18.0
-12.0
-6.0
0.0
m T
, °C
m T = temperature at BBR m-value = 0.300 MPa/s DSRo T = temperature at DSR = 1.0 kPa
Example for PG 64-22 + Mohawk Oil Dataset at 25 % Recycling Rate
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• High quality straight-run asphalts are generally BBR stiffness limited
• Aging increases BBR m limiting T faster than BBR-S T
• Asphalt softened with Mohawk oil is significantly more m-value limited
• Re-Recycling increases BBR m T due to loss of relaxation back bone rigidity (C-O C=O etc.) &/or phase incompatibility
Evolution of BBR m-S with Re-Recycling
0
1
2
3
4
5
6
7
8
m-S
, °C
PG 64-22PG 58-28PG 64-22 + Mohawk
-3.5
-2.5
-1.5
-0.5
0.5
m-S
, °C
PG 64-22
PG 58-28
PG 64-22 + Mohawk
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Straight-Run Asphalt Outperforms Mohawk Oil
faster aging
LTPG = Low Temperature Performance Grade
• Both PGs straight-run asphalts showed smaller loss in LTPG during aging
• PG 64-22 softened with Mohawk oil showed faster aging rates
• After 2nd recycling, relaxation properties (m-value) slightly worsen
0
2
4
6
8
10
12
14
Aged 1 Aged 2 Aged 3 Aged 4
LT
PG
Lo
ss D
uri
ng
Ag
ing
, °C
PG 64-22
PG 58-28
PG 64-22 + Mohawk
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Further Re-Recycling Not Evidenced in FTIR
No Change in FTIR with Re-Recycling
C=O C-O
• No significant change in FTIR spectra with re-recycling
• Oxidation evidenced, but not at a field sample level
• Analysis beyond FTIR, XRF, CHNS necessary for PAHs
0
0.2
0.4
0.6
0.8
1
5001000150020002500300035004000
Re
lati
ve
Ab
sorb
an
ce
Wavenumber, cm-1
Aged 4
Aged 3
Aged 2
Aged 1
Virgin PG 64-22
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Conclusion: Re-Recycling Viable with Limitations
0
0.2
0.4
0.6
0.8
1
1 2 3 4 5 6 7 8 9 10
w/w
No. of Recycling Cycles
RAP 10 RAP 9
RAP 8 RAP 7
RAP 6 RAP 5
RAP 4 RAP 3
RAP 2 RAP 1
Virgin
At 25% Recycling Rate, 6.25% Material at 2+ Cycles & 1.56% at 3+ Cycles
• Straight-run asphalts outperform oil softeners, that includes harder PG
• Softening with oils does not bring desired effect in improved performance
• At moderate recycling rates (25%) dilution minimizes impact
Next Steps:
• Enhance understanding of phase stability & formation of condensed aromatic rings and link it to relaxation properties
Question & Comments?
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