Effect of Crumb Rubber on RheologicalProperties of Asphalt Binder and Aggregate
Packing of Asphalt Mixtures
Tirupan Mandal and Hussain BahiaUniversity of Wisconsin-Madison, USA
Hypothesis and Objective
•Hypothesis:– Crumb rubber size, rubber concentration, and reaction
time plays an important role in the rheologicalproperties of rubber modified binders and aggregatepacking of rubberized asphalt mixtures
•Objective:– Evaluate the effect of crumb rubber particles on the
rheological properties of asphalt binders and theaggregate packing of the rubber modified asphaltmixtures
Rubber Modified Binder Preparation
Factor Levels DescriptionBase Binder 1 PG 64-22
Crumb Rubber Size 2 0.595 mm (Coarse) and0.075 mm (Fine)
Crumb RubberConcentration 3 10%, 15%, and 20%
Blending Duration(or Reaction Time) 2 Green and Reacted
Selection of Reaction Times- Using Hand-held Viscometer @ 180±5 °C
0100020003000400050006000700080009000
10000
0 1 2 3 4 5 6 7 8
Visc
osity
(cP)
Time (hr)
Fine Rubber 15% 0.075-mm Rubber20% 0.075-mm Rubber10% 0.075-mm Rubber
0
500
1000
1500
2000
2500
3000
0 1 2 3 4 5 6 7 8
Visc
osity
(cP)
Time (hr)
Coarse Rubber 15% 0.595-mm Rubber10% 0.595-mm Rubber20% 0.595-mm Rubber
Green and Reacted times selected from these graphs!
Rubberized Asphalt Mixture Preparation
Size (mm)% Passing
Coarse Gradation Fine Gradation37.5 100.00 100.0025 100.00 100.0019 99.73 100.00
12.5 78.64 94.259.5 64.47 80.40
4.75 41.12 63.702.36 27.37 43.901.18 18.73 28.720.6 12.90 19.180.3 7.82 11.86
0.15 4.87 7.750.075 3.24 5.98
CompactionTemperature (CT):
155°C
MixingTemperature (MT):
145°C
From Viscosity-Temperature Profile
AC: 5.4% AC: 4.8%
Binder Testing Methods
Test Method Binder Type EvaluationParameters/Response Testing Standard
Cup and Bob Original Viscosity -NA-
Multiple Stress CreepRecovery (MSCR) RTFO Jnr
Stress Sensitivity AASHTO TP70
High Temperature(HT) Performance
Grading
Original andRTFO G*/sinδ AASHTO T315
Elastic Recovery (ER)-DSR RTFO Elastic Recovery AASHTO T XXX-13
Linear AmplitudeSweep (LAS) PAV Fatigue
AASHTO TP 101-12
Binder Testing Methods- Bob and Cup
Output: Viscosity
Binder Testing Methods- MSCR
• Creep stress:0.1kPa, 3.2 kPa
• 10 cycles– 1 sec constant creep
stress– 9 sec zero stress
• Output: Creepcompliance (Jnr)and PercentRecovery (%R) at 0.1kPa, and 3.2 kPa
MSCR B5 46ºC
0.001
0.01
0.1
1
10
0 25 50 75 100 125 150 175 200time (s)
g
DataModel PredictionStress: 0.1 kPa
Stress: 3.2 kPaStra
in
Binder Testing Methods- ER-DSR
Typical strain curve for elastic recovery test inthe DSR
- Temperature: 25°C- Conditioning Time: 20
minutes- Constant strain rate of
0.02315 1/s is applied for 2minutes.
- This step is run in straincontrolled mode and thenfollowed by a constant zeroshear stress for a period of30 minutes.
- This step is run in stresscontrolled mode andcorresponds to the recoverypart of the test.
Binder Testing Methods- LAS
The test involves two steps:- An initial 100 cycles applied
at 0.1% strain to determineundamaged linearviscoelastic properties, and
- A final step that consists oframping strain amplitude,beginning at 0.1% andending at 30% appliedstrain, over 3100 cycles ofloading at 10 Hz.
Fatigue law on log-scale (Hintz 2012)
Aggregate Packing Analysis- iPas2
Cutting Sections(Roohi et al. 2012)
Microstructural parameters
10% FineRubber - 2 h
10% FineRubber - 5 h
15% FineRubber - 2 h
15% FineRubber - 5 h
20% FineRubber - 2 h
20% FineRubber - 5 h
1 rpm 3.8 3.0 10.8 8.3 28.1 12.010 rpm 2.2 1.8 4.3 3.9 10.6 6.6100 rpm 1.8 1.5 2.8 2.8 6.4 4.6
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Visc
osity
(Pa.
s)
Viscosity @ 135°C
Fine Rubber
Binder Test Results - Viscosity
10% CoarseRubber - 2 h
10% CoarseRubber - 5 h
15% CoarseRubber - 2 h
15% CoarseRubber - 5 h
20% CoarseRubber - 1 h
20% CoarseRubber - 4 h
1 rpm 1.9 2.0 4.1 4.5 18.1 17.010 rpm 1.5 1.6 2.6 2.9 7.9 7.9100 rpm 1.2 1.2 1.6 1.9 3.7 4.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Visc
osity
(Pa.
s)
Viscosity @ 135°C
Coarse Rubber
- Viscosity increases with increase in crumb rubber concentration, and decrease withincrease in shear rate
- Binder modified with fine crumb rubber is more viscous than coarse crumb rubber
Binder Test Results –High TemperatureTrue Grade (TG)
Binder10% -GreenBinder
10% -ReactedBinder
15% -GreenBinder
15% -ReactedBinder
20% -GreenBinder
20% -ReactedBinder
0.075-mm Fine RubberUnaged Binder 78.2 76.3 82 81.7 91.1 85.6
RTFO Aged Binder 78 73.6 78.7 78.8 89.8 83.20.595-mm Coarse Rubber
Unaged Binder 77.2 76.7 80.4 81 87.3 87.5RTFO Aged Binder 81 77.8 84.7 82.6 87.7 91.5
- No change in TG for different reaction times- TG increases with increase in crumb rubber concentration
- 4 times grade bump for 20% concentration
Binder Test Results - MSCR
10% FineRubber -2 Hours
10% FineRubber -5 Hours
15% FineRubber -2 Hours
15% FineRubber -5 Hours
20% FineRubber -2 Hours
20% FineRubber -5 Hours
%Recovery 12.55 5.79 20.17 20.41 54.62 33.49JnR 1.43 2.60 1.24 1.22 0.23 0.67
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
JnR
% R
ecov
ery
Fine Rubber - 3.2 kPa Stress Level
10%Coarse
Rubber -2 Hours
10%Coarse
Rubber -5 Hours
15%Coarse
Rubber -2 Hours
15%Coarse
Rubber -5 Hours
20%Coarse
Rubber -1 Hours
20%Coarse
Rubber -4 Hours
%Recovery 8.57 5.03 17.87 18.56 52.19 46.83JnR 1.02 1.59 0.69 0.78 0.14 0.23
0.000.200.400.600.801.001.201.401.601.80
0.00
10.00
20.00
30.00
40.00
50.00
60.00
JnR
% R
ecov
ery
Coarse Rubber - 3.2 kPa Stress Level
- The %Recovery was lower, and the Jnr was higher for all the reactedbinders
0
10
20
30
40
50
60
70
80
90
100
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
%Re
cove
ry
Jnr (kPa-1)
AASHTHO TP-70 Limit 10% Fine Rubber - 2 Hours10% Fine Rubber - 5 Hours 15% Fine Rubber - 2 Hours15% Fine Rubber - 5 Hours 20% Fine Rubber - 2 Hours20% Fine Rubber - 5 Hours 10% Coarse Rubber - 2 Hours10% Coarse Rubber - 5 Hours 15% Coarse Rubber - 2 Hours15% Coarse Rubber - 5 Hours 20% Coarse Rubber - 1 Hours20% Coarse Rubber - 4 Hours
Binder Test Results- Jnr vs. %Recovery at 3.2 kPa Stress Level
Only 20% Crumb Rubber Concentration Passes!
Passing %Recovery
Failing %Recovery
Binder Test Results – ER-DSR
10% Fine Rubber 15% Fine Rubber 20% Fine Rubber 10% CoareRubber
15% CoarseRubber
20% CoarseRubber
GreenBinder 57% 63% 72% 61% 73% 83%
ReactedBinder 50% 64% 65% 59% 73% 80%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
Elas
tic R
ecov
ery (
%)
Green BinderReacted Binder
- 20% concentration has highest ER value!- ER value is less for reacted binder similar to MSCR results
Binder Test Results - LAS
0
5000
10000
15000
20000
25000
30000
35000
40000
Nf
Nf 2.5% Nf 5%
- Coarser rubber performs better in fatigue than finer!- Nf drops for reacted binder
Aggregate Packing Analysis– On Green Binders
0.0
1000.0
2000.0
3000.0
4000.0
5000.0
6000.0
10%
Fine
rRu
bber
Gree
nBi
nder
20%
Fine
rRu
bber
Gree
nBi
nder
20%
Coar
ser
Rubb
erGr
een
Bind
er
TPL (
mm
/100
cm2 )
Fine GradationTotal Proximity Length
0.0
1000.0
2000.0
3000.0
4000.0
5000.0
6000.0
7000.0
8000.0
10% Finer Rubber GreenBinder
20% Finer Rubber GreenBinder
20% Coarser RubberGreen Binder
TPL (
mm
/100
cm2 )
Coarse GradationTotal Proximity Length
Coarser rubber performs better!
Aggregate Packing Analysis– Green vs. Reacted Binders
0
1000
2000
3000
4000
5000
6000
7000
8000
20% Finer RubberGreen Binder
20% Finer RubberReacted Binder
20% Coarser RubberGreen Binder
20% Coarser RubberReacted Binder
TPL (
mm
/100
cm2 )
Total Proximity Length
Green binder performs better!
Conclusions
• Rubber size, rubber concentration, and reaction time play animportant role in the rheological properties of the rubbermodified binders
• Binders modified with coarser rubber (0.595-mm) has betterrheological properties compared to the finer rubber (0.075-mm)
• Binders modified with higher rubber concentration (20%)performs better for both the sizes of rubber than the lowerconcentration, and also passes the AASHTO TP-70 MSCRcriteria
• Green binders, for both the rubber sizes, show betterrheological properties than the reacted binders
Conclusions
• It is found that rubber size and reaction time could haveimportant effects on aggregate packing duringcompaction, and thus performance
• Green binders for both the size of rubber are found tohave better aggregate packing than the reacted rubbermodified binders.
Thank you!
Questions?