Modification of the Rolling Thin Film Oven

(RTFO) Test for Realistic Short-term Aging of

Asphalt Rubber Binders

M. Zia Alavi, Post-Doc Scholar

Xai Lau, Graduate Student

David Jones, Associate Director

John Harvey, Professor

52nd Petersen Asphalt Research Conference Western Research Institute

July 13-15, 2015 Laramie, Wyoming

Introduction

Asphalt Rubber Binder

• ASTM D6114 Definition:

–A blend of paving grade asphalt, ground

vulcanized recycled tire rubber, and additive, as

needed.

–Must have at least 15% rubber by weight of total

binder

–No restriction on the amount of natural rubber.

Introduction

…

• Caltrans Definition:

– A combination of asphalt binder, crumb rubber modifier (CRM), and asphalt modifier (i.e., Ext. oil).

– Must have at least 18 to 22 percent CRM by weight in total blend.

– CRM must contain 25.0±2.0 percent high natural crumb rubber.

– Only ambient grinding process is allowed for producing CRM. Fiber and metals can be taken out cryogenically.

– 2 to 6% extender oil must be used by weight of base binder.

Introduction

Production of Asphalt Rubber Binder in California

• When adding CRM, the asphalt binder plus

extender oil temperature must be between

190°C (375°F) and 225°C (440°F).

• Mixing/interaction duration must be at least

45 minutes.

• During mixing/interaction period the

temperature of asphalt rubber binder must be

between 177°C (350°F) and 218°C (425°F).

Introduction

Mixing Temp. for Asphalt Rubber Binder

• Caltrans Section 39-1.08B Mixing

“Asphalt rubber binder must be between 190°C (375°F) and 218°C (425°F) when mixed

with aggregate.”

Conventional binder: “Asphalt binder must be between 135°C (275°F) and 190°C (375°F) when mixed with aggregate.”

Problem statement

Limitations of the Current RTFO Test Method

• RTFO testing temperature and time is developed based on short-term aging of neat binders.

• It is not appropriate for asphalt rubber binder, because:

a) Aging temperature is not simulating asphalt rubber binder temperature during mix production.

b) Non-uniform aging of asphalt rubber binder. (the RTFO bottles are not fully coated while testing).

c) It is difficult to obtain sufficient amount of asphalt rubber binder from the bottles after testing.

Objective Realistic Short-Term Aging of Asphalt Rubber Binder

• Current RTFO testing condition:

– Temperature: 163°C.

– Duration: 85 min.

– Sample size: 35 g of binder per bottle.

Proposed modification for asphalt rubber binder:

– Increase testing temperature to 190°C to simulate rubberized mix production temperature.

– Modify the amount of binder sample corresponding to 35 g of base binder in each bottle.

– Change testing time ???

Experimental Plan

Experimental Plan

Lab produced binders

Base binder

No Ext.

4% Ext. oil.

Type I

(No Ext. Oil)

CRM passing 0.25 mm (#60)

CRM passing 2.36 mm (#8) and retained

on 0.25 mm (#60)

Type II

(4% Ext. Oil)

CRM passing 0.25 mm (#60)

CRM passing 0.25 mm (#60)

Field produced binders

Round Robin phase II binders

(A, B, and C)

Field projects

(At least from 3 projects)

Asphalt Rubber Binder Preparation

• Base binder: PG64-16

• Extender oil: 4% by weight of

base binder (VSSI)

• Crumb rubber: 18% by total wt. of

binder

• Mixing condition: 195±3°C for 85

min

– 15 min for adding rubber

– 45 minutes at 2000 rpm

– 30 minutes at 1000 rpm

• Sample size: ¾ of gallon.

Sample ID: TI-60, T2-60, T1-8, T2-8

Test Methods

Rheology:

High temperature performance-related properties

Concentric Cylinder Geometry

Chemistry:

Degree of oxidation ( FTIR measurements)

Degree of volatilization

Selecting Appropriate Testing Geometry

Parallel Plate Limitations

2mm parallel plate geometry is not suitable for binders with particulates

as large as 2.00 mm (passing #8).

• 8mm gap required for 2mm rubber particles (AASHTO T315).

• Problems with trimming especially with increased gap.

• Result may not be a true representation of asphalt rubber binder rheology.

1 mm 2 mm

Selecting Appropriate Testing Geometry Proposing concentric cylinder (cup&bob)

o Gap size: ~6 mm o Non-linear shear stress

distribution

o Conversion factor must

be determined using a

reference material, since

it is not just geometry

dependent.

Concentric-Cylinder (CC) vs. Parallel Plate (PP)

Critical factor Concentric cylinder (CC)

Parallel plate (PP)

Sample trimming No Yes

Testing duration Long Short

Testing temperature

High High and intermediate

Required material Large volume Little volume

Standard test method

Not available AASHTO T315, ASTM D7175

Comparison of CC and PP for neat binder

Statistically, there is no significant difference between PP and CC measurements. (95% CI)

Measurements at 64°C C

C.O

rigin

al

PP

.Orig

inal

CC

.RT

FO

PP

.RT

FO

CC

.TF

O

PP

.TF

O

1.5

2.0

2.5

G*/

sin(

d) (

kPa)

Geometry*Aging_Condition Complex Shear Modulus G* (kPa)

Phsa

e An

gle

d (D

egre

e)

85

86

87

88

89

1.5 2.0 2.5

58−22 64−16

85

86

87

88

89

70−10

CCPP

Parameter Df Sum Sq Mean Sq F Value Pr (>F)

Geometry

Binder type

Residuals

1

2

50

0.033

17.15

1.360

0.033

8.575

0.027

1.223

315.28

-

0.274

2e-16

-

Results and Discussion

Results and Discussion Improvement of RTFO Bottle Coating (uniform aging)

35 g

45 g

Aging Temp: 163°C Aging Temp: 190°C

35 g

45 g

Results and Discussion

Pros and Cons of the Proposed Modified RTFO

Advantages

• Fully coating of the bottle

• produce more RTFO residue.

• Initial pre-coat of the bottle is

much easier.

• Residue is more readily

poured out of the glass.

• Easier to scrape the residue.

• produces more RTFO residue.

Disadvantage(s):

• Extra fumes and smoke

while running the test.

• Possible overheating of the

binder (procedure will be

validated using field

produced binders/mixes)

Results and Discussion

G*/sin(δ) at 64°C

2 1

11

7

13 11

4 3

19

14

27

21

3 2

19

13

27 25

7 5

27

18

47

40

6 4

27

18

49

42

0

10

20

30

40

50

60

PG64-16 PG64-16+Ext T1-60 T2-60 T1-8 T2-8

G*/

sin

(δ)

kP

a

unaged

RTFO @ 163°C 35 g

RTFO @ 163°C 45 g

RTFO @ 190°C 35 g

RTFO @ 190°C 45 g

Results and Discussion

Phase angle at 64°C

86 87

70

73

66

69

82 83

63 65

57 59

83 84

62

65

57 57

77

80

56

58

51 51

79 81

55

58

50 50

45

50

55

60

65

70

75

80

85

90

PG64-16 PG64-16+Ext T1-60 T2-60 T1-8 T2-8

Ph

as

e a

ng

le (δ

), °

unaged

RTFO @ 163°C 35 g

RTFO @ 163°C 45 g

RTFO @ 190°C 35 g

RTFO @ 190°C 45 g

Results and Discussion

High PG Limit

69

66

89

84

91

89

68

66

86

83

91

88

67

65

86

82

91 90

74

71

92

88

98 97

72

69

92

87

99 99

64

69

74

79

84

89

94

99

104

PG64-16 PG64-16+Ext T1-60 T2-60 T1-8 T2-8

Hig

h P

G (°C

)

unaged

RTFO @ 163°C 35 g

RTFO @ 163°C 45 g

RTFO @ 190°C 35 g

RTFO @ 190°C 45 g

Results and Discussion

G* vs δ relationship at 64°C (block diagram)

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

45 60 75 90

Sh

ea

r M

od

ulu

s, G

* (k

Pa

)

Phase angle, δ (°)

PG64-16

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

45 60 75 90S

he

ar

Mo

du

lus

, G

* (k

Pa

)

Phase angle, δ (°)

PG64-16+Ext.

1.E-03

1.E+02

45 55 65 75 85Sh

ea

r M

od

ulu

s,

G*

(kP

a)

Phase angle, δ (°)

PG64-16 Unaged RTFO (163°C_85min_35g) Mod. RTFO (190°C_85min_45g)

Results and Discussion

G* vs δ relationship at 64°C (block diagram)

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

45 60 75 90

Sh

ea

r M

od

ulu

s, G

* (k

Pa

)

Phase angle, δ (°)

T1- 60

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

45 55 65 75 85S

he

ar

Mo

du

lus

, G

* (k

Pa

)

Phase angle, δ (°)

T2- 60

1.E-03

1.E+02

45 55 65 75 85Sh

ea

r M

od

ulu

s,

G*

(kP

a)

Phase angle, δ (°)

PG64-16 Unaged RTFO (163°C_85min_35g) Mod. RTFO (190°C_85min_45g)

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

45 60 75 90

Sh

ea

r M

od

ulu

s, G

* (k

Pa

)

Phase angle, δ (°)

T1- #8

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

45 60 75 90

Sh

ea

r M

od

ulu

s, G

* (k

Pa

)

Phase angle, δ (°)

T2- #8

Results and Discussion

G* vs δ relationship at 64°C (block diagram)

1.E-03

1.E+02

45 55 65 75 85Sh

ea

r M

od

ulu

s,

G*

(kP

a)

Phase angle, δ (°)

PG64-16 Unaged RTFO (163°C_85min_35g) Mod. RTFO (190°C_85min_45g)

Summary of Findings

• As expected, increasing short-term aging

temperature resulted in:

– Increasing binder stiffness

– reducing phase angle.

• Larger sample size result reduced the aging effect.

However, it is not as effective as aging temperature.

• Increasing the aging temperature to 190°C

increased the high PG temperature by up to 9°C.

Work in Progress…

• Analyzing change in chemistry of asphalt binder

– Quantifying degree of oxidation (Carbonyl and Sulfoxide functional groups)

– Quantifying degree of volatilization

• Comparing RTFO and TFO test results

• Testing field blended asphalt rubber binders

• Comparing properties of binder in rubberized mix and modified and conventional RTFO aged binders

• Evaluating RTFO test duration, if needed.