Anti-Oxidants Effect on Bitumen Rheology and Mixes...

ISSAEST, Fairbanks, AK, USA, August 2-5, 2015

Samer Dessouky, David Contreras, Jeremy Sanchez

University of Texas – San Antonio

Daewook Park

Kunsan National University, South Korea

Anti-Oxidants Effect on Bitumen Rheology

and Mixes Mechanical Performance

International Symposium on Systematic Approaches to Environmental Sustainability in Transportation


Outline

Pavement Aging

Aging/AO Mechanism

Objectives

Rheological Properties

SI/CMI analysis

Bitumen Morphology

Mixes mechanical properties

Summary


Pavement Aging

Exposure to temperature and air, the

oil phase become volatile, resulting

in an increase in stiffness.

Asphalt oxidation (aging) leads to: brittleness in asphalt binder

decrease fatigue resistance,

reduce thermal stability,

loss of aggregate bonding, and

moisture damage (stripping)

Aging occurs during pavement

construction and continue under

traffic


Aging Mechanism

Aging denotes changes in physical and chemical

properties.

There are many different aging mechanisms, vary

considerably depending on bitumen composition, polymer

additives, and environmental conditions.

Physical changes (reversible), reflect a molecular rearrangement

over time

chemical changes (irreversible) shown in thermal oxidation, or chain

ruptures and post-crosslinking.


Anti-oxidant Mechanism

There are four compounds of AOs that inhibit

oxidation of hydrocarbons in bitumen

1) Hindered Phenols to terminate chain through reaction with peroxyl

radicals,

2) Inhibitors to terminate chains through reaction with alkyl radicals,

3) Agents to decompose peroxides with no free radicals formation

4) Agents to consume di-oxygen to prevent oxidation.


Objectives

Identify anti-oxidant (AO) additive(s) to control

aging of asphalt bitumen

Evaluate the influence of AO in bitumen rheology

and mixture performance


Anti-Oxidants Purpose

Co-polymers

SBR Improve thermo-plastic properties

SBS Improve elasticity and adhesion

properties and maintain low viscosity

SEBS Improve resistance to weathering

Hindered phenols

HP1 (Vitamin

E) Stability at in-service temperatures

HP2 Viscosity stability and controlling

thermo-oxidation

HP3 Thermal stabilizer protects against

thermal degradation


Materials/Equipment

• PG64-22 (Valero) / 3% AO

(wt.)

• Mixing at 1500-2000rpm and

149oC (IKA® RW20 mixer)

• Short-term (RTFO) long-term

(PAV) aging

• Rheology: RV, DSR and BBR

Testing AASHTO Accredited

UTSA Bitumen Laboratory

RV DSR BBR RTFO PAV


Rheological Properties

Bitumen/ additives

RV DSR BBR

Unaged Unaged RTFO RTFO+PAV RTFO+PAV

Viscosity (Pa.s)

|G*|/sind (kPa)

|G*|/sind,

(kPa)

|G*|sind, (kPa)

S (kPa) m-

value

135°C 76°C 76°C 31°C -12°C

PG64-22 0.56 0.55 4.83 1211 144.67 0.32

PG64 + SBR 3.56 4.06 8.14 1154 122.54 0.25

PG64 + SBS 4.00 3.96 8.98 1400 137.70 0.25

PG64 + SEBS 2.28 3.87 6.93 1741 124.80 0.28

PG64 + HP1 0.63 0.82 2.84 966 89.38 0.32

PG64 + HP2 0.32 1.67 4.16 851 69.80 0.32

PG64 + HP3 0.39 1.27 3.92 2602 117.37 0.30

PG64+SBR+HP2 2.60 2.24 9.19 853 75.16 0.31


Temperature Sweep

40

50

60

70

80

90

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

20 40 60 80 100

Ph

ase

An

gle

(d

eg)

|G*

| (P

a)

Temperature (C)

PG64 PG64+SBR PG64+SBR+HP2


Quantify the effect of AO in the rheological properties due to short/long

term aging at high, intermediate and low temperatures

Stiffening Indices (SI)

RTFOooG

G

d

d

sin/||

sin/|| SI

*

*

Rutting

PAVRTFOooG

G

d

d

sin||

sin|| SI

*

*

Fatigue

PAVRTFOoS

S

SICreep



0

0.5

1

1.5

2

PG

64

-22

SB

R

SB

S

SE

BS

HP

1

HP

2

HP

3

SB

R+

HP

2

Sti

ffen

ing

In

dex

(R

utt

ing

)

0

0.5

1

1.5

2

2.5

PG

64

-22

SB

R

SB

S

SE

BS

HP

1

HP

2

HP

3

SB

R+

HP

2

Sti

ffen

ing

In

dex

(F

ati

gu

e)

0

0.5

1

1.5

2

PG

64

-22

SB

R

SB

S

SE

BS

HP

1

HP

2

HP

3

SB

R+

HP

2

Sti

ffen

ing

In

dex

(C

reep

) PAVRTFOoS

S

SICreep

PAVRTFOooG

G

d

d

sin||

sin|| SI

*

*

Fatigue

RTFOooG

G

d

d

sin/||

sin/|| SI

*

*

Rutting



0

4

8

12

16

20 40 60 80 100

Stif

fen

ing

Ind

ex

Temperature (C)

Stiffening Index (Fatigue) Stiffening Index (Rutting)

Stiffening index = 1

0.0

0.5

1.0

1.5

2.0

20 40 60 80 100St

iffe

nin

g In

dex

Temperature (C)

Stiffening Index (Fatigue) Stiffening Index (Rutting)

Stiffening zone after RTFO aging

Softening zone after RTFO+PAV aging

PG64/SBR PG64/SBR/HP2


40

50

60

70

80

90

1.E+02 1.E+04 1.E+06

Ph

ase

an

gle

(d

eg)

|G*| (Pa)

non-aged RTFO RTFO+PAV

40

50

60

70

80

90

1.E+02 1.E+04 1.E+06

Ph

ase

an

gle

(d

eg)

|G*| (Pa)


40

50

60

70

80

90

1.E+02 1.E+04 1.E+06

Ph

ase

an

gle

(d

eg)

|G*| (Pa)


Black Diagram

PG64/

SBR PG64/

SBR/HP2

PG64

Rheological properties independent from temperature/frequency


Complex Modulus Index (CMI)

Ratio of G* for aged to non-aged bitumen to assess thermal

stability

Determined using DSR temperature sweep at different aging level

CMI (RTFO) % =100*[G*(RTFO)/G* (Unaged)]

CMI (PAV) % = 100*[(G*(PAV+RTFO)-G*(RTFO))/G*(Unaged)]


Complex Modulus Index (CMI)

CMIRTFO CMIPAV

0

100

200

300

400

500

20 40 60 80 100

CM

I RTF

O(%

)

Temperature (C)

RTFO (PG64) RTFO (PG64+SBR)

RTFO (PG64+SBR+HP2)

0

200

400

600

800

1,000

20 40 60 80 100C

MI P

AV

(%)

Temperature (C)

PAV (PG64) PAV (PG64+SBR)

PAV (PG64+SBR+HP2)

HP2 additives are effective to control oxidation and

improving thermal stability


AO Role on Bitumen Structure

Polymers modifications tend to form a continuous network

within the bitumen (Airey 2003).

As polymers undergo thermal oxidation, free radicals are

generated. The HP2 role is to scavenge these radicals

and prevent the polymers network from degrading and

breaking apart (Li et al. 2010).


PG

64

/S

BR

/H

P2

P

G6

4/

SB

R

Bitumen Morphology

White areas: polymer/additives, grey areas: asphaltenes/maltenes

Polymer network breaking apart was less severe in case of HP2

Fluorescence Microscopy

Chain area (pixel * pixel)

•PG64/SBR: 35

•PG64/SB/HP2: 70


Mechanical Performance of Mixes

Bending beam fatigue Indirect Tensile Dynamic Modulus and

Flow Number


Stripping Inflection Point: HWTT


HWTT

HP2 reduced rutting by more than 2mm

compared to SBR.

The stripping was determined at 6000, 6000 and

7000 cycles for the base, SBR-blend and HP2-

enhaned mix, respectively.

HP2 improved the stripping resistance and rutting

performance of the bituminous mix.


Summary

A blend of HP2 with SBR has reduced excessive

stiffness after PAV aging but improve resistance

to rutting in early life of bitumen.

Microscopic images showed HP2 to help forming

more homogenous composition after long-term

oxidation

HP2 has shown better moisture resistance

HWTD


Ongoing Testing

Expand binder testing to PG 70and PG 76

Chemical composition using GPC and FTIR

Imaging by SEM

Thank you

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Anti-Oxidants Effect on Bitumen Rheology and Mixes...

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