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

transcript

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

• 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,

|G*|sind, (kPa)

S (kPa) m-

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

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

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

sin/||

sin/|| SI

Rutting

PAVRTFOooG

sin|| SI

Fatigue

PAVRTFOoS

SICreep

) PAVRTFOoS

SICreep

PAVRTFOooG

sin|| SI

Fatigue

RTFOooG

sin/||

sin/|| SI

Rutting

20 40 60 80 100

Temperature (C)

Stiffening Index (Fatigue) Stiffening Index (Rutting)

Stiffening index = 1

20 40 60 80 100St

Temperature (C)

Stiffening Index (Fatigue) Stiffening Index (Rutting)

Stiffening zone after RTFO aging

Softening zone after RTFO+PAV aging

PG64/SBR PG64/SBR/HP2

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

|G*| (Pa)

non-aged RTFO RTFO+PAV

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

|G*| (Pa)

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

|G*| (Pa)

Black Diagram

SBR PG64/

SBR/HP2

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

20 40 60 80 100

Temperature (C)

RTFO (PG64) RTFO (PG64+SBR)

RTFO (PG64+SBR+HP2)

20 40 60 80 100C

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).

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

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

Ongoing Testing

Expand binder testing to PG 70and PG 76

Chemical composition using GPC and FTIR

Imaging by SEM

Thank you

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

Documents