SuperPave Asphalt Specifications

ENCI 579 6 1

SuperPave Asphalt Specifications

• Previous asphalt specifications– physical property specifications

• penetration

• viscosity

• ductility

– conducted at standard test temperatures

– results used to determine if the material meets specification criteria

– tests are empirical in nature• results are related to pavement performance through

experience

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• Penetration test– indicates stiffness of the asphalt

– relationship between stiffness and pavement performance has to be gained from experience

• In some tests this relationship may not be very good

• Current empirical tests and specifications do not give information for the entire range of typical pavement temperatures

ENCI 579 6 3

SuperPave Asphalt Specifications• Viscosity test

– fundamental measure of flow• only provides information about higher temperature

viscous behavior at the standard test temperatures of 60 C and 135 C

• Penetration test• only describes consistency at a medium temperature

of 25 C

• lower temperature elastic behavior cannot be realistically determined from this data to predict low temperature performance

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• Empirical asphalt specifications– can classify different asphalts with the same

grading

– in fact these asphalts may have different temperature and performance characteristics

– because these asphalts are graded the same one might erroneously expect the same characteristics during construction and the same performance during hot and cold weather conditions

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• Strategic Highway Research Program SHRP - Canadian component C SHRP

• Began research in 1987 into developing a new system for specifying asphalt cement and asphalt mixes

• asphalt cement specifications are referred to as binder specifications– intended for both modified and unmodified asphalt

cements

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• Superpave asphalt binder specification– new test procedures and new equipment

– specified criteria remains constant but the temperature at which the criteria must be achieved changes for various grades

– tests measure physical properties that can be related directly to field performance by engineering principles

– tests are conducted at temperatures that are encountered by in-service pavements

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• The central theme of the Superpave Binder Specification is its reliance on testing asphalt binders in conditions that simulate the three critical stages during the binder’s life– tests performed on the original asphalt represent

the first stage of transport, storage and handling

– the second stage represents the asphalt during mix production and construction and is simulated by aging the binder in a rolling thin film oven

ENCI 579 6 9


– The thin film oven test exposes thin binder films to heat and air and approximates the aging of asphalt during mixing and construction

– The third stage occurs as the binder ages over a long period of time as part of the hot mix asphalt pavement layer. This stage is simulated for the specification by the pressure aging vessel. The procedure exposes binder samples to heat and pressure in order to simulate years of in-service aging in a pavement

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Superpave Asphalt Binder Tests

• Superpave Binder Aging Procedures– Asphalt binder ages:

• volatilization of light oils present in the asphalt

• oxidation by reacting with oxygen in the environment

– Rolling Thin Film Oven Test (RTFOT)• simulates both types of aging in the mixing and

placement of asphalt mix because of the high temperatures and air flow involved in the process

– Pressure Aging Vessel (PAV)• simulates in service aging

ENCI 579 6 13


– Pressure Aging Vessel (PAV)• simulates in service aging dominated by oxidation

and not volatilization because of the relative moderate in-service temperatures

• binder samples that have been aged in the PAV have already been aged in the RTFOT

• Consequently, the PAV residue represents binder that has been exposed to all of the environmental conditions to which binders are subjected to during production and service

ENCI 579 6 14


• Rolling Thin Film Oven Test (RTFOT)• AASHTO T240 ASTM D 2872

– provides aged asphalt binder that can be used for further testing of physical properties

– determines the mass quantity of volatile lost during the process

• indication of the aging that may occur in the asphalt during mixing and construction operations

• specified as 1% maximum

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• Pressure Aging Vessel (PAV)• AASHTO PP1

– simulates the effects of long term in-service aging of asphalt

– Uses binder that has previously been aged in the RTFOT since asphalt that is exposed to long term aging has also been through the mixing and construction process

– exposes the binder to high pressure and temperature for 20 hours

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• Dynamic Shear Rheometer (DSR)• AASHTO TP5

– Asphalt Behavior depends on both loading time and temperature and this test evaluates both effects

– measures rheological properties• complex shear modulus

• phase angle

– intermediate to high temperatures

– original binder RTFOT & PAV residues

ENCI 579 6 20


• Dynamic Shear Rheometer (DSR)– used to characterize both elastic and viscous

behavior

– G* (G star) complex shear modulus• measures the total resistance of the asphalt to

deformation

• elastic component (recoverable deformation)

• viscous component (non-recoverable deformation) (delta)

• indicates the relative amounts of recoverable and non-recoverable deformation

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ENCI 579 6 22

Superpave Asphalt Binder Tests• Values of G* and for asphalts are highly

dependant on temperature and frequency of loading– High temperatures

• behavior is viscous with no capacity for recovering or rebounding

= 90°

– Low temperatures• behavior is elastic witch rebounds from deformation = 0°

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• Superpave asphalt binder specification– Dynamic Shear Rheometer (DSR)

• Permanent Deformation– G*/sin at test temperature > 1.00 kPa original

binder– G*/sin at test temperature > 2.20 kPa RTFOT

binder

• Fatigue Cracking– G* (sin ) at test temperature < 5000 kPa PAV

binder

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• Rotational Viscometer• ASTM D4402

– used to determine the flow characteristics of the asphalt binder

– ensure that the asphalt is fluid enough to be pumped and handled at the hot mix facility

– measured on the original asphalt binder

– test temperature at 135 C

– maximum viscosity 3 Pa s

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• Bending Beam Rheometer (BBR)• AASHTO TP1

– measures low temperature properties of asphalt that are too stiff to be measured by the DSR

– BBR (stiffness) used in conjunction with the Direct Tension Test (strength and stretching ability before breaking)

– BBR measures deflection or creep under a constant load and temperature

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• Bending Beam Rheometer (BBR)– test temperatures are related to a pavement’s lowest

service temperature when the asphalt binder acts more like an elastic solid

– PAV asphalt binder

– test measures the performance characteristics of binders as if they had been exposed to hot mixing and some in-service aging

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• Bending Beam Rheometer (BBR)– applying a constant load (980mN) to the center of

the asphalt beam and measuring the deflection during the 4 minute test creep stiffness (S) and creep rate (m) can be calculated

– creep load simulates thermal stresses that gradually build up in a pavement when temperature drops

– Creep Stiffness (S) resistance of the binder to creep loading and the m-value is the change in asphalt stiffness with time during loading

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• Bending Beam Rheometer (BBR)– Low temperature cracking

• Creep Stiffness (S) @ 60s < = 300 Mpa

• S is between 300 to 600 Mpa the Direct Tension test may be used in lieu of the creep stiffness requirement

• m value (m) @ 60s > = .3

ENCI 579 6 35

Superpave Asphalt Binder Tests• Direct Tension Tester

• AASHTO TP3

– strong relationship between stiffness of asphalt binders and the amount of stretching they undergo before breaking

– asphalts that undergo considerable stretching before failure are called “ductile”

– those that break without much stretching are called “brittle”

– it is important that asphalts be capable of a minimal amount of elongation

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• Direct Tension Tester– typically stiffer asphalts are more brittle and softer

asphalts more ductile

– creep stiffness as measured by the BBR is not adequate enough to completely characterize the capacity of asphalts to stretch before breaking

• some asphalts exhibit high creep stiffness but can also stretch farther before breaking

– therefore SHRP specifications recognize these stiff but ductile binders

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• Direct Tension Tester– these asphalts are allowed to have high creep

stiffness (300 to 600 Mpa) if they can also display reasonable ductile behavior at low temperatures

– if creep stiffness < 300 Mpa the direct tension test is not required

– PAV asphalt binder

– test measures the performance characteristics of binders as if they had been exposed to hot mixing and some in-service aging

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Low Temperature Cracking MP1(a)

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SuperPave Binder Specifications

– Intended to improve performance by limiting the potential for asphalt to contribute towards

• permanent deformation

• low temperature cracking

• fatigue cracking

– required physical specifications remain constant for all performance grades (PG)

– the temperatures at which these properties must be reached vary depending on the climate in which the binder is expected to be used

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PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82

(Rotational Viscosity) RV

90 90 100 100 100 (110) 100 (110) 110 (110)

(Flash Point) FP

46 52 58 64 70 76 82

46 52 58 64 70 76 82

(ROLLING THIN FILM OVEN) (ROLLING THIN FILM OVEN) RTFO RTFO Mass Loss Mass Loss << 1.00 % 1.00 %

(Direct Tension) DT

(Bending Beam Rheometer) BBR Physical Hardening

28

-34 -40 -46 -10 -16 -22 -28 -34 -40 -46 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -10 -16 -22 -28 -34

Avg 7-day Max, oC

1-day Min, oC

(PRESSURE AGING VESSEL) (PRESSURE AGING VESSEL) PAVPAV

ORIGINALORIGINAL

> 1.00 kPa

< 5000 kPa

> 2.20 kPa

S < 300 MPa m > 0.300

Report Value

> 1.00 %

20 Hours, 2.07 MPa

10 7 4 25 22 19 16 13 10 7 25 22 19 16 13 31 28 25 22 19 16 34 31 28 25 22 19 37 34 31 28 25 40 37 34 31

(Dynamic Shear Rheometer) DSR G* sin

( Bending Beam Rheometer) BBR “S” Stiffness & “m”- value

-24 -30 -36 0 -6 -12 -18 -24 -30 -36 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 0 -6 -12 -18 -24

-24 -30 -36 0 -6 -12 -18 -24 -30 -36 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 0 -6 -12 -18 -24

PPerformance erformance GGrades M320 (MP1)rades M320 (MP1)

(Dynamic Shear Rheometer) DSR G*/sin

(Dynamic Shear Rheometer) DSR G*/sin

< 3 Pa.s @ 135 oC

> 230 oC

CEC

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SuperPave Asphalt Specifications

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