Introduction of a performance grade specification for ... · Behaviour of bitumen Elastic and...

Introduction of a performance grade

specification for bituminous binders

SAT seminars15 – 18 March 2016

Overview

• Reason for transition to PG spec

• Basis of the specification

• Behaviour of bitumen

• Rheometry

• Age Hardening

• Performance grade specification

Reasons for transition

• Recent technological developments in SA

• Limitations of current specification

• Success in the USA

Recent developments

• Implementation of SAPDM

– More advanced response and damage models

– Binder performance characteristics and ageing

• Revised national asphalt mix design method

– Adoption of a binders specifications based on

engineering properties for optimal performance

of asphalt layers

• Ongoing increase in traffic loading intensity

Limitations of current spec

SANS 4001-BT1 - “industrial grading system”

– Cannot meet challenges associated with the

technological developments

– Merely defines the “consistency” of the binder

over a range of temperatures (from 25°C - 135°C)

in terms of surrogate properties such as:• Penetration

• softening point

• dynamic viscosity;

Consistency measurements

Short term

Limitations / cont.

• Compliance limits:

– neat and short term aged binder

– no assessment of the in-service longer term

ageing characteristics - durability

• Does not cover critical factors related to:

– Traffic levels and speeds

– Climate (especially temperature ranges)

Question

• How are binder grades selected for

specific applications?

• On what basis are decisions made to use

modified binders?

Success in USA of a PG spec

Implementation in 1995 yielded benefits:

• Test conditions suited to specific conditions of climate

and traffic;

• Rheological properties of bitumen - better

understanding of behaviour of binders in a range of

operating conditions;

• The importance of assessing long term ageing

resistance;

• Market shifts to accommodate regional requirements

in terms of binder grades; and

• Rational decisions on need or otherwise to modify

bitumen

Basis of PG specification

Structural requirements

• Bituminous layers to resist :

• Distortion – permanent deformation; and

• Fracture due to:

– Fatigue or loss of durability

– Temperature fluctuations

• In addition they should be durable i.e.

maintain their properties to counter distress

for a long period.

Basis of PG specification

• Gauge binder’s resistance to 3 types of

damage:– Permanent deformation (viscous flow at high

temp)

– Cracking (fatigue / durability) at intermediate

temp)

– Temperature fracture at low temp

• Assure durability i.e. maintain their properties

to counter distress for a long period

• Facilitate workability

Specification framework

Performance related selection of binders on

basis of:

• Traffic volumes and speed

• Climate (max and min temperatures)

• Binder durability

Additionally requirements for

• Safety

• Workability– storage stability

– handling and application at elevated temperature.

Laboratory resource economy

Speciality lab equipment limited to:

• Dynamic shear rheometer (DSR)

• Rolling thin film oven (RTFO)

• Pressure Ageing Vessel (PAV)

• Bending beam rheometer (BBR)

Behaviour of bitumen

Elastic and viscous behaviour, depending on:

• Temperature; and

• loading duration or frequency.

Visco-elastic character of bitumen

• variable response behaviour under varied

loading times and temperatures changes.

• Viscous behaviour defined by viscosity:

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Visco-elastic behaviour

Stress

Strain

time

time


Stress

Strain

time

time

Elastic


Stress

Strain

time

time

Visco-elastic Elastic

strain


Stress

Strain

time

time

Elastic

strain

Delayed elastic,

viscous strain


Stress

Strain

time

time

Elastic

strain

Delayed elastic,

viscous strain

Elastic recovery


Stress

Strain

time

time

Elastic

strain

Delayed elastic,

viscous strain

Elastic recovery

Delayed elastic

recovery

permanent,

viscous strain

Rheology

• Rheology - study of the flow and deformation

of matter (soft solids)

• Fundamental engineering property of

bituminous binders influenced by:

– temperature

– chemical composition

– structure of binder molecules

Rheometry

Lab techniques to determine rheological

properties

• Measurement of:

– elastic and viscous behaviour under:

• type and frequency of loading

• temperature of the specimen

• Two types of instruments in general use :

– Dynamic shear rheometer

– Bending beam rheometer

Dynamic shear rheometer

Categories of measurement:

• Fundamental rheological properties

• Creep behaviour of a bituminous binder

• Fatigue behaviour

• Low temperature behaviour

Fundamental properties

• Values of δ are:

• Purely elastic material: δ = 0 °

• Purely viscous material: δ = 90 °

G* & δ

• G* alone cannot describe the behaviour

asphalt

• δ is also required

δ for straight bitumen: 88 – 89°

for modified binders: can be 60°

act in a more elastic manner.

Creep behaviour

• DSR test - extent of recovery after stress relaxation

• Multi stress creep recovery (MSCR)

• 1-s constant stress, a 9-s recovery period

• Repeated 30 times

– 10 cycles are performed at 0.1 kPa - condition

– 10 more cycles at 0.1 kPa stress level and

– 10 cycles at 3.2 kPa stress level.

Creep behaviour

• Non-recoverable compliance, JNR

• �� =�� !�"#��"$��%�

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Low temperature behaviour

• Binder’s ability to resist low temperature

cracking

• BBR measures low temperature stiffness and

stress relaxation properties of binders

δ = PL3/48EI

BBR outputs

Outputs:

• Creep stiffness (S)

• m-value, the slope of the creep stiffness, both after 60 s

• Δ T(c) = Diff in temp at which S = 300 and m = 0.3

Slope = m

Overview




• Rheometry

• Age Hardening


Age hardening

Age hardening

• Rheological and performance related

properties assessed on:

• unaged

• short term aged – RTFOT

• long term aged – PAV

Long term aged

• Long term ageing – not covered by the current

specification – is simulated in a Pressure

Ageing Vessel (PAV) as per ASTM D6521

G*RTFOT/G*Original

G*PAV/G*Original

at 10 rads/sec at an

intermediate temperature

Overview




• Rheometry

• Age Hardening


Performance grade specification

• Specification to cover:

– Operating categories

– Performance characteristics– Viscous flow

– Fatigue / durability cracking

– Low temperature cracking

– Storage Stability

– Safety

– Pumping and handling

Performance criteria

• Key goal: limiting the potential of the binder

to contribute to permanent deformation,

fatigue cracking and low temperature cracking

• Give assurance binder – (glue) – can augment

the role and function of the other

components of the layer to perform

adequately ….

Performance criteria/cont…

• Measurement of the rheological properties of

binders in a DSR and BBR - formulation of

criteria that would limit:

– excessive permanent or plastic deformation at

elevated temperatures;

– fatigue failure (durability cracking) at intermediate

temperatures; and

– thermal fracture due to large fluctuations in layer

temperatures.


• Performance criteria

• Safety and workability

• Specification framework

– Operating categories

– Viscous flow

– Fatigue / durability cracking

– Low temperature cracking

– Storage Stability

– Safety


Safety and workability

Three requirements covered :

• Safety – flash point

• Workability – viscosity at elevated temperatures to

give assurance that it can be:

– pumped

– sprayed

– mixed with aggregate and

– asphalt compacted

– Storage stability – (modified binders) compatibility of the

base bitumen and the modifier


• Performance criteria

• Safety and workability

• Specification framework


• Operating categories;

– Climate

– Traffic

• Resistance to viscous flow;

• Resistance to fatigue / durability cracking;

– Reporting of G*and δ over frequency range • at intermediate temperature

• on original, RTFO and PAV aged binder;

• Low temperature cracking;

• Workability– Storage stability

– Safety;


Operating category: Climate

• Climate is taken into account by a grading

designation related to:

– the average 7-day max pavement design temp

– minimum grading temp

• Max pavement design temp 58°C & 64°C

• Min grading temperatures -22°C & -16°C

Operating category: Traffic

• Traffic will be classified in terms of volume

and speed

• Standard, Heavy, Very Heavy and Extreme, Design ESALsa

(million)

Traffic Load Rate

Standingb Slowc Standardd

0.3 to < 3 H S S

3 to < 10 V H H

10 to < 30 E V V

≥ 30 E E E

a Anticipated traffic in the design lane over a 20 year periodb Standing traffic –average speed <20 km/hc Slow traffic –average speed 20 to 70 km/hd Standard traffic – average speed > 70 km/h

Operating category - Classification

Classification58S

-22

64S

-16

58H

-22

64H

-16

58V

-22

64V

-16

58E

-22

64E

-16

Maximum pavement design

temperature, Tmax (˚C)58 64 58 64 58 64 58 64

Minimum grading temperature,

Tmin (˚C)-22 -16 -22 -16 -22 -16 -22 -16

Test temperature benchmarks:

1. High temperature, Tmax: max pavement design temp e.g. 58°C, 64°C

2. Intermediate temperature: 12�3 + 12%� 2 + 4⁄ °7

3. Low temperature: Tmin: Tmin, i.e. [12%�+10°]7



– Climate

– Traffic




• Reporting of G*and δ frequency sweeps at intermediate

temperature on original binder, RTFO and PAV aged binder;

• Storage stability;

• Workability

– Safety;

– Pumping and handling; and

Viscous flow

• Binder’s susceptibility to :

– contribute to permanent deformation

– causing flushing of bituminous layers (incl. seals)

• DSR testing

– RTFO aged binder*

– at Tmax - non-recoverable compliance, JNR

* “S” class binders: G*/sinδ unaged binder at Tmax

simulate handling conditions of binders in this category -

not used in asphalt mixes

Fatigue / durability cracking

• Durability cracking (fatigue and thermal effects)

• Current proposal: Glover-Rowe parameter

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"%�AC

• In USA:

– correlates with ductility at 15°C

– Linked to damage onset and significant cracking as follows:

• Damage onset (5 cm ductility):

• Significant cracking (3 cm ductility):

• Establish values for SA based on report values

• Tests at intermediate temperature

• Alternative Δ T(c) (BBR) difference in temp

S = 300, m= 0.3

GR = 180 kPa

GR = 450 kPa

G-R profiles

Source: Rowe

Δ T(c)

Source: Rowe



– Climate

– Traffic




• Reporting of G*and δ frequency sweeps at intermediate

temperature on original binder, RTFO and PAV aged binder;

• Storage stability;

• Workability

– Safety;

– Pumping and handling; and

Low temperature cracking

• The resistance of the binder to (low)

temperature fracture will be assessed by:

– BBR testing

• an upper limit of creep stiffness (to limit its brittleness)

• stress relaxation characteristics m

• specimens tested at the low temperature.

Safety and workability

• Safety:

– The flash point by Cleveland Open Cup Tester

• Storage stability:

– Difference in G* (Tmax and 10 rads/second) of

binder in the top and bottom of the container

• Pumping and handling:

– Viscosity of unaged binder at 135°C

Work to be done

• Requirements and compliance limits for

resistance to fatigue / durability cracking.

• Reporting of the frequency sweeps at the

intermediate temp on original, RTFOT and PAV

aged binder will be mandatory

• Once sufficient data has come to hand,

compliance limits will be proposed for

implementation

Proposed spec for trial implementation

Property Performance grade

58S

-22

64S

-16

58H

-22

64H

-16

58V

-22

64V

-16

58E

-22

64E

-16

Maximum pavement design temperature, Tmax (˚C) 58 64 58 64 58 64 58 64

Minimum grading temperature, Tmin (˚C) -22 -16 -22 -16 -22 -16 -22 -16

Original binder

G*/sinδ, 10 rads/sec at Tmax, minimum (kPa) 1.0 1.0 N/A

G*, δ, @ 0.05 to 20 rads/sec, at [(Tmax + Tmin)/2 + 4]°C Report

Viscosity (Pa.s) @ 135°C, maximum 3.0

Flash Point (˚C), minimum 230

Storage stability, maximum % diff, G*T and G*B

@ 10 rads/sec at Tmax

10

RTFO binder

Maximum Mass Change (m/m %) 0.3 0.3 1.0

JNR @ Tmax., (kPa-1) maximum 4.5 4.5 2.0 2.0 1.0 1.0 0.5 0.5


Ageing Ratio, G*RTFOT/G*Original, @ 10rads/sec, maximum 3.0

PAV binder

S (60s) at Tmin + 10oC , MPa, maximum 300

m (60s) at Tmin + 10oC, minimum 0.300

ΔTc (0C), minimum –5


Ageing Ratio, G*PAV/G*Original, (@ 10rads/sec), maximum 6.0

Footnote

• General purpose bitumen produced at SA

refineries

– would in all probability comply with the

requirements of the two “S” grades

– compliance with higher grades - high traffic ,

elevated temps – will, most likely, require

modification by the secondary binder industry

• Will the technology be exported to Africa?

Rheology

Introduction of a performance grade specification for ... · Behaviour of bitumen Elastic and...

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