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
Visco-elastic behaviour
Stress
Strain
time
time
Elastic
Visco-elastic behaviour
Stress
Strain
time
time
Visco-elastic Elastic
strain
Visco-elastic behaviour
Stress
Strain
time
time
Elastic
strain
Delayed elastic,
viscous strain
Visco-elastic behaviour
Stress
Strain
time
time
Elastic
strain
Delayed elastic,
viscous strain
Elastic recovery
Visco-elastic behaviour
Stress
Strain
time
time
Elastic
strain
Delayed elastic,
viscous strain
Elastic recovery
Delayed elastic
recovery
permanent,
viscous strain
Visco-elastic behaviour
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
• Reason for transition to PG spec
• Basis of the specification
• Behaviour of bitumen
• Rheometry
• Age Hardening
• Performance grade specification
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
• Reason for transition to PG spec
• Basis of the specification
• Behaviour of bitumen
• Rheometry
• Age Hardening
• Performance grade specification
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 grade specification
• Performance criteria
• Safety and workability
• Specification framework
– Operating categories
– Viscous flow
– Fatigue / durability cracking
– Low temperature cracking
– Storage Stability
– Safety
– Pumping and handling
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 grade specification
• Performance criteria
• Safety and workability
• Specification framework
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;
– Pumping and handling
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
Specification framework
• Operating categories;
– Climate
– Traffic
• Resistance to viscous flow;
• Resistance to fatigue / durability cracking;
• Low temperature cracking;
• 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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• 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
Specification framework
• Operating categories;
– Climate
– Traffic
• Resistance to viscous flow;
• Resistance to fatigue / durability cracking;
• Low temperature cracking;
• 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
G*, δ, @ 0.05 to 20 rads/sec, at [(Tmax + Tmin)/2 + 4]°C Report
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
G*, δ, @ 0.05 to 20 rads/sec, at [(Tmax + Tmin)/2 + 4]°C Report
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
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