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Performance testing at high service temperatures of asphalt mixtures for airfield pavements
Nicol Botha
1.00
1.10
1.20
1.30
1.40
1.50
1.60
1.70
1.80
10
15
20
25
30
35B7
27-2
00
B737
-300
B767
-300
ER
A300
-C4
B777
-200
B737
-700
A320
-200
B777
-300
ER
A320
NEO
A380
-800
B747
-8
B747
-400
ER
B787
-9
B737
MAX
B787
-8
A340
-600
A380
-800
F
A350
-900
A321
neo
A350
-100
0
A330
-900
neo
B787
-10
B777
-9
80's 90's CURRENT FUTURE
Tire Pressure (MPa)W
heel
Loa
d (t
on)
Wheel Load
Tire Pressure
Developments in aircraft industry
1.00
1.10
1.20
1.30
1.40
1.50
1.60
1.70
1.80
10
15
20
25
30
35B7
27-2
00
B737
-300
B767
-300
ER
A300
-C4
B777
-200
B737
-700
A320
-200
B777
-300
ER
A320
NEO
A380
-800
B747
-8
B747
-400
ER
B787
-9
B737
MAX
B787
-8
A340
-600
A380
-800
F
A350
-900
A321
neo
A350
-100
0
A330
-900
neo
B787
-10
B777
-9
80's 90's CURRENT FUTURE
Wheel Load
Tire Pressure
Airfield Pavements – Structural Performance of Asphalt Mix
• Permanent deformation (rutting) of airfield pavements was never a big concern • Conventional (traditional) asphalt mixes performed satisfactorily• Changes to the aircraft manufacturing industry is playing a role in current asphalt
performance• More and more airfield pavements fail in permanent deformation • Rutting of airfield pavements has a serious impact on airport operations
0
50
100
150
200
250
0 0.5 1 1.5 2 2.5 3
Dep
th b
elow
sur
face
(mm
)
Depth Confinement Factor (kz)
Airfield Pavements – Structural Performance of Asphalt Mix
Known rut prediction models (e.g. MEPDG) hints that the biggest risk for
permanent deformations are approximately in the upper 100mm of
the asphalt layers
These models may be valid for typical highway
pavement loading conditions
This is a misperception based on actual field performance of
airfield pavements
Considers sensitivities relating to temperature and loading time – but not airfield loading
conditions
Majority of rutting
Airfield Pavements – Structural Performance of Asphalt Mix PM
APE
N20
5mm
Airfield Pavements – Structural Performance of Asphalt Mix PM
APE
N31
5mm
Traditional vs. Performance Based Asphalt Specifications
TRADITIONAL PERFORMANCE BASED
Chocolate Fudge Cake
200g plain chocolate, broken into chunks (use one with a low cocoa content - we used Waitrose plain Belgian chocolate)
200g butter
200g light brown muscovado sugar100ml soured cream
2 eggs, beaten200g self-raising flour5 tbsp cocoa powder
hundreds and thousands, to decorate
For the icing100g plain chocolate
170g can condensed milk100g butter
Adoption of Performance Based Asphalt Specifications
Performance Based Asphalt Specifications and Testing
European experience shows that satisfactory pavement performance is more likely obtained with performance-based asphalt requirements
FAA is moving towards asphalt mix performance based specifications (FAA AC 150/5370-10H, 2018)
South Africa is moving towards performance based specifications (Sabita Manual 35 – Level II and III mix design)
Structural Mix Performance
Resistance to permanent
deformation
Traffic related densification
Mix durability
FatigueMix stiffness
Fracture toughness
(resistance to crack
propagation)
Low temperature performance
Asphalt Mix Characteristics - Volumetrics
•Improved aggregate packing
•Aggregate shape•Filler content and type
•Proper classification in terms of PG
•Polymer modification•Bitumen content•Bitumen film thickness
•Voids filled with asphalt
•Voids at refusal density
BITUMENAIR VOIDS
AGGREGATES
Asphalt Mix Creep PerformanceCu
mul
ativ
e Ax
ial S
trai
n
Number of Load Repetitions
AVOID
Performance Tests Available
Typical asphalt performance test
• Flow Number• Dynamic Modulus• Triaxial Cyclic Compression Testing
• Hamburg Wheel Tracking Test• Asphalt Pavement Analyzer• Wheel path rutting (EN) - Small Device• Wheel path rutting (EN) - Large Device• Model Mobile Load Simulator (MMLS3)
• Fatigue
Triaxial tests
Wheel tracking tests
Four-point beam fatigue test
Wheel Tracking TestsHamburg Wheel tracking Test (HWTT)
Wheel path rutting (EN) - Large Device
Asphalt Pavement Analyzer (APA)• Steel wheel• Dependent on benchmark performance
(i.e. not an accurate reflection of actual field performance)
• Rigidity of the blank steel wheel tends to overestimate permanent deformation
• Pressurized hose• Tire pressures: 0.7 MPa - 1.7 MPa• Dependent on benchmark performance
(i.e. not an accurate reflection of actual field performance)
• Current benchmark value for airfield pavements mainly based on US conditions
• Pneumatic (inflated) tire• Tire pressure: 600 kPa• Wheel load: 5 000 N• Various temperatures and
loading conditions• produces rut profiles similar to
field performance
Model Mobile Load Simulator (MMLS3)• Pneumatic (inflated) tire• Various temperatures and loading conditions• Superior flexibility• Tire pressure: Adjustable• Wheel load: Adjustable• Lateral wander simulated
Flow Number
Flow number = Number of load repetitions to reach the start of tertiary creep
The creep slope could vary for different asphalt mixes having the same flow number
Not considered a true performance based criterion
Merely an indicator of the risk of permanent deformation
Provides no information about the creep slope (Stage 2)
Cum
ulat
ive
Axia
l Str
ain
Number of Load Repetitions
Triaxial Cyclic Compression Testing
Controlled confinement Controlled (dynamic) vertical
stress Controlled test temperature
Can be used to specify testing temperatures for different regions
Confinement with asphalt depth can be varied
Cum
ulat
ive
Axia
l Str
ain
Number of Load Repetitions
Concluding Remarks
Changes in the aircraft manufacturing industry
Field performance of current airfield asphalt pavements demands a shift in how the mixes are specified
Airfield vs. highway pavement performance
Using benchmark values obtained from different regions
Performance testing
More demanding loading conditions
Performance specifications closes the gap between field and laboratory performance
Loading conditions varies significantly – do not use highway pavement performance models for airfield pavements
Asphalt performance varies for different climatic regions and loading conditions
Know test limitations and boundary conditions
QUESTIONS?