2017 CalAPA Fall Asphalt Pavement Conference presentation: An overview and analysis of long-life (perpetual) asphalt pavements on the state highway system in California. Presented by Dr. John Harvey of the University of California Pavement Research Center.

1. Long Life Asphalt Pavement
and Mix Design
John Harvey
University of California Pavement Research Center
CalAPA
Sacramento
25 October, 2017

2. Current Long-Life Rehabilitation
Strategies
200-225
mm PCC
100-150 mm
CTB
150 mm
AS
CSOL
Crack and Seat PCC,
Place Thick AC Overlay
FDAC
Remove PCC or AC,
Replace with partial or
full-depth
AC structure
Remove PCC, Replace
with 200-300 mm
Concrete Slab
Retain or replace
existing base
Typical now
150-300
mm AC
150-200
mm CTB
or GB

3. Typical Structures Needing Long-Life Rehabilitation
• Rural
– Asphalt
– Fatigue cracking
– Reflection cracks
from CTB, PCC, old
asphalt
• Urban
– Cracked jointed
plain PCC
– No dowels
3

4. General Principles
• Site investigation (minimize surprises)
• Keep material types relatively simple
– Reduces the risk of construction quality issues
– Helps control costs
– Faster construction
• Materials properties = materials + compaction
• Performance related tests
• Drive distresses to occur at the surface
• Ensure bonding between layers during
construction
4

5. Crack, Seat and Overlay
Bottom layer - cracking
Middle layer – cracking, rutting
Top layer – rutting, cracking
Base layers
Sacrificial layer – safety, noise
Cracked and Seated PCC
0.08-0.15 ft (25-50 mm )
fabric
0.15-0.33 ft (50-100 mm)
Varying
thickness
0.10 ft (30 mm)
subgrade
Existing grade

6. Full-Depth Asphalt Concrete
Bottom layer - cracking
Middle layer – cracking, rutting
Top layer – rutting, cracking
subgrade
Sacrificial layer – safety, noise
granular base (recycled PCC,
CTB, granular)
0.08-0.15 ft (25-50 mm)
0.15-0.33 ft (50-100 mm)
Varying
thickness
0.15-0.25 ft (50-75 mm )
0-0.50 ft (0-150 mm )
Existing grade

7. California Design Criteria
• Structure
– 40 year design life
– 95% reliability (within project) using CalME
– Structure designed for rutting (total rut, all
layers considered), bottom-up fatigue
cracking
• Surface layers
– 15 year design life for sacrificial layer
– 40 years for rutting of top layer
7

8. Sacrificial Surface Layer
• Sacrificial layer (safety, noise)
– Rubberized hot mix open-graded
– Shorter design life than rest of pavement
– When removed,
also removes
top-down cracks
8

9. HMA
RHMA-G
OGFC
RHMA-O
OBSI noise with SRTT tire at 60 mph
Performance over 15 years
Increased noise

10. Permanent Top Layer
• Top layer (rutting, top-down cracking)
– Polymer-modified dense-graded asphalt
– Thickness (75-100 mm) depends on expected depth
of high temperatures
– Critical shear
stresses typical
at 50 mm depth
10

11. 0
5
10
15
20
25
30
-
50,000 100,000 150,000 200,000
HVS Load Applications
RutDepth,mm
Conv. mix G*=82 MPa
Typical mix
Typical mix
76-mm polymer
modified mix G*=32 MPa
Polymer better than stiffer conventional
HVS Rut Test Results
Temperature = 50 C at 50 mm depth

12. Bottom-Up Fatigue Cracking
• Focus on compaction using conventional
materials
• Increased stiffness to reduce tensile
strains at bottom
– Ideas from Australia, UK, France (bitume dur,
Enrobés à Module Elevé [EME])

13. Middle Layer
• Primary structural layer
– Good rutting resistance (may carry traffic until surface
constructed)
– Good fatigue resistance
– Stiff
• Stiff conventional asphalt, not polymer
– Polymer modified asphalt usually softer than
conventional asphalt at moderate temperature,
reduces bending resistance
– Use higher RAP binder replacement to make stiffer
– No WMA to help ensure blending
• Thickness determined by CalME design
13

14. Reduction of Air-Voids 8% to 5 %
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
200 250 300 350 400 450 500
Total AC thickness(mm)
FatigueLife(ESAL)
AR4000c (8% av,5% ac),AR4000c (8% av,5%ac)
AR4000c(5% av,5% ac),AR4000c(5% av,5% ac)
Traffic Index 15
Traffic Index 17
PG58-28
5% air-voids
8% air-voids

15. Rich-Bottom Layer
• Definition
– Same gradation and RAP content as top layer
– 0 to 3 % air-voids
– Asphalt content increased (contractor choice) to
facilitate compaction
• 50 to 75 mm (0.15-0.25 ft) optimal thickness
• Benefit is from increased compaction, not
increased asphalt content
• Must be out of zone of rutting risk
– More than about 150 mm (0.5 ft) below surface
depending on climate, traffic

16. Effect of Rich Bottom
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
200 250 300 350 400 450 500
Total AC thickness (mm)
FatigueLife
AR4000c (8% av,5% ac),AR4000c (8% av,5%ac)
AR4000c(5% av,5% ac),AR4000c(5% av,5% ac)
AR4000c (5% av,5% ac), AR4000c (2%av ,5% ac)
AR4000c (5% av,5% ac), AR4000c(2% av,5.5% ac)
Traffic Index 15
Traffic Index 17
8% AV
5% AV
5% AV, 2% AV bottom same %binder
5% air-void, 2% AV bottom +0.5%binder

17. Must Have Good Bonding
• Tack coat required between all lifts
• Often use paving asphalt as tack on long-life
instead of emulsion
• Cracking life can be halved if lose bond
17

18. Mechanistic-Empirical Design
CalME
• Introduced in 2006
• Focus on rehabilitation and preservation
• Incremental – Recursive approach
– Simulation runs one increment of loads/temperatures at
a time
– Calculates damage and
permanent deformation
– Adjusted stiffnesses
are used as input for
the next increment
• Outputs damage,
surface cracking,
IRI, and rut depth

19. Projects to
Date
• Long Beach
projects under
Hveem, AR
binder
• Last three
projects included
25% RAP, PG
• Next project:
I-5 Sacramento,
Superpave
I-5 Weed 2012
I-5
Red Bluff
2011
I-80
Dixon
2013
I-710 Long Beach
2002, 2006

20. Main feedback from last three
projects
• Try to make the mix design time go faster
• Changes in specifications and testing:
– Simplified flexural fatigue testing approach
• Cut testing time by about 1/3
• No extrapolation
– Use of Repeated Load Triaxial with AMPT
instead of shear test
• No extrapolation
– Added Semi-circular beam
20

21. Performance Related Tests
Rolling wheel compaction; Contractors built molds at plant
Design Parameters
Test
Method
Sample
Air Voids
Requirement
HMA-LL-Top
HMA-LL-
Middle
HMA-LL-
Rich Bottom
Permanent deformation (percent): 2,3
Maximum PAS7 at 10,000 cycles
Maximum PAS7 at 20,000 cycles
AASHTO
TP 79
Modified1
Mix
Specific6
XXX
XXX
XXX
XXX
Not
Required
Beam stiffness (psi): 3,4
Minimum stiffness at the 50th
cycle at given testing strain level
AASHTO T
321
Modified1
Mix
specific6
YYY at
XXX×10-6
in./in. strain
YYY at
YYY×10-6
in./in. strain
Not
Required
Beam fatigue: 3,4
Minimum of 1,000,000 cycles to
failure at this strain
Minimum of 250,000 cycles to
failure at this strain
AASHTO T
321
Modified1
Mix
specific6
XXX×10-6
in./in.
XXX×10-6
in./in.
XXX×10-6
in./in.
XXX×10-6
in./in.
XXX×10-6
in./in.
XXX×10-6
in./in.
Semicircular beam fracture
potential:
Flexibility Index
AASHTO
TP 1241
Mix
specific6
YYY
YYY
YYY
Moisture Sensitivity: 5
Minimum repetitions
AASHTO T
324
Modified1
Per test
method
20,000 20,000
Not
Required

22. Laboratory Tests – Estimated testing
times for three mixes, one iteration
Rolling wheel compaction; Contractors built molds at plant
• Starting point: Superpave mix design (Top, Middle)
• Week 1: Repeated Load Triaxial Top mix
– Multiple binder contents
– Binder content meets RLT permanent strain requirement
• Week 2, 3: Fatigue (Top), Mix Design (Middle)
– Flexural fatigue
• Week 3, 4: Fatigue (Middle), Mix Design (Rich Bottom)
– Rich Bottom mix design using gyratory compaction to get
2% AV, same gradation as surface mix but with
conventional binder
• Week 5, 6: Fatigue (Rich Bottom)
• Repeat as needed for any mix if do not meet requirements

23. Current Performance Based
Laboratory Tests – Fatigue Testing
Rolling wheel compaction; Contractors built molds at plant

24. Mix Design Guidance – Alternative ideas
to improve rutting and/or fatigue
Rolling wheel compaction; Contractors built molds at plant

25. Questions?