SUPERPAVE
FHWA Condensed Superpave
Asphalt Specifications
Lecture Series
What is Superpave
• Final product of the 1987-1993 FHWA Strategic
Highway Research Program to investigate better
pavement materials & design methods.
• Superior Performing Asphalt Pavements = Superpave
• Produced new standards for aggregates and bituminous
binders used in paving as well as mix design changes.
Aggregates
Usually refers to a soil that has in some way
been processed or sorted.
100
100
90
72
65
48
36
22
15
9
4
Aggregate Size Definitions
• Nominal Maximum Aggregate Size
– one size larger than the first sieve to
retain more than 10%
• Maximum Aggregate Size
– one size larger than nominal maximum
size
100
99
89
72
65
48
36
22
15
9
4
Percent Passing
100
max density line
restricted zone
control point
0
.075
.3
2.36
4.75
9.5
nom
max
size
max
size
12.5
Sieve Size (mm) Raised to 0.45 Power
19.0
Superpave Aggregate Gradation
Percent Passing
100
Design Aggregate Structure
0
.075 .3
2.36
12.5
19.0
Sieve Size (mm) Raised to 0.45 Power
Superpave Mix Size
Designations
Superpave
Designation
37.5 mm
25 mm
19 mm
12.5 mm
9.5 mm
Nom Max Size
(mm)
37.5
25
19
12.5
9.5
Max Size
(mm)
50
37.5
25
19
12.5
Gradations
* Considerations:
- Max. size < 1/2 AC lift thickness
- Larger max size
+ Increases strength
+ Improves skid resistance
+ Increases volume and surface area of agg
which decreases required AC content
+ Improves rut resistance
+ Increases problem with segregation of particles
- Smaller max size
+ Reduces segregation
+ Reduces road noise
+ Decreases tire wear
Percent Crushed Fragments in
Gravels
• Quarried materials always 100% crushed
• Minimum values depended upon traffic
level and layer (lift)
• Defined as % mass with one or more
fractured faces
Rounded Aggregates in Pavement
• Crushed face aggregates help to reduce
shear plane slides and mass deformation of
the pavement structure.
Percent Crushed Fragments in
Gravels
0% Crushed
100% with 2 or More
Crushed Faces
Coarse Aggregate Angularity
Criteria
Traffic
Depth from Surface
Millions of ESALs < 100 mm
> 100
mm
< 0.3
--/-55/-<1
--/-65/-<3
50/-75/-< 10
60/-85/80
< 30
80/75
95/90
< 100
95/90
100/100
100/100
100/100
>100
First number denotes % with one or more fractured faces
Second number denotes % with two or more fractured faces
Asphalt Cements
Background
History of Specifications
Background
• Asphalt
– Soluble in petroleum
products
– Generally a by-product of
petroleum distillation
process
– Can be naturally occurring
• Tar
– Resistant to
petroleum products
– Generally by-product
of coke (from coal)
production
Penetration Testing
• Sewing machine needle
• Specified load, time, temperature
100 g
Initial
Penetration in 0.1 mm
After 5 seconds
Penetration Specification
• Five Grades
•
•
•
•
•
40 - 50
60 - 70
85 - 100
120 - 150
200 - 300
Ductility
Typical Penetration Specifications
Penetration
40 - 50
200 - 300
Flash Point, C
Ductility, cm
450+
100+
350+
100+
Solubility, %
99.0+
99.0+
Retained Pen., %
55+
37+
Ductility, cm
NA
100+
Viscosity Graded Specifications
Types of Viscosity Tubes
Asphalt Institute Tube
Zietfuchs Cross-Arm
Tube
Table 1 Example
AC 2.5
Visc, 60C
250 + 50
Visc, 135C
Penetration
80+
200+
Visc, 60C
<1,250
Ductility
100+
AC 40
4,000 + 800
300+
20+
<20,000
10+
Penetration Grades
Viscosity, 60C (140F)
AC 40
100
50
40
50
AC 20
60
70
AC 10
85
100
AC 5
120
150
10
5
200
300
AC 2.5
Asphalt Cements
New Superpave Performance Graded Specification
PG Specifications
• Fundamental properties related to
pavement performance
• Environmental factors
• In-service & construction temperatures
• Short and long term aging
High Temperature Behavior
• High in-service temperature
– Desert climates
– Summer temperatures
• Sustained loads
– Slow moving trucks
– Intersections
Viscous Liquid
Pavement Behavior
(Warm Temperatures)
• Permanent deformation (rutting)
• Mixture is plastic
• Depends on asphalt source, additives, and
aggregate properties
Permanent Deformation
Courtesy of FHWA
Function of warm weather and traffic
Low Temperature Behavior
• Low Temperature
– Cold climates
– Winter
• Rapid Loads
– Fast moving trucks
Elastic Solid
Pavement Behavior
(Low Temperatures)
• Thermal cracks
– Stress generated by contraction due to drop in
temperature
– Crack forms when thermal stresses exceed
ability of material to relieve stress through
deformation
• Material is brittle
• Depends on source of asphalt and aggregate
properties
Thermal Cracking
Courtesy of FHWA
Superpave Asphalt Binder Specification
The grading system is based on Climate
PG 64 - 22
Performance
Grade
Min pavement
temperature
Average 7-day max
pavement temperature
Pavement Temperatures are Calculated
• Calculated by Superpave software
• High temperature
– 20 mm below the surface of mixture
• Low temperature
– at surface of mixture
Pave temp = f (air temp, depth, latitude)
Concentric Cylinder Rheometers
 Concentric
Cylinder
t Rq =
Mi
2 p Ri2 L
g=
WR
Ro - Ri
Dynamic Shear Rheometer (DSR)
• Parallel Plate
Shear flow varies with
gap height and radius
Non-homogeneous flow
2M
tR =
p R3
RQ
gR =
h
Short Term Binder Aging
• Rolling Thin Film Oven
– Simulates aging from hot mixing and construction
Pressure Aging Vessel
(Long Term Aging)
• Simulates aging of an asphalt
binder for 7 to 10 years
• 50 gram sample is aged for 20
hours
• Pressure of 2,070 kPa (300 psi)
• At 90, 100 or 110 C
Bending Beam Rheometer
Deflection Transducer
Computer
Air Bearing
Load Cell
Fluid Bath
Direct Tension Test
Load
Stress = s = P / A
DL
sf
D Le
Strain
ef
Summary
Construction
Rutting
Fatigue
Cracking
Low Temp
Cracking
[DTT]
[RV]
No aging
[DSR]
[BBR]
RTFO
Short Term Aging
PAV
Long Term Aging
Superpave Binder
Purchase Specification
Superpave Asphalt Binder Specification
The grading system is based on Climate
PG 64 - 22
Performance
Grade
Min pavement
temperature
Average 7-day max
pavement temperature
Performance Grades
CEC
Avg 7-day Max, oC
1-day Min, oC
PG 46
PG 52
PG 58
PG 64
PG 70
PG 76
PG 82
-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
ORIGINAL
> 230 oC
< 3 Pa.s @ 135 oC
(Flash Point)
(Rotational Viscosity)
(Dynamic Shear Rheometer)
> 1.00 kPa
46
52
52
90
< 5000 kPa
10 7
S < 300 MPa
4
25
22 19
m > 0.300
100
64
100
0
-6
Report Value
28
22 19
16
13 31
-12 -18 -24 -30 -36
-6 -12 -18 -24 -30
0
(Bending Beam Rheometer)
> 1.00 %
(Direct Tension)
-24 -30 -36
-18 -24
0
-6
100 (110)
16
25
-12 -18 -24 -30 -36 -6
-12 -18 -24 -30
0
76
82
PAV
100 (110)
( Bending Beam Rheometer)
-24 -30 -36
18 -24
70
DSR G* sin 
7
82
Mass Loss < 1.00 %
(Dynamic Shear Rheometer)
13 10
76
DSR G*/sin 
58
90
70
RTFO
(PRESSURE AGING VESSEL)
20 Hours, 2.07 MPa
DSR G*/sin 
64
(Dynamic Shear Rheometer)
46
RV
58
(ROLLING THIN FILM OVEN)
> 2.20 kPa
FP
25 22
19 16
34
31 28
BBR “S” Stiffness
-6 -12 -18 -24 -30
BBR
0
-6
25
110 (110)
22 19
37
34 31 28
25
40 37
28 31
34
& “m”- value
-12 -18 -24 -30
0
-6
-12 -18 -24
0
-6
-12 -
0
-6
-12 -18 -24
0
-6 -12
Physical Hardening
DT
-6
-12 -18 -24 -30
0
-6 -12 -18 -24 -30
How the PG Spec Works
CEC
Spec Requirement
1-day Min, C
Remains Constant
Avg 7-day Max, oC
o
PG 46
PG 52
PG 58
PG 64
PG 70
PG 76
PG 82
-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
ORIGINAL
> 230 oC
< 3 Pa.s @ 135 oC
(Flash Point)
(Rotational Viscosity)
(Dynamic Shear Rheometer)
> 1.00 kPa
46
64
RTFO
52
90
58
90
100
10 7
S < 300 MPa
4
25
22 19
m > 0.300
16
28
25
22 19
16
13 31
0
-6
Report Value
-12 -18 -24 -30 -36
-6 -12 -18 -24 -30
0
(Bending Beam Rheometer)
> 1.00 %
(Direct Tension)
-24 -30 -36
-18 -24
0
-6
-12 -18 -24 -30 -36 -6
-12 -18 -24 -30
0
76
100 (110)
DSR G* sin 
7
82
82
PAV
100 (110)
( Bending Beam Rheometer)
-24 -30 -36
18 -24
70
(Dynamic Shear Rheometer)
13 10
76
Mass Loss < 1.00 %
64
100
Test Temperature
< 5000 kPa
Changes
70
DSR G*/sin 
(Dynamic Shear Rheometer)
(PRESSURE AGING VESSEL)
20 Hours, 2.07 MPa
DSR G*/sin 
64
(ROLLING THIN FILM OVEN)
46
RV
5858
52
> 2.20 kPa
FP
25 22
19 16
34
31 28
BBR “S” Stiffness
-6 -12 -18 -24 -30
BBR
0
-6
25
110 (110)
22 19
37
34 31 28
25
40 37
28 31
34
& “m”- value
-12 -18 -24 -30
0
-6
-12 -18 -24
0
-6
-12 -
0
-6
-12 -18 -24
0
-6 -12
Physical Hardening
DT
-6
-12 -18 -24 -30
0
-6 -12 -18 -24 -30
PG Binder Selection
PG 52-28
PG 58-22
> Many agencies have
established zones
PG 58-16
PG 64-10
Summary of How to Use
PG Specification
• Determine
– 7-day max pavement temperatures
– 1-day minimum pavement temperature
• Use specification tables to select test
temperatures
• Determine asphalt cement properties
and compare to specification limits
Asphalt Concrete Mix
Design
History
Hot Mix Asphalt Concrete
(HMA)
Mix Designs
• Objective:
– Develop an economical blend of aggregates and
asphalt that meet design requirements
• Historical mix design methods
– Marshall
– Hveem
• New
– Superpave gyratory
Requirements in Common
• Sufficient asphalt to ensure a durable pavement
• Sufficient stability under traffic loads
• Sufficient air voids
– Upper limit to prevent excessive environmental
damage
– Lower limit to allow room for initial densification due
to traffic
• Sufficient workability
MARSHALL
MIX
DESIGN
Marshall Mix Design
• Developed by Bruce Marshall for the
Mississippi Highway Department in the late
30’s
• WES began to study it in 1943 for WWII
– Evaluated compaction effort
• No. of blows, foot design, etc.
• Decided on 10 lb.. Hammer, 50 blows/side
• 4% voids after traffic
• Initial criteria were established and
upgraded for increased tire pressures and
loads
Marshall Mix Design
• Select and test aggregate
• Select and test asphalt cement
– Establish mixing and compaction
temperatures
• Develop trial blends
– Heat and mix asphalt cement and
aggregates
– Compact specimen (100 mm diameter)
Marshall Design Criteria
Light Traffic
ESAL < 104
Compaction
Stability N (lb.)
Medium Traffic
10 4 < ESAL< 10
Heavy Traffic
ESAL > 106
35
50
75
3336 (750)
5338 (1200)
8006 (1800)
Flow, 0.25 mm (0.1 in)
8 to 18
8 to 16
8 to 14
Air Voids, %
3 to 5
3 to 5
3 to 5
Voids in Mineral Agg.
(VMA)
Varies with aggregate size
Asphalt Concrete Mix
Design
Superpave
Superpave Volumetric Mix
Design
• Goals
– Compaction method which simulates field
conditions
– Accommodates large size aggregates
– Measure of compactibility
– Able to use in field labs
– Address durability issues
• Film thickness
• Environmental
Compaction
Key Components of Gyratory Compactor
height
measurement
reaction
frame
tilt bar
rotating
base
control and data
acquisition panel
loading
ram
mold
Compaction
• Gyratory compactor
– Axial and shearing action
– 150 mm diameter molds (6” vs. 4” Marshall)
• Aggregate size up to 37.5 mm
• Height measurement during compaction
– Allows densification during compaction to be
evaluated
Ram pressure
600 kPa
1.25o
Three Points on SGC Curve
% Gmm
Nmax
Ndes
Nini
10
100
Log Gyrations
1000
SGC Critical Point Comparison
%Gmm= Gmb / Gmm
Gmb = Bulk Mix Specific Gravity from compaction
at N cycles
Gmm = Max. Theoretical Specific Gravity
Compare to allowable values at:
NINI : %Gmm < 89%
NDES: %Gmm < 96%
NMAX: %Gmm < 98%
Design Compaction
% Gmm
• Ndes based on
–
–
average design high air
temp
traffic level
• Log Nmax = 1.10 Log Ndes
• Log Nini = 0.45 Log Ndes
Nmax
Ndes
Nini
10
100
1000
Log Gyrations
Superpave Testing
• Specimen heights
• Mixture volumetrics
–
–
–
–
Air voids
Voids in mineral aggregate (VMA)
Voids filled with asphalt (VFA)
Mixture density characteristics
• Dust proportion
• Moisture sensitivity
Superpave Mix Design
• Determine mix properties at NDesign and compare to
criteria
–
–
–
–
–
–
–
Air voids
VMA
VFA
%Gmm at Nini
%Gmm at NDES
%Gmmat Nmax
Dust proportion
4% (or 96% Gmm)
See table
See table
< 89%
< 96%
< 98%
0.6 to 1.2
Superpave Mix Design
Gyratory Compaction Criteria