2. Sources of Information
• American Association of State Highway
Transportation Officials (AASHTO)
• Federal Highway Administration (FHWA)
• Departments of Transportations (DOT) for individual
States
• National Asphalt Pavement Association (NAPA)
• National Center for Asphalt Technology (NCAT)
• The Asphalt Institute (AI)
Asphalt Binder
Superpave Specifications
2
3. Superpave Asphalt Binder Specification
The grading system is based on Climate
PG 64 - 22
Min pavement
temperature
Performance
Grade
Average 7-day max
pavement temperature
Asphalt Binder
Superpave Specifications
3
7. Permanent Deformation
• Addressed by high temp stiffness
– G*/sin δ on unaged asphalt binder > 1.00
kPa
– G*/sin δ on RTFO aged asphalt binder >
2.20 kPa
Heavy Trucks
Asphalt Binder
Superpave Specifications
> Early part of
pavement
service life
7
9. Fatigue Cracking
• Addressed by intermediate
temperature stiffness
– G*sin δ on RTFO & PAV aged
asphalt binder < 5000 kPa
> Later part of
pavement service life
Asphalt Binder
Superpave Specifications
9
13. PG Binder Selection
PG 52-28
PG 58-22
Asphalt Binder
> Many agencies have
established zones
PG 58-16
Superpave Specifications
PG 64-10
13
14. Developed from Air
Temperatures >
20 years
• Superpave Weather Database
SHR
A-6 4 P
– 6500 stations in U.S. and Canada
8A
• Annual air temperatures
– hottest seven-day temp (avg and std
dev)
– coldest temp (avg and std dev)
• Calculated HMA pavement temps used in
PG selection
Asphalt Binder
Superpave Specifications
14
15. Reliability
• Percent Probability of Not Exceeding
Design Temp
> using Normal Distribution
Reliability is area under curve
to the left of Tdes
frequency of
observed temps
(Total area under
curve = 100 %)
Tavg
Asphalt Binder
Tdes
Superpave Specifications
15
16. Observed Air Temperatures
Topeka, KS
50 % reliability
average summer
very hot summer
98 % reliability
36
40
> this data - standard
deviation of 2°C
7-Day Maximum Air Temperatures
Asphalt Binder
Superpave Specifications
16
17. Observed Air Temperatures
Topeka, KS
36
very cold winter
40
average winter
-31 -23
> standard
deviation of 4°C
-40
-30
Asphalt Binder
-20
-10
0
10
20
Superpave Specifications
30
40
50
60
17
18. Convert to Pavement
Temperature
• Calculated by Superpave software
• High Temperature
– 20 mm (1.78”) below surface of
mixture
• Low Temperature
– at surface of mixture
Pavt Temp = f ( Air Temp, Depth, Latitude )
Asphalt Binder
Superpave Specifications
18
22. Effect of Rounding to Standard
Grades
-16
-22
needed grade
for 50% reliability
-28
selected grade
for 50% reliability
Rounding depends
on actual temps!
-28
-23
Minimum Pavement Temperatures
Asphalt Binder
Superpave Specifications
22
23. Effect of Loading Rate
on Selection
90 kph
• Dilemma
– specified DSR loading rate is 10 rad/sec
– what about longer loading times ?
• Use asphalt binder with more stiffness at
higher temperatures
– slow - - increase one high temperature grade
– stationary - - increase two high temperature grades
– no effect on low temperature grade
Asphalt Binder
Superpave Specifications
23
24. Effect of Loading Rate
on Selection
• Example
– for toll road
– for toll booth
– for weigh stations
90 kph or
56 mph
PG 64-22
PG 70-22
PG 76-22
Slow
Stopping
Asphalt Binder
Superpave Specifications
24
25. Effect of Traffic Amount
on Selection
80 kN ESALs
• 10 - 30 x 106 ESAL
– Consider increasing - - one high temp grade
• 30 x 106 + ESAL
– Recommend increasing - - one high temp grade
> Equivalent Single Axle Loads
Asphalt Binder
Superpave Specifications
25
30. Summary of How to Use
PG Asphalt Binder 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 Binder
Superpave Specifications
30
One of the primary purposes of the Superpave asphalt binder testing is to use that data for the development of a purchase specification for asphalt binders.
These are the general references for all asphalt binder and HMA related topics. Websites for each of these organizations can be found using any search engine.
The PG Binder binder designation is based on expected extremes of hot and cold pavement temperatures.
This is the asphalt binder specification - it is defined by AASHTO T 312.
The approach to the PG system represents a change in philosophy. The specification requirement does not change; the temperature which the value has to meet changes with grade.
The high temperature stiffness is measured with the DSR using the asphalt binder in two different aging conditions. The non-aged condition is checked in case the asphalt binder is not sufficiently aged in the plant. The RTFO-aged residue is checked to ensure that the material has sufficient stiffness after mixing with the aggregate in the plant.
These values are minimums.
For fatigue cracking, the DSR is used a third time, to measure an intermediate stiffness on the PAV-aged residual. This is a check to see how stiff the asphalt binder will be after it has been in service for a period of time.
For fatigue cracking there is a maximum value.
For low temperature cracking the asphalt binder is aged in the PAV. The asphalt binder is tested with the BBR for a maximum stiffness (<= 300 MPa) and a minimum m-value (m>0.30).
If the asphalt binder passes the m-value but fails the stiffness value it is then tested in the direct tension device and checked.
These miscellaneous requirements have been used for years.
The viscosity requirement is there to insure that the material can be pumped.
The flash-point is there for safety reasons.
Mass loss indicates the amount of volatiles evaporating during the mixing and construction process.
Many states have divided their territory into different regions. How many regions depends on the variation of climates.
We use a normal distribution to describe the range of temperatures at a site. By selecting a higher reliability, you can move further out on the “tail” and reduce the amount of risk of encountering a temperature that exceeds the design temperature.
For this example - Topeka, KS was used. 98% reliability is approximately 2 standard deviations.
These are the high and low temperature ranges for Topeka.
The software can be used to calculate the HMA pavement temperatures (using air temperatures, depth and latitude).
For the low temperature use the air temperature.
As the speed decreases, the needed stiffness for the asphalt binder increases.
As the amount of traffic increases there is a need for a stiffer asphalt binder.
The ESAL (equivalent single axle load) concept was developed at the AASHO road test. It is a method of measuring truck volume.
This provides a brief summary of the steps needed to determine if an material meets a particular PG asphalt binder specification.
