What is super pave?
In the 1980s, many state transportation departments were experiencing widespread
premature deterioration of asphalt pavements. To address this problem the Strategic
Highway Research Program (SHRP) undertook a program of asphalt research that
eventually led to a new asphalt mixture design and analysis system called Super
pave. Super pave stands for Superior Performing Asphalt Pavements.
The Super pave system includes a performance-based asphalt binder
specification,
a mix design analysis system, many new test procedures, and new equipment. The
Strategic Highway Research Program was established by Congress in 1987 as a five (5)
year, $150-million research program to improve the performance and durability of our
highway system.
In 1991, Congress authorized The Federal Highway Administration (FHWA) to
initiate full-scale implementation of Superpave and other SHRP research results.
This process began in 1993 when SHRP delivered its final research findings. States,
FHWA, and industry all took advantage of techniques such as state pooled-fund
equipment buys, expert task groups, mobile laboratories, user-producer group, the
American Association of State Highway and Transportation Officials (AASHTO) Lead
States Program, and Super pave Centers to implement the research results.
Super pave is a comprehensive system for the design of paving mixes that are
tailored to the unique performance requirements dictated by the traffic, environment
(climate), and structural section at a pavement site. It enhances pavement
performance through the selection and combination of the most suitable asphalt
binder and aggregate.
Super pave represents the integration of several products of the SHRP
asphalt
research program into a single system for the design and analysis of paving mixes.
It encompasses new material specifications, test methods, equipment, software, and
mixture design method.
A) Limitations on Current AC Physical Tests & Specifications
1- Empirical and not performance-based.
2- Not representative for the wide range of climatic conditions (low
temperatures).
3- Long-term aging is not considered.
4- Same asphalt cement grade can behave differently in the field.
5- Modified asphalt binders are not considered.
B) Superior Performing Asphalt Pavements (Super Pave)
1- Super Pave is the result of the 5-year SHRP (Strategic Highway Research Program)
that was launched in
1987.
2- $50-million research effort.
3- To develop performance-based tests and specifications for asphalt binders and
HMA mixtures.
C) Super Pave Binder Tests & Specification Features
1- Modified & unmodified asphalt binders are considered.
2- Performance-based tests.
3- Asphalt binder is tested at its three critical stages: i. Unaged ii.
Short-term aging iii.
Long-term aging
4- The entire range of pavement temperatures is considered.
5- Can control three specific types of HMA pavement distresses:
a) Rutting b) Fatigue cracking c) Thermal cracking
6- Test procedures and specifications were developed in SI units
D) Super Pave Physical Tests for Asphalt Binders
1- Rolling Thin Film Oven (RTFO)
2- Pressure Aging Vessel (PAV)
3- Rotational Viscometer (RV)
4- Dynamic Shear Rheometer (DSR)
5- Bending Beam Rheometer (BBR)
6- Direct Tension Tester (DTT)
1. Pressure Aging Vessel (PAV) AASHTO R 28
1. Pressure Aging Vessel (PAV) AASHTO R 28
a) Heat RTFO aged asphalt binder until fluid enough to pour. Stir sample and
pour 50 g into a
preheated sample pan.
b) Place pans in a pan holder and place inside preheated PAV.
c) Seal the PAV and allow it to return to the aging temperature. What
temperature? (90, 100, 110
°C) (194, 212, 230 °F)
d) Once the PAV has reached the desired temperature, pressurize the PAV to 300
psi (2.07 MPa) and
maintain the pressure for 20 hours.
e) Gradually release the pressure and remove the pans from the PAV.
f) Place the pans in an oven set at 325°F (163°C) for 15 minutes, then scrape
into a single
container sized so that the depth of the residue in the container is between 0.55
and 1.57 inches (14
and 40 mm).
g) Degas the sample in a vacuum to remove entrapped air.
h) Store for use in physical property tests.
Pressure Aging Vessel (PAV) AASHTO R 28
EN 13302 ASTM D2196 AASHTO T316 ASTM D44022
The Rotational Viscometer (RV) is used to determine the viscosity of asphalt
binders in the high
temperature range of production (manufacturing) and construction (mixing, placement
and compaction). The
RV test is always conducted at 275°F (135°C).
a) Preheat spindle, sample chamber, and viscometer environmental chamber
(Thermosel) to 275°F
(135°C)
b) Heat unaged asphalt binder until fluid enough to pour. Stir the sample,
being careful not to
entrap air bubbles
c) Pour appropriate amount of asphalt binder into sample chamber. The sample
size varies according
to the selected spindle
d) Insert sample chamber into RV temperature controller unit and carefully
lower spindle into
sample
e) Bring sample to the desired test temperature (typically 275°F (135°C))
within approximately 30
minutes and allow it to equilibrate
f) Rotate spindle at 20 RPM
g) Once the sample has reached temperature and equilibrated, take 3 viscosity
readings from RV
display, allowing 1 minute between each reading. Viscosity (dynamic/absolute) is
reported as the average
of 3 readings
h) The test takes 1.5 hours
Rotational Viscometer (RV) ASTM D 4402
The basic RV test measures the torque required to maintain a constant rotational
speed (20 RPM) of a
cylindrical spindle while submerged in an asphalt binder at a constant temperature
(typically 275°F
(135°C)).
This torque (proportional to viscosity) is then converted to a viscosity and
displayed
automatically by the RV.
Typical Values:
o RV viscosities depend upon the material measured and the test temperature.
o Super Pave testing is done at 275°F (135°C) and typical dynamic viscosity
values for asphalt
binders at this temperature are 0.2 to 2 Pa·s.
o The AI recommends using a value of about 0.28 Pa·s for compaction
temperatures.
o at high in-service pavement temperatures (e.g., on a hot summer day of 140°F
(60°C)) dynamic
viscosity can be around 200 Pa·s.
▪ Typical Values:
o Some representative dynamic viscosities are:
o PG 64-22 asphalt binder at 275°F (135°C) ≈ 0.570 Pa·s
o PG 76-22 asphalt binder at 275°F (135°C) ≈ 1.800 Pa·s
o Water at room temperature = 0.001 Pa·s
o Motor oil at room temperature = 0.088 Pa·s
o Liquid Honey at room temperature = 2 Pa·s
o Mayonnaise at room temperature = 5 Pa·s
3. Dynamic Shear Rheometer (DSR) AASHTO T 315
ASTM D4402 AASHTO M320-10 AASHTO T315-12 AASHTO M332-14 AASHTO T350-14 AASHTO
TP 70 ASTM D7405-10A EN
14770 ASTM D7175-08 ASTM D4402 M
▪ The DSR is used to characterize the viscous and elastic behavior of asphalt
binders at medium
(fatigue cracking) to high temperatures (rutting).
▪ Asphalt binders are viscoelastic. This means they behave partly like an
elastic solid
(deformation due to loading is recoverable – it is able to return to its original
shape after a load is
removed) and partly like a viscous liquid (deformation due to loading is
nonrecoverable – it cannot
return to its original shape after a load is removed).
Dynamic Shear Rheometer (DSR) AASHTO T 315
a) Heat the asphalt binder until the binder is sufficiently fluid to pour the
test specimens.
b) Heat the DSR to the test temperature. This preheats the upper and lower
plates, which allows the
specimen to adhere to them.
c) Place the asphalt binder sample between the test plates.
d) Put the test plates just in contact.
e) Trim the excess material.
f) Bring the specimen to the test temperature. Start the test only after the
specimen has been at
the desired temperature for at least 10 minutes.
g) The DSR conditions the specimen for 10 cycles at a frequency of 10 rad/sec
(1.59Hz).
h) The DSR takes test measurements over the next 10 cycles and then the
software reduces the data
to produce a value for G* and δ
▪Rutting Prevention: In order to resist rutting, an asphalt binder should be
stiff (it should not
deform too much) and it should be elastic (it should be able to return to its
original shape after load
deformation). Therefore, the complex shear modulus elastic portion, G*/sinδ, should
be maximized.
▪ Fatigue Cracking Prevention: In order to resist fatigue cracking, an asphalt
binder should be
elastic (able to rebound and not cracking) but not too stiff (excessively stiff
substances will crack
rather than deform-then-rebound). Therefore, the complex shear modulus viscous
portion, G*sinδ, should
be minimized.
▪ The basic DSR test uses a thin asphalt binder sample sandwiched between two
circular plates. The
lower plate is fixed while the upper plate oscillates back and forth across the
sample at 10 rad/sec
(1.59 Hz; 55 mph) to create a shearing action.
▪ DSR tests are conducted on unaged, RTFO aged and PAV aged asphalt binder
samples.
▪ The larger the phase angle (δ), the more viscous the material is.
o Purely elastic material: δ = 0 degrees
o Purely viscous material: δ = 90 degrees
▪ G* and δ are used as predictors of HMA rutting and fatigue cracking. Early in
pavement life to
mid-life rutting is the main concern (on unaged and RTFO aged samples), while later
in pavement life
fatigue cracking becomes the major concern (PAV aged samples).
4. Rolling Thin Film Oven (RTFO)
AASHTO T 240 and ASTM D 2872
The Rolling Thin-Film Oven (RTFO) provides simulated short term aged asphalt
binder for physical
property testing. Asphalt binder is exposed to elevated temperatures to simulate
manufacturing and
placement aging. The RTFO also provides a quantitative measure of the volatiles lost
during the aging
process.
The basic RTFO procedure takes unaged asphalt binder samples in cylindrical
glass bottles and
places these bottles in a rotating carriage within an oven. The carriage rotates
within the oven while
the 325°F (163°C) temperature ages the samples for 85 minutes. Samples are then
stored for use in
physical properties tests or the PAV. The standard Rolling Thin-Film Oven test is:
• AASHTO T 240 and ASTM D 2872.
* Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test)
Basic Procedure
* Heat a sample of asphalt binder until it is fluid to pour. Stir sample to ensure
homogeneity and
remove air bubbles.
2- If a determination of mass change is desired, label two RTFO bottles and
weigh them empty. These
are designated as the “mass change” bottles. Record the weights.
3-Pour 1.23 oz (35 g) of asphalt binder into each bottle Immediately after
pouring each bottle,
turn the bottles on their side without rotating or twisting and place them on a
cooling rack.
4-Allow all bottles to cool 60 to 180 minutes.
5-After cooling, weigh the two mass change bottles again. Record the weights.
6-Place the bottles in the RTFO oven carousel close the door, and rotate the
carousel at 15 RPM for
85 minutes.
During this time, maintain the oven temperature at 325°F (163°C) and the
airflow into the bottles
at 244 in3/min (4000 ml/min).
6-Remove the bottles one at a time from the carousel, setting the mass change
bottles aside.
Residue from the remaining bottles should be transferred to a single container.
Remove residue from each
bottle by first pouring as much material as possible, then scraping the sides of the
bottle to remove
any remaining residue. There is no standard scraping utensil but at least 90 percent
of the asphalt
binder should be removed from the bottle. RTFO residue should be tested within 72
hours of aging.
7-After cooling the two mass change bottles for 60 – 180 minutes, weigh them
and discard their
residue. Record the weights.
5. Bending Beam Rheometer (BBR) AASHTO T 313
ASTM D6648 AASHTO T313 EN 14771
▪ As surrounding temperatures drop, pavements contract and build up internal
stresses. If this
contraction occurs fast enough the pavement may crack because it does not have time
to relax these
stresses.
▪ This type of crack, typically called a “thermal crack” or transverse crack,
can result from either
of two mechanisms: a) Single thermal cycle below the critical temperature. A single
severe drop in
temperature causes stress to build up to a critical point that causes cracking
quickly.
▪ This type of crack, typically called a “thermal crack” or transverse crack,
can result from either
of two mechanisms: b) Multiple thermal cycles above the critical temperature.
Repeated thermal
contraction and expansion above the critical temperature can cause stresses to build
up and eventually
cause cracking.
The BBR is a test designed to measure the AC ‘s resistance to these thermal
stresses (stiffness) and
the stress relaxation rate. Asphalt binders that are not too stiff at low
temperatures and able to relax
built-up stresses are desirable.
▪ Because low-temperature cracking is a phenomenon found mostly in older
pavements, the test is run
on PAV aged samples.
▪ A sample of asphalt binder is molded into a beam measuring 6.25 ´ 12.5 ´ 127
mm.
▪ This sample is then simply supported at two points 102 mm apart in a
controlled temperature fluid
bath.
▪ The beam is then loaded at the midpoint by a 100 g load = 0.98 N of force.
▪ The beam deflection is measured at 8, 15, 30, 60, 120 and 240 seconds.
▪ Beam stiffness (flexural creep stiffness), is calculated for these times.
▪ Creep stiffness is a measure of thermal stresses. A higher creep stiffness
value indicates higher
thermal stresses.
▪ Beam stiffness (flexural creep stiffness)
In order to determine the stress relaxation properties of an asphalt binder, creep
stiffness
calculations are made at 8, 15, 30, 60, 120 and 240 seconds of loading.
▪ A curve, called the stiffness master curve, is then fitted to these points and
is of the form:
▪ The slope of this master stiffness curve at 60 seconds, designated by the
letter “m-value”, is a
measure of the rate at which the asphalt binder relieves stress.
▪ A lower m-value indicates a lesser ability to relax stresses.
▪Bending Beam Rheometer (BBR) AASHTO T 313
a) Set the BBR fluid bath to the desired test temperature.
b) Heat the PAV aged asphalt binder until fluid enough to pour.
c) Stir the heated sample to remove air bubbles and pour into two aluminum BBR
molds. d) Allow molds
to cool, then trim the top of sample flush with mold.
e) Demold samples.
f) Place beams in the BBR bath at test temperature for 60 minutes to condition
them.
g) Place the test beam on the test supports.
h) Apply the 0.98 N test load and maintain the load constant for 240 seconds.
During this period,
readings of deflection over time are recorded.
I) Repeat for the second beam.
Approximate test time is 3 hours (from sample preparation to end of test)
6. Direct Tension Tester (DTT) AASHTO T 314
EN 12697-26 ANNEX E EN 12697-26 ANNEX D AASHTO TP 107-14
▪ There is a good relationship between the stiffness of ACs and the amount of
stretching
(ductility) they undergo before breaking at low temperatures.
▪ The DTT was developed to address stiff, ductile asphalt binders (cannot be
addressed by the BBR).
Ex. Modified asphalts.
▪ The DTT is used when the BBR creep stiffness is between 300 and 600 MPa at
low pavement service
temperatures.
▪ Below 300 MPa the DTT need not be used because the BBR would be adequate.
▪ The DTT test provides a measure of low-temperature stiffness and relaxation
properties of asphalt
binders. These parameters indicate an asphalt binder’s ability to resist
low-temperature cracking.
▪ Because low-temperature cracking is a phenomenon found mostly in older
pavements, the test is run
on PAV aged samples at low temperatures
▪The basic DTT test measures the stress and strain at failure of a specimen of
asphalt binder
pulled apart at a constant rate of elongation.
▪ Failure identification:
1. Fracture, failure strain is defined as the strain at the moment of fracture.
Flow without fracture, failure strain is defined as the strain corresponding to the
maximum stress
observed. The test should not be continued past 10 percent strain; if the sample has
not failed by 10
percent strain, record failure strain as “greater than 10 percent”.
▪ Failure location: Ideally failure should occur in the gage section. If failure
occurs in the
throat section, note and record this occurrence.
Direct Tension Tester (DTT) AASHTO T 314
Procedure:
a) Heat PAV aged asphalt binder until fluid to pour. Stir to ensure homogeneity.
b) Pour the heated sample into two DTT molds.
c) Allow molds to cool for 30 – 60 minutes at room temperature, then trim the
top of sample flush
with mold.
d) Demold sample.
e) Apply 0.45 lb (2 N) pulling force.
f) Set the strain rate to 1 mm/min.
g) Test temperature is in the 0 to − 36 °C range. h) Test a total of 6 samples
as described above to
ensure repeatability.
References
pavement interactive. (2015). Retrieved from pavement: https://pavementinteractive.org/
Corbett, L.W. and Merz, R.E. (1975). Asphalt Binder Hardening in the Michigan Test
Road After 18 Years
of Service. Transportation Research Record 544. Transportation Research Board,
National Research
Council, Washington, D.C. pp. 27-34.↵
Roberts, F.L.; Kandhal, P.S.; Brown, E.R.; Lee, D.Y. and Kennedy, T.W. (1996). Hot
Mix Asphalt
Materials, Mixture Design, and Construction. National Asphalt Pavement Association
Education Foundation.
Lanham, MD
