HIGHWAY CONSTRUCTION MATERIAL & PRACTICE Age hardening is a result of a number of factors, the principal ones being Oxidation.  The reaction of oxygen with the asphalt binder. Volatilization.  The evaporation of the lighter constituents of asphalt binder.  It is primarily a function of temperature and occurs principally during HMA production. Polymerization.  The combining of like molecules to form larger molecules.  These larger molecules are thought to cause a progressive hardening.

2. Basic road construction materials includes
 soils,
 aggregates,
 bitumen and
 Portland cement

3.  Bitumen is defined as an amorphous, black or
dark-colored, (solid, semi-solid, or viscous)
cementitious substance ,composed
principally of high molecular weight
hydrocarbons, and soluble in carbon
disulfide.
 For civil engineering applications, bituminous
materials include primarily asphalts and tars

4.  Asphalts may occur in nature (natural
asphalts) or may be obtained from petroleum
processing (petroleum asphalts). Tars do not
occur in nature and are obtained as
condensates in the processing of coal,
petroleum, oil-shale, wood or other organic
materials

5.  Asphalt binders are most commonly
characterized by their physical properties. An
asphalt binder’s physical properties directly
describe how it will perform as a constituent
in HMA pavement.

6.  Durability is a measure of how asphalt binder
physical properties change with age
(sometimes called age hardening). In
general, as an asphalt binder ages, its
viscosity increases and it becomes more stiff
and brittle.

7. Age hardening is a result of a number of factors,
the principal ones being
 Oxidation. The reaction of oxygen with the
asphalt binder.
 Volatilization. The evaporation of the lighter
constituents of asphalt binder. It is primarily a
function of temperature and occurs principally
during HMA production.
 Polymerization. The combining of like
molecules to form larger molecules. These larger
molecules are thought to cause a progressive
hardening.

8.  Separation. The removal of the oily
constituents, resins or asphaltenes from the
asphalt binder by selective absorption of
some porous aggregates.
 There is no direct measure for asphalt binder
aging. Rather, aging effects are accounted
for by subjecting asphalt binder samples to
simulated aging then conducting other
standard physical tests

9.  Asphalt binder aging is usually split up into
two categories
 Short-term aging. This occurs when asphalt
binder is mixed with hot aggregates in an
HMA mixing facility.
 Long-term aging. This occurs after HMA
pavement construction and is generally due
to environmental exposure and loading.

10. Typical aging simulation tests are:
 Thin-film oven (TFO) test
 Rolling thin-film oven (RTFO) test
 Pressure aging vessel (PAV)

13.  Rheology is the study of deformation and
flow of matter. Deformation and flow of the
asphalt binder in HMA is important in
determining HMA pavement
performance. HMA pavements that deform
and flow too much may be susceptible to
rutting and bleeding, while those that are too
stiff may be susceptible to fatigue or thermal
cracking. HMA pavement deformation is
closely related to asphalt binder rheology.

14. Penetration test following basic procedure:
 Melt and cool the asphalt binder sample under controlled
conditions.
 Measure the penetration of a standard needle into the
asphalt binder sample under the following conditions:
 Load = 100 grams
 Temperature = 25° C (77° F)
 Time = 5 seconds
 The depth of penetration is measured in units of 0.1 mm
and reported in penetration units (e.g., if the needle
penetrates 8 mm, the asphalt penetration number is
80). Penetration grading is based on the penetration test.
The standard penetration test is:
AASHTO T 49 and ASTM D 5: Penetration of Bituminous
Materials

15.  The softening point is defined as the temperature
at which a bitumen sample can no longer support
the weight of a 3.5-g steel ball. Basically, two
horizontal disks of bitumen, cast in shouldered
brass rings , are heated at a controlled rate in a
liquid bath while each supports a steel ball. The
softening point is reported as the mean of the
temperatures at which the two disks soften
enough to allow each ball, enveloped in bitumen,
to fall a distance of 25 mm (1.0 inch) (AASHTO,
2000).
 The standard softening point test is:
AASHTO T 53 and ASTM D 36: Softening Point of
Bitumen (Ring-and-Ball Apparatus)

17.  The ductility test measures asphalt binder
ductility by stretching a standard-sized
briquette of asphalt binder to its breaking
point. The stretched distance in centimeters
at breaking is then reported as ductility.
The standard ductility test is:
 AASHTO T 51 and ASTM D 113: Ductility of
Bituminous Materials

18.  The rotational viscometer (RV) is used in the
Superpave system to test high temperature
viscosities (the test is conducted at 135° C
(275° F)). 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. This torque is
then converted to a viscosity and displayed
automatically by the RV.

19.  Asphalt cement like most other materials,
volatilizes (gives off vapor) when heated. At
extremely high temperatures (well above those
experienced in the manufacture and construction
of HMA) asphalt cement can release enough
vapor to increase the volatile concentration
immediately above the asphalt cement to a point
where it will ignite (flash) when exposed to a
spark or open flame. This is called the flash
point. For safety reasons, the flash point of
asphalt cement is tested and controlled.
 The fire point, which occurs after the flash point,
is the temperature at which the material (not just
the vapors) will sustain combustion.

20.  A typical flash point test involves heating a small sample
of asphalt binder in a test cup. The temperature of the
sample is increased and at specified intervals a test flame
is passed across the cup. The flash point is the lowest
liquid temperature at which application of the test flame
causes the vapors of the sample to ignite. The test can be
continued up to the fire point – the point at which the test
flame causes the sample to ignite and remain burning for
at least 5 seconds.
 Standard flash point tests are:
 AASHTO T 48 and ASTM D 92: Flash and Fire Points by
Cleveland Open Cup (more common for asphalt cement
used in HMA)
 AASHTO T 73 and ASTM D 93: Flash-Point by Pensky-
Martens Closed Cup Tester

21.  Penetration Grading
 Viscosity Grading
 Superpave Performance Grade (PG)

22.  The penetration grading system was developed in the early
1900s to characterize the consistency of semi-solid
asphalts. Penetration grading quantifies the following asphalt
concrete characteristics:
 Penetration depth of a 100 g needle 25° C (77° F)
 Flash point temperature
 Ductility at 25° C (77° F)
 Solubility in trichloroethylene
 Thin-film oven test(accounts for the effects of short-term aging)
Penetration grading’s basic assumption is that the less viscous the
asphalt, the deeper the needle will penetrate. This penetration
depth is empirically correlated with asphalt binder performance.

23.  Therefore, asphalt binders with high
penetration numbers (called "soft") are used
for cold climates while asphalt binders with
low penetration numbers (called "hard") are
used for warm climates.

24.  In the early 1960s an improved asphalt grading system
was developed that incorporated a rational scientific
viscosity test. This scientific test replaced the empirical
penetration test as the key asphalt binder
characterization. Viscosity grading quantifies the
following asphalt binder characteristics:
 Viscosity at 60° C (140° F)
 Viscosity at 135° C (275° F)
 Penetration depth of a 100 g needle applied for 5 seconds
at 25° C (77° F)
 Flash point temperature
 Ductility at 25° C (77° F)
 Solubility in trichloroethylene
 Thin film oven test(accounts for the effects of short-term
aging)

25.  Viscosity is measured in poise (cm-g-s =
dyne-second/cm2, named after Jean Louis
Marie Poiseuille). The lower the number of
poises, the lower the viscosity and thus the
more easily a substance flows. Thus, AC-5
(viscosity is 500 ± 100 poise at 60° C (140°
F)) is less viscous than AC-40 (viscosity is
4000 ± 800 poise at 60° C (140° F)).

26.  The previous grading systems are somewhat
limited in their ability to fully characterize
asphalt binder for use in HMA
pavement. Therefore, as part of the Superpave
research effort new binder tests and
specifications were developed to more accurately
and fully characterize asphalt binders for use in
HMA pavements. These tests and specifications
are specifically designed to address HMA
pavement performance parameters such as
rutting, fatigue cracking and thermal cracking.

27.  Superpave performance grading (PG) is based on
the idea that an HMA asphalt binder’s properties
should be related to the conditions under which
it is used. For asphalt binders, this involves
expected climatic conditions as well as aging
considerations. Therefore, the PG system uses a
common battery of tests (as the older
penetration and viscosity grading systems do)
but specifies that a particular asphalt binder
must pass these tests at specific temperatures
that are dependant upon the specific climatic
conditions in the area of use.

28. Superpave performance grading uses the
following asphalt binder tests:
 Rolling thin film oven (RTFO)
 Pressure aging vessel (PAV)
 Rotational viscometer (RV)
 Dynamic shear rheometer (DSR)
 Bending beam rheometer (BBR)
 Direct tension tester (DTT)

29.  Superpave performance grading is reported using
two numbers – the first being the average seven-
day maximum pavement temperature (°C) and the
second being the minimum pavement design
temperature likely to be experienced (°C).
 Thus, a PG 58-22 is intended for use where the
average seven-day maximum pavement
temperature is 58°C and the expected minimum
pavement temperature is -22°C. Notice that
these numbers are pavement temperatures and
not air temperatures