CE6503_Highway_Materials_Lec1_April21.pptx.pdf

CE 6503 : Highway Materials
Dr. M. Neaz Murshed
Dept. of C.E.

Course Syllabus
2
• Origin, production, specifications, properties and uses of
bituminous materials;
• Binder mixtures;
• Design and analysis of bituminous paving mixes;
• Field operations, surface treatments, stabilization methods;
• Aggregates, base, subbase and subgrade;
• Cement concrete in pavement construction.

References:
3
• Traffic & Highway Engineering.
• -Nicholas J. Garber.
• Asphalt Materials and Mix Design Manual.
• -By Irving Kett
• Highway Engineering.
• -By Paul H. Wright.
• Principles of Transportation Engineering.
• -By Partha Chakroborty

Origin of Bituminous Material:
4
• Naturally occurring deposits of bituminous materials are
formed from the remains of ancient, microscopic algae and
other once-living things.
• When these organisms died, their remains were deposited in
the mud on the bottom of the ocean or lake where they lived.
• Under the heat and pressure of burial deep in the earth, the
remains were transformed into materials such as bitumen,
kerogen, or petroleum.

5
• Kerogen is solid, insoluble organic matter in sedimentary
rocks.
• Comprising an estimated 1016 tons of carbon, it is the most
abundant source of organic compounds on earth, exceeding
the total organic content of living matter 10,000-fold.
• It is insoluble in normal organic solvents and it does not have
a specific chemical formula.
• Upon heating, kerogen converts in part to liquid and gaseous
hydrocarbons. Petroleum and natural gas form from kerogen.

6
• During the early and mid 20th century when “Town gas” was
produced, tar was a readily available product and extensively
used as the binder for road aggregates.
• The addition of tar to macadam roads led to the word
Tarmac, which is now used in common parlance to refer to
road-making materials.
• However, since the 1970s, when natural gas succeeded town
gas, asphalt has completely overtaken the use of tar in these
applications.

7
• Asphalt is by no means a product of our modern civilization
which is attested by the fact that remains of saber-tooth tigers
and other prehistoric animals have been found in the La
Brea Tar Pits in Los Angeles.
• In reality, these so-called "tar pits" are deposits of natural
asphalt.

Historical Development:
8
• The first recorded use of asphalt dates back to 3800 B. C. in
Mesopotamia where the material was used as an adhesive
mortar for building stones and paving blocks.
• Reservoirs, canals, and bathing pools constructed with these
blocks were made watertight with this material found in
natural deposits in the region.

9
• Asphalt was first used in paving in the middle of the
nineteenth century.
• Natural deposits of rock asphalt from the Rhone Valley in
France served as the source for this construction.
• In 1876 portions of Pennsylvania Avenue in Washington, D. C ,
were paved using Trinidad lake asphalt.

10
Trinidad Lake Asphalt

Bituminous Materials:
11
• Bitumen:
• A bitumen (according to ASTM) is a class of black or dark-
colored (solid, semisolid, or viscous) cementitious substances,
natural or manufactured, composed principally of high molecular
weight hydrocarbons , of which asphalts, tars, pitches, and
asphaltites are typical.
• By definition it is soluble in carbon disulfide.
• Two types are used in construction:-
1. Asphalt &
2. Tar

12
1.Asphalt:
• Asphalt (according to ASTM) is a dark brown to black cementitious
material in which the predominating constituents are bitumens which
occur in nature or are obtained by refining petroleum.
• There are two sources of asphalt:-
(1) those occurring naturally, and
(2) those obtained by the refining of petroleum.
• In both cases, asphalt is the product of fractional distillation of
petroleum, whether over short periods of time as in the refinery or
longer periods as in nature.

13
2. Tar:
• Tars do not occur in nature since they are product of chemical change.
• For example, tars are products of the destructive distillation (as
distinguished from fractional distillation in the case of asphalt) of a
number of organic materials such as coal, wood and sugar.
• Tar obtained from the destructive distillation of bituminous coal is a
crude tar which must undergo further refinement to obtain road tar.
• Tar can also be produced from petroleum by chemical rather than
physical change; that is, the destructive distillation of petroleum.

14
Sl. Asphalt Tar
1 Black to brown in color Usually found in brown color
2 Obtained from fractional distillation of
crude oil
Obtained by destructive distillation
of coal or wood
3 Soluble in carbon disulfide and carbon
tetra chloride
Soluble in toluene
4 Molecular weight range for road
bitumen is 400 to 5000
Molecular weight range for road tar
is 150 to 3000
5 Consists of large amount of aromatic
hydrocarbon
Consist of large amount of oily
matter with lower molecular weight
6 Bitumen show resistance to coating
road aggregate and also does not
retain in presence of water
Tar coats more easily and retain it
better in presence of water
7 Free carbon content is less Free carbon content is more
8 It shows more resistance to
weathering action
It shows less resistance to
weathering action
9 Lower temperature susceptibility Higher temperature susceptibility

Sources of Asphalt:
16
Asphalt is the product of fractional distillation of petroleum and this fractional
distillation process can occur over a long period of time in nature resulting in
deposits of material known as natural asphalts or in a short period of time in the
refinery resulting in manufactured asphalts.
The refinery is the primary source of asphalt today. Since natural asphalts
historically have been utilized in paving, it is worth while to include a brief
discussion of these materials as well as the manufactured products.
• Natural Asphalts. Natural asphalts can exist either in the relatively pure
form in nature or in impregnated rock deposits.
• Of these natural asphalts, two still have commercial significance
• (1) Trinidad lake asphalt, and
• (2) Gilsonite.

Sources of Asphalt:
18
Natural Deposits
• Natural deposits of asphalt occur as either
1. Native asphalt or 2. Rock asphalt.
• Native Asphalt:
• The largest deposit of native asphalt is known to have existed in Iraq
several thousand years ago. Native asphalts also have been found in
Trinidad, Bermuda, and the La Brea asphalt pits in Los Angeles,
California.
• Native asphalt was at one time used extensively as binders in highway
construction.
• The properties of native asphalt vary from one deposit to another,
particularly with respect to the amount of insoluble material the asphalt
contains.
• The Trinidad deposit, for example, contains about 40 percent insoluble

Sources of Asphalt:
19
Natural Deposits
• Rock asphalt
• It is a natural deposit of sandstone or limestone rocks filled with asphalt.
• Deposits have been found in California, Texas, Oklahoma, and Alabama.
• The amount of asphalt varies from one deposit to another and can be as
low as 4.5 percent and as high as 18 percent.
• Rock asphalt can be used to surface roads after the mined or quarried
material has been suitably processed.
• This process includes adding suitable mineral aggregates, asphalt binder,
and oil, which facilitates the flowing of the material.
• Rock asphalt is not used widely because of its high transportation costs.

Sources of Asphalt:
20
Petroleum Asphalt
• At present the primary source of asphalt is that
obtained from the refining of petroleum.
• The heavier or more viscous portions of certain
crude oils are asphalts.
• The breakdown of such a crude is shown
schematically on the right.
• Asphalt base crudes can vary in consistency
and color from that of a burgundy wine to
material as black and viscous as the asphalt
itself.

Sources of Asphalt:
21
Petroleum Asphalt (2)
• All crude oils do not contain asphalt as the heavier portions. In general,
there are two other classifications for crude, depending upon their base
or more viscous constituents- (1) paraffin and (2) mixed base crudes.
• The paraffin or wax base crudes are those in which material left after
fractional distillation of the more volatile constituents is essentially a
paraffin wax.
• The mixed base crudes are those in which the heavier portions are a
mixture of wax and asphalt. Special treatment is necessary to separate

Sources of Asphalt:
22
• Example: Water at the reference temperature and pressure has Gs=1.
Accordingly, the API Gravity Index of water is 10. The API GI is thus inversely
related to the specific gravity of the material.
The quantity of asphalt obtained from crude petroleum is
dependent on the American Petroleum Institute (API) gravity of the
petroleum. In general, large quantities of asphalt are obtained
from crude petroleum with low API gravity

Sources of Asphalt:
23
• Generally speaking, the lower the API GI of a petroleum, the higher will be
its asphalt content, and the lower its content of volatile phases like gasoline
and kerosene.

Refining Processes:
24
• The refining processes used to obtain petroleum asphalts can be divided
into two main groups:
1. Fractional distillation and
2. Destructive distillation (cracking).
• The fractional distillation processes involve the separation of the
different materials in the crude petroleum without significant changes in
the chemical composition of each material.
• The destructive distillation processes involve the application of high
temperature and pressure, resulting in chemical changes.

Refining Processes:
25
Fractional Distillation:
• The fractional distillation process removes the different volatile materials
in the crude oil at successively higher temperatures until the petroleum
asphalt is obtained as residue.
• Steam or a vacuum is used to gradually increase the temperature. Steam
distillation is a continuous flow process in which the crude petroleum is
pumped through tube stills or stored in batches, and the temperature is
increased gradually to facilitate the evaporation of different materials at
different temperatures.
• Tube stills are more efficient than batches and are therefore preferred in
modern refineries.
• Immediately after increasing the temperature of the crude in the tube
still, it is injected into a bubble tower which consists of a vertical cylinder
into which are built several trays or platforms stacked one above the

Refining Processes:
26

Refining Processes:
27
Fractional Distillation: (2)
• The first separation of materials occurs in this tower.
• The lighter fractions of the evaporated materials collect on the top tray,
and the heavier fractions collect in successive trays, with the heaviest
residue containing asphalt remaining at the bottom of the distillation
tower.
• The products obtained during this first phase of separation are gasoline,
kerosene distillate, diesel fuel, lubricating oils, and the heavy residual
material that contains the asphalt .
• The various fractions collected are stored and refined further into

Refining Processes:
28

Refining Processes:
29
Fractional Distillation: (3)
• A desired consistency of residue can be obtained by continuing the
distillation process. Attainment of the desired consistency is checked
by measuring the temperature of the residue or by observing the
character of the distillate.
• The residue becomes harder the longer the distillation process is
continued.
• Further processing of the heavy residue obtained after the first
separation will give asphalt cement of different penetration grades—
slow-curing and rapid-curing asphalts—depending on the additional

Refining Processes:
30
Fractional
Distillatio
n:

Refining Processes:
31
Destructive Distillation:
• Cracking processes are used when larger amounts of the light
fractions of materials (such as motor fuels) are required.
• Intense heat and high pressures are applied to produce chemical
changes in the material.
• Although several specific methods of cracking exist, the process
generally involves the application of temperatures as high as 1100° F
and pressure higher than 735 lb/in2
to obtain the desired effect.
• The asphalt obtained from cracking is not used widely in paving,
because it is more susceptible to weather changes than that produced
from fractional distillation.

Description And Uses Of Bituminous Binders:
32
Bituminous binders can be classified into three general
groups:
1. Asphalt cement,
2. Asphalt cutbacks, and
3. Emulsified asphalt.
Blown asphalt and road tars are also other types of
bituminous material that now are not used commonly in
highway construction.

33
1. Asphalt cement:
• Obtained after separation of the lubricating oils.
• They are semisolid hydrocarbons with certain physiochemical
characteristics that make them good cementing agents.
• They are also very viscous, and when used as a binder for
aggregates in pavement construction, it is necessary to heat both
the aggregates and the asphalt cement prior to mixing the two
materials.
• For several decades, the particular grade of asphalt cement has
been designated by its penetration and viscosity, both of which
give an indication of the consistency of the material at a given
temperature.
• The penetration is the distance in 0.1 mm that a standard needle
will penetrate a given sample under specific conditions of loading,

34
1. Asphalt cement: (2)
• The softest grade used for highway pavement construction has a
penetration value of 200 to 300, and the hardest has a penetration
value of 40 to 50.
• For some time now, however, viscosity has been used more often
than penetration to grade asphalt cements.
• USE:
• Used mainly in the manufacture of hot-mix, hot-laid asphalt
concrete.
• Asphalt concrete can be used in a variety of ways, including
the construction of highways and airport pavement surfaces
and bases, parking areas, and industrial floors.
• The specific use of a given sample depends on its grade.

Asphalt Cement Grading
35
 Penetration Grading
• Developed in the early 1900s to characterize the consistency of
semi-solid asphalts.
• Basic assumption- the less viscous the asphalt, the deeper the
needle will penetrate.
• This penetration depth is empirically (albeit only roughly)
correlated with asphalt binder performance.
• 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.

36
• Penetration grading key advantages and disadvantages-
Advantages Disadvantages
The test is done at 25° C (77° F),
which is reasonably close to a typical
pavement average temperature.
The test is empirical and does not
measure any fundamental
engineering parameter such as
viscosity.
May also provide a better correlation
with low-temperature asphalt binder
properties than the viscosity test,
which is performed at 60° C (140°
F).
Shear rate is variable and high
during the test. Since asphalt
binders typically behave as a non-
Newtonian fluid at 25° C (77° F), this
will affect test results.
Temperature susceptibility (the
change in asphalt binder rheology
with temperature) can be determined
by conducting the test at
temperatures other than 25° C (77°
F).
Temperature susceptibility (the
change in asphalt binder rheology
with temperature) cannot be
determined by a single test at 25° C
(77° F).
The test is quick and inexpensive.
Therefore, it can easily be used in
The test does not provide
information with which to establish

37
• AASHTO M 20 and ASTM D 946 Penetration Grades
Penetration Grade Comments
40 – 50 Hardest grade.
60 - 70 Typical grades used in the
U.S.
85 - 100
120 – 150
200 – 300 Softest grade. Used for
cold climates such as
northern Canada (Roberts
et al., 1996[1])

38
• 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
that occurs during mixing with hot aggregate)
Retained penetration
Ductility at 25° C (77° F)

40
 Viscosity Grading
• Developed in the early 1960s to incorporate 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):
Viscosity at 60° C (140° F)
Ductility at 25° C (77° F)

42
• Viscosity grading can be done on original (as-supplied) asphalt
binder samples (called AC grading) or aged residue samples
(called AR grading).
• The AR viscosity test is based on the viscosity of aged residue from
the rolling thin film oven test.
• With AC grading, the asphalt binder is characterized by the
properties it possesses before it undergoes
the HMA manufacturing process.
• The AR grading system is an attempt to simulate asphalt binder
properties after it undergoes a typical HMA manufacturing
process and thus, it should be more representative of how asphalt
binder behaves in HMA pavements.

43
 Viscosity Grading : key advantages and disadvantages-
Advantages Disadvantages
Unlike penetration depth, viscosity is a
fundamental engineering parameter.
The principal grading (done at 60°
C (144° F)) may not accurately
reflect low-temperature asphalt
binder rheology.
Test temperatures correlate well with:
- 25° C (77° F) – average pavement temp.
- 60° C (140° F) – high pavement temp.
- 135° C (275° F) – HMA mixing temp.
When using the AC grading
system, thin film oven test residue
viscosities can vary greatly with
the same AC grade. Therefore,
although asphalt binders are of the
same AC grade they may behave
differently after construction.
Temperature susceptibility (the change in
asphalt binder rheology with temperature)
can be somewhat determined because
viscosity is measured at three different
temperatures (penetration only is measured
at 25° C (77° F)).
The testing is more expensive and
takes longer than the penetration
test.
Testing equipment and standards are widely

44
• 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)).
• Typical grades used for HMA paving in the U.S. are AC-10, AC-20,
AC-30, AR-4000 and AR 8000.

45
 Viscosity Grading : key advantages and disadvantages-
Stan
dard
Grading based on
Original Asphalt (AC)
Grading based on Aged
Residue (AR)
AAS
HTO
M
226
AC-
2.5
AC-
5
AC-
10
AC-
20
AC-
30
AC-
40
AR-
10
AR-
20
AR-
40
AR-
80
AR-
160
AST
M D
338
1
AC-
2.5
AC-
5
AC-
10
AC-
20
AC-
30
AC-
40
AR-
100
0
AR-
200
0
AR-
400
0
AR-
800
0
AR-
160
00

46
 Superpave Performance Grade (PG)
• Due to inadequacy of penetration and viscosity based grading
systems, the Strategic Highway Research Program (SHRP) in US
conducted a Project between 1987 and 1993 in order to overcome
the shortcomings of empirical systems.
• One consequence of this Project was a performance based binder
specification with a new set of tests.
• The final product of the SHRP bitumen research program is a new
system referred to as SUPERPAVE, which stands for Superior
Performing Asphalt Pavements and called as binder specification
because it is intended to function equally well for modified and
unmodified bitumen.
• These tests and specifications are specifically designed to address
HMA pavement performance parameters such as rutting, fatigue
cracking and thermal cracking.

47
• In Superpave grading system, binders are classified according to
their performance in extreme hot and cold temperatures and
called as performance grading (PG) bitumen.
• The main purpose of grading and selecting asphalt binder using
the PG system is to make certain that the binder has the
appropriate properties for environmental conditions in field.
• PG asphalt binders are selected to meet expected climatic
conditions as well as traffic speed and volume adjustments.
Therefore, the PG system uses a common set of tests to measure
physical properties of the binder that can be directly related to
field performance of the pavement at its service temperatures by
engineering principles.

48
• The Superpave performance grading (PG) specification classifies
asphalt binders into performance grades that change at 6°C
intervals according to the service temperature.
• As an example, in Superpave Performance Grade Bitumen PG 64-
22, PG indicates that it is a performance graded binder. The first
number (64) means that the binder meets high temperature
physical properties up to 64 degrees centigrade. The last number
(-22) indicates the binder meets low temperature physical
properties down to -22 degrees centigrade.
• These numbers also correspond to average seven day maximum
pavement temperature and minimum pavement temperature
respectively for a level of reliability determined using temperature
data from weather stations in the region where binder is to be
used.

49
(e.g., Styrene-butadiene-styrene (SBS))

50
(e.g., Styrene-butadiene-styrene (SBS))

52
2. Asphalt Cutbacks:
• The asphalt cutbacks are-
a) slow-curing asphalts,
b) medium-curing cutback asphalts, and
c) rapid-curing cutback asphalts.
• They are used mainly in cold-laid plant mixes, road mixes (mixed-
in-place), and as surface treatments.

53
2. Asphalt Cutbacks: (2)
a) Slow-Curing Asphalts
• Slow-curing (SC) asphalts can be obtained directly as slow-curing
straight run asphalts through the distillation of crude petroleum
or as slow-curing cutback asphalts by “cutting back” asphalt
cement with a heavy distillate, such as diesel oil.
• They have lower viscosities than asphalt cement and are very
slow to harden.
• Slow-curing asphalts usually are designated as SC-70, SC-250,
SC-800, or SC-3000, where the numbers relate to the approximate
kinematic viscosity in centistokes at 60°C (140°F).
• Specifications for SC asphalt is given in ASTM D 2026.

54

55
b. Medium-Curing Cutback Asphalts
• Medium-curing (MC) asphalts are produced by fluxing, or cutting
back, the residual asphalt (usually 120 to 150 penetration) with
light fuel oil or kerosene.
• The term “medium” refers to the medium volatility of the
kerosene-type diluter used.
• Medium curing cutback asphalts harden faster than slow-curing
liquid asphalts, although consistencies of the different grades are
similar to those of the slow-curing asphalts.
• However, the MC-30 is a unique grade in this series as it is very
fluid and has no counterpart in the SC and RC series.

56
• The fluidity of medium-curing asphalts depends on the amount of
solvent in the material.
• MC-3000, for example, may have only 20 percent of the solvent by
volume, whereas MC-70 may have up to 45 percent.

57
• Uses: For the construction of pavement bases, surfaces, and
surface treatments.
• Specification for MC asphalt is given in ASTM D 2027.

58

59
c. Rapid-Curing Cutback Asphalts
• Rapid-curing (RC) cutback asphalts are produced by blending
asphalt cement with a petroleum distillate that will evaporate
easily, thereby facilitating a quick change from the liquid form at
the time of application to the consistency of the original asphalt
cement.
• Gasoline or naphtha generally is used as the solvent for this series
of asphalts.
• The grade of rapid-curing asphalt required dictates the amount of
solvent to be added to the residual asphalt cement.

60
c. Rapid-Curing Cutback Asphalts
• For example, RC-3000 requires about 15 percent of distillate,
whereas RC-70 requires about 40 percent.
• Uses: These grades of asphalt can be used for jobs similar to
those for which the MC series is used.
• Specifications for RC asphalt is given in ASTM D 2028.

61

62
3. Emulsified Asphalt:
• Emulsified asphalts are produced by breaking asphalt cement,
usually of 100 to 250 penetration range, into minute particles and
dispersing them in water with an emulsifier.
• These minute particles have like-electrical charges and therefore
do not coalesce. They remain in suspension in the liquid phase as
long as the water does not evaporate or the emulsifier does not
break.
• In asphalt emulsions, lightly heated asphalt is run through a
colloidal mill together with an emulsifying agent to produce 5-10
μm sized globules. The asphalt globules are mixed with water to
form a liquid mixture of roughly 75% asphalt and 25% water by
mass. The emulsifying agent coats the asphalt globules and
imparts a surface charge that makes the globules repel rather

63
3. Emulsified Asphalt:
• Emulsified asphalts are produced by breaking asphalt cement,
usually of 100 to 250 penetration range, into minute particles and
dispersing them in water with an emulsifier.
• These minute particles have like-electrical charges and therefore
do not coalesce. They remain in suspension in the liquid phase as
long as the water does not evaporate or the emulsifier does not
break.
• In asphalt emulsions, lightly heated asphalt is run through a
colloidal mill together with an emulsifying agent to produce 5-10
μm sized globules. The asphalt globules are mixed with water to
form a liquid mixture of roughly 75% asphalt and 25% water by
mass. The emulsifying agent coats the asphalt globules and
imparts a surface charge that makes the globules repel rather

64
3. Emulsified Asphalt: (2)
• Asphalt emulsions therefore consist of asphalt, which makes up
about 55 to 70 percent by weight, water, and an emulsifying agent,
which in some cases also may contain a stabilizer.
Emulsions are typically classified by four different factors:
1) Charge:
• The emulsifying agent can impart either a positive or negative
charge on the asphalt globules.
• Anionic emulsions have negative charges on the asphalt, whereas
cationic emulsions have positive charges.
• Anionic emulsions should be used with aggregates that have
positive surface charges (such as limestone), and cationic emulsions
with aggregates having negative surface charges (such as quartz,
siliceous gravels, etc.).

65
3) Emulsified Asphalt: (3)
• In the alpha-numeric designation system for emulsions, the letter
“C” indicates that an emulsion is cationic. Lack of the letter “C” in
the designation indicates that the emulsion is anionic.
• When an emulsion is mixed with an appropriate aggregate, the
asphalt in the emulsion coalesces on the aggregate causing the
mixture to “set” or “break.” The water can then be
squeezed/pumped out of the asphalt-aggregate mixture, or it can
gradually evaporate away.
4) Setting rate:
• Emulsions are further classified on the basis of how quickly the
asphalt will coalesce; i.e., revert to asphalt cement.
• The terms RS, MS, and SS have been adopted to simplify and
standardize this classification.

DESCRIPTION AND USES OF BITUMINOUS BINDERS:
66
2) Setting rate:
• These (RS, MS, SS) are relative terms only and mean rapid-
setting, medium-setting, and slow-setting, respectively. The
tendency to coalesce is closely related to the mixing of an
emulsion.
• An RS emulsion has little or no ability to mix with an aggregate,
an MS emulsion is expected to mix with coarse but not fine
aggregate, and an SS emulsion is designed to mix with fine
aggregate.
3) Viscosity:
• Emulsions are further subdivided by their viscosity. In the alpha-
numeric designation system, an digit of either 1 or 2 indicates the
relative viscosity of the emulsion, with digit “1” indicates a

67
3) Viscosity:
• The digit “h” can also be used in the designation for emulsions to
indicate the underlying hardness or viscosity of the asphalt
cement as opposed to that of the emulsion itself.
• Example: The designation CRS-1 indicates a cationic, rapid-
setting emulsion of normal viscosity suitable for mixing with
coarse aggregates in which the base asphalt cement also has
normal viscosity.
• Example: The designation SS-1h indicates an anionic, slow-
setting emulsion of normal viscosity in which the base asphalt
cement has a higher than normal viscosity.

68
4) Float:
• The "HF" preceding some of the anionic MS grades indicates
high-float, as measured by the Float Test (ASTM D 139 or
AASHTO 50). High-float emulsions have a quality, imparted by the
addition of certain chemicals, that permits a thicker asphalt film
on the aggregate particles with minimum probability of drainage.
• Three grades of high-float, medium-setting anionic emulsions
designated as HFMS have been developed and are used mainly in
cold and hot plant mixes and coarse aggregate seal coats.
• Example: The designation HFMS-2 for an emulsion indicates
that it is a medium setting high-float anionic emulsion with a
higher than normal viscosity.

70
• Emulsified asphalts are used in cold-laid plant mixes and road mixes
(mixed in-place) for several purposes, including the construction of
highway pavement surfaces and bases and in surface treatments.
• Specifications for the use of emulsified asphalts are given in AASHTO
M140 and ASTM D977.

71
• Emulsified asphalts are used in cold-laid plant mixes and road mixes
(mixed in-place) for several purposes, including the construction of
highway pavement surfaces and bases and in surface treatments.
• Specifications for the use of emulsified asphalts are given in AASHTO
M140 and ASTM D977.

72
4. Blown Asphalts:
• Blown asphalt is obtained by blowing air through the
semisolid residue obtained during the latter stages of the
distillation process.
• The process involves stopping the regular distillation while
the residue is in the liquid form and then transferring it into a
tank known as a converter.
• The material is maintained at a high temperature while air is
blown through it. This is continued until the required
properties are achieved.
• Blown asphalts are relatively stiff compared to other types of
asphalts and can maintain a firm consistency at the maximum
temperature normally experienced when exposed to the
environment.

73
4. Blown Asphalts: (2)
• Blown asphalt generally is not used as a paving material.
However, it is very useful as a roofing material, for automobile
undercoating, and as a joint filler for concrete pavements.
• If a catalyst is added during the air-blowing process, the
material obtained usually will maintain its plastic
characteristics, even at temperatures much lower than that at
which ordinary asphalt cement will become brittle.
• The elasticity of catalytically blown asphalt is similar to that of
rubber, and it is used for canal lining.

74
5. Road Tars:
• Tars are obtained from the destructive distillation of such
organic materials as coal. Their properties are significantly
different from petroleum asphalts.
• In general, they are more susceptible to weather conditions
than similar grades of asphalts, and they set more quickly
when exposed to the atmosphere.
• The American Society for Testing Materials (ASTM) has
classified road tars into three general categories based on the
method of production.
a. Gashouse coal tars are produced as a by-product in
gashouse retorts in the manufacture of illuminating gas
from bituminous coals.

75
5. Road Tars: (2)
b. Coke-oven tars are produced as a by-product in coke
ovens in the manufacture of coke from bituminous coal.
c. Water-gas tars are produced by cracking oil vapors at high
temperatures in the manufacture of carbureted water gas.
• Road tars also have been classified by AASHTO into 14
grades: RT-1 through RT-12, RTCB-5, and RTCB-6.
• RT-1 has the lightest consistency and can be used effectively
at normal temperatures for prime or tack coat.
• The viscosity of each grade increases as the number
designation increases to RT-12, which is the most viscous.

76
5. Road Tars: (3)
• RTCB-5 and RTCB-6 are suitable for application during cold
weather, since they are produced by cutting back the specific
grade of tar with easily evaporating solvent. Detailed
specifications for the use of tars are given by
• AASHTO Designation M52-78.

Properties of Asphalt Materials
77
The properties of asphalt materials pertinent to pavement
construction can be classified into four main categories:
1. Consistency
2. Aging and temperature sustainability
3. Rate of curing
4. Resistance to water action
1. Consistency
• The consistency properties of an asphalt material usually are
considered under two conditions:
(1) variation of consistency with temperature and
(2) consistency at a specified temperature.

78
1. Consistency: Variation of Consistency with Temperature
• The consistency of any asphalt material changes as the
temperature varies. The change in consistency of different
asphalt materials may differ considerably even for the same
amount of temperature change.

79
• For example, if a sample of blown semisolid asphalt and a
sample of semisolid regular paving-grade asphalt with the
same consistency at a given temperature are heated to a high
enough temperature, the consistencies of the two materials
will be different at the high temperatures with the regular
paving-grade asphalt being much softer than the blown
asphalt.
• Further increase in temperature eventually will result in the
liquefaction of the paving asphalt at a temperature much
lower than that at which the blown asphalt liquefies.

80
• If these two asphalts then are cooled down gradually to about
the freezing temperature of water, the blown asphalt will be
much softer than the paving-grade asphalt.
• Thus, the consistency of the blown asphalt is affected less by
temperature changes than the consistency of regular paving-
grade asphalt.
• The temperature susceptibility of a given asphalt depends on
the crude oil from which the asphalt is obtained, although
variation in temperature susceptibility of paving-grade
asphalts from different crudes is not as high as that between
regular paving-grade asphalt and blown asphalt.

81
1. Consistency: Consistency at a Specified Temperature
• The consistency of an asphalt material will vary from solid to
liquid depending on the temperature of the material.
• It is therefore essential that when the consistency of an
asphalt material is given, the associated temperature also
should be given.

82
2. Aging and Temperature Sustainability
• When asphaltic materials are exposed to environmental
elements, natural deterioration gradually takes place, and the
materials eventually lose their plasticity and become brittle.
This change is caused primarily by chemical and physical
reactions that take place in the material.
• This natural deterioration of the asphalt material is known as
weathering. For paving asphalt to act successfully as a
binder, the weathering must be minimized as much as
possible. The ability of an asphalt material to resist

83
• Some of the factors that influence weathering are oxidation,
volatilization, temperature, and exposed surface area.
• Oxidation: Oxidation is the chemical reaction that takes place
when the asphalt material is attacked by oxygen in the air. This
chemical reaction causes gradual hardening (eventually
permanent hardening) and considerable loss of the plastic
characteristics of the material.
• Volatilization: Volatilization is the evaporation of the lighter
hydrocarbons from the asphalt material. The loss of these lighter

84
• Temperature: It has been shown that temperature has a
significant effect on the rate of oxidation and volatilization. The
higher the temperature, the higher the rates of oxidation and
volatilization. The relationship between temperature increase
and increases in rates of oxidation and volatilization is not linear;
however; the percentage increase in rate of oxidation and
volatilization is usually much greater than the percentage
increase in temperature that causes the increase in oxidation
and volatilization. It has been postulated that the rate of organic
and physical reactions in the asphalt material approximately
doubles for each 10°C (50° F) increase in temperature.

85
• Surface Area: The exposed surface of the material also
influences its rate of oxidation and volatilization. There is a
direct relationship between surface area and rate of oxygen
absorption and loss due to evaporation in grams/cm3/minute. An
inverse relationship, however, exists between volume and rate of
oxidation and volatilization. This means that the rate of
hardening is directly proportional to the ratio of the surface area
to the volume. This fact is taken into consideration when asphalt
concrete mixes are designed for pavement construction in that
the air voids are kept to the practicable minimum required for
stability to reduce the area exposed to oxidation.

86
3. Rate of Curing
Curing is defined as the process through which an asphalt material
increases its consistency as it loses solvent by evaporation.
• Rate of Curing of Cutbacks:
• The rate of curing of any cutback asphalt material depends on the
distillate used in the cutting-back process.
• The rate of curing is affected by both inherent and external
factors. The important inherent factors are-
 Volatility of the solvent
 Quantity of solvent in the cutback
 Consistency of the base material

87
3. Rate of Curing : Rate of Curing of Cutbacks
• The more volatile the solvent is, the faster it can evaporate from
the asphalt material, and therefore, the higher the curing rate of
the material.
• This is why gasoline and naphtha are used for rapid-curing
cutbacks, whereas light fuel oil and kerosene are used for
medium-curing cutbacks.
• For any given type of solvent, the smaller the quantity used, the
less time is required for it to evaporate, and therefore, the faster
the asphalt material will cure.
• Also, the higher the penetration of the base asphalt, the longer it
takes for the asphalt cutback to cure.

88
3. Rate of Curing : Rate of Curing of Cutbacks:
• The important external factors that affect curing rate are
 Temperature
 Ratio of surface area to volume
 Wind velocity across exposed surface
• These three external forces are related directly to the rate of
curing in that the higher these factors are, the higher the rate of
curing. Unfortunately, these factors cannot be controlled or
predicted in the field, which makes it extremely difficult to
predict the expected curing time.
• The curing rates of different asphalt materials usually are
compared with the assumption that the external factors are held
constant.

89
3. Rate of Curing: Rate of Curing for Emulsified Asphalts
• The curing and adhesion characteristics of emulsions (anionic
and cationic) used for pavement construction depend on the rate
at which the water evaporates from the mixture.
• When weather conditions are favorable, the water is displaced
relatively rapidly, and so curing progresses rapidly. When
weather conditions include high humidity, low temperature, or
rainfall immediately following the application of the emulsion, its
ability to properly cure is affected adversely.
• Although the effect of surface and weather conditions on proper
curing is more critical for anionic emulsions, favorable weather
conditions also are required to obtain optimum results for
cationic emulsions. A major advantage of cationic emulsions is
that they release their water more readily.

90
4. Resistance to Water Action
• When asphalt materials are used in pavement construction, it is
important that the asphalt continues to adhere to the aggregates
even with the presence of water.
• If this bond between the asphalt and the aggregates is lost, the
asphalt will strip from the aggregates, resulting in the
deterioration of the pavement.
• The asphalt therefore must sustain its ability to adhere to the
aggregates even in the presence of water. In hot-mix, hot-laid
asphalt concrete, where the aggregates are thoroughly dried
before mixing, stripping does not normally occur and so no
preventive action is usually taken.
• However, when water is added to a hot-mix, cold-laid asphalt
concrete, commercial antistrip additives usually are added to

91
• Temperature Effect on Volume of Asphaltic Materials
• The volume of asphalt is affected by changes in temperature
significantly.
• The volume increases with an increase in temperature and
decreases with a decrease in temperature.
• The rate of change in volume is given as the coefficient of
expansion, which is the volume change in a unit volume of the
material for a unit change in temperature.
• Because of this variation of volume with temperature, the
volumes of asphalt materials usually are given for a temperature
of 60° F (15.6° C).
• Volumes measured at other temperatures are converted to the
equivalent volumes at 60°F by using appropriate multiplication
factors published by the ASTM in their Petroleum Measurement

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