CE 467 Lesson 7 - Bituminous Materials
CE 467 Lesson 7 - Bituminous Materials
CE 467 Lesson 7 - Bituminous Materials
Bituminous Paving
Materials
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Lesson Objectives
The lesson is intended to;
Equip students with knowledge of different types
of bituminous materials and the properties used in
their characterisation.
Introduce students to different grades of bitumen.
Explain the design of hot-mix asphalt.
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Learning Outcomes
At the end of the lesson, students should be able to;
Demonstrate knowledge of the different types of
bituminous materials used in flexible pavement
construction.
Select the appropriate bituminous binder grade for
a road project.
Undertake design of hot-mix asphalt.
4 Types of Asphalt Cements
Asphalt (also known as bitumen) is the residual product of
the distillation of heavy crude petroleum.
Solid asphalt types obtained from the distillation process
are:
1. Straight-run asphalt (direct from the vacuum distillation
stage)
2. Air-blown asphalt (vacuum distillation residue
subjected to air-blowing process to harden the
material)
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Asphalt Cements cont’d
3. Blended asphalt (a mixture of soft and hard bitumen)
Softening Point
• This is the temperature at which an asphalt cement
or binder changes from solid to liquid state.
• The harder an asphalt cement, the higher its
softening point and vice versa.
• The softening point temperature is also referred to as
the Ring and Ball temperature (TR&B).
10 Grading of Asphalts
Asphalt cements are placed under different standard grades
based on their hardness or degree of fluidity in order to make
it possible for users to differentiate between them and/or to
select the type appropriate for use.
Asphalt cements may be graded on the basis of either
penetration at 25oC or viscosity at 60oC or performance
(Superpave).
Grading may also be based on the properties of the aged
residue.
11 Penetration Grading
Penetration Penetration
• Based on
Grade Min. Max
penetration, five
standard asphalt 40-50 40 50
grades exist.
60-70 60 70
• The standard grades
are detailed in the 85-100 85 100
table. 120-150 120 150
200-300 200 300
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Penetration Grading cont’d
The numerical values for each grade represent the range
within which the penetration for that particular grade lies.
• Grading of asphalts
may also be based Viscosity Absolute Viscosity
on the viscosity of
the fresh sample at Grade Range (Poise)
60oC (absolute Min Max
viscosity).
AC-2.5 200 300
• The standard
viscosity grades are AC-5 400 600
as given in the AC-10 800 1200
table.
AC-20 1600 2400
AC-40 3200 4800
14 Viscosity Grading cont’d
“AC” designates "asphalt cement"
The numerical value of each grade represents one
hundredth of the absolute viscosity with a tolerance of 20%.
For example, AC-20 grade has an absolute viscosity mid-
range value of 2000 poise with the range being 1600-2400
poise. Therefore, any asphalt cement whose absolute
viscosity falls within this range is graded as AC-20.
There is no direct correspondence between viscosity grades
and penetration grades. However, most 60-70 pen. grades,
for example, will qualify as AC-20 grades and vice versa. In
spite of that, AC-20 grades are not equivalent to 60-70 pen.
grades.
Performance Grading
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• The Superpave Performance Grading (PG) has been developed to
address hot-mix asphalt (HMA) pavement performance parameters
such as rutting, fatigue cracking and thermal cracking.
• The top several rows (all the rows above the "original binder" row) are
used to designate the desired PG grade. For instance, if the average
7-day maximum pavement design temperature is greater than 52oC
but less than 58oC then the “PG 58" column is used.
• The temperatures directly under the “< 58" cell (negative values)are
selected based on the minimum pavement design temperature in oC
to complete the grade designation.
16 Performance Grading cont’d
• Tests are run on the original binder (no simulated aging), Rolling
Thin Film Oven (RTFO) residue (simulated short-term aging) and
Pressure Aging Vessel (PAV) residue (simulated long-term aging) in
order to fully characterize the asphalt binder throughout its life.
• Tests run on the binder are listed in the left-hand column. They are
not necessarily listed by their common names but the applicable
AASHTO test procedure listed. For instance, "Flash Point Temp. T
48, Minimum (oC)" means that the flash point is measured
according to AASHTO T48 and that the value in the adjacent
column represents the minimum allowable in degrees Centigrade.
17 Table 1. Performance Grading Asphalt Binder Specifications
(from AASHTO, 2001)
PG 46 PG 52 PG 58 PG 64
Performance Grade
34 40 46 10 16 22 28 34 40 46 16 22 28 34 40 10 16 22 28 34 40
Average 7-day Maximum Pavement Design
< 46 < 52 < 58 < 64
Temperature, oCa
Minimum Pavement Design Temperature, oCa -34 -40 -46 -10 -16 -22 -28 -34 -40 -46 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40
ORIGINAL BINDER
Flash Point Temp, T 48, Minimum (oC) 230
b
Viscosity, ASTM D 4402:
135
Maximum, 3 Pa*s, Test Temp, oC
Dynamic Shear, TP 5:c
G*/sinf , Minimum, 1.00 kPa 46 52 58 64
o
Test Temp @ 10 rad/s, C
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19 Asphalt Durability
The durability of an asphalt cement is its resistance to changes
(for the worse) in its original properties in service.
To serve as a good binder, an asphalt cement must have the
following characteristics:
1. Good adhesion to aggregates.
2. Good viscosities at processing and application
temperatures.
3. Ability to deform easily without rupture in order to resist
stresses while existing as a component of an asphaltic
pavement (visco-elastic behaviour).
20 Asphalt Age-hardening
When asphalt ages, it becomes hard and brittle and prone to
cracking.
The major cause of aging is oxidation caused by the reaction
between the asphalt and oxygen in the air, aided by high
temperatures.
The reaction causes chemical changes in the asphalt which
makes the asphalt brittle.
Age-hardening in service will cause an asphalt pavement to
exhibit the following failures: disintegration, ravelling and all
kinds of cracking.
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Liquefied Asphalts
Asphalts from the distillation process usually exist in a solid
form at room temperature and lower but may be
produced in a liquefied form to enable use without or
with a minimum application of heat.
Two types of liquefied asphalts exist:
a) Asphalt emulsions (bitumen emulsions)
b) Cutback asphalts (cutback bitumen).
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a) Asphalt Emulsions
An asphalt emulsion is a liquefied asphalt obtained by
the dispersion of asphalt globules or droplets (less than 5-
10 microns) in water containing an emulsifying agent (a
soap-like substance which acts as a stabiliser).
Without the emulsifying agent the asphalt globules will
coalesce and stay out of suspension since asphalt is an
organic material so ordinarily will not mix with water.
The emulsifying agent, depending on type, will impart
either positive (+) charges or negative (-) charges to the
surface of the asphalt globules which will make the
globules repel one another and stay in suspension.
23 Emulsions cont’d
When the globules carry electro-positive charges, the
emulsion is called cationic emulsion; if they carry
electro-negative charges, the emulsion is called anionic
emulsion.
a) Mixture Preparation
63.5 (1)
Q Qo
h
where,
Q=the quantity of aggregates required
Qo=quantity used for trial specimen
h=trial specimen height (mm)
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weight of asphalt
Asphalt content , Pb 100 (2)
weight of asphalt weight of aggregates
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Based on the above definition, the amount of asphalt
required to mix with a given weight of aggregates to attain a
target asphalt content (Pb) for the mix is;
Wag
Wb
100 (3)
1
Pb
where,
Wb=weight of asphalt cement required
Wag=weight of aggregates taken
Pb=target asphalt content in %
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Specimens must be prepared to asphalt contents that
vary in 0.5% increments.
At least two of the test specimens must have asphalt
content above the optimum and two below.
Usually six different asphalt contents are selected
requiring a total of 18 Marshall specimens to be
scheduled, i.e., three samples for each asphalt
content.
The weighed aggregates are dried in an oven and
maintained at a temperature about 30oC above the
mixing temperature.
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WSSD Wsub
Vmb (4)
w
Hence, the bulk density (ρmb)of the compacted sample
becomes;
Wa
mb w (5)
WSSD Wsub
ρw=density of water
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1
2
Vvoidless (8)
Theoretical Maximum Density cont’d
53 Suppose a loose mixture of known weight is dropped in a graduated
cylinder initially filled with water to a known volume mark (Fig. 2 (a)).
The water level will rise to a new volume mark to reflect the volume of the
loose mix introduced (Fig. 2 (b)).
The difference in the water volumes will be the voidless volume if that
quantity of loose mix were to be compacted to expel all air voids.
VMA
Vv Vbe
100
(10)
Vmb
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Note that, of the total bitumen volume in the mix, part will be
absorbed into the pores in the aggregates and not be available
for coating the aggregates.
By substituting weights for volumes, it can be shown
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that;
mb
VTM 1001
(12)
mm
(100 Pb )Gmb (13)
VMA 100
Gsb
VTM
VFA 1001 (14)
VMA
where,
Pb=asphalt content in %
Gsb=bulk specific gravity of the aggregates used in the mix
𝜌𝑚𝑏
Gmb=bulk specific gravity of the mix (Gmb= )
𝜌𝑤
ρmb , ρmm = bulk density and theoretical maximum density of
the compacted specimen, respectively.
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Once the density and voids analysis have been completed, the
relevant data are presented in graphical form by preparing the
following plots:
o Bulk density vs. Asphalt content
o Marshall Stability vs. Asphalt content
o Flow vs. Asphalt content
o Air voids content (VTM) vs. Asphalt content
o VMA vs. Asphalt content
o VFA vs. Asphalt content
As a precaution, it is necessary to check that the plots exhibit
characteristics similar to the corresponding plots in Fig. 3.
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Step 2:
Enter the appropriate curves in the data plots and
determine the values of the following parameters
corresponding to the average asphalt content;
• Stability
• Flow
• Air voids (VTM)
• VFA
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Step 3:
Compare the values of the above parameters obtained
from the plots with the specification values or limits (see
Table 5).
If all the specification values are met, the mix formulation is
accepted, otherwise, the mixture design process should
start all over again by first adjusting the gradation to vary
slightly from the previous while still keeping within the
acceptable gradation limits.
66 Table 5. GHA Marshall Mix Design Specs
Mix Criteria Light traffic Medium traffic Heavy traffic
(<104ESALs) (104-106 ESALs) (>106ESALs
Min. Max. Min. Max. Min. Max.
Compaction 35 50 75
blows/face
Stability (N) 3368 - 5338 - 8006 -
Flow (units of 8 18 8 16 8 14
0.25mm)
Air Voids 3 5 3 5 3 5
Content (%)
Voids filled with 70 80 65 78 65 75
Asphalt (%)
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END OF LESSON
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