CHAPTER - 3 Highway Materials

DEPARTMENT OF CIVIL ENGINEERING
1 Highway Engineering II (CENG 4183)

CHAPTER 3: HIGHWAY MATERIALS
1. General, At the end of this chapter, students will be

2. Highway materials: able to
2.1 Soils  At the end of the course, students would
understand:
2.2 Aggregates
 Identify the classification of soil with respect
2.3 Bituminous to Engineering properties by laboratory
3.3 Portland cement works.
 Differentiate materials used in base and sub-
base construction that are available in the
location of construction
By Haile G. December 2022

SUBGRADE SOILS
2
 The sub-grade is the undermost layer of a pavement and as such is one of

the main concerns of a pavement design.
 Many pavement failures could be traced to insufficient consideration given

to the natural sub-grade material, especially in the case of problematic
soils, the identification of which is of paramount importance and half the
solution towards the mitigation measures.
 Sub grades usually consist of fine grained cohesive or non cohesive soils.
 All these materials exhibit a stress dependent behavior implying that both
the stiffness and the shear strength increase with increasing confinement.
Chapter 3 – Highway Materials

SUBGRADE SOILS
3
 Soil is the most important foundation and construction material for

pavement structures.
 Foundation material for all pavements as undisturbed in situ sub grade
material or transported and reworked embankment material
 Construction material for pavement structures either in its natural form
(sand and gravel) or in a processed form as stabilized layer.
 Soil investigation is, thus, an integral part of the location, design and
construction of highways.

Soil Surveys and Investigations
4
 Along with traffic and economic criteria, the design of a

road and of a road’s pavement in particular, is based on
the surface and sub soils conditions, and the characteristics
and quality of construction materials used.
 Soil survey for highway purposes involve the exploration of
the soils along the highway routes and the identification of
suitable soils for use as sub base and fill materials.

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 The results of soil investigation provide pertinent information about

soil and rock for a decision on one or more of the following subjects
 Selection of roadway alignment
 Decision of the need for sub grade or embankment foundation

treatment
 Investigation of slope stability in cuts and embankments
 Location and design of ditches and culverts
 Selection and design of the roadway pavement
 Location and evaluation of suitable borrow and construction

materials, and
 Design of foundations for bridges and other structures
6
 In selecting the alignment of a new highway the first step is

normally to define a number of conceivable(possible) corridors
between the end termini of the road.
 The next step is to select the best corridor for the proposed road
and define within it one or more different alignments.
 These alignments are compared, and a final selection is made for
design purposes.
 The process involves continuous searching and selecting, using
increasingly more detailed knowledge of sub-grade soils at each
decision-making stage.

7
 Before a field investigation is carried out at the site, preliminary information

regarding soil condition can often be obtained from the following sources
i. Geological and agricultural soil maps. These often indicate the types of soil or
geological formation that cover the area being investigated.
ii. Aerial photographs. Terrain information visible on air photos can be used for
identification of most of the common bedrock types associated residual soils,
transported soils, and organic soils.
iii. Satellite images. Satellite images are employed as a supplemental to air photos
or as a substitute for air photos for geological studies and soil investigations.
iv. Area reconnaissance. Reconnaissance survey aids in securing broad understanding
of soil conditions and associated engineering problems that may be encountered.
v. The visual examination of vegetation cover, roadway cuts, and valleys in the
area can give clue. The depth of water level in adjacent wells may indicate the
elevation of the groundwater table.
8
 Field investigations and sample collection for laboratory tests are

commonly carried out by the following four methods.
 Geophysical methods (seismic or electrical). The seismic refraction method relies
on the principle that the velocity of sound in soils and rocks is different for
different materials. It is particularly useful in predicting the depth to bedrock.
The electrical resistivity mainly depends on the content of clay minerals,
moisture content, and type and concentration of electrolyte in the soil-water.
An increasing content of clay, water or electrolyte causes decreasing the
resistivity of soils.
 Test pits or trenches: suitable for shallow depths only to sample soils and rocks
and register soil profiles.
 Hand augers: suitable for shallow depths only to obtain disturbed or mixed
samples of soils.
 Boring test holes and sampling with drill rigs: the principal method for detailed
soils investigations.
Depth of investigations
9
 The design depth is defined as the depth from the finished road level to the depth
that the load bearing strength of the soil no longer has an effect on the
pavement’s performance in relation to traffic loading.
 Properties of soil below the design depth may indirectly affect pavement
performance, but are generally unrelated to traffic loading.
 The depth of test pits and borings should in no case be less than 1.5m below the
proposed sub grade level unless rock material is encountered.
 A preliminary vertical alignment may be required at the time of the soil survey in
order to ensure that soil samples are actually taken at levels that fall within the
design depth of the road.
Depth of investigations
10
 For ordinary work, it is quite sufficient to go to a depth of about 3m

below the proposed foundation level in areas of cut and 3m below the
existing ground in areas of fill investigations in cuttings deeper than 3m
could be impractical and special equipment may have to be required.
 If possible, postponement of sampling until the time of construction

should be considered under such conditions.
 Evaluation of sub grade strength in embankment areas should be

based on the best possible information about likely sources of fill
materials for use within the design depth.
SAMPLING AND FREQUENCY
11
 Common investigations should cover basic data collection, such as depth and
nature of soils (sub grade and embankment materials), and should be limited
to test pits and hand augers.
 The common investigations can be for new roads and/or existing roads.
 Once the alignment of a new road is finalized, investigations for soil sampling
along the alignment can be initiated. The frequency of sampling depends on
the field conditions.
 As a standard guideline, at least one representative soil sample should be
collected per kilometer of the proposed roadway alignment, with more
frequent samples where there are significant changes in soil type.
 Significant changes are those which affect the general classification of the soils
as well as their bearing strength (CBR).
 The sampling location may be alternatively on the left and right
edge of the proposed roadway.
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 Table 3-1 gives a recommended sampling frequency and the corresponding

tests which may be altered depending on the variations in soil types along the
alignment.
 Spacing in specific locales may be increased where the sub grade exhibits a
fair degree of homogeneity, and conversely be decreased where variations
become evident, or when problem soils or design problems are encountered.
 Table 3-1 Design depth (Tanzania pavement Design manual, 1999)

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 The recommended approximate quantity (mass) of sample required

may be determined by verifying the tests required and referring to
Table 3-2 below.
 It is simpler, and generally preferable, to retrieve in the field each
sample large enough to conduct all required tests in the laboratory.
 This allows for a better selection of representative samples in the
laboratory prior to compaction and CBR testing.
 If logistics preclude the taking and transportation of large quantities
of samples, careful examination of the soils in the field must be
conducted and judgment must be exercised to select truly
representative samples for compaction and CBR testing.

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 Table 3-2: Minimum Mass of Sample Required (Soils and Gravels)

15
 For the purpose of taking representative samples, pits shall be dug

mostly in anticipated cut areas (since these cuts will expose the sub
grade support of the future pavement and provide embankment
materials), if possible down to at least 30 cm below the expected sub
grade level.
 Further, in the case of a new alignment, the depth of any pit should in
no case be less than 1.5 m unless rock or other material impossible to
excavate by hand is encountered.
 The position (in plan and elevation) of each test pit must be accurately
determined and recorded.
 This implies that geotechnical and topographical tasks must be
coordinated in the field. In every test pit, all layers, including topsoil,
shall be accurately described and their thicknesses measured.
16
 All layers of more than 30 cm (except topsoil) shall be sampled. This will
promote a proper assessment of the bulk of the materials excavated in cuts
and to be used in embankments.
 Care shall be taken, when retrieving samples, to secure and preserve a small
but sufficient quantity of soil for the purpose of measuring the moisture content
in the laboratory.
 Measuring the in-situ moisture content is particularly desirable at the
anticipated sub grade level.
 The log of each test pit shall be accurately drawn and included in the Soils
and Materials Report.
 Photographs should also be taken of the test pit location, as well of the soils
horizons in the test pit which will help for reporting the investigations and
interpreting the results.

RECOMMENDED TESTS ON SOIL SAMPLES
17
 For new road alignments, the following tests shall

normally be conducted, as a minimum, on the collected
soil samples:
1. Grain Size Analysis (AASHTO T88)
2. Atterberg Limits (AASHTO T89, T90)
3. Moisture Content (AASHTO T265)
4. Compaction Test (AASHTO T180)
5. CBR Test (AASHTO T193)
Atterberg Limits
18
 The Swedish soil scientist Albert Atterberg originally defined seven “limits of
consistency” to classify fine-grained soils, but in current engineering practice only
two of the limits, the liquid and plastic limits, are commonly used. (A third limit,
called the shrinkage limit, is used occasionally.)
 The Atterberg limits are based on the moisture content of the soil.
 The plastic limit is the moisture content that defines where the soil changes from a
plastic (flexible) to semi-solid state.
 The liquid limit is the moisture content that defines where the soil changes from a
viscous fluid to a plastic state.
 The shrinkage limit is the moisture content that defines where the soil volume will
not reduce further if the moisture content is reduced a wide variety of soil
engineering properties have been correlated to the liquid and plastic limits, and
these Atterberg limits are also used to classify a fine-grained soil according to
the Unified Soil Classification system or AASHTO system.

Equipment:
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 Liquid limit device, Porcelain (evaporating) dish, Flat grooving tool

with gage, Eight moisture cans, Balance, Glass plate, Spatula, Wash
bottle filled with distilled water, Drying oven set at 105°C.

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21

22

Analysis:
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Liquid Limit:
(1) Calculate the water content of each of the liquid
limit moisture cans after they have been in the oven
for at least 16 hours.
(2) Plot the number of drops, N, (on the log scale)
versus the water content (w). Draw the best-fit straight
line through the plotted points and determine the
liquid limit (LL) as the water content at 25 drops.

Plastic Limit:
24
(1) Calculate the water content of each of the plastic limit

moisture cans after they have been in the oven for at least
16 hours.
(2) Compute the average of the water contents to
determine the plastic limit, PL. Check to see if the
difference between the water contents is greater than the
acceptable range of two results (2.6 %).
(3) Calculate the plasticity index, PI=LL-PL.
 Report the liquid limit, plastic limit, and plasticity index
to the nearest whole number, omitting the percent
designation.
Con’t
25

Moisture(water) content
26
 This test is performed to determine the water

(moisture) content of soils. The water content is the
ratio, expressed as a percentage, of the mass of
“pore” or “free” water in a given mass of soil to the
mass of the dry soil solids.
 The consistency of a fine-grained soil largely
depends on its water content.
 The water content is also used in expressing the
phase relationships of air, water, and solids in a
given volume of soil.

Equipment:
27
 Drying oven, Balance, Moisture can, Gloves, Spatula

Test Procedure:
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1. Record the moisture can and lid number. Determine and record the mass
of an empty, clean, and dry moisture can with its lid (MC)
2. Place the moist soil in the moisture can and secure the lid. Determine
and record the mass of the moisture can (now containing the moist soil)
with the lid (MCMS).
3. Remove the lid and place the moisture can (containing the moist soil) in
the drying oven that is set at 105 °C. Leave it in the oven overnight.
4. Remove the moisture can. Carefully but securely, replace the lid on the
moisture can using gloves, and allow it to cool to room temperature.
Determine and record the mass of the moisture can and lid (containing
the dry soil) (MCDS).
5. Empty the moisture can and clean the can and lid.
Data Analysis:
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Compaction Test
30
 Compaction is the process by which air is excluded

from a soil mass to bring the particles closer together
and thus increase its density (dry density)
 Compaction test can be:-
A. Standard compaction [proctor] test
 Standard amount of compactive effort :-3 layers and 2.5kg
hammer with 56 blows with in standard mold of diameter
101.6 fallen from 305mm height
B. Modified compaction [proctor] test
 Heavy density test 5 layers with 56 blows using 4.5kg
hammer fallen from a height of 457mm with same standard
mold diameter

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34

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CBR Test
36
 The California bearing ratio is one of the soil test used to

characterize sub-grade soil.
 California bearing ratio is the ratio of force per unit area
required to penetrate in to a soil mass with a circular
plunger of 50 mm diameter at the rate of 1.25mm/min.
 It is a simple strength test that compares the bearing
capacity of soil with that of a well- graded crushed stone.
 It was developed by the California Division of Highways
around 1930.
 Higher CBR = stronger sub-grade
 Low CBR = weak sub-grade

CBR Test
37
CBR can be
 One point CBR - standard
 Three point CBR –modified
 CBR test involves applying load to a small
penetration piston at a rate of 1.25 mm per minute

and recording the total load at penetrations
ranging from 0.64 mm up to 7.62 mm

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39

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CALCULATION OF CBR FROM LOAD PENETRATION CURVE
41
 Plot the load penetration curve in natural scale,

load on Y - axis and penetration on X – axis as
shown in Fig: 2.9.2.
 If the curve is uniformly convex upwards although
the initial portion of the curve may be concave
upwards due to surface irregularities make
correction by drawing a tangent to the upper curve
at the point of contra flexure as below

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43

.
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Factors Affecting CBR

 The compaction moisture content used and field density
achieved
 Moisture changes during service life Sub-grade
variability
 The Sequences of earthwork construction

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 The reason behind the soil sample soaked in

water for 7 days in the CBR test is given below;
 The CBR value of soil sample not immersed in water is
72.27%
 The CBR value of soil sample soaked in water for 3
days is 6.75%
 CBR value of soil sample soaked in water for seven
days is 6%

Soil Classification
46
Basically ,we have two different systems of

classification of soil for construction use
1. AASHTO system
2. USCS system
Reading Assignment

AASHTO
47

USCS
48
Unified soil classification system for

Unified soil classification system for coarse
fine grained soils
grained soils

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 Soil Plasticity chart as per Unified soil classification system

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UNBOUNDED PAVEMENT
MATERIALS

UNBOUNDED PAVEMENT MATERIALS
51
 The choice of pavement material is largely depends on the type

and cost of natural materials locally available.
 A thorough assessment of the local resources in road making
materials is essential to select the most economical pavement.
 In selecting and using natural gravels, their inherent variability must
be taken into account which requires reasonably comprehensive
characterization testing to determine representative properties.
 In circumstances where several types of base are suitable the final
choice should take into account the expected level of future
maintenance and the total cost over the expected life of the
pavement.
 The use of locally available materials is encouraged, particularly at
low traffic volumes.
Sources of Aggregate
52
 Hard rocks, sand and gravels are important sources of aggregates.

 Pulverized concrete and asphalt pavements as well as recycled and waste materials are
other sources of aggregate.
 Bedrocks are classified into igneous, sedimentary and metamorphic rock according to
their mode of formation.
 Sand or gravel deposits might be composed of different mineral particles such as
limestone, sandstone, and granite depending up on the original bedrock sources of
particles.
 The property of crushed aggregate produced in quarries from bedrock depends on the
type of bed rock.
 Igneous and metamorphic rocks are usually hard and form excellent aggregates.
 Sedimentary rocks like limestone and dolomite (softer than igneous rocks) are still used
as an aggregate for most purposes. While shale (Composed of clay grains) is very
weak which disintegrate when easily when exposed to weather and is a poor
aggregate material.

Sources and Properties of Aggregate
53
Aggregate Rock Type Strength Durability

Granite Igneous Good Good
Diabase Igneous Good Good
Limestone Sedimentary Good Fair
Sandstone Sedimentary Fair Fair
Shale Sedimentary Poor Poor
Quartzite Metamorphic Good Good
Aggregate types based on size
54
Some typical terms used in describing aggregates are:

1. Fine aggregate (Sand sizes) – aggregate particles mainly between 4.75mm (No.4) and
75NM (No. 200) in size.
2. Course aggregate (gravel sizes) – aggregate particles mainly larger than 4.75mm (No.4)
3. Pit run – aggregate from a sand or gravel pit, with no processing.
4. Crushed gravel – pit gravel (or gravel and sand) that has been put through a crusher
either to break many of the rounded gravel particles to a smaller size or to produce
rougher surfaces.
5. Crushed rock – aggregate from the crushing of bedrock. All particles are angular, not
rounded as in gravel.
6. Screenings – the chips and dust or powder that are produced in the crushing of bedrock
for aggregates.
7. Concrete Sand – sand that has been washed (usually) to remove dusts and fines.
8. Fines – silt, clay or dust particles smaller than 75Nm (No.200) usually undesirable
impurities in aggregates. Chapter 3 – Highway Materials
Particle Shape & Texture
55
 Particle Shape & Texture

Condition of aggregates
56
Bulk Specific Gravity, Dry
Apparent Specific Gravity

Properties of Aggregate
57
 Tests for Aggregate

1) Determination of the particle size distribution
 The particle size distribution shall be determined in accordance with:
 AASHTO T 27 Test Method for Sieve Analysis of Fine and Coarse Aggregates
2) Determination of the Flakiness Index
 British Standard 812, Part 105
3) Determination of the specific gravity and water absorption
 AASHTO T 85 Specific Gravity and Absorption of Coarse Aggregate
 AASHTO T 84 Specific Gravity and Absorption of Fine Aggregate
4) Determination of the moisture content
 The moisture content in the laboratory shall be determined in accordance with
AASHTO T 255 Method for Total Moisture Content of Aggregate by Drying.
Properties of Aggregate
58
 Tests for Aggregate

5) Determination of the Aggregate Crushing Value
 British Standard 812, Part 110
6) Resistance to abrasion of coarse aggregate by use of the Los Angeles

machine
 AASHTO T 96
7) Soundness of Aggregates
 AASHTO T 104

LA Abrasion (ASTM C131)
59
• Step 1. Prepare specific aggregate gradation.

Use different number of steel balls.

LA Abrasion
60

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LA Abrasion
%Loss = Original mass (g) – mass remain after test (g) * 100 %
Original mass (g)
• LAT value of good aggregates for cement, bitumen

concretes and other high pavements should be less than
30% and value up to 50% are allowed in base course.

Soundness Test
AASHTO T104
62
• The most common soundness test involves repeatedly submerging

an aggregate sample in a saturated solution of sodium or
magnesium sulfate.

Soundness Test
63
 Aggregates durability is another important

properly to measure the resistance to freezing and
toughing.
 This process is repeated for five cycles. On completion,
the percentage lost or broken down is calculated.
%Loss = Original mass – mass remain after test * 100 %

Original mass
 The average loss in weight of aggregates to be used in pavement
construction after 10 cycles shouldn't exceed 12% when tested with sodium
Sulphate and 18% when tested with magnesium Sulphate.

Aggregate Crushing Test
64
 The designed to aggregate crushing value provides

a relative measure of resistance to crushing under
gradually applied compressive load.
Aggregate crushing value = Crushed material passing 2-36mm * 100%
Original weight passing 12.5 retained 95mm
 The aggregate crushing value of good quality to be

used in base course shall not exceed 45% and that
for surface course shall be less than 30%.

Aggregate Impact Test
65
 Is designed to evaluate the toughness of stone or

the resistance of the aggregate to fracture under
repeated impacts.
Aggregate impact value = Crushed material passing 2-36mm * 100%

Original weight passing 12.5 retained 9.5mm
• The aggregate impact value should not normally

exceed 30% for aggregates to be used in wearing
course and 35 - 40% in base courses.

Flakiness and elongation index test
66
Flakiness and elongation index are measures for

shape and texture of aggregates.
• Flakiness - the % by weight of aggregate particles
whose least dimension/thickness is less than 3/5 of
their mean size.
• Elongation - the % by weight of aggregate particles
whose greatest dimension/length is greater than 1.8
times of their mean size.
• Flakiness and elongation index value of aggregates
used in road construction in excess of 15% are
generally undesirable.
Gradation
67
 Different Types
 Specifications limits e.g. AASHTO
 To Reach Desired Gradation
 Crushing
 Scalping
 Blending

AASHTO Specification
68

Theoretical Gradation
69
 Theoretical gradations generally take the following
form:
 P = 100 (d/D)x
 Where, P = percent passing
 d = size of sieve opening
 D = largest size in gradation
 The basic idea of the theory is that the amount of

material of a given size should be just sufficient to fill
the voids between aggregates of larger size
 Fuller suggested a value of 0.5 for x, however, a value
of 0.45 for x is being used in Superpave gradations.
Types of Gradations
70

Gradation Types
71
 Uniformly (Open) graded-Few
points of contact-Poor interlock
(shape dependent)-High
permeability
 Well (Dense) graded-Good

interlock-Low permeability
 Gap graded-Only limited sizes-

Good interlock-Moderate
permeability

Unbounded base and sub base material
72
 This chapter gives guidance on the selection of unbound materials for use as
base course, sub-base, capping and selected sub grade layers. The main
categories with a brief summary of their characteristics are shown in Table 3-2.
 Table 3-2: Properties of Unbound Materials (ERA)
 Notes: These specifications may be modified according to site conditions, material type and principal use.
And where GB = Granular base course, GS = Granular sub-base, GC = Granular capping layer.

Base Course Materials
73
 A wide range of materials can be used as unbound base course including

crushed quarried rock, crushed and screened, mechanically stabilized,
modified or naturally occurring “as dug” or “pit run” gravels.
 Their suitability for use depends primarily on the design traffic level of the
pavement and climate.
 However, all base course materials must have a particle size distribution
and particle shape which provide high mechanical stability and should
contain sufficient fines (amount of material passing the 0.425 mm sieve) to
produce a dense material when compacted.

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 Crushed Stone
 Graded crushed stone (GB1). This material is produced by crushing fresh, quarried
rock (GB1) and a 'crusher-run', or alternatively the material may be separated by
screening and recombined to produce a desired particle size distribution.
 Alternate gradation limits, depending on the local conditions for a particular
project, are shown in Table 3-3.
 After crushing, the material should be angular in shape with a Flakiness Index of
less than 35%, and preferably of less than 30%.
 If the amount of fine aggregate produced during the crushing operation is
insufficient, non-plastic angular sand may be used.
 In constructing a crushed stone base course, the aim should be to achieve maximum
impermeability compatible with good compaction and high stability under traffic.

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 Table 3-3: Grading Limits for Graded Crushed Stone Base Course Materials
(GB1)

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 Crushed Stone
 These are a minimum Ten Per Cent Fines Value (TFV) (BS 812, Part 111)
and limits on the maximum loss in strength following a period of 24
hours of soaking in water.
 Alternatively, requirements expressed in terms of the results of the
Aggregate Crushing Value (ACV)(BS 812, Part 110) may be used: the
ACV should preferably be less than 25 and in any case less than 29.
 Other simpler tests e.g. the Aggregate Impact Test (BS 812, Part 112)
may be used in quality control testing provided a relationship between
the results of the chosen test and the TFV has been determined.
 Unique relationships do not exist between the results of the various tests
but good correlations can be established for individual material types
and these need to be determined locally.
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 Naturally Occurring Granular materials, Boulders, Weathered Rocks
 Normal requirements for natural gravels and weathered rocks (GB2, GB3).
 A wide range of materials including lateritic, calcareous and quartzite gravels, river
gravels, boulders and other transported gravels, or granular materials resulting from
the weathering of rocks can be used successfully as base course materials.
 Table 3-4 contains three recommended particle size distributions for suitable materials
corresponding to maximum nominal sizes of 37.5 mm, 20 mm and 10 mm.

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 Table 3-4: Recommended Particle Size Distributions for Mechanically Stable Natural
Gravels and Weathered Rocks for Use as Base Course Material (GB2, GB3)

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 All grading analyses should be done on materials that have been

compacted. This is especially important if the aggregate fraction is
susceptible to breakdown under compaction and in service.
 For materials whose stability decreases with breakdown, an
aggregate hardness based on a minimum soaked Ten Per Cent Fines
Value of 50 KN may be specified.
 The fines of these materials should preferably be non-plastic but
should normally never exceed a PI of 6. If the PI approaches the
upper limit of 6, it is desirable that the fines content be restricted to
the lower end of the range. To ensure this, a maximum PP of 60 is
recommended or alternatively a maximum Plasticity Modulus (PM) of
90 where:
PM = PI x (percentage passing the 0.425 mm sieve)

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 Materials of marginal quality. Naturally occurring gravels which do not normally meet the
normal specifications for base course materials have occasionally been used successfully.
 They include lateritic, calcareous and volcanic gravels. In general their use should be
confined to the lower traffic categories unless local studies have shown that they have
performed successfully at higher levels.
 Laterite gravels with plasticity index in the range of 6-12 and plasticity modulus in the
range of 150-250 is recommended for use as base course material for T3 level of traffic
volume. The values towards higher range are valid for semi-arid and arid areas of
Ethiopia, i.e. with annual rainfall less than 500 mm.

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 The calcareous gravels, which include calcretes and marly lime stones, deserve
special mention.
 Typically, the plasticity requirements for these materials, all other things being
equal, can be increased by up to 50% above the normal requirements in the
same climatic area without any detrimental effect on the performance of
otherwise mechanically stable bases.
 Strict control of grading is also less important and deviation from a continuous
grading is tolerable.
 Cinder gravels can also be used as a base course material in lightly trafficked
surface dressed roads.

Sub Base Course Materials
82
 The sub-base is an important load spreading layer in the

completed pavement.
 It enables traffic stresses to be reduced to acceptable levels in
the sub-grade, it acts as a working platform for the construction
of the upper pavement layers and it acts as a separation layer
between sub-grade and base course.
 Under special circumstances, it may also act as a filter or as a
drainage layer.
 In wet climatic conditions, the most stringent requirements are
dictated by the need to support construction traffic and paving
equipment.

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 In these circumstances, the sub-base material needs to be more

tightly specified.
 In dry climatic conditions, in areas of good drainage, and where the
road surface remains well sealed, unsaturated moisture conditions
prevail and sub-base specifications may be relaxed.
 The selection of sub-base materials will therefore depend on the
design function of the layer and the anticipated moisture regime,
both in service and at construction.

84
 BEARING CAPACITY: -
 A minimum CBR of 30 per cent is required at the highest anticipated
moisture content when compacted to the specified field density, usually a
minimum of 95 per cent of the maximum dry density achieved in the ASTM
Test D 1557 (Heavy Compaction).
 Under conditions of good drainage and when the water table is not near
the ground surface the field moisture content under a sealed pavement will
be equal to or less than the optimum moisture content in the ASTM Test
Method D 698 (Light Compaction). In such conditions, the sub-base material
should be tested in the laboratory in an unsaturated state.
 Except in arid areas, if the base course allows water to drain into the lower
layers, as may occur with unsealed shoulders and under conditions of poor
surface maintenance where the base course is pervious, saturation of the
sub-base is likely.
85
 BEARING CAPACITY: -
 In these circumstances, the bearing capacity should be
determined on samples soaked in water for a period of four
days.
 The test should be conducted on samples prepared at the
density and moisture content likely to be achieved in the field.
 In order to achieve the required bearing capacity, and for
uniform support to be provided to the upper pavement, limits
on soil plasticity and particle size distribution may be required.
 Materials which meet the recommendations of Tables 3-5 and
3-6 will usually be found to have adequate bearing capacity.

86
 Material meeting the requirements for severe conditions will

usually be of higher quality than the standard sub-base (GS). If
materials to these requirements are unavailable, trafficking trials
should be conducted to determine the performance of alternative
materials under typical site conditions.
 In the construction of low-volume roads, local experience is often
invaluable and a wider range of materials may often be found to
be acceptable. In Ethiopia, laterite is one of the widely available
materials and can be used as a sub-base material. Laterite
meeting the gradation requirements of Table 3-6 can be used for
traffic levels up to 3x106 ESA provided the following criteria is
satisfied:

87
 Table 3-5: Recommended Plasticity Characteristics for Granular SubBases (GS)
 Table 3-6: Typical Particle Size Distribution for Sub-Bases (GS) Which Will Meet
Strength Requirements

88
 SUB-BASE AS A FILTER OR SEPARATING LAYER

 This may be required to protect a drainage layer from blockage by a finer material or to prevent migration of
fines and the mixing of two layers. The two functions are similar except that for use as a filter the material needs
to be capable of allowing drainage to take place and therefore the amount of material passing the 0.075 mm
sieve must be restricted.
 The following criteria is used to evaluate a sub base as a separating or filter layer:
a) The ratio D15(coarse layer) should be less than 5
D85(fine layer)
Where D15 is the sieve size through which 15% by weight of the material passes and D85 is the
sieve size through which 85% passes.
b) The ratio D50(coarse layer) should be less than 25
D50(fine layer)
For a filter to possess the required drainage characteristics a further requirement is:
c) The ratio D15(coarse layer) should lie between 5 and 40
D15(fine layer)
 These criteria may be applied to the materials at both the base course/sub-base and the sub-
base/subgrade interfaces.
Selected Sub-grade Materials & Capping Layers (GC)
89
 These materials are often required to provide sufficient cover on weak sub-
grades.
 They are used in the lower pavement layers as a substitute for a thick sub-base
to reduce costs, and a cost comparison should be conducted to assess their cost
effectiveness.
 As an illustrative example, approximately 30 cm of “GC” material (as
described below) placed on an S1 or S2 subgrade will allow selecting a
pavement structure as for an S3 subgrade.
 An additional 5 cm of “GC” material may allow considering an S4 subgrade
class.
 The requirements are less strict than for sub-bases.
 A minimum CBR of 15 per cent is specified at the highest anticipated moisture
content measured on samples compacted in the laboratory at the specified
field density.

Selected Subgrade Materials & Capping Layers (GC)
90
 This density is specified as a minimum of 95 % of the maximum dry density in

the ASTM Test D1557 (Heavy Compaction).
 In estimating the likely soil moisture conditions, the designer should take into
account the functions of the overlying sub-base layer and its expected moisture
condition and the moisture conditions in the subgrade.
 If either of these layers is likely to be saturated during the life of the road,
then the selected layer should also be assessed in this state.
 Recommended gradings or plasticity criteria are not given for these materials.
However, it is desirable to select reasonably homogeneous materials since
overall pavement behavior is often enhanced by this.
 The selection of materials which show the least change in bearing capacity
from dry to wet is also beneficial.

Gravel Surfaced Roads
91
 Figure 3-2. Expected Performance of Gravel Wearing Course Materials

92
 Material Characteristics: - Soils used for improved subgrade layers shall be

non-expansive, non-dispersive and free from any deleterious matter. They
shall comply with the requirements shown in Table 3-7.

93
 Performance Characteristics Of Gravel Wearing Course
 The materials for gravel wearing course should satisfy the following requirements that
are often somewhat conflicting:
 They should have sufficient cohesion to prevent raveling and corrugating (especially in dry
conditions)
 The amount of fines (particularly plastic fines) should be limited to avoid a slippery surface
under wet conditions.
 Figure 3-2 shows the effect of the Shrinkage Product (SP) and Grading Coefficient (GC)
on the expected performance of gravel wearing course materials.
 Excessive oversize material in the gravel wearing course affects the riding quality in
service and makes effective shaping of the surface difficult at the time of maintenance.

GRAVEL WEARING COURSEMATERIAL SPECIFICATION
94
 Selected material shall consist of hard durable angular particles of fragments of

stone or gravel. The material shall be free from vegetable matter and lumps or balls
of clay.
 Type 1
 The grading of the gravel after placing and compaction shall be a smooth curve
within and approximately parallel to the envelopes detailed in Table 3-3.
 The material shall have a percentage of wear of not more than 50 at 500
revolutions, as determined by AASHTO T96. The material shall be compacted to a
minimum in-situ density of 95% of the maximum dry density determined in
accordance with the requirements of AASHTO T 180. The plasticity index should
be not greater than 15 and not less than 8 for wet climatic zones and should be
not greater than 20 and not less than 10 for dry climatic zones.
 The linear Shrinkage should be in a range of 3-10%. Note that the above
gradation and plasticity requirements are only to be used with angular particles
and that crushing and screening are likely to be required in many instances for this
purpose.
95
 Type 2 & 3
 These materials may be more rounded particles fulfilling the following:
 The Plasticity Index lies in a range of 5-12% in wet areas, and in any case less
than 16% in other areas
 Use of more rounded particles may allow the use of river gravel. Trials should
nevertheless be conducted to verify whether crushing occurs under traffic or
whether crushing should be considered prior to use. Subject to trials, a minimum
percentage by weight of particles with at least one fractured face of 40%
may be considered. This requirement may also be expressed in terms of
crushing ratio.
 Except for very low traffic, the CBR should be in excess of 20 after 4 days of
soaking at 95% of maximum dry density under Heavy Compaction. For very
low traffic, the requirement may be relaxed to a CBR of 15.
96
 Type 4
 This material gradation allows for larger size material and corresponds to the
gradation of a base course material. The use of this gradation of materials is
subject to the local experience and shall be used with PIs in a range of 10-20.
 Type 5 & 6
 These materials gradations are recommended for smaller size particles. They
may be used if sanctioned by experience with plasticity characteristics as for
material Type 1.
 Type 1 gravel wearing course which is one of the best material alternatives
which shall be used on all roads which have AADTdesign greater than 50. Type 1
material shall also be used for all routine and periodic maintenance activities
for both major and minor gravel roads. Type 1 or Type 4 gravel wearing
course material may be used on new construction of roads having AADTdesign
less than 50.
97
 Table 3-8 Gradation requirements for gravel wearing course (ERA)

Blending of Aggregates
98
 Reasons for Blending

 Obtain desirable gradation
 Single natural or quarried material not enough
 Economical to combine natural and processed

materials

Blending Stockpiles
99
 Plot individual gradations

 Plot specification limits
 Can be used for initial assessment
 Can blend be made from available materials?
 Identification of critical sieves
 Establish trial proportions

Methods of Proportioning
100
 Graphical Methods
 Rothfutch’s
Method
 Graphical Methods(two aggregates)
 Analytical Method
 Trail and Error Method

Rothfuchs method
101
 The method described by Rothfuchs has been found most

useful as it is reasonably quick and simple and can be
applied to blends of any number of components. It consists
essentially of the following stages:
1. The cumulative curve of the design aggregate's particle-size
distribution is plotted, using the usual linear ordinates for
the percentage passing, but choosing the scale of sieve
sizes which allows the particle-size distribution to be
plotted as a straight line. This is readily done by drawing
an inclined straight line and marking on it the sizes
corresponding to the various percentages passing.
2. The particle-size distribution curves of the stone fractions
(including filler) to be mixed are plotted on this scale. It
will generally be found that they are not straight lines.
Rothfuchs method
102
3. With the aid of a transparent straight-edge, the

straight lines which most nearly approximate the
particle-size distribution curves of each component
are drawn. This is done by selecting for each curve a
straight line such that the areas enclosed between it
and the curve are minimal and are balanced about the
straight line.
4. The opposite ends of these straight lines are joined
together and the proportions for mixing can be read
from the points where these joining lines cross the
diagonal straight line which represents the design
grading.
Rothfuchs method
103
Problem 4.1
 The particle-size distributions of three fractions of stone and
filler available to produce the required design grading are
given in Table A1. Note that for greater accuracy a wet
particle-size analysis should be carried out on these
components.
 The design or specification grading is also given in the
Right-hand column of the table.

Rothfuchs method
104
 In Fig. the required grading of the blend is represented by the

diagonal straight line 0-0’. The vertical ordinates of the grading
sheet are graduated for percentages from 0 to 100 on a linear
scale.
 The horizontal scale for sieve aperture size is graduated by drawing
for each sieve size a vertical line which cuts the diagonal at a point
where the ordinate equals the percentage passing that sieve, i.e.
100% for 19.0 mm, 90% for 13.2 mm, 78% for 6.7 mm and so on.

Rothfuchs method
105
 The size distributions of the fractions to be mixed (A, B, C and D in the Table)
are plotted on this scale of sieve size giving lines EFO’ (fraction A), GHI
(fraction B), JKL (fraction C) and OPQ (fraction D) in Fig.
 The nearest straight lines to these size distributions are drawn with the aid of
a transparent straight-edge, by the 'minimum balanced areas' method
described above. They are the broken lines RO’, TS, VU and OW.
 The opposite ends of these lines are joined giving the chain lines RS, TU and
VW. The points where these lines cross the required distribution line
(diagonal 0-0’) are marked by the circles 1, 2 and 3.
 The proportions in which the four fractions should be mixed are obtained
from the difference between the ordinates of these points and are shown on
the right-hand side of Fig. (sections A, B, C and D).
 The theoretical particle-size distribution which will result from mixing the
fractions in these proportions is given in Table A2. Although not identical to
the design grading, it is closeChapter
enough3 – Highway Materials
for practical purposes.
Rothfuchs method
106
TA1 Particle size distribution of components
Sieve size Design of spec.

A B C D
(mm) grading
19 100 _ _ _
13.2 85 100 _ _ 100
6.7 30 90 _ _ 90
4.75 0 70 100 _ 78
2.36 0 25 95 _ 61
1.18 0 10 70 _ 45
0.6 0 0 50 100 30
0.3 0 0 30 95 22
0.15 0 0 10 80 16
0.075 0 0 0 50 12
Rothfuchs method
107
Sieve
Design of
size A B C D
spec. grading
(mm)
19 100 _ _ _
13.2 85 100 _ _ 100
6.7 30 90 _ _ 90
4.75 0 70 100 _ 78
2.36 0 25 95 _ 61
1.18 0 10 70 _ 45
0.6 0 0 50 100 30
0.3 0 0 30 95 22
0.15 0 0 10 80 16
0.075 0 0 0 50 12
Aggregate blending chart – Rothfuchs’s method

Rothfuchs method
108
TA2 Theoretical blend resulting from Rothfuchs’s method

Percentage of each 22% of 45% of 25% of
8% of D Total cumulative grading
fraction A B C
passing Retained
(mm) (mm)
19 13.2 3.3 3.3 100
13.2 6.7 12.1 4.5 16.6 96.7
6.7 4.75 6.6 9 15.6 80.1
4.75 2.36 20.25 1.25 21.5 64.5
2.36 1.18 6.75 6.25 13 43
1.18 0.6 4.5 5 9.5 30
0.6 0.3 5 0.4 5.4 20.5
0.3 0.15 5 1.2 6.2 15.1
0.15 0.075 2.5 2.4 4.9 8.9
0.075 4 4 4
Graphical Methods(two aggregates)
109
 Graphical Methods(two aggregates)

1. The percent passing the various sizes for aggregate A are plotted on the right hand
vertical scale (representing 100 % of aggregate A)
2. The percent passing the various sizes for aggregate B are plotted on the left hand
vertical scale (representing 100 % of aggregate B)
3. Connect the points common to the same size with straight lines label
4. For a particular size, indicate on the straight line when the line crosses the
specification limits measured on the vertical
5. That portion of the line between the two points represents the proportion of
aggregate A and B, measured on the horizontal scale, that will not exceed
specification limits for the particular size.
6. The portion of the horizontal scale designated by two vertical lines, when the
projected vertically, is within specification limits for all sizes and represents the limits
of proportions possible for all satisfactory blends. In this case 43 to 54 percent of
aggregate A will be meet specification when blended. From the fig. below we can
see that the percent of blended material passing the 0.60 mm and 0.075mm sieves
will be controlling values for keeping the blend within specification limits.
7. For blending, usually the midpointChapter
of that
3 – horizontal scale is selected for the blend.
Highway Materials
In this case 48 percent aggregate A and 52 percent aggregate B.
110
Example 4.2
Blend aggregate A and B in the table below to meet the specification given in same table
Sieve (mm) Spec. (%) Aggr. A Aggr. B

19 100 100 100
12.5 80-100 90 100
9.5 70-90 59 100
4.75 50-70 16 96
2.36 35-50 3.2 82
0.6 18-29 1.1 51
0.3 13-23 0 36
0.15 8-10 0 21
0.075 4-10 0 9.2

111

Bituminous /Asphalt Cement Materials
112
 Bitumen is a petroleum product obtained by the distillation of

petroleum crude
 Bitumen is a hydrocarbon material of either natural or
pyrogenous origin, found in gaseous, liquid, semisolid or solid
form
 Asphalt Cement Composition
 Composition of the asphalt influences binder behavior and
performance of the asphalt concrete
 Asphaltenes - larger, discrete solid (black) inclusions; high
viscosity component
 Resins - solid or semisolid at room temp; fluid when
heated, brittle when cold
 Oils - colorless liquid; low viscosity

113
 Production
 The portion of bituminous material present in petroleum
may widely differ depending on the source
 Almost all the crude petroleum's contain considerable
amounts of water along with crude oil
 Hence the petroleum should be dehydrated before the
distillation

114

115
Petroleum-Based Asphalts

116
 Definitions and terminology

 Asphalt or bitumen:
 The residuum produced from the distillation of crude petroleum at “atmospheric
and under reduced pressures in the presence or absence of steam”.
 Asphalt is a black or dark brown solid or viscous liquid at room temperature;
insoluble in water at 20 °C; partially soluble in aliphatic organic solvents; and
soluble in carbon disulfide, chloroform, ether, and acetone.
 Natural asphalts or natural bitumens:
 It is naturally occurring deposits of asphalt-like material.
 While these deposits have physical properties that are similar to those of
petroleum-derived asphalt, the composition is different.
 Natural asphalt deposits occur in various parts of the world, mainly as a result
of mineral oil seepage from the ground.
 The best known natural deposit is Trinidad’s Pitch Lake; asphalt deposits can
also be found in Venezuela, the Dead Sea, Switzerland, and the Athabasca oil
sands in northeastern Alberta.
117
 Asphalt cement:
 It is an asphalt that is refined to meet specifications for
paving, roofing, industrial, and special purposes.
 Asphalt cements are used mainly as binders (4–10% of
the mixture) in hot-mix asphalts and serve to hold the
aggregate together.
 Penetration-grade asphalts:
 It is asphalt that that are further processed by air-blowing,
solvent precipitation, or propane deasphalting.
 A combination of these processes may be used to produce
different grades that are classified according to their
penetration value.
118
 Cutback asphalt:
 Asphalt that is liquefied by the addition of diluents (typically petroleum
solvents).
 It is used in both paving and roofing operations, depending on whether a
paving or roofing asphalt is liquefied.
 It is further classified according to the solvent used to liquefy the asphalt
cement to produce rapid-, medium-, or slow-curing asphalt.
 Rapid-curing cutback asphalts are made by adding gasoline or naphtha and
are mainly used as surface treatments, seal coats, and tack coats.
 Medium curing cutback asphalts are made by the addition of kerosene, and
slow-curing cutback asphalts are made by the addition of diesel or other gas
oils.
 Medium- and slow-curing cutback asphalts are mainly used as surface
treatments, prime coats, tack coats, mix-in-place road mixtures, and patching
mixtures.

119
 Emulsified asphalt:
 It is a mixture of two normally immiscible components (asphalt and
water) and an emulsifying agent (usually soap).
 It is used for seal coats on asphalt pavements, built-up roofs, and other
waterproof coverings.
 Emulsified asphalts are further graded according to their setting rate
(i.e., rapid, medium, and slow).
 Rapid-setting grades are used for surface treatment, seal coating;
medium-setting grades are used for patch mixtures; and slow-setting
grades are used for mix-in-place road mixtures, patch mixtures, tack
coats, fog coats, slurry seals, and soil stabilization.
 Hot-mix asphalt:
 paving material that contains mineral aggregate coated and cemented
together with asphalt cement.

120
 Tests for Bituminous Materials

 Bituminous materials, commonly referred to as premixes,
are manufactured in asphalt mixing plants and laid hot
(hence the other used designation, “hot-mix”).
 In-situ mixing can also be used for making base courses
for lower standard roads.

121
Desirable Properties of Bitumen

 It should be fluid enough at the time of mixing to coat the aggregate
evenly by a thin film
 It should have low temperature susceptibility
 It should show uniform viscosity characteristics
 Bitumen should have good amount of volatiles in it, and it should not lose
them excessively when subjected to higher temperature
 The bitumen should be ductile and not brittle
 The bitumen should be capable of being heated to the temperature at
which it can be easily mixed without any fire hazards
 The bitumen should have good affinity to the aggregate and should not
be stripped off in the continued presence off water
122
Tests for Bituminous Materials

 Quality control tests for Bitumen  Tests for Rate of Curing
 Consistency tests  Distillation test for cutback and
 Saybolt Fural Viscosity test emulsions
 Kinematic Viscosity test  Specific gravity test
 Penetration test (PEN) on AC and  Loss on heating test
AR  Flash & Fire point test
 Float test
 Viscosity test
 Softening point test
 Viscosity on asphalt cement (AC)
 Ductility test
 Viscosity on aged residue (AR)
 Thin Film Oven test
 Solubility test
 Performance Grading

123
1. Penetration Test
 Significance
 The penetration test determine the hardness or softness of bitumen
 The bitumen grade is specified in terms of the penetration value
 30/40 and 80/100 grade bitumen are commonly used
 In hot climates lower penetration grade bitumen is preferred and vise versa
 Consistency of bitumen varies with temperature, constituents, refining process, etc.
 Viscosity is an absolute property, but could not be determined easily
 Too soft for penetration, too hard for orifice then perform float test
 Basic principle of penetration test: measurement of penetration in units of 1/10th
of a mm of a standard needle of 100 gm in a bitumen sample kept at 25°C for
5 seconds
 Higher penetration implies softer grade
124
 Penetration test for Bitumen

125
Penetration test for Bitumen

Procedure
 Heat the bitumen to softening point +90 C
0
 Pour the bitumen into the container at least 10 mm above the expected penetration
 Place all the sample containers to cool in atmospheric temperature for 1 hour
 Place the sample containers in temperature controlled water bath at a temperature

of 250 C ± 1o C for a period of 1 hour
 Fill the transfer dish with water from the water bath to cover the container
completely
 Take off the sample container from the water bath, place in transfer dish and
place under the middle of penetrometer
 Adjust the needle to make a contact with surface of the sample
 See the dial reading and release the needle exactly for 5 seconds
 Note the final reading
 Difference between the initial and final readings is taken as the penetration value
in 1/10th of mm
126
 Penetration test for Bitumen

127
 Penetration Test
 Penetration of 100g weight in 5s at 25oC (77oF)
is measured in units of 0.1 mm (e.g., 70 PEN = 7
mm penetration)
 Characteristics of Penetration Test

 Fast, simple, low cost test
 Empirical; not related to property; similar PEN values can yield wide range of
behavior;
 Effect of T not considered
128
Penetration test for Bitumen

Discussion
 Test is highly influenced by the pouring temperature, size of
needle, weight of needle, test temperature, duration of release of

needle
 High penetration grade is desirable in colder regions
 Penetration below 20 will result in cracking
 For lower penetration, bonding is difficult, but once achieved will
remain for a long time

129
 Penetration Grades
 Specifications for Asphalt Cement by Penetration Graded
 Characteristics of AC Grading
 More expensive equipment than for PEN
 More technician skill required
 Not applicable for non-Newtonian fluids
 Wide range in behaviorChapter 3 – Highway Materials
for same AC grade
130
2. Ductility Test
Significance
 The ductility of bitumen improves the physical interlocking of the
aggregate bitumen mixes
 Under traffic loads the pavement layer is subjected to repeated
deformation. The binder material of low ductility would crack and thus
provide pervious pavement surface
 The test is believed to measure the adhesive property of bitumen and
its ability to stretch
 Ductility and penetration go together, in general, but exception can
happen
 Ductility is the distance in cm to which a standard briquette of bitumen
can be stretched before the thread breaks
 Ductile materials is one which elongates when held in tension

131
 Ductility Test
 Procedure
 The bitumen sample is melted to temperature of 75oC to 100oC above the approx. softening point until it is fluid
 It is strained through IS sieve 30, poured in mould assembly and placed on a brass plate, after a solution of
glycerine or dextrine is applied over all surfaces of the mould exposed to bitumen
 Thirty to forty minutes after the sample is poured into the moulds, the plate assembly along with the sample is
placed in water bath maintained at 27oC for 30 minutes
 The sample and mould assembly are removed from water bath and excess bitumen material is cut off by leveling
the surface using hot knife
 After trimming the specimen, the mould assembly containing sample is replaced in water bath maintained at
27oC for 85 to 95 minutes
 The slides of the mould are then removed and the clips are carefully hooked on the machine without causing any
initial strain
 The pointer is set to read zero
 The machine is started and the two clips are thus pulled apart horizontally
 While the test is in operation, it is checked whether the sample is immersed in water up to a depth of at least
10mm
 The distance at which the bitumen threadChapter
breaks is3 recorded
– Highway(inMaterials
cm) and reported as ductility value
132
 Ductility Test

133
 Ductility Test

134
 Ductility Test Discussion

 Ductility of bitumen is affected by the
pouring temperature, briquette size,

placement of briquette, test
temperature, rate of pulling
 Ductility value ranges from 5-100.
Low value implies cracking. Some

minimum ductility is needed for
flexural strength
 The lack of ductility does not
necessarily indicate poor quality.

135
Ductility Test
Discussion
 Ductility of bitumen is affected by the pouring temperature,
briquette size, placement of briquette, test temperature, rate of

pulling
 Ductility value ranges from 5-100. Low value implies cracking.
Some minimum ductility is needed for flexural strength

 The lack of ductility does not necessarily indicate poor quality.

136
3. Softening Point Test

Significance
 Bitumen does not melt, but change gradually from solid to liquid
 Softening point is the temperature at which the bitumen attains
particular degree of softening under specified test conditions

 Ring and ball apparatus is used for the test

137
Softening Point Test

138

Procedure
o
 Heat the bitumen to a temperature between 125 C to 150 C
o
 Heat the rings at the same temperature on a hot plate & place on glass
plate coated with glycerin
 Fill up the rings with bitumen
 Cool for 30 minutes in air and level the surface with a hot knife
 Set the rings in the assembly and place in the bath containing distilled
water at 5oC and maintain that temperature for 15 minutes
 Place the balls on the rings and Raise the temperature uniformly at 5 oC
per minute till the ball passes trough the rings
 Note the temperature at which each of the ball and sample touches the
bottom plate of the support
 Temperature shall be recorded as the softening point of bitumen

139
 Softening Point Test

140

Discussion
 Test is affected by quality of liquid, weight of ball, rate of
heating etc
 It gives an idea of the temperature at which the bituminous
material attains a certain viscosity

 Bitumen with higher softening point is used in warmer places
 Softening point is very critical for thick films like joint and crack
fillers, to ensure they will not flow

141
4. Asphalt Cement (AC) Viscosity

 Temperature/Viscosity Relationships
 Viscosity
  = η(d/dt) for an ideally viscous material (Newtonian fluid)
 η given in units of Poise (P)
 1P = 1x10-1 Pascal sec (Pa s)
= 1 (g/cm) s
 Newtonian fluid - linear relationship
between shear stress and shear strain

rate at a given T.
 (e.g., air, ethanol, water is close)
 The slope is the viscosity

142
 Viscosity
 Water η = 1x10-3 Pa s, at room temp
 Motor oil = 1
 Asphalt = 105 to 107, at service temps
= 1, when heated
 Lava = 1011-1012

143
 Viscosity Tests (cont’d)

 The viscosity test utilizes a gravity-flow capillary viscometer.
This viscometer is mounted in a thermostatically controlled,
constant-temperature bath;
 For kinematic viscosity: 135C or 275F
 For absolute viscosity: at 60C or 140F
 With the viscometer mounted in the bath, asphalt is poured
into the large opening of the viscometer until it reaches the
filling line.
 The filled tube remains in the bath at test temperature for a
specified period of time to make sure that the tube and
asphalt are at the same temperature.

144

 A slight pressure is applied to the large opening
of the tube, or a slight vacuum to the small
opening, thus causing the asphalt to start flowing
over the siphon section just above the filling line.
 Gravity causes the asphalt to flow downward in
the vertical section of capillary tubing.

145

 A timer is started when the asphalt reaches the first
timing mark and is stopped when it reaches the
second mark.
 The time interval, multiplied by a calibration factor
for the tube, determines viscosity of the asphalt
cement in units of centistokes (Kinematic) or poises (Pa
s) (Absolute)

146

Figure : Asphalt binder temperature-viscosity relationship.
147
 Viscosity Grades
 AC grades are based on measurements of
absolute viscosity of asphalt tested at 60oC
 AR grades are based on the absolute viscosity
tested at 60oC of asphalt after being aged in a
rolling thin-film oven (RTFO)
 The viscosity grades indicate the viscosity in
hundreds of Poises ±20%.

148
 AC Grades
 Specifications for Asphalt Cement by Viscosity Grade

149
 AR Grades
 Specifications for Asphalt Cement by AR Grades
 Characteristics AR Grades
 More expensive equipment than for PEN, AC
 More technician skill required than for PEN
 Not applicable for non-Newtonian fluids
 Wide range in behavior for3 same
Chapter ARMaterials
– Highway grade
150
 Comparison of Grading Schemes

151
5. RTFO Test (ASTM D2872)

 The Rolling Thin-Film Oven -
Binder (RTFO) test is made by

placing a 50 cm3 asphalt
cement sample in a cylindrical
flat-bottomed pan 5.5” of
inside diameter and 3/8”
depth. The asphalt layer is
about 1/8” deep.

152
 RTFO Test
 The sample and container are placed on a shelf,
which rotates approximately 5 to 6 revolutions per
minute, in a ventilated oven maintained at 325oF for
5 hr. The asphalt cement is then poured into a
standard container used for the penetration test or
the viscosity test.

153
6. Performance Grade
 Research under the Strategic Highway Research Program
(SHRP)’s Superpave program lead to the introduction of
Performance Grades in 1993. Addresses concerns with earlier
grading schemes:
 PEN value does not correlate to a material property
 AC, AR grades rely on tests performed at T higher than

service T; do not reliably predict performance
 PEN and Viscosity are measured at 2 different
temperatures

154
 Summary of PG Tests

155
 Performance Grade
 PG XX-YY
 XX = 7- day maximum pavement temperature, C 52-70C in
6C increments
 YY = minimum expected pavement temperature, C in 6C
increments
 Example: PG 64-16
 Average 7-day maximum pavement temperature in summer
near 64C, and minimum pavement temperature in winter near
-16C.
 Considers rutting at high T and cracking at low T

156
 Assignment
 Specific gravity
 Loss on heating
 Flash & Fire point
 Viscosity
 Solubility

157
 Modifications to Asphalt Cement

 Cutbacks
 Allow easy placement without high T
 Emulsions
 Allow easy placement without high T, lower
toxicity/fire hazard
 Air-blown asphalt
 Less susceptible to T

158
 Cutbacks
 Volatile components are mixed with asphalt cement
to make a liquid product. After volatilization,
asphalt binder remains.
 Medium Curing (MC):
 Asphalt cement mixed with a solvent of
intermediate volatility, such as kerosene. Uses a
softer asphalt base than RC cutbacks.
 MC-30, MC-70, MC-250, MC-800, MC-3000

159
 Cutbacks
 Slow Curing (SC):
 Asphalt cement mixed with a low volatile oil/fuel.
 SC-70, SC-250, SC-800, SC-3000
 Gradation based kinematic viscosity measured at 140F.

 Ex. Viscosity of SC-800 is 800+20% centistokes

160
 Cutbacks…
 Rapid Curing (RC):
 Asphalt cement mixed with a volatile solvent, such as gasoline
or naphtha. Uses a harder asphalt base than MC cutbacks.
 RC-70, RC-250, RC-800, RC-3000

161
• Composition of cutbacks
• RC cutback asphalt is used primarily for surface treatments and tack

coat.
• MC cutbacks asphalt is typically used for prime coat, surface
treatments,
• and stockpile patching mixes.
• SC cutbacks may be used as surface spray for dust control (least
common). Chapter 3 – Highway Materials
162
Asphalt Emulsions
 Asphalt emulsions = water + asphalt + emulsifying
agent
 = suspension of asphalt in water or water in
asphalt; may be cationic, anionic, nonionic

163
 Asphalt Emulsions (cont’d)

 Some advantages:
 Like cutbacks, asphalt emulsions can be use with hot or cold
aggregate
 Unlike asphalt cements, can be used on dry, damp, or wet
aggregate
 Avoids fire and toxicity issues associated with cutbacks
 Applications include: cold in-place recycling, cold mixing, tack
coats, surface treatment, patching

Chapter 3 – Highway Materials 164
 Reading Assignment
• Portland Cement Materials
165
THANK YOU

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DEPARTMENT OF CIVIL ENGINEERING

1 Highway Engineering II (CENG 4183)

1. General, At the end of this chapter, students will be

By Haile G. December 2022

 The sub-grade is the undermost layer of a pavement and as such is one of

 Many pavement failures could be traced to insufficient consideration given

Chapter 3 – Highway Materials

 Soil is the most important foundation and construction material for

Chapter 3 – Highway Materials

 Along with traffic and economic criteria, the design of a

Chapter 3 – Highway Materials

 The results of soil investigation provide pertinent information about

 Decision of the need for sub grade or embankment foundation

 Location and design of ditches and culverts

 Selection and design of the roadway pavement

 Location and evaluation of suitable borrow and construction

 In selecting the alignment of a new highway the first step is

Chapter 3 – Highway Materials

 Before a field investigation is carried out at the site, preliminary information

 Field investigations and sample collection for laboratory tests are

 For ordinary work, it is quite sufficient to go to a depth of about 3m

 If possible, postponement of sampling until the time of construction

 Evaluation of sub grade strength in embankment areas should be

 Table 3-1 gives a recommended sampling frequency and the corresponding

Chapter 3 – Highway Materials

 The recommended approximate quantity (mass) of sample required

Chapter 3 – Highway Materials

 Table 3-2: Minimum Mass of Sample Required (Soils and Gravels)

Chapter 3 – Highway Materials

 For the purpose of taking representative samples, pits shall be dug

Chapter 3 – Highway Materials

 For new road alignments, the following tests shall

Chapter 3 – Highway Materials

 Liquid limit device, Porcelain (evaporating) dish, Flat grooving tool

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

(1) Calculate the water content of each of the plastic limit

Chapter 3 – Highway Materials

 This test is performed to determine the water

Chapter 3 – Highway Materials

 Drying oven, Balance, Moisture can, Gloves, Spatula

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

 Compaction is the process by which air is excluded

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials

 The California bearing ratio is one of the soil test used to

Chapter 3 – Highway Materials

 Three point CBR –modified

 CBR test involves applying load to a small

penetration piston at a rate of 1.25 mm per minute

Chapter 3 – Highway Materials

Chapter 3 – Highway Materials