LECTURE NO. 17 (Handout) PAVEMENTS AND BITUMINOUS MATERIALS

1
LECTURE NO. 17 (Handout)PAVEMENTS AND BITUMINOUS
MATERIALS

• Objectives
• To introduce types of pavements
• To explain various bituminous materials,
  emphasizing asphalts
• To explain properties of asphalts

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PAVEMENT Definition

• Pavement is defined as a road or highway with
  hard, smooth, and leveled surface made using a
  suitable material such as Portland cement
  concrete or asphalt concrete

Asphalt concrete pavement
Portland cement concrete pavement
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PAVEMENT Classification

• Pavements are classified as flexible or rigid
  depending on how they distribute surface loads
• Flexible pavements are those which are surfaced
  (i.e., paved) with bituminous materials such as
  asphalt concrete
• Asphalt concrete possess a lower stiffness (EI)
  than Portland cement concrete due to lower
  modulus of elasticity of asphalt concrete as
  compared to Portland cement concrete
• Due to lower stiffness of asphalt concrete the
  total structure of a flexible pavement "bends" or
  "deflects" under traffic loads. This is the logic
  behind calling such a pavement as "flexible
  pavement.
• Flexible pavements distribute the wheel load over
  a cone-shaped area under the wheel, reducing the
  imposed unit stresses as depth increases, as
  shown below

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PAVEMENT Classification----contd.

• Rigid pavements are those which are surfaced
  (i.e., paved) with Portland cement concrete
• Portland cement concrete possess a substantially
  higher stiffness (EI) than asphalt concrete due
  to higher modulus of elasticity of Portland
  cement concrete as compared to asphalt concrete
• Due to high stiffness of Portland cement concrete
  the total structure of a rigid pavement "bends"
  or "deflects" very little under traffic loads.
  This is the logic behind calling such a pavement
  as rigid pavement.
• Rigid pavements act as flexural members and
  distribute the wheel load fairly uniformly over
  the area under the pavement slab, as shown below
• Rigid pavements comprise only 7 percent of U.S.
  paved roads

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PAVEMENT Elements of flexible pavement

• A flexible pavement consists of four elements, as
  follows
• Subgrade Prepared roadbed consisting of natural
  or imported soil
• Subbase course A layer between the subgrade and
  the base course, made from materials superior to
  that of subgrade. In case of a good quality of
  subgrade, the subbase course is omitted.
• Base course This is the layer directly below the
  asphalt concrete layer and generally consists of
  aggregate (either stabilized or unstabilized).
• Surface course This is the top layer and the
  layer that comes in contact with traffic.  It may
  be composed of one or several different asphalt
  concrete sublayers.
• The above four elements of flexible pavement are
  shown below

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PAVEMENT Elements of rigid pavement

• A flexible pavement consists of four elements, as
  follows
• Subgrade Prepared roadbed consisting of natural
  or imported soil
• Subbase course This is the layer (or layers)
  under the base layer.  A subbase is not always
  needed and therefore may often be omitted .
• Base course This is the layer directly below the
  Portland cement concrete layer and generally
  consists of aggregate or stabilized subgrade.
• Surface course This is the top layer and the
  layer that comes in contact with traffic.  It
  consists of the Portland cement concrete slab.
• The above four elements of rigid pavement are
  shown below

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BITUMINOUS MATERIALS Introduction

• Bituminous material (or bitumen) is a solid,
  semisolid, or viscous cementitious material
  (i.e., binder) natural or manufactured, and
  composed of hydrocarbons
• Bitumen are usually fairly hard at normal
  temperatures. When heated, they soften and flow.
• Bitumens possess a number of properties that make
  them useful in the construction industry
• When mixed with aggregates in their hot fluid
  state, and then allowed to cool, they solidify
  and bind the aggregates together, forming a
  pavement surface.
• The most common bituminous materials are, as
  follows
• Asphalts (available as natural deposits or are
  produced from petroleum processing)
• Tars (obtained through the destructive
  distillation of materials such as wood, coal, and
  shale, i.e., by heating wood or coal or shale in
  absence of air)
• Pitches (obtained through further processing of
  tars)

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BITUMINOUS MATERIALS Classification

• Classification of bituminous materials is shown
  below

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ASPHALTS

• Asphalts are the most common and most widely used
  bituminous materials
• The term asphalt refers to a black cementitious
  material which varies widely in consistency from
  solid to semisolid at normal temperatures
• Asphalts are found as natural deposits or are
  produced from petroleum crude
• The classification of asphalts is already
  presented in the previous slide
• Natural Rock asphalts are rock deposits
  containing bituminous materials which have been
  used for road surfaces in localities where they
  occur
• Native asphalts are obtained from asphalt lakes
  in Trinidad and other Caribbean areas, these were
  used in some of the earliest pavements in North
  America
• Petroleum asphalts are products of the
  distillation of crude oil. These asphalts are
  used as the most common bituminous paving
  materials

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PETROLEUM ASPHALTS

• Petroleum asphalts are produced from the residual
  matter (i.e., impurities) present in the crude
  oil
• Higher-grade crude oil (i.e., crude oil with less
  residual matter) may contain as little as 10
  asphalt , whereas lower-grade crude oil (i.e.,
  crude oil with more residual matter) may contain
  as much as 90 asphalt
• A flow chart showing production of different
  types of asphalts are shown in the adjoining
  figure.

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TYPES OF PETROLEUM ASPHALTS

• Following types of petroleum asphalts are used in
  pavement construction
• Asphalt cement
• Emulsified asphalt
• Liquid or cutback asphalt

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TYPES OF PETROLEUM ASPHALTS Asphalt cement

• Asphalt cement (also called paving asphalt) are
  the primary asphalt products produced by the
  distillation of crude oil.
• At ambient temperatures asphalt cement is a
  black, sticky, semisolid and a highly viscous
  material
• It is strong and durable cement with excellent
  adhesive and waterproofing characteristics. It is
  also highly resistant to the action of most
  acids, alkalis and salts
• The largest use of asphalt cement is in the
  production of asphalt concrete, which is
  primarily used in the construction of flexible
  pavements throughout the world
• The asphalt cement can readily be liquefied by
  applying heat for mixing with mineral aggregates
  to produce asphalt concrete

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TYPES OF PETROLEUM ASPHALTS Asphalt
cement---contd.

• Several standard grades of asphalt cement, based
  on consistency, are available commercially.
• Two methods, viscosity and penetration are used
  to classify asphalt cements into different
  grades, as follows
• The viscosity grades based on original asphalt
  cements (AC), as specified in ASTM D3381 are AC
  5 AC 10 AC 20 AC 30 and AC 40 (The
  numerical values indicate viscosity at 140 ºF in
  hundreds of poise)
• The penetration grades, as specified in ASTM D946
  are 200-300 120-150 85-100 60-70 and 40-50
  (higher the penetration, the softer the asphalt
  cement, therefore, 40-50 is the hardest grade and
  200-300 is the softest grade

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TYPES OF PETROLEUM ASPHALTS Asphalt
cement---contd.
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TYPES OF PETROLEUM ASPHALTS Emulsified asphalt

• Emulsified asphalt (also simply called emulsion)
  is a mixture of asphalt cement, water, and
  emulsifying agent
• Because the asphalt cement will not dissolve in
  water, asphalt cement and water exist in separate
  phases as shown in the following figure
• To mix the asphalt cement with water, an
  emulsifying agent (usually a type of soap) is
  added

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TYPES OF PETROLEUM ASPHALTS Emulsified
asphalt-----contd.

• Process of manufacture of emulsified asphalt
  consists passing the hot asphalt cement and water
  containing the emulsifying agent under pressure
  through a colloid mill, as shown in the following
  figure

• The colloid mill breaks up the asphalt cement and
  disperses it, in the form of very fine droplets,
  in the water carrier
• The emulsified asphalt when used, the emulsion
  sets as the water evaporates
• The emulsion usually contains 55-75 asphalt
  cement and up to 3 emulsifying agent, with
  balance being water

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TYPES OF PETROLEUM ASPHALTS Emulsified
asphalt-----contd.

• Two most commonly used types of emulsified
  asphalts are specified in ASTM D977 and ASTM
  D2397
• Anionic electro-negatively charged asphalt
  droplets
• Cationic electro-positively charged asphalt
  droplets
• Anionic emulsions adhere better to aggregate
  particles with positive surface charges (e.g.,
  limestone)
• Cationic emulsions adhere better to aggregate
  particles with negative surface charges (e.g.,
  sandstone, quartz, siliceous gravel). Cationic
  emulsions also work better with wet aggregates
  and in colder weather
• The anionic emulsified asphalts include rapid
  setting (RS), medium setting (MS), and slow
  setting (SS), as specified in ASTM D977
• The cationic emulsified asphalts include rapid
  setting (CRS), medium setting (CMS), and slow
  setting (CSS), as specified in ASTM D2397

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TYPES OF PETROLEUM ASPHALTS Emulsified
asphalt-----contd.

• Selection and uses of emulsified asphalts are
  given in ASTM D3628. Generally, they are used as
  follows

Type of emulsified asphalts Uses
Rapid-setting Surface treatments and penetration macadam's
Medium-setting Open-graded cold asphalt-aggregate mixtures
Slow-setting Track coat, fog seal, dense-graded cold asphalt-aggregate mixtures, and slurry seals
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TYPES OF PETROLEUM ASPHALTS Liquid or cutback
asphalt

• Liquid asphalts or cutback asphalts are asphalt
  cements mixed with a solvent to reduce their
  viscosity to make them easier to use at ordinary
  temperatures
• They are commonly heated and then sprayed on
  aggregates
• Upon evaporation of the solvent, they cure or
  harden and cement the aggregate particles
  together
• Types and grades, as given below, are based on
  the type of solvent, which governs viscosity and
  the rates of evaporation and curing
• Rapid-Curing (RC). Produced by adding a light
  diluent of high volatility (generally gasoline or
  naphtha) to asphalt cement. These are used
  primarily for tack coat and surface treatments.
  Specifications for RC type given in ASTM
  D2028.
• Medium-Curing (MC). Produced by adding a medium
  diluent of intermediate volatility (generally
  kerosene) to asphalt cement. These are generally
  used for prime coat, stockpile patching mixtures,
  and road-mixing operations. Specifications for
  MC type given in ASTM D2027.
• Slow-Curing (SC). Produced by adding oils of low
  volatility (generally diesel or other gas oils)
  to asphalt cement. They are also called road
  oils. They are generally used for prime coat,
  stockpile-patching mixtures, and as dust
  palliatives. Specifications for SC type given
  in ASTM D2026.

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TYPES OF PETROLEUM ASPHALTS Liquid or cutback
asphalt------contd.

• Cutback asphalts are commercially available in
  different grades, as shown in the following Fig.
• The thinnest and most fluid grade is designated
  by the suffix number 30, which is available in MC
  type only

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TYPES OF PETROLEUM ASPHALTS Liquid or cutback
asphalt------contd.

• Emulsified asphalts are increasingly being used
  in lieu of cutback asphalts for the following
  reasons
• Environmental regulations Emulsions are
  relatively pollution free
• Loss of high-energy products When cutback
  asphalts cure, the diluents which are high
  energy, high price products are wasted into
  atmosphere
• Safety Emulsions are safe to use
• Lower application temperature Emulsions can be
  applied at relatively low temperatures saving the
  fuel costs. Emulsions can also be applied
  effectively to a damp pavement, whereas dry
  conditions are required for cutback asphalts

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PROPERTIES OF ASPHALTS

• Following are the properties of asphalt that are
  of great importance in pavement design and
  construction
• Consistency
• Specific gravity
• Ductility
• Purity
• Flash point
• Rate of curing
• Aging or hardening
• Resistance to reaction with water
• Durability

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PROPERTIES OF ASPHALTSConsistency

• Consistency describes the degree of fluidity of
  asphalt cement at any particular temperature
• Consistency of asphalt cement is measured in
  terms of viscosity and penetration values
• Softening point is also measured to determine the
  temperature at which an asphalt changes its phase
  from solid to liquid

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PROPERTIES OF ASPHALTSConsistency Viscosity

• Viscosity is a measure of the resistance to flow
  and is the fundamental consistency measurement in
  absolute units
• There are many methods to measure the viscosity
• Absolute viscosity (in Pa-s or poise, 1 poise
  0.1 Pa-s) measured at 140 ºF, as per the ASTM
  D2171 specifications
• Kinematic viscosity (in cm2/s or stoke, 1 stoke
  100 centistokes 1 cm2/s) measured as per the
  ASTM D2170 specifications
• kinematic viscosity absolute viscosity/density
• Viscosity decreases (i.e. materials become more
  fluid) as temperature increases
• A very viscous fluid is very thick

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PROPERTIES OF ASPHALTSConsistency
Viscosity----contd.

• Following figure illustrates typical
  temperature-viscosity relationships for asphalts

• Grades of asphalt materials and temperatures at
  which they are used depend to a great extent on
  their viscosity
• Plant temperatures for mixing asphalt-paving
  materials are usually specified in terms of
  viscosity
• Temperature limits corresponding to viscosities
  of 1.5 to 3.0 cm2/s (150 to 300 centistokes) are
  sometimes used
• For example, the plant temperatures for
  heating the asphalts A, B, and C (as shown in the
  figure) will respectively be in the following
  ranges corresponding to viscosities of 150 to 300
  centistokes 153 ºC to 167 ºC 148 to 163 ºC and
  137 ºC to 149 ºC.

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PROPERTIES OF ASPHALTSConsistency Penetration

• Penetration test (ASTM D5) is used to measure the
  consistency of asphalt empirically (i.e.,
  indirectly)
• Penetration is the consistency of asphalt
  expressed as the distance in tenths of a
  millimeter that a standard needle penetrates a
  sample of asphalt vertically under standard
  conditions of loading (100 g), time (5 seconds),
  and temperature (77 F), as shown in figure below

Asphalt cements have an upper limit on
penetration value of 300 (i.e., 30 mm)
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PROPERTIES OF ASPHALTSConsistency Softening
point

• Softening point is measured by ring and ball (R
  B) method in accordance with ASTM D36, as shown
  in the following figure

Softening point can simply be defined as the
temperature at which asphalt cement cannot
support the weight of a steel ball and starts
flowing.
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PROPERTIES OF ASPHALTSSpecific gravity

• Specific gravity and density of asphalt can be
  determined using the procedure described in ASTM
  D70.
• Since the volume of asphalt changes with
  temperature (with the change from semisolid to
  liquid state), the specific gravity of asphalt is
  expressed at a given temperature (usually at 77
  F or 60 F)
• Petroleum asphalts have specific gravity values
  close to unity (0.95 1.05)
• Specific gravity of asphalt decreases with
  increasing temperature. For example, asphalt
  cement has a specific gravity of 1.0176 at a
  temperature of 10 F, 1.0 at 60 F, and 0.9187
  at 300 F.
• A knowledge of specific gravity is essential to
  determine the percentage of voids in a compacted
  material. Also, its measurement is required to
  convert the volume measurement of asphalt to the
  units of mass

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PROPERTIES OF ASPHALTSDuctility

• Ductility test is performed on the asphalt cement
  samples in accordance with ASTM D113.
• Ductility test measures the distance in
  centimeters that a standard briquette of asphalt
  cement will stretch (_at_ 5 cm/min at 77 F) before
  breaking, as shown in the following figure

• Ductility is sometimes used as an indirect gage
  of adhesion and cohesion of asphalt
• Adhesion is the ability to stick to aggregate
  particles in the asphalt concrete
• Cohesion is the ability to hold the aggregate
  particles firmly in place

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PROPERTIES OF ASPHALTSPurity

• Refined asphalt cements consist of almost pure
  bitumen, which by definition is entirely soluble
  in carbon disulfide. Only very little amounts of
  impurities are generally present in refined
  asphalt cements
• To determine the purity of asphalt cement, a
  solubility test is conducted in accordance with
  ASTM D2042

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PROPERTIES OF ASPHALTSFlash point

• If asphalt cement is heated to a high enough
  temperature, it gives off enough vapor to flash
  (ignite) in presence of spark or open flame
• Flash point is the temperature below that of the
  fire point, which is the temperature where a
  material combusts.
• Flash point test is conducted in accordance with
  ASTM D92 to indicate the temperature to which
  asphalt cement may be safely heated without the
  danger of instantaneous flash in the presence of
  an open flame

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PROPERTIES OF ASPHALTSRate of curing

• The process of evaporation of solvents from
  cutback asphalts, and the attendant thickening of
  the material, is called curing.
• Curing can also be described as the change in
  consistency of an asphalt due to the progressive
  loss of diluents by evaporation
• The rate of curing, or the time required for a
  cutback asphalt to harden (from its original
  liquid consistency) and develop a consistency
  that is satisfactory for the function as a binder
  in pavements is an important property of cutback
  asphalts
• The rate of curing is influenced by the following
  factors
• Volatility or evaporation rate of the solvent
• The amount of solvent
• Penetration (or viscosity) of the asphalt base
• Temperature and humidity of the environment
• Wind velocity
• Surface area of the pavement

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PROPERTIES OF ASPHALTSAging or hardening

• Aging or hardening is the process under which
  asphalt becomes harder and brittle due to
  increase in the viscosity of asphalt caused by
• the evaporation and oxidation of the lighter,
  oily constituents during mixing at high
  temperatures, called volatilization (short-term
  aging or hardening)
• the oxidation of the oils to resins and resins to
  asphaltenes when used over a period of years
  (long-term or in-service aging or hardening)

Durability of pavement is adversely affected by
aging
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PROPERTIES OF ASPHALTSResistance to action of
water

• Asphalt materials designed for pavements should
  be able to withstand the effects of water
• The durability of the pavement is greatly
  affected by the ability of asphalt to adhere to
  aggregate particles in the presence of water
• Loss of bond in the presence of water may lead to
  pavement deterioration

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PROPERTIES OF ASPHALTSDurability

• Durability can be defined as the property that
  permits a pavement material to withstand the
  detrimental effects of moisture, air, and
  temperature.
• The performance and durability of an asphaltic
  pavement are affected by a number of factors,
  including mix design, properties of aggregates,
  workmanship, and the properties of the asphalt.
• Asphalt pavements fail or crack due to three main
  causes
• Permanent deformation or rutting occurring at
  high temperatures as the asphalts softens and the
  mix loses elasticity
• Fatigue cracking due to high volume of load
  applications and aging of the asphalt
• Low-temperature cracking as asphalt becomes
  brittle and the pavement shrinks in cold weather