Highway Material

1
Transportation Engineering - I
Highway Material . Dr. Attaullah Shah
2
Types of Roadway material

• Currently, there are two primary types of
  pavement surfaces Portland cement concrete
  (PCC) and hot-mix asphalt concrete (HMAC).
• Below this wearing course are material layers
  that provide structural support for the pavement
  system. These may include either (a) the
  aggregate base and sub base layers, or (b)
  treated base and sub base layers, and the
  underlying natural or treated subgrade. The
  treated layers may be cement-treated,
  asphalt-treated or lime-treated for additional
  structural support.
• There are various methods by which pavement
  layers are designed. For example, HMAC may be
  designed using the Marshall, Hveem, or Superpave
  mix design systems. PCC may be designed using the
  American Concrete Institute (ACI) or the Portland
  Cement Association (PCA) method.

3
Hot-Mix Asphalt Concrete

• HMAC consists primarily of mineral aggregates,
  asphalt cement (or binder), and air.
• It is important to have suitable proportions of
  asphalt cement and aggregates in HMAC so as to
  develop mixtures that have desirable properties
  associated with good performance.
• These performance measures include the resistance
  to the three primary HMAC distresses permanent
  deformation, fatigue cracking, and low
  temperature cracking.
• Permanent deformation refers to the plastic
  deformation of HMAC under repeated loads. This
  permanent deformation can be in the form of
  rutting (lateral plastic flow in the wheel paths)
  or consolidation (further compaction of the HMAC
  after construction).
• Aggregate interlock is the primary component that
  resists permanent deformation with the asphalt
  cement playing only a minor role. Angular,
  rough-textured aggregates will help reduce
  permanent deformation. To a significantly lesser
  extent, a stiffer asphalt cement may also provide
  some minor benefit.

4

• Cracking can be subdivided into two broad
  categories load associated cracking and non-load
  associated cracking. Load associated cracking has
  traditionally been called fatigue cracking. In
  this scenario, repeated stress applications below
  the maximum tensile strength of the material
  eventually lead to cracking.
• Factors associated with the development of
  fatigue cracking include the in-situ properties
  of the structural section, asphalt cement,
  temperature, and traffic.
• Non-load associated cracking has traditionally
  been called low-temperature cracking. During
  times of rapid cooling and low temperatures, the
  stress experienced by the HMAC may exceed its
  fracture strength. This leads to immediate
  cracking.

5
Aggregates Specification and test

• Traditional aggregate specifications for HMA
  include the American Association of State Highway
  and Transportation Officials (AASHTO) M29 (ASTM
  D1073) Standard Method of Test for Fine
  Aggregate for
• Bituminous Paving Mixtures,
• ASTM D692 Standard Specification for Coarse
  Aggregate for Bituminous Paving Mixtures, and
• ASTM D242 Standard Specification for Mineral
  Filler for Bituminous Paving Mixtures.
• The quality of aggregates depend on the
  following
• coarse aggregate angularity
• fine aggregate angularity
• flat, elongated particles, and
• clay content

6
Asphalt Cement Specification and Tests

• Penetration Grading System
• ASTM D946 Standard Specification for
  Penetration-Graded Asphalt Cement for Use in
  Pavement Construction
• This specification includes five penetration
  grades ranging from a hard asphalt graded at
  40-50 to a soft asphalt cement graded at
  200-300. The sections below discuss the tests
  used to classify penetration grades
• Following tests conducted to classify the
  penetration grades
• Penetration Test AASHTO T49 (ASTM D5) Standard
  Method of Test for Penetration of Bituminous
  Mixtures In this procedure, a needle is
  typically loaded with a 100-g weight and allowed
  to penetrate into an asphalt cement sample for 5
  sec. Prior to conducting the test, the asphalt
  cement sample is brought to the testing
  temperature, typically 258C (778F).
• Flash Point Test (ASTM D92) Standard Method of
  Test for Flash and Fire Points by Cleveland Open
  Cup In this procedure, a brass cup partially
  filled with asphalt cement is heated at a given
  rate. A flame is passed over the surface of this
  cup periodically and the temperature at which
  this flame causes an instantaneous flash is
  reported as the flash point.

7

• Ductility Test Ductility is the number of
  centimeters a standard briquette of asphalt
  cement will stretch before breaking.
• This property is determined using AASHTO T51
  (ASTM D113) Standard Method of Test for
  Ductility of Bituminous Mixtures (AASHTO, 2003).
• Solubility Test Solubility is the percentage of
  an asphalt cement sample that will dissolve in
  trichloroethylene. This property is determined
  using AASHTO T44 (ASTM D2042) Standard Method of
  Test for Solubility of Bituminous Materials
  (AASHTO, 2003).
• Thin-Film Oven Test The TFO test is used to
  approximate the effect of short-term aging during
  the mixing process. This test is conducted using
  AASHTO T179 (ASTM D1754) Standard Method of Test
  for Effect of Heat and Air on Asphalt Materials
  (Thin-Film Oven Test) (AASHTO, 2003).
• Absolute and Kinematic Viscosity Tests Viscosity
  can be defined as a fluids resistance to flow.
  In the asphalt paving industry, two tests are
  used to measure viscosity absolute and
  kinematic viscosity tests. Absolute viscosity is
  determined using AASHTO T202 (ASTM D2171)
  Standard Method of Test for Viscosity of Asphalt
  by Vacuum Capillary Viscometer (AASHTO, 2003).
  Kinematic viscosity is determined using AASHTO
  T201 (ASTM D2170) Standard Method of Test for
  Kinematic Viscosity of Asphalts (Bitumen)
  (AASHTO, 2003).

8
(No Transcript)
9
Design of Hot-Mix Asphalt Concrete

• Mix design method named after Marshall. AASHTO
  adopted this mix design procedure as AASHTO R-12
  Standard Recommended Practice for Bituminous
  Mixture Design Using the Marshall and Hveem
  Procedures
• Step 1. Aggregate Evaluation
• Step 2. Asphalt Cement Evaluation
• Step 3. Preparation of Marshall Specimens
• Prepare the Marshall specimens in accordance to
  the requirements set in AASHTO R-12. Compact
  three replicate specimens at five asphalt
  contents.
• Step 4. Marshall Stability and Flow
• Step 5. Density and Void Analysis
• Step 6. Tabulating and Plotting Test Results
• Step 7. Optimum Asphalt Content Determination

10
Emulsified and Cutback Asphalts

• Asphalt cement can be emulsified with an
  emulsifying agent and water to form asphalt
  emulsions or dissolved in suitable petroleum
  solvents to form cutback asphalts.
• Cutback asphalts consist primarily of asphalt
  cement and a solvent. The speed at which they
  cure is related to the volatility of the solvent
  (diluent) used.
• Cutbacks made with highly volatile solvents will
  cure faster as the solvent will evaporate more
  quickly. Conversely, cutbacks made with less
  volatile solvents will cure slower as the solvent
  will evaporate slower.
• The standard practice for selecting cutback
  asphalts is covered in ASTM D2399 Standard
  Practice for Selection of Cutback Asphalts
  (ASTM, 2003)
• Asphalt Emulsions Asphalt emulsions consist
  primarily of asphalt cement, water, and an
  emulsifying agent. They should be stable enough
  for pumping, mixing, and prolonged storage.

11
Pavement Distresses and Performance

• These distresses could be developed due to
  traffic load repetitions, temperature, moisture,
  aging, construction practice, or combinations.
• Fatigue Cracking are a series of longitudinal
  and interconnected cracks caused by the repeated
  applications of wheel loads. This type of
  cracking generally starts as short longitudinal
  cracks in the wheel path and progress to an
  alligator cracking pattern (interconnected
  cracks) as shown in Figure. This type of distress
  will
  eventually lead to a loss of the structural
  integrity
• of pavement system.
• Rutting Rutting is defined as permanent
  deformation in the
  wheel path as shown in Figure.Rutting can occur
  due to (a) unstable HMA, (b) densification of
  HMA, (c) deep settlement in the subgrade.

12
(No Transcript)
13
Traffic Flow

• Complex between vehicles and drivers, among
  vehicles
• Stochastic variability in outcome, cannot
  predict with certainty
• Theories and models
• Macroscopic aggregate, steady state
• Microscopic disaggregate, dynamics
• Human factor driver behavior

14
Speed (v)

• Rate of motion
• Individual speed
• Average speed
• Time mean speed
• Arithmetic mean
• Space mean speed
• Harmonic mean

15
Individual Speed
(1)
Spot Speed
16
Time Mean Speed
Mile post
Observation Period
17
Space Mean Speed
Observation Distance
Observation Period
18
Volume (q)

• Number of vehicles passing a point during a given
  time interval
• Typically quantified by Rate of Flow (vehicles
  per hour)

19
Volume (q)
20
Density (k)

• Number of vehicles occupying a given length of
  roadway
• Typically measured as vehicles per mile (vpm),
• or vehicles per mile per lane (vpmpl)

21
Density (k)
22
Density (k)
23
Spacing (s)

• Front bumper to front bumper distance between
  successive vehicles

S1-2
S2-3
24
Headway (h)

• Time between successive vehicles passing a fixed
  point

T3sec
T0 sec
h1-23sec
25
Spacing and Headway
spacing
headway
26
Spacing and Headway
What are the individual headways and the average
headway measured at location A during the 25 sec
period?
A
27
Spacing and Headway
What are the individual headways and the average
headway measured at location A during the 25 sec
period?
A
h1-2
h2-3
28
Lane Occupancy

• Ratio of roadway occupied by vehicles

L1
L2
L3
D
29
Clearance (c) and Gap (g)

• Front bumper to back bumper distance and time

Clearance (ft) or Gap (sec)
Spacing (ft) or headway (sec)