Asphalt and Asphalt Concrete

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Asphalt and Asphalt Concrete

• History
• Asphalt and Tar Material
• Engineered Asphalt Cements
• Hot-mixed asphalt
• Cutbacks
• Emulsions
• Properties of Asphalt

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History

• 3500 B.C. natural bitumen used to line reservoirs
  by the Greeks
• First US asphalt in NY and NJ
• Automobile drove the ACC industry

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Bitumen and Asphalt

• Bitumen non-volatile hydrocarbon, soluble in
  carbon disulfide, very complex material structure
• Coal tar, asphalt (processed oil residue)
• Asphalt (combination of asphaltine, resin, oil)
• Asphaltine (C/Hgt0.8)
• Resin (0.8gtC/Hgt0.6)
• Oil (C/H lt 0.6)
• Specific Gravity 0.95 1.05

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Asphalt Characterization

• Flash Point temperature at which a substance
  will ignite with a open flame
• Rolling Thin-Film Oven indicator of the aging
  effect of short term high temperatures when
  producing ACC.
• Viscosity rotational viscometer measures the
  viscosity at a standard temperature (135C)
• Complex Shear Modulus dynamic shear rheometer
• Flexural Creep bending beam rheometer measure
  creep stiffness
• Tensile Strength

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Engineered Asphalt Cement

• Hot mixed asphalt (pavements)
• Viscous semi-solid
• Flows for heating into liquid range
• Cutback asphalt
• Viscous liquid
• Cut with oil distillates
• Emulsion asphalt
• Viscous liquid
• Cut with water

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Emulsions Asphalt Binder Liquefied with Water
-
Water
-
reduces viscosity
è
Emulsifier gives surface charge to asphalt
droplets suspended
è
in water medium
Anionic

Negative charge
Ÿ
Alkaline (Basic) aggregate
Ÿ
Good with limestones (positive charge)
Ÿ
Cationic

Positive charge
Ÿ
Acidic aggregate
Ÿ
Good with silica gravels (negative charge)
Ÿ
Consistency controlled by amount of water
è
Stability controlled by choicer of emulsifier
è
Environmentally correct
è
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Properties of Asphalt Cement

• Adhesion property to connect dissimilar
  materials
• Cohesion property to connect similar materials
• 3M scotch tape is adhesive, not cohesive
• Silly putty is cohesive, not adhesive
• Asphalt is adhesive and cohesive

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Flow properties

• Consistency measure of fluidity at a given
  temperature
• Absolute Viscosity, poises
• Kinetic Viscosity, centistokes
• Penetration empirical measure of ease to
  penetration
• Penetration of 1 mm diameter needle.

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As an example, a PG 64
-
28 is acceptable for use in a
climatic region where the maximum temperature is
64C and the minimum temperature is
-
28C.
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Alternative Grading System
Grade Viscosity Abs., Poises Kinetic, cStokes Viscosity Abs., Poises Kinetic, cStokes Penetration Flash Point C
AC-2.5 250 125 220 163
AC-5 500 175 140 177
AC-10 1000 250 80 219
AC-20 2000 300 60 232
AC-30 3000 350 50 232
AC-40 4000 400 40 232
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Asphalt and Asphalt Concrete

• Asphalt Concrete
• Aggregates
• Properties
• Pavements
• Mixture Design

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Asphalt Concrete

• Aggregates
• clean and dry aggregates are necessary for
  adhesion (no dust, no water)
• interlocking nature creates internal friction
  which is important to the long-term properties of
  the asphalt concrete.
• angular shape aggregates 50-80 with 2 angular
  faces

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ACC Importance of Aggregate

• Asphalt cement has no strength at temperatures gt
  60C
• Stability of pavements in hot weather is due to
  internal friction in the aggregates

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Asphalt Concrete Mixtures

• Mixtures of aggregate and asphalt cement binder
• about 95 aggregate by weight
• about 75 aggregate by volume
• ideally, 3-5 air voids

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Asphalt Concrete

• Flexibility
• high binder content
• low viscosity binder
• Short-term Loadings
• elastic properties of binder-aggregate matrix

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Asphalt Concrete

• Long-term Durability
• fluid properties of binder
• dry clean aggregates
• water causes stripping
• strong porous angular stone
• durable aggregates (LA abrasion)

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Asphalt Concrete

• Workability Ease in which material is handled
  and laid and compacted.
• poor compaction leads to deformation and the
  permeability of water and air.
• temperature affects workability
• Strength
• high viscosity binder
• crushed stone aggregates (interlock)

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Pavement Section
ACC Surface
ACC Base
Granular Subbase
Subgrade
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Asphalt Pavement Distress
Cracking
Traffic Associated Fatigue
Rutting
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Asphalt Concrete Applications

• Roofing,
• slurry
• composition shingles
• Sealants
• waterproofing for foundations, etc
• electrical insulation

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Asphalt Concrete Applications

• Pavements
• Hot Mixed Asphalt Cement
• (asphaltine, resin)
• Emulsions (repairs, small jobs)
• moist or dry aggregates
• hot or cold applications
• no fuel or solvents
• anionic or cationic

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Asphalt Concrete Applications

• Cutbacks (on the way out)
• RC - flash point in 27C !!!
• hard base (hot regions)
• MC - safer
• softer base (cold regions)
• SC - Road Oils
• rural roads, sealants

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Primary Distress Modes HMA Pavements
Rutting
Rutting
Fatigue Cracking
Fatigue Cracking
5
-
15 m
Moisture Damage?
Thermal Cracking
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Temperature Regimes where Distress Predominates
Low
-
temperature thermal
Plexiglas
Shrinkage cracking
Intermediate
-
temperature
Salt Water
traffic
-
associated fatigue
Consistency
Taffy
High
-
temperature
Molasses
rutting
-
25
75
50
25
0

Approximate Temperature,
C