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Asphalt and Asphalt Concrete. History Asphalt and Tar Material Engineered Asphalt Cements Hot-mixed asphalt Cutbacks Emulsions Properties of Asphalt. 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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asphalt and asphalt concrete
Asphalt and Asphalt Concrete
  • History
  • Asphalt and Tar Material
  • Engineered Asphalt Cements
    • Hot-mixed asphalt
    • Cutbacks
    • Emulsions
  • Properties of Asphalt
history
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
slide3

Sources of “Natural” Asphalt Cement

Natural asphalts are refined by nature

è

Trinidad Lake asphalt

è

very hard, mined commercially

§

Washington, DC 1870’s

§

Gilsonite in Utah

è

very hard, mined commercially

§

contains fine sand

§

Rock asphalt Kentucky, Texas

è

sandstone impregnated with asphalt

§

“Tar“ sands

è

in Canada (Athabasca)

§

La Brea “tar” pits in California

§

bitumen and asphalt
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/H>0.8)
    • Resin (0.8>C/H>0.6)
    • Oil (C/H < 0.6)
  • Specific Gravity = 0.95 – 1.05
slide5

Composition of Asphalt Cement

Large organic molecules of varying size and polarity

è

Carbon

80

-

87%

Nitrogen

0

-

1%

Hydrogen

9

-

11%

Sulfur

0.5

-

7%

Oxygen

2

-

8%

Heavy metals

0

-

0.5%

Heavy metals play important role

Asphaltenes

Contribute to polarity

§

Resins

Molecular structure very complex

è

Oils

Asphaltenes

-

largest and most polar

§

Resins

-

intermediate, also polar

§

Oils

-

smallest, paraffin

-

like, non

-

polar

§

Colloidal model

è

Asphaltenes surrounded by resins

§

Oils continuous medium

§

slide6

Refinery Operation

OIL WELL

FIELD STORAGE TANKS

LIGHT

SOLVENTS

DISTILLATE

GASOLENE

PUMPING

MEDIUM

STATION

DISTILLATE

JET FUEL

HEAVY

LUBRICANTS

DISTILLATE

TOWER

DISTILLATION

HEATING OIL

RESIDUAL

ASPHALT

CEMENTS

STORAGE

CONDENSERS

TUBE

AND

HEATER

Lighter molecules vaporize

COOLERS

Asphalt cement remains

Residual varies in consistency

asphalt characterization
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
engineered asphalt cement
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
slide10

Water

Asphalt

Binder

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

properties of asphalt cement
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
flow properties
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.
slide13

Performance-Graded Asphalt Binders

Maximum

Temperature

ºC)

Minimum Temperature (

(

ºC)

PG 46

-

34

-

40

-

46

-

10

-

16

-

22

-

28

-

34

-

40

-

46

PG 52

PG 58

-

16

-

22

-

28

-

34

-

40

PG 64

-

10

-

16

-

22

-

28

-

34

-

40

PG 70

-

10

-

16

-

22

-

28

-

34

-

40

PG 76

-

10

-

16

-

22

-

28

-

34

PG 82

-

10

-

16

-

22

-

28

-

34

As an example, a PG 64

-

28 is acceptable for use in a

climatic region where the maximum temperature is

64°C and the minimum temperature is

-

28°C.

slide14

Selection of Grading Temperatures

Pavement

Air Temperature

Temperature

Maximum 7

-

day

(Running Average)

Temperature

-

28

-

22

-

16

64 70 76 82

Given that the minimum measured air temperature for a site is

-

21°C and

the maximum 7

-

day average temperature is 73°C, which PG grade should

Here, use PG 76

-

22.

be used for this site.

asphalt and asphalt concrete16
Asphalt and Asphalt Concrete
  • Asphalt Concrete
    • Aggregates
    • Properties
  • Pavements
  • Mixture Design
asphalt concrete
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
acc importance of aggregate
ACC: Importance of Aggregate
  • Asphalt cement has no strength at temperatures > 60C
  • Stability of pavements in hot weather is due to internal friction in the aggregates
asphalt concrete mixtures
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
asphalt concrete20
Asphalt Concrete
  • Flexibility
    • high binder content
    • low viscosity binder
  • Short-term Loadings
    • elastic properties of binder-aggregate matrix
asphalt concrete21
Asphalt Concrete
  • Long-term Durability
    • fluid properties of binder
    • dry clean aggregates
    • water causes “stripping”
    • strong porous angular stone
    • durable aggregates (LA abrasion)
asphalt concrete22
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)
pavement section
Pavement Section

ACC Surface

ACC Base

Granular Subbase

Subgrade

asphalt pavement distress
Asphalt Pavement Distress

Cracking

Traffic Associated Fatigue

Rutting

asphalt concrete applications
Asphalt Concrete Applications
  • Roofing,
    • slurry
    • composition shingles
  • Sealants
    • waterproofing for foundations, etc
    • electrical insulation
asphalt concrete applications26
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
asphalt concrete applications27
Asphalt Concrete Applications
  • Cutbacks (on the way out)
    • RC - flash point in 27°C !!!
      • hard base (hot regions)
    • MC - safer
      • softer base (cold regions)
    • SC - “Road Oils”
      • rural roads, sealants
slide28

Primary Distress Modes HMA Pavements

Rutting

Rutting

Fatigue Cracking

Fatigue Cracking

5

-

15 m

Moisture Damage?

Thermal Cracking

slide29

Temperature Regimes where Distress Predominates

Low

-

temperature thermal

Plexiglas

Shrinkage cracking

Intermediate

-

temperature

Salt Water

traffic

-

associated fatigue

Consistency

Taffy

Molasses

High

-

temperature

rutting

-

25

0

25

50

75

°

Approximate Temperature,

C