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
Sources of “Natural” Asphalt Cement
 Natural asphalts are refined by nature
 Trinidad Lake asphalt
 very hard, mined commercially
 Washington, DC 1870’s
 Gilsonite in Utah
 very hard, mined commercially
 contains fine sand
 Rock asphalt Kentucky, Texas
 sandstone impregnated with asphalt
 “Tar“ sands
 in Canada (Athabasca)
 La Brea “tar” pits in California
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
Composition of Asphalt Cement
 Large organic molecules of varying size and polarity
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

Oils
 Asphaltenes - largest and most polar
 Resins - intermediate, also polar
 Oils - smallest, paraffin -like, non -polar
 Colloidal model
 Asphaltenes surrounded by resins
 Oils continuous medium
Refinery Operation
OIL WELL
FIELD STORAGE TANKS
LIGHT
DISTILLATE
PUMPING
STATION
MEDIUM
DISTILLATE
HEAVY
DISTILLATE
TOWER
DISTILLATION
TUBE
HEATER
GASOLENE
JET FUEL
LUBRICANTS
HEATING OIL
RESIDUAL
STORAGE
SOLVENTS
CONDENSERS
AND
COOLERS
ASPHALT
CEMENTS
Lighter molecules vaporize
Asphalt cement remains
Residual varies in consistency
Asphalt Characterization
Flash Point:
open flame
temperature at which a substance will ignite with a
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
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
- Asphalt Binder Liquefied with Water
Emulsions
 Water - reduces viscosity
 Emulsifier gives surface charge to asphalt droplets suspended
in water medium
Water
 Anionic
 Negative charge
Asphalt
 Alkaline (Basic) aggregate
Binder
 Good with limestones (positive charge)
 Cationic
 Positive charge
 Acidic aggregate
 Good with silica gravels (negative charge)
 Consistency controlled by amount of water
 Stability controlled by choicer of emulsifier
 Environmentally correct
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
Consistency:

Absolute Viscosity, poises


measure of fluidity at a given temperature
shear _ stress
 poises  0.1Pa  s 
shear _ rate
Kinetic Viscosity, centistokes
Absolute viscosity

density g / cm3 
Penetration:

empirical measure of ease to penetration
Penetration of 1 mm diameter needle.
Performance-Graded Asphalt Binders
Maximum
Temperature
(ºC)
Minimum Temperature (ºC)
PG 46
PG 52
PG 58
-10
PG 64
-34
-40
-46
-46
-16
-22
-28
-34
-40
-16
-22
-28
-34
-40
-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.
Selection of Grading Temperatures
Pavement
Temperature
-28 -22 -16
Air Temperature
Maximum 7 -day
(Running Average)
Temperature
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
be used for this site. Here, use PG 76 -22.
Alternative Grading System
Grade
Viscosity
Abs., Poises
Penetration
Kinetic, cStokes
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
Asphalt and Asphalt Concrete
Asphalt Concrete


Aggregates
Properties
Pavements
Mixture Design
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
Asphalt cement has
no strength at
temperatures > 60C
Stability of
pavements in hot
weather is due to
internal friction in
the aggregates
Modulus, Pa
ACC: Importance of Aggregate
-40
-20
0
20
Temperature, C
40
60
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 Concrete
Flexibility


high binder content
low viscosity binder
Short-term Loadings

elastic properties of binder-aggregate
matrix
Asphalt Concrete
Long-term Durability





fluid properties of binder
dry clean aggregates
water causes “stripping”
strong porous angular stone
durable aggregates (LA abrasion)
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
ACC Surface
ACC Base
Granular Subbase
Subgrade
Asphalt Pavement Distress
Consistency
Cracking
Traffic Associated Fatigue
Rutting
-40
-20
0
20
Temperature, C
40
60
Asphalt Concrete Applications
Roofing,


slurry
composition shingles
Sealants


waterproofing for foundations, etc
electrical insulation
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 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
Primary Distress Modes HMA Pavements
Rutting
5 - 15 m
Thermal Cracking
Fatigue Cracking
Moisture Damage?
Temperature Regimes where Distress Predominates
Low-temperature thermal
Shrinkage cracking
Salt Water
Taffy
Molasses
Consistency
Plexiglas
Intermediate-temperature
traffic-associated fatigue
High-temperature
rutting
-25
0
25
50
75
Approximate Temperature, C