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 Oxygen 9-11% 2-8% Sulfur Heavy metals 0.5 -7% 0-0.5% Heavy metals play important role  Contribute to polarity  Molecular structure very complex  Asphaltenes - largest and most polar   Oils - smallest, paraffin -like, non -polar  Colloidal model  Resins - intermediate, also polar Asphaltenes surrounded by resins  Oils continuous medium Asphaltenes Resins Oils

Refinery Operation

OIL WELL FIELD STORAGE TANKS TOWER DISTILLATION PUMPING STATION LIGHT DISTILLATE MEDIUM DISTILLATE HEAVY DISTILLATE SOLVENTS GASOLENE JET FUEL LUBRICANTS HEATING OIL STORAGE TUBE HEATER RESIDUAL ASPHALT CEMENTS CONDENSERS AND COOLERS

Lighter molecules vaporize Asphalt cement remains Residual varies in consistency

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

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

 Water - reduces viscosity  Emulsifier gives surface charge to asphalt droplets suspended in water medium  Anionic  Negative charge  Alkaline (Basic) aggregate  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 Water Asphalt Binder

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: measure of fluidity at a given temperature  Absolute Viscosity, poises  

shear shear

_ _

stress



poises rate

 0 .

1

Pa



s

  Kinetic Viscosity, centistokes    Absolute viscosity

density



g

/

cm

3  Penetration: empirical measure of ease to penetration Penetration of 1 mm diameter needle.

Performance-Graded Asphalt Binders Maximum Temperature ( ºC) PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82 -10 -10 -10 -10 -10 Minimum Temperature (ºC) -16 -16 -16 -16 -16 -16 -22 -22 -22 -22 -22 -22 -28 -28 -28 -28 -28 -28 -34 -34 -34 -34 -34 -34 -34 -40 -40 -40 -40 -40 -46 -46 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 Air Temperature Maximum 7 -day (Running Average) -28 -22 -16 Temperature 64 70 76 82 Given that the minimum measured air temperature for a site is °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 AC-2.5

AC-5 AC-10 AC-20 AC-30 AC-40 Viscosity Abs., Poises Kinetic, cStokes 250 500 1000 2000 3000 4000 125 175 250 300 350 400 Penetration Flash Point °C 220 163 140 80 177 219 60 50 40 232 232 232

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

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

-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

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 5 - 15 m Thermal Cracking Moisture Damage?

Temperature Regimes where Distress Predominates Plexiglas Salt Water Taffy Molasses Low-temperature thermal Shrinkage cracking Intermediate-temperature traffic-associated fatigue High-temperature rutting -25 0 25 50 75 Approximate Temperature,  C