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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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Presentation on theme: "Asphalt and Asphalt Concrete History Asphalt and Tar Material Engineered Asphalt Cements Hot-mixed asphalt Cutbacks Emulsions Properties of Asphalt."— Presentation transcript:

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

2 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

3 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

4 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

5 Composition of Asphalt Cement  Large organic molecules of varying size and polarity Carbon80-87%Nitrogen0-1% Hydrogen9-11%Sulfur0.5-7% Oxygen2-8%Heavy metals0-0.5% Heavy metals play important role  Contribute to polarity  Molecular structure very complex  Asphaltenes-largest and most polar  Resins-intermediate, also polar  Oils-smallest, paraffin-like, non-polar  Colloidal model  Asphaltenes surrounded by resins  Oils continuous medium Asphaltenes Resins Oils

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7 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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9 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

10 Emulsions Asphalt Binder Liquefied 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

11 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

12 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.

13 As an example, a PG is acceptable for use in a climatic region where the maximum temperature is 64°C and the minimum temperature is-28°C.

14 Selection of Grading Temperatures Temperature 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 Pavement Temperature Air Temperature Maximum 7-day (Running Average)

15 Alternative Grading System GradeViscosity Abs., Poises Kinetic, cStokes PenetrationFlash Point °C AC AC AC AC AC AC

16 Asphalt and Asphalt Concrete Asphalt Concrete Aggregates Properties Pavements Mixture Design

17 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

18 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

19 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

20 Asphalt Concrete Flexibility high binder content low viscosity binder Short-term Loadings elastic properties of binder-aggregate matrix

21 Asphalt Concrete Long-term Durability fluid properties of binder dry clean aggregates water causes “stripping” strong porous angular stone durable aggregates (LA abrasion)

22 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)

23 Pavement Section ACC Surface ACC Base Granular Subbase Subgrade

24 Asphalt Pavement Distress Cracking Rutting Traffic Associated Fatigue

25 Asphalt Concrete Applications Roofing, slurry composition shingles Sealants waterproofing for foundations, etc electrical insulation

26 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

27 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

28 Primary Distress Modes HMA Pavements Rutting Fatigue Cracking 5-15 m Thermal Cracking Moisture Damage?

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


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