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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. 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

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  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 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 §

  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 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 §

  6. 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

  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

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. Alternative Grading System

  15. Asphalt and Asphalt Concrete • Asphalt Concrete • Aggregates • Properties • Pavements • Mixture Design

  16. 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

  17. 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

  18. 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

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

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

  21. 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)

  22. Pavement Section ACC Surface ACC Base Granular Subbase Subgrade

  23. Asphalt Pavement Distress Cracking Traffic Associated Fatigue Rutting

  24. Asphalt Concrete Applications • Roofing, • slurry • composition shingles • Sealants • waterproofing for foundations, etc • electrical insulation

  25. 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

  26. 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

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

  28. 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

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