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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 The natural bitumen was coal tar with volatile oils. The oils would evaporate to set the asphalt Sidewalks in Brooklyn (1865) were first major use of asphalt concrete in US. The first pavements were in Newark, NJ (1870).

3 Sources of “Natural” Asphalt Cement
è Natural asphalts are refined by nature Trinidad Lake asphalt very hard, mined commercially Washington, DC 1870’s Gilsonite in Utah 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 Tar comes from the destructive distilling of coal, wood, shale to form “pitch” and then adding the distilled non-volitle Asphaltine provide the body of AC Resin provide the adhesion and ductility Oil provides the viscosity and flow As oils evaporate, AC stiffens. Resins age by oxidizing (loss of ductility and adhesion) All properties tend toward pure asphaltine as AC ages.

5 Composition of Asphalt Cement
è Large organic molecules of varying size and polarity Carbon 80 - 87% Nitrogen 1% Hydrogen 9 11% Sulfur 0.5 7% Oxygen 2 8% Heavy metals 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

6 Refinery Operation Lighter molecules vaporize Asphalt cement remains
FIELD STORAGE TANKS PUMPING STATION LIGHT DISTILLATE HEAVY ASPHALT CEMENTS STORAGE TOWER DISTILLATION RESIDUAL CONDENSERS AND COOLERS TUBE HEATER MEDIUM OIL WELL SOLVENTS GASOLENE JET FUEL LUBRICANTS HEATING OIL Lighter molecules vaporize Asphalt cement remains Residual varies in consistency 3 types of petroleum asphaltic crude (Texas heavy crude) paraffin crude (Saudi light crude) Mixed crude

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 70C to 150C viscous liquid -20C to 70C viscoelastic solid < -20C brittle solid

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 Cut with water Slow cure (diesel oil), Med. Cure (kerosene), Fast cure (gas or naptha)

10 Emulsions Asphalt Binder Liquefied with Water
- è Water - reduces viscosity è Emulsifier gives surface charge to asphalt droplets suspended in water medium Anionic Water Asphalt Binder Ÿ Negative charge Ÿ Alkaline (Basic) aggregate Ÿ Good with limestones (positive charge) Cationic Ÿ Positive charge Ÿ Acidic aggregate Ÿ Good with silica gravels (negative charge) è Consistency controlled by amount of water è Stability controlled by choicer of emulsifier è Environmentally correct

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 Adhesion: property to stick to aggregate particles (property to connect dissimilar materials) Cohesion: ability to stick particles together (property to connect similar materials)

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. Abs. Viscosity is measured by drawing a material through a tube with a controlled vacuum. Kinetic viscosity is determined by using a rotating viscometer. Penetration is distance a 1mm needle under a constant 100g load penetrates a 25C materia in 5 seconds, expressed in 0.1mm, e.g. 11mm = 110 pen Examples of viscosity: Water Poises Diesel Poises 50 SAE Oil 10 Poises (liquid) Soft tar 1000 Poises (semi-liquid) 300 pen AC Poises (semi-solid) 15 pen AC 100,000,000 Poises (solid)

13 Performance-Graded Asphalt Binders
Maximum Temperature ( ºC) Minimum Temperature ( PG 46 - 34 40 46 PG 52 10 16 22 28 PG 58 - 16 22 28 34 40 PG 64 10 PG 70 PG 76 PG 82 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.

14 Selection of Grading Temperatures
- 28 22 16 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. Pavement Air Temperature Maximum 7 day (Running Average)

15 Alternative Grading System
Grade Viscosity Abs., Poises Kinetic, cStokes Penetration Flash Point °C AC-2.5 250 125 220 163 AC-5 500 175 140 177 AC-10 1000 80 219 AC-20 2000 300 60 232 AC-30 3000 350 50 AC-40 4000 400 40

16 Asphalt and 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 Short-term Loadings 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 Traffic Associated Fatigue Rutting

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 Rutting Fatigue Cracking 5 - 15 m Fatigue Cracking Moisture Damage? Thermal Cracking

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

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