Asphalt and Asphalt Concrete History Asphalt and Tar

Asphalt and Asphalt Concrete History Asphalt and Tar Material Engineered Asphalt Cements n n n 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 è Natural asphalts are refined by nature è Trinidad Lake asphalt § very hard, mined commercially § Washington, DC 1870’s è Gilsonite in Utah § very hard, mined commercially § contains fine sand è Rock asphalt Kentucky, Texas § sandstone impregnated with asphalt è “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 n Coal tar, asphalt (processed oil residue) Asphalt (combination of asphaltine, resin, oil) n n n 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 è 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 è Oils § Asphaltenes - largest and most polar § Resins - intermediate, also polar § Oils - smallest, paraffin -like, non -polar è 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 (135 C) Complex Shear Modulus: dynamic shear rheometer Flexural Creep: bending beam rheometer measure creep stiffness Tensile Strength

Engineered Asphalt Cement Hot mixed asphalt (pavements) n n Viscous semi-solid Flows for heating into liquid range Cutback asphalt n n Viscous liquid Cut with oil distillates Emulsion asphalt n n Viscous liquid Cut with water

- Asphalt Binder Liquefied with Water Emulsions è Water - reduces viscosity è Emulsifier gives surface charge to asphalt droplets suspended in water medium Water § Anionic ŸNegative charge Asphalt ŸAlkaline (Basic) aggregate Binder ŸGood with limestones (positive charge) § Cationic ŸPositive charge ŸAcidic aggregate ŸGood with silica gravels (negative charge) è Consistency controlled by amount of water è Stability controlled by choicer of emulsifier è Environmentally correct

Properties of Asphalt Cement Adhesion: property to connect dissimilar materials Cohesion: property to connect similar materials n n n 3 M 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 n Absolute Viscosity, poises n Kinetic Viscosity, centistokes Penetration: n 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 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -40 PG 70 -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 Flash Point °C Kinetic, c. Stokes 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-40 400 40 232

Asphalt and Asphalt Concrete n n Aggregates Properties Pavements Mixture Design

Asphalt Concrete Aggregates n n n 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 > 60 C Stability of pavements in hot weather is due to internal friction in the aggregates

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

Asphalt Concrete Long-term Durability n n n 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. n n poor compaction leads to deformation and the permeability of water and air. temperature affects workability Strength n n high viscosity binder crushed stone aggregates (interlock)

Pavement Section ACC Surface ACC Base Granular Subbase Subgrade

Asphalt Pavement Distress Cracking Traffic Associated Fatigue Rutting

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

Asphalt Concrete Applications Pavements n Hot Mixed Asphalt Cement w (asphaltine, resin) Emulsions (repairs, small jobs) n n moist or dry aggregates hot or cold applications no fuel or solvents anionic or cationic

Asphalt Concrete Applications Cutbacks (on the way out) n RC - flash point in 27°C !!! w hard base (hot regions) n MC - safer w softer base (cold regions) n SC - “Road Oils” w 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