Presentation on theme: "Asphalt and Asphalt Concrete"— Presentation transcript:
1Asphalt and Asphalt Concrete HistoryAsphalt and Tar MaterialEngineered Asphalt CementsHot-mixed asphaltCutbacksEmulsionsProperties of Asphalt
2History3500 B.C. natural bitumen used to line reservoirs by the GreeksFirst US asphalt in NY and NJAutomobile drove the ACC industryThe natural bitumen was coal tar with volatile oils. The oils would evaporate to set the asphaltSidewalks in Brooklyn (1865) were first major use of asphalt concrete in US. The first pavements were in Newark, NJ (1870).
3Sources of “Natural” Asphalt Cement èNatural asphalts are refined by natureTrinidad Lake asphaltvery hard, mined commerciallyWashington, DC 1870’sGilsonite in Utahcontains fine sandRock asphalt Kentucky, Texassandstone impregnated with asphalt“Tar“ sandsin Canada (Athabasca)La Brea “tar” pits in California
4Bitumen and AsphaltBitumen: non-volatile hydrocarbon, soluble in carbon disulfide, very complex material structureCoal 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 – 1.05Tar comes from the destructive distilling of coal, wood, shale to form “pitch” and then adding the distilled non-volitleAsphaltine provide the body of ACResin provide the adhesion and ductilityOil provides the viscosity and flowAs oils evaporate, AC stiffens.Resins age by oxidizing (loss of ductility and adhesion)All properties tend toward pure asphaltine as AC ages.
5Composition of Asphalt Cement èLarge organic molecules of varying size and polarityCarbon80-87%Nitrogen1%Hydrogen911%Sulfur0.57%Oxygen28%Heavy metals0.5%Heavy metals play important roleContribute to polarityMolecular structure very complexAsphalteneslargest and most polarResinsintermediate, also polarOilssmallest, paraffinlike, nonpolarColloidal modelAsphaltenes surrounded by resinsOils continuous mediumAsphaltenesResinsOils
6Refinery Operation Lighter molecules vaporize Asphalt cement remains FIELD STORAGE TANKSPUMPINGSTATIONLIGHTDISTILLATEHEAVYASPHALTCEMENTSSTORAGETOWERDISTILLATIONRESIDUALCONDENSERSANDCOOLERSTUBEHEATERMEDIUMOIL WELLSOLVENTSGASOLENEJET FUELLUBRICANTSHEATING OILLighter molecules vaporizeAsphalt cement remainsResidual varies in consistency3 types of petroleumasphaltic crude (Texas heavy crude)paraffin crude (Saudi light crude)Mixed crude
7Asphalt Characterization Flash Point: temperature at which a substance will ignite with a open flameRolling 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 rheometerFlexural Creep: bending beam rheometer measure creep stiffnessTensile Strength
870C to 150C viscous liquid-20C to 70C viscoelastic solid< -20C brittle solid
9Engineered Asphalt Cement Hot mixed asphalt (pavements)Viscous semi-solidFlows for heating into liquid rangeCutback asphaltViscous liquidCut with oil distillatesEmulsion asphaltCut with waterSlow cure (diesel oil), Med. Cure (kerosene), Fast cure (gas or naptha)
10Emulsions Asphalt Binder Liquefied with Water -èWater-reduces viscosityèEmulsifier gives surface charge to asphalt droplets suspendedin water mediumAnionicWaterAsphaltBinderŸNegative chargeŸAlkaline (Basic) aggregateŸGood with limestones (positive charge)CationicŸPositive chargeŸAcidic aggregateŸGood with silica gravels (negative charge)èConsistency controlled by amount of waterèStability controlled by choicer of emulsifierèEnvironmentally correct
11Properties of Asphalt Cement Adhesion: property to connect dissimilar materialsCohesion: property to connect similar materials3M scotch tape is adhesive, not cohesiveSilly putty is cohesive, not adhesiveAsphalt is adhesive and cohesiveAdhesion: property to stick to aggregate particles (property to connect dissimilar materials)Cohesion: ability to stick particles together (property to connect similar materials)
12Flow propertiesConsistency: measure of fluidity at a given temperatureAbsolute Viscosity, poisesKinetic Viscosity, centistokesPenetration: empirical measure of ease to penetrationPenetration 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 penExamples of viscosity:Water PoisesDiesel Poises50 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)
13Performance-Graded Asphalt Binders MaximumTemperature(ºC)Minimum Temperature (PG 46-344046PG 5210162228PG 58-1622283440PG 6410PG 70PG 76PG 82As an example, a PG 64-28 is acceptable for use in aclimatic region where the maximum temperature is64°C and the minimum temperature is-28°C.
14Selection of Grading Temperatures -282216Given that the minimum measured air temperature for a site is21°C andthe maximum 7day average temperature is 73°C, which PG grade shouldbe used for this site.Here, use PG 7622.PavementAir TemperatureMaximum 7day(Running Average)
15Alternative Grading System GradeViscosityAbs., Poises Kinetic, cStokesPenetrationFlash Point°CAC-2.5250125220163AC-5500175140177AC-10100080219AC-20200030060232AC-30300035050AC-40400040040
16Asphalt and Asphalt Concrete AggregatesPropertiesPavementsMixture Design
17Asphalt 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
18ACC: Importance of Aggregate Asphalt cement has no strength at temperatures > 60CStability of pavements in hot weather is due to internal friction in the aggregates
19Asphalt Concrete Mixtures Mixtures of aggregate and asphalt cement binderabout 95% aggregate by weightabout 75% aggregate by volumeideally, 3-5% air voids
20Asphalt Concrete Flexibility Short-term Loadings high binder content low viscosity binderShort-term Loadingselastic properties of binder-aggregate matrix
21Asphalt Concrete Long-term Durability fluid properties of binder dry clean aggregateswater causes “stripping”strong porous angular stonedurable aggregates (LA abrasion)
22Asphalt ConcreteWorkability: Ease in which material is handled and laid and compacted.poor compaction leads to deformation and the permeability of water and air.temperature affects workabilityStrengthhigh viscosity bindercrushed stone aggregates (interlock)