AsphaltEngr. Ahmad Sameer NawabKardan University
Contents• Asphalt• Etymology• Chemistry• Geological origin• Modern usage
Asphalt• Asphalt is a sticky, black and highly viscous liquid or semi-solid formof petroleum.• It may be found in natural deposits or may be a refined product.• it is a substance classed as a pitch.• Until the 20th century, the term asphaltum was also used.• The terms asphalt and bitumen are often used interchangeably tomean both natural and manufactured forms of the substance
Note• The terms bitumen and asphalt are mostly interchangeable, exceptwhere asphalt is used as an abbreviation for asphalt concrete.• This article uses "asphalt/bitumen" where either term is acceptable.• The terms asphalt and bitumen are often used interchangeably tomean both natural and manufactured forms of the substance.• In American English, asphalt (or asphalt cement) is the carefullyrefined residue from the distillation process of selected crude oils.• Outside the United States, the product is often called bitumen.• Geological terminology often prefers the term bitumen.• Common usage often refers to various forms of asphalt/bitumen as"tar", such as at the La Brea Tar Pits.• Another term, mostly archaic, refers to asphalt/bitumen as "pitch".• The pitch used in this mixture is sometimes found in natural depositsbut usually made by the distillation of crude oil.
Terms• The viscosity of a fluid is a measure of its resistance to gradualdeformation by shear stress or tensile stress.• For liquids, it corresponds to the informal notion of "thickness". Forexample, honey has a higher viscosity than water.• Viscosity is due to friction between neighboring parcels of the fluidthat are moving at different velocities• Petroleum is a naturally occurring flammable liquid consisting of acomplex mixture of hydrocarbons of various molecular weights andother liquid organic compounds, that are found in geologicformations beneath the Earths surface
Terms• Pitch is a name for any of a number of viscoelastic, solid polymers.• Pitch can be made from petroleum products or plants.• Petroleum-derived pitch is also called bitumen or asphalt.• Pitch produced from plants is also known as resin.• The viscoelastic Property• Tar pitch is a viscoelastic polymer.• This means that even though it seems to be solid at roomtemperature and can be shattered with a hard impact, it is actuallyfluid and will flow over time, but extremely slowly
Etymology• The word asphalt is derived from the late Middle English, in turnfrom French asphalte, based on Late Latinasphalton, asphaltum, which is the latinisation of the Greekἄσυαλτος (ásphaltos, ásphalton), a word meaning"asphalt/bitumen/pitch.
Etumology• Modern usage• In British English, the word asphalt is used to refer to a mixture ofmineral aggregate and asphalt/bitumen (also called tarmac incommon parlance).• The earlier word asphaltum is now archaic and not commonly used.• In American English, asphalt is equivalent to the British bitumen.However, asphalt is also commonly used as a shortened form ofasphalt concrete (therefore equivalent to the British asphalt ortarmac)
Chemistry• The substance is completely soluble in carbon disulfide, andcomposed primarily of a mixture of highly condensed polycyclicaromatic hydrocarbons.• it is most commonly modeled as a colloid, with asphaltenes as thedispersed phase and maltenes as the continuous phase (thoughthere is some disagreement amongst chemists regarding itsstructure).• It is almost impossible to separate and identify all the differentmolecules of asphalt, because the number of molecules withdifferent chemical structure is extremely large.• Most natural bitumens contain sulfur and several heavymetals, such asnickel, vanadium, lead, chromium, mercury, arsenic, selenium, andother toxic elements.
Chemistry• Bitumens can provide good preservation of plants and animalfossils.• Asphalt/bitumen can sometimes be confused with "tar", which is asimilar black, thermoplastic material produced by the destructivedistillation of coal.• During the early and mid-20th century when town gas wasproduced, tar was a readily available product and extensively usedas the binder for road aggregates.• The addition of tar to macadam roads led to the word tarmac, whichis now used in common parlance to refer to road-making materials.• However, since the 1970s, when natural gas succeeded towngas, asphalt/bitumen has completely overtaken the use of tar inthese applications.
Chemistry• Natural deposits of asphalt/bitumen include lakes such as the PitchLake in Trinidad and Tobago and Lake Bermudez inVenezuela, Gilsonite, the Dead Sea, asphalt/bitumen-impregnatedsandstones known as bituminous rock and the similar "tar sands".• Asphalt/bitumen can be separated from the other components incrude oil (such as naphtha, gasoline and diesel) by the process offractional distillation, usually under vacuum conditions.• A better separation can be achieved by further processing of theheavier fractions of the crude oil in a de-asphalting unit, which useseither propane or butane in a supercritical phase to dissolve thelighter molecules which are then separated.• Further processing is possible by "blowing" the product: namelyreacting it with oxygen.• This makes the product harder and more viscous.
Chemistry• Asphalt/bitumen is typically stored and transported at temperaturesaround 150°C (300°F).• Sometimes diesel oil or kerosene are mixed in before shipping toretain liquidity; upon delivery, these lighter materials are separatedout of the mixture.• This mixture is often called "bitumen feedstock", or BFS.• Some dump trucks route the hot engine exhaust through pipes inthe dump body to keep the material warm.• The backs of tippers carrying asphalt/bitumen, as well as somehandling equipment, are also commonly sprayed with a releasingagent before filling to aid release.• Diesel oil is no longer used as a release agent due to environmentalconcerns.
Geological origin• Naturally occurring deposits of asphalt/bitumen are formed from theremains of ancient, microscopic algae (diatoms) and other once-living things.• These remains were deposited in the mud on the bottom of theocean or lake where the organisms lived.• Under the heat (above 50 °C) and pressure of burial deep in theearth, the remains were transformed into materials such asasphalt/bitumen, kerogen, or petroleum.• Deposits at the La Brea Tar Pits are an example.• There are structural similarities between asphalt/bitumen and theorganic matter in carbonaceous meteorites.• However, detailed studies have shown these materials to be distinct.
Modern usage• The primary use of asphalt/bitumen is in road construction, where itis used as the glue or binder mixed with aggregate particles tocreate asphalt concrete.• Its other main uses are for bituminous waterproofingproducts, including production of roofing felt and for sealing flatroofs.
Modern Use• Rolled asphalt concrete• The largest use of asphalt/bitumen is for making asphalt concrete forroad surfaces and accounts for approximately 85% of the asphaltconsumed in the United States.• Asphalt concrete pavement material is commonly composed of 5%asphalt/bitumen cement and 95% aggregates (stone, sand, andgravel).• Due to its highly viscous nature, asphalt/bitumen cement must beheated so it can be mixed with the aggregates at the asphalt mixingplant.• Asphalt concrete paving is widely used in airports around the world.• Due to the sturdiness and ability to be repaired quickly, it is widelyused for runways dedicated to aircraft landing and taking off.
Modern Use• Mastic asphalt• Is a type of asphalt which differs from dense graded asphalt (asphaltconcrete) in that it has a higher asphalt/bitumen (binder)content, usually around 7–10% of the whole aggregate mix, asopposed to rolled asphalt concrete, which has only around 5%added asphalt/bitumen.• This thermoplastic substance is widely used in the building industryfor waterproofing flat roofs and tanking underground.• Mastic asphalt is heated to a temperature of 210 °C (410 °F) and isspread in layers to form an impervious barrier about 20 millimeters(0.8 in) thick.
Modern Use• Asphalt Emulsion• A number of technologies allow asphalt/bitumen to be mixed atmuch lower temperatures.• These involve mixing with petroleum solvents to form "cutbacks"with reduced melting point, or mixtures with water to turn theasphalt/bitumen into an emulsion.• Asphalt emulsions contain up to 70% asphalt/bitumen and typicallyless than 1.5% chemical additives.• There are two main types of emulsions with different affinity foraggregates, cationic and anionic.• Asphalt emulsions are used in a wide variety of applications.• Chipseal involves spraying the road surface with asphalt emulsionfollowed by a layer of crushed rock, gravel or crushed slag.
Modern Use• Asphalt Emulsion• Slurry seal involves the creation of a mixture of asphalt emulsionand fine crushed aggregate that is spread on the surface of a road.• Cold-mixed asphalt can also be made from asphalt emulsion tocreate pavements similar to hot-mixed asphalt, several inches indepth and asphalt emulsions are also blended into recycled hot-mixasphalt to create low-cost pavements.
Modern Use• Asphalt/bitumen is used to make Japan black, a lacquer knownespecially for its use on iron and steel.• Asphalt/bitumen also is used in paint and marker inks by somegraffiti supply companies (primarily Molotow) to increase theweather resistance and permanence of the paint and/or ink, and tomake the color much darker.• Asphalt/bitumen is also used to seal some alkaline batteries duringthe manufacturing process.• Lacquer• In a general sense, lacquer is a somewhat imprecise term for a clear orcoloured wood finish that dries by solvent evaporation.• It is also often a curing process as well that produces a hard, durable finish
Modern Use• Petroleum production, alternatives and bioasphalt• Naturally occurring crude Asphalt/bitumen impregnated insedimentary rock is the prime feed stock for petroleum productionfrom "Oil sands“.• currently under development in Alberta, Canada. Canada has mostof the worlds supply of natural asphalt/bitumen, covering 140,000square kilometers (an area larger than England).• Asphalt/bitumen can now be made from nonpetroleum-basedrenewable resources such as sugar, molasses and rice, corn andpotato starches.• Asphalt/bitumen can also be made from waste material by fractionaldistillation of used motor oils, which is sometimes disposed byburning or dumping into landfills.
Modern Use• Nonpetroleum-based asphalt/bitumen binders can be made light-colored. Lighter-colored roads absorb less heat from solarradiation, and have less surface heat than darker surfaces, reducingtheir contribution to the urban heat island effect.
Terms• Oil sands, tar sands or, more technically, bituminous sands, area type of unconventional petroleum deposit.• The oil sands are loose sand or partially consolidated sandstonecontaining naturally occurring mixtures of sand, clay, andwater, saturated with a dense and extremely viscous form ofpetroleum technically referred to as bitumen (or colloquially tar dueto its similar appearance, odour and colour).• Molasses is a viscous by-product of the refining ofsugarcane, grapes, or sugar beets into sugar.• Starch or amylum is a carbohydrate consisting of a large number ofglucose units joined by glycosidic bonds.• This polysaccharide is produced by all green plants as an energystore. It is the most common carbohydrate in the human diet and iscontained in large amounts in such staple foods aspotatoes, wheat, maize (corn), rice, and cassava.
Terms• Fractional distillation• is the separation of a mixture into its component parts, orfractions, such as in separating chemical compounds by their boilingpoint by heating them to a temperature at which one or morefractions of the compound will vaporize.• It is a special type of distillation.• Generally the component parts boil at less than 25 °C from eachother under a pressure of one atmosphere (atm).• If the difference in boiling points is greater than 25 °C, a simpledistillation is used.
Engr. Ahmad Sameer NawabKardan University2013Civil Engineering Faculty
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