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PART ONE Bituminous Pavements and Surfaces Bituminous pavements and surfaces are composed of compacted aggregate and bitumen. The aggregate transmits the load from the surface to the base, takes the abrasive wear of traffic, and provides a nonskid surface. The bitumen (bituminous binder) holds the aggregate together, prevents the displacement and loss of aggregate, and provides a waterproof cover for the base. Bituminous surfaces— ã Are particula
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  Bituminous Materials 1-1 PART ONE Bituminous Pavements and Surfaces Bituminous pavements and surfaces are composed of compacted aggregate andbitumen. The aggregate transmits the load from the surface to the base, takes theabrasive wear of traffic, and provides a nonskid surface. The bitumen (bituminousbinder) holds the aggregate together, prevents the displacement and loss ofaggregate, and provides a waterproof cover for the base.Bituminous surfaces—ã Are particularly adaptable to stage construction because engineers can addcourses to existing pavement for reinforcement if the load or the amount oftraffic increases.ã Are flexible, allowing for slight adjustments due to subgrade settlement withoutdetrimental effects.ã Provide a resilient, waterproof medium that protects the base from water andtraffic.ã Are less affected by temperature changes than concrete.ã Resist wear, weathering, and deterioration.ã Are highly versatile and meet temporary, expedient, and light trafficrequirements where concrete is unjustifiable.ã Lack measurable beam action to carry loads over weak spots in the subbase.(The subbase must have an adequate, uniform bearing strength; and the basemust have adequate thickness, bearing capacity, and cohesion.)Bituminous pavements are comparable to concrete pavements and are designed tocarry heavy traffic volume and heavy loads on highways, roads, streets, and airfields. Chapter 1 Bituminous Materials Asphalt pavements are composed of asphalt and aggregate. Asphalt-concrete pavement is the highest quality asphalt pavement. It consists ofwell-graded aggregate and asphalt cement (AC) that are heated andblended together in exact proportions at a hot-mix plant.  FM 5-4361-2 Bituminous Materials TYPESOF BITUMEN 1-1. Asphalt and tar bitumens are used in road and airfield construction. (See FM 5-472  for field identification of tar and asphalt paving compounds.) ASPHALT 1-2. Asphalt is a natural or man-made by-product of petroleum distillation.Natural asphalt is found in nature, either as lake (pit) or rock asphalt:ã  Lakeasphalt. It is formed when crude oil seeps to the surface of theearth and lighter fractions (volatile materials) are driven off by thea ction of sun a nd wind. La rge deposits of la ke a spha lt exist inTrinidad and Venezuela.ã  Rock asphalt.  It occurs in more than one form. It may be asphaltthat is impregnated in porous rocks, or it may be asphalt that ishardened into rock-like forms.1-3. Manufactured asphalt is more uniform in quality than natural asphalt.AC is the residue (waste product) of crude-oil distillation. It is used alone or incombination with other materials to form asphalt cutbacks and emulsions. Allthree bituminous compounds (lake, rock, and manufactured) are referred to asasphalt. Use natural asphalt when it is locally available; otherwise, usemanufactured asphalt. TAR 1-4. Tar is extracted from coal. Coal-gas tar is a by-product of coke production,and water-gas tar is distilled from tar vapors. Both are produced, condensed,and collected during the production of illuminating gas and are used in pavingtar. Water-gas tar combines with coal-gas tar as a flux. The two types ofpaving tar are road tar (RT) and road-tar cutback (RTCB). ASPHALT CEMENT 1-5. AC consistency varies in relation to the amount of volatile substances inthe residue. The penetration (hardness) test measures the distance in units of1/100 centimeter that a standard blunt needle of a penetrometer, under a forceof 100 grams, will penetrate an AC sample at 77° F in 5 seconds. (See  FM 5-472  for more details on the penetration test.)1-6. There are nine paving grades of AC. Each grade is designated by apenetration-grade number, an asphalt-petroleum (AP) number, and a relative-consistency (hardness) indicator (hard, medium, or soft). (See  Table1-1. ) SECTION I - BITUMEN  FM 5-436Bituminous Materials 1-3 ASPHALT CUTBACK  1-7. Asphalt cutback is produced during the refining process or from heatedAC that is cut back with a volatile petroleum distillate (cutter stock). Incontrast to AC, asphalt cutback is workable at low temperatures. Naphtha,gasoline, kerosene, jet fuel, diesel oil, and fuel oil can be used as cutter stocks.The three types of asphalt cutback are based on the rate of curing:ã  Slow-curing(SC)asphaltcutback. It contains diesel oil or fuel oil.ã  Medium-curing (MC) asphalt cutback.  It contains a less volatilesubstance, such as kerosene or jet fuel.ã  Rapid-curing (RC) asphalt cutback.  It contains a highly volatilecutter stock that evaporates rapidly, such as naphtha or gasoline.1-8. The viscosity (resistance to flow) of asphalt cutback varies according tothe amount of cutter stock added and the type of AC used. As the amount ofcutter stock increases, the viscosity decreases. Each type of asphalt cutback isproduced in four standard grades of kinematic viscosity—70, 250, 800, and3,000 centistokes. The numerical grade is the lowest kinematic viscosity limitat 140°F, and the upper limit is twice the lower limit. Therefore, RC-250 has akinematic viscosity range of 250 to 500 centistokes at 140°F. ASPHALT EMULSION 1-9. Asphalt emulsion is a nonflammable liquid substance that is produced bycombining asphalt and water with an emulsifying agent such as soap, dust, orcertain colloidal clays. The emulsifying agent promotes emulsification andcontrols certain physical properties of the emulsion. Emulsion is deposited ona surface; and when the water and asphalt break (separate), they leave a thinfilm of AC. Table 1-1. Paving Grades of AC PenetrationGrade AP RelativeConsistency 40-50 7 Hard50-60* 6 Hard60-70 5 Hard70-80* 4 Hard85-100 3 Medium100-120* 2 Medium120-150 1 Medium150-200* 0 Soft200-300 00 Soft*Penetration grade is no longer readily available. It isprovided to facilitate field identification if necessary.  FM 5-4361-4 Bituminous Materials 1-10. The two kinds of emulsions—anionic and cationic—are establishedaccording to their electrical charge. The use of anionic (negatively charged)emulsion is restricted because it does not adhere easily to negatively chargedsiliceous aggregates. However, certain cationic (positively charged) emulsionsimprove adherence to negatively charged aggregates. In addition, cationicemulsions coat damp aggregates better than anionic emulsions.1-11. The three basic types of emulsions are rapid setting (RS), mediumsetting (MS), and slow setting (SS). The setting rate, which is the rate ofasphalt and water separation, depends on the amount and kind of emulsifyingagent used. Asphalt emulsion is graded on the basis of viscosity and groupedaccording to its use. (See  Table1-2 .)1-12. Emulsions are nonflammable and liquid at ordinary temperatures.Using water in an emulsion is a disadvantage in freezing weather because thewater freezes and breaks the emulsion. Emulsions are also difficult to store orstockpile since they tend to break while still in unopened drums. Due to thesedisadvantages, emulsions are not used extensively in the theater of operations(TO). TAR 1-13. RT is ma nufa ctured in 12 gra des of viscosity (ha rdness) a t atemperature of 77°F. Grades 1 through 7 are liquid, and grades 8 through 12are semisolid to solid. Liquid RT contains more liquid coal distillates thansolid RT.1-14. RT is reduced w ith a coa l-ta r distilla te to form RTCB, w hich ismanufactured only in viscosity grades 5 and 6. Highly volatile coal distillate,such as benzene or a solution of naphthalene and benzol, is used to cut backthe heavy grades of RT to produce RTCB. RTCB is similar to asphalt cutbackand cures rapidly. The viscosity grades of RTand RTCB are comparable to theviscosity gra des of a spha lt cutba ck a nd AC. (See  FM 5-472  for moreinformation.) Table 1-2. Asphalt Emulsions Emulsion Type Viscosity Grade Mixing Ability AnionicRS RS-1, RS-2 SprayingMS MS-2 Mixing and sprayingSS SS-1, SS-1H Mixing and sprayingCationicRS-C RS-2C, RS-3C SprayingMS-C MS-C Mixing (sand) and sprayingSS-C SS-C, SS-CH Mixing and spraying
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