第二课沥青及沥青混合料Asphalt $ Mix AsphaltText: Asphalt &Asphalt Paving Materials1Asphalt DefinedThe black cementing agent known as asphalt has been used for road construction for centuries. Although there are natural deposits of asphalt , or rock asphalt , most used today is produced during the refining of crude oil. Asphalt is a constituent of most petroleums and is isolated through the refining process.Asphalt is called a bituminous material because it contains bitumen, a hydrocarbon material soluble in carbon disulfate. The tar obtained from the destructive distillation of soft coal also contains bitumen. Both petroleum asphalt and coal tar are referred to as bituminous materials. Because their properties differ greatly , petroleum asphalt should not be confused with coal tar . Petroleum asphalt is composed almost entirely of bitumen while the bitumen content in coal tar is relatively low. The two materials should be treated as separate entities.One of the characteristics and advantages of asphalt as an engineering construction and maintenance materials is its versatility. Although a semi-solid at ordinary temperratures , asphalt may be liquefied by applying heat, dissolving it in solvents, or emulsifying it. Asphalt is a strong cement that is readily adhesive and highly waterproof and durable, making it particularly useful in road building. It is also highly resistant to the actions of most acids, alkalis, and salts.1.1Asphalt BinderAsphalt is produced in a variety of types and grades ranging from hard-brittle solids to near water-thin liquids. The semi-solid form known as asphalt binder is the basic material used in Hot-Mix Asphalt(HMA) pavements. Liquid asphalt is produced when asphalt binder is blended or “cut back” with petroleum distillates or emulsified with water and an emulsifying agent.At ambient air temperatures, asphalit binder is a black, sticky , highly viscous material. It is a strong and durable binder with excellent adhesive and waterproofing characteristics. Applying heat, which facilitates mixing with mineral aggregates to produce HMA , can readily liquefy asphalt binders.The largest use of asphalt binder is for HMA . After compacting and cooling to air temperature, HMA is a very strong material with the ability to sustain heavy traffic loads while remaining flexible enough to withstand ambient environmental conditions and stress. Over 96 percent of the hard-surfaced roads in the United States are paved using HMA.1.2 Emulsified AsphaltsEmulsified asphalts(also known as emulsions) are low-viscosity mixtures of tiny asphalt binder droplets, water and emulsifying agents. The emulsifying agent coats the surfaces of the asphalt droplets and keeps them suspended in the water prior to application. After application, the asphalt emulsion breaks and the water separates and evaporates. Emulsions are brownish in color during application, but after breaking, the asphalt binder returns to its original black color. Emulsions are used for a Tack Coat between subsequent layers of HMA to aid in binding thelayers together.Cut-back asphalts are low-viscosity liquid asphalt mixtures manufactured by diluting (cutting back ) Asphalt Binders with petroleum solvents (cutter stock or diluent). After application, the petroleum solvent evaporates, leaving the asphalt binder residue. Cut-back asphalts may be used as a tack coat between subsequent layers of HMA, particularly when ambient air temperatures are cool.2. Asphalt Binder GradingAsphalt binders appropriate for pavement construction were previously graded based on resistance to penetration and/or viscosity measures. Currently ,asphalt binders are graded based on the temperature range over which the binder retains certain desirable characteristics. These desirable characteristics include adequate flexibility to resist cold temperature cracking and sufficient rigidity to resist warm temperature rutting. The current grading system is known as the Performance Grading(PG) system.Performance grading specifications were developed as part of the Strategic Highway Research Program (SHRP) and are a major component of SUPERPA VE. Binders are specified on the basis of the climate andpavement temperatures in which the binder is expected to serve, pavement Age Performance graded (PG) binders used in Minnesota vary from north to south and with intended use; however, PG 58-28 is the most commomly used grade. The first number (58) represents the average 7-day maximum pavement design temperature in degrees Celsius. This maximum temperature establishes the upper temperature limit for the binder ti retain adequate rigidity to resist rutting .The second number (-28) represents the minimum pavement design temperature in degrees Celsius. The minimum temperature established the lower limit for the binder to retain sufficient flexibility to resist thermal cracking.Physical properties of the binders are measured at various temperatures both before and after laboratory aging. The laboratory aging is conducted to simulate field cinditions imposed during the HMA production prosess as well as from long-term environmental exposure.3. Hot-Mix Asphalt (HMA)Hot-Mix Asphalt is known by many different names: HMA, asphalt concrete, plant mix, bituminous concrete, and many others. It is a combination of two primary ingredient s—aggregates and asphalt binder. The aggregates total approximately 95 percent of the total mixture by weight. They are mixed with approximately 5 percent asphalt binder to produce HMA.The aggregates and asphalt are combined in a manufacturing plant capable of producing specified materials. Plant equipment includes: cold bins for storage and controlled proportioning of graded aggregate; a dryer for drying and heating aggregates to the required mixing temperature;a pug mill or drum for combining the graded, heated aggregate and liquid asphalt cement according to specified mix formulas and tanks for storing the heated liquid asphalt.HMA is transported by truck to the paving site where it is spread to a uniform thickness with a mechanical paving or finishing machine. The material is then compacted to the required degree by heavy, self-propelled rollers, producing a smooth pavement course.The paving or finishing machine places the HMA at temperatures between approximately 225°and 300° F ,depending on the mixture characteristics, layer thickness and ambient conditions. The material should be compacted before the mix temperature falls below optimum compaction temperature, dependent on ambient conditions, to achieve adequate density.Covering more than 96 percent of the nation’s paved highways, HMA is the most widely used paving material in the United States. For versatility, durability, and ease of construction, it has no equal.4. The Activity To Modify Asphalt PropertiesThe characteristics of asphalt may be improved by means of various other techniques.Pitch, when added to asphalt, has the effect of increasing the rate at which the binder oxidizes on exposure to the atmosphere. One of the effects of oxidation is that the binder loses flexbility and therefore becomes harder and more susceptible to the abrasive effects to traffic; and therefor becames harder and more susceptible to the abrasive effects of traffic; an oxidized binder is thus likely to wear away in preference to particles of coarse aggregate set in the surface, allowing the chippings to protrude from the surface and improve the skidding resistance. Pitch-bitumen mixtures should contain of the order of ten percent pitch by mass. Note that it is possible to the penetration of a binder at the refinery by blowing air through it, thus encouraging oxidation.Rubber may be added to asphalt to asphalt in various ways as liquid latex, for example, or in powder form. The effect of adding about four per cent of natural rubber by weight of binder is , unsurprisingly, to improve the elastic properties of the binder. This is advantageous where a asphaltic surfacing may be expected otherwise to crack - as for example when laid over an old jointed concrete pavement, where reflection cracking may be expected over the movement joints. Tests 10 have suggested that rubberized asphalt is effective in these circumstances.Sulphur may be used as a partial substitute for some asphalts, and experimental work has been carried out in this field in the US. The economic benefits of using sulphur extended asphalt (SEA), whose binder consists of such a mixture, depend on the relative costs of the two materials. In the UK there is currently little cost benefit to be obtained from the use of sulphur, and SEA is therefore not used.Sulphur provides the benefit of a strong and durable material. However its use should be approached with caution since at temperatures above 140℃sulphur will take up water to yield the unpleasant gases surphur dioxide and hydrogen sulphide and and the consequent environmental draw backs during the laying process militate against the use of sulphur in urban areas.Words and ExpressionsAsphalt：沥青；asphaltene：沥青质；asphaltic：沥青的，含沥青的；cementing agent：粘结剂；deposits：矿藏；crude oil：原油；constituent：构成的，组织的，成分的；petroleums：原油；isolate：隔离；refine：精炼，炼制；bituminous：含沥青的；bitumen ：沥青；hydrocarbon ：碳氢化合物，烃；soluble：可溶的；carbon disulfate：二硫化碳；Tar：焦油；destructive distillation：分馏；soft coal：烟煤；coal tar：煤焦油；refer to：属于、归类于；Compose：组成；Entity：实体、存在；Versatility:多才多艺、多用途；semi-solid:半固体；ordinary temperrature:常温；Liquefy:液化；Solvent:溶剂；Emulsify:乳化；readily：容易的、无困难的；adhesive：粘结；Waterproof：防水性；Durable：耐久性；resistant：有抵抗力；acids, alkalis, and salts：酸、碱、盐；Binder：包扎工、包扎工具、（建）粘结料；Asphalt Binder：沥青结合料、沥青料；hard-brittle：硬、脆；Blended：混合；cut back：稀释；emulsifying agent：乳化剂；ambient：周围的；ambient air temperature：环境温度；Sticky：胶粘的；viscous：粘性的；Applying heat：加热；Facilitate：使容易、使便利；readily ：容易的；Liquefy：液化；hard-surfaced roads：硬化道路；Emulsified Asphalts：乳化沥青；Emulsions：乳胶、乳液；Suspend：悬浮；Break：破乳；Brownish：棕色的；Tack Coat：粘层；Tack ：图钉；subsequent：随后的；Aid：辅助；Cut-back asphalts：稀释沥青；Dilute：稀释，变淡；cutter stock：？？？Diluent：稀释剂；appropriate：适当的；resistance：抵抗力、阻力；penetration：针入度；range over：范围；desirable：称心如意；Rigidity：刚度；rutting：车辙；Performance Grading(PG)：性能分级；Strategic：战略的；SUPERPA VE：Superior Performing Asphalt Pavement ：高性能沥青路面；Specified：指定的，详细说明；Age Performance：老化性能；intend：打算；resist rutting：抗车辙；thermal：温度的；Simulate：模拟；imposed：使……强加于；Exposure：暴露；Plant：厂拌的；aggregate：集料；Approximately：大约；manufacturing plant：加工厂；capable：有能力；cold bin：冷料仓；proportioning：成比例的；pug mill ：搅拌机；drum：筒；tank：箱；Site：现场；Propell：推动；Optimum:最适合的；Modify：修改；by means of：用、依靠；means ：方法、手段、财力；Pitch：硬沥青；Oxidize：氧化；oxidation：氧化作用；Susceptible：易被影响的、敏感的；Abrasive：研磨的；wear away：使……磨损；Preference：偏爱、优先、选择权；in preference to：优先于；coarse aggregate ：粗集料；chippings ：碎屑、薄片；protrude：伸出、突出；skidding：刹车；mass：质量；latex：橡胶浆；Otherwise：否则；otherwise to ：不那样的；jointed ：有接缝的；reflection cracking：反射裂缝；Sulphur：硫；硫化的；Substitute：代替、代用品；sulphur extended asphalt：掺硫沥青；Approach：靠近；Caution：小心、告诫、警告；take up：吸收；Yield：产生、产出；surphur dioxide：二氧化硫；hydrogen sulphide：硫化氢；draw back：弊端；Militate：起作用、发生影响；Reading MaterialBitumen and its Properties。