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1、外文文献翻译外文文献翻译原文：Asphalt Mixtures-Applications, Theory and Principles1 . ApplicationsAsphalt materials find wide usage in the construction industry. The use of asphalt as a cementing agent in pavements is the most common of its applications, however, and the one that will be considered here.Asphalt pr
2、oducts are used to produce flexible pavements for highways and airports. The term “flexible” is used to distinguish these pavements from those made with Portland cement, which are classified as rigid pavements, that is, having beam strength. This distinction is important because it provides they key
3、 to the design approach which must be used for successful flexible pavement structures.The flexible pavement classification may be further broken down into high and low types, the type usually depending on whether a solid or liquid asphalt product is used. The low types of pavement are made with the
4、 cutback, or emulsion, liquid products and are very widely used throughout this country. Descriptive terminology has been developed in various sections of the country to the extent that one pavement type may have several names. However, the general process followed in construction is similar for mos
5、t low-type pavements and can be described as one in which the aggregate and the asphalt product are usually applied to the roadbed separately and there mixed or allowed to mix, forming the pavement.The high type of asphalt pavements is made with asphalt cements of some selected penetration grade. Fi
6、g. 1 A modern asphalt concrete highway. Shoulder striping is used as a safely feature.Fig. 2 Asphalt concrete at the San Francisco International Airport.They are used when high wheel loads and high volumes of traffic occur and are, therefore, often designed for a particular installation. 2 . Theory
7、of asphalt concrete mix designHigh types of flexible pavement are constructed by combining an asphalt cement, often in the penetration grade of 85 to 100, with aggregates that are usually divided into three groups, based on size. The three groups are coarse aggregates, fine aggregates, and mineral f
8、iller. These will be discussed in detail in later chapter.Each of the constituent parts mentioned has a particular function in the asphalt mixture, and mix proportioning or design is the process of ensuring that no function is neglected. Before these individual functions are examined, however, the c
9、riteria for pavement success and failure should be considered so that design objectives can be established.A successful flexible pavement must have several particular properties. First, it must be stable, that is to resistant to permanent displacement under load. Deformation of an asphalt XX 大学 学生毕业
10、设计第 3 页 共 13 页pavement can occur in three ways, two unsatisfactory and one desirable. Plastic deformation of a pavement failure and which is to be avoided if possible. Compressive deformation of the pavement results in a dimensional change in the pavement, and with this change come a loss of resilie
11、ncy and usually a degree of roughness. This deformation is less serious than the one just described, but it, too, leads to pavement failure. The desirable type of deformation is an elastic one, which actually is beneficial to flexible pavements and is necessary to their long life.The pavement should
12、 be durable and should offer protection to the subgrade. Asphalt cement is not impervious to the effects of weathering, and so the design must minimize weather susceptibility. A durable pavement that does not crack or ravel will probably also protect the roadbed. It must be remembered that flexible
13、pavements transmit loads to the subgrade without significant bridging action, and so a dry firm base is absolutely essential.Rapidly moving vehicles depend on the tire-pavement friction factor for control and safety. The texture of the pavement surfaces must be such that an adequate skid resistance
14、is developed or unsafe conditions result. The design procedure should be used to select the asphalt material and aggregates combination which provides a skid resistant roadway.Design procedures which yield paving mixtures embodying all these properties are not available. Sound pavements are construc
15、ted where materials and methods are selected by using time-tested tests and specifications and engineering judgments along with a so-called design method.The final requirement for any pavement is one of economy. Economy, again, cannot be measured directly, since true economy only begins with constru
16、ction cost and is not fully determinable until the full useful life of the pavement has been recorded. If, however, the requirements for a stable, durable, and safe pavement are met with a reasonable safety factor, then the best interests of economy have probably been served as well.With these requirements in mind, the functions of the constituent parts can be examined with consideration give to how each part contributes to now-established objectives
