1、XX 大 学 学生毕业设计 第 1 页 共 12 页 外文文献翻译 原文： Asphalt Mixtures-Applications, Theory and Principles 1 . Applications Asphalt 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 c
2、onsidered here. Asphalt products 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 be
3、cause it provides they key 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
4、 pavement are made with the 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 cons
5、truction is similar for most 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 se
6、lected penetration grade. XX 大 学 学生毕业设计 第 2 页 共 12 页 Fig. 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,
7、often designed for a particular installation. 2 . Theory of asphalt concrete mix design High 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 gr
8、oups are coarse aggregates, fine aggregates, and mineral filler. 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. Bef
9、ore these individual functions are examined, however, the criteria 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 d
10、isplacement under load. Deformation of an asphalt pavement can occur in three ways, two unsatisfactory and one desirable. Plastic deformation XX 大 学 学生毕业设计 第 3 页 共 12 页 of a pavement failure and which is to be avoided if possible. Compressive deformation of the pavement results in a dimensional chan
11、ge in the pavement, and with this change come a loss of resiliency 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 pa
12、vements and is necessary to their long life. The pavement should 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 probabl
13、y also protect the roadbed. It must be remembered that flexible 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
14、 pavement surfaces must be such that an adequate skid resistance 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 al
15、l these properties are not available. Sound pavements are constructed 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, canno
16、t be measured directly, since true economy only begins with construction 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 inte
17、rests 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 or requirements. The functions of the aggregates is to carry the load imposed
18、 on the pavement, and this is accomplished by frictional resistance and interlocking between the individual pieces of aggregates. The carrying capacity of the asphalt pavement is, then, related to the surface texture (particularly that of the fine aggregate) and the density, or “compactness,”, of the aggregates. Surface texture varies with different aggregates, and while a rough surface
