道路工程外文文獻(xiàn)翻譯---瀝青混合料的應(yīng)用、理論和原則-其他專業(yè)-文庫(kù)吧資料
2025-01-27 01:38本頁(yè)面
【正文】 y 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 peration grade. XX 大 學(xué) 學(xué)生畢業(yè)設(shè)計(jì) 第 2頁(yè) 共 12 頁(yè) 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, often designed for a particular installation. 2 . Theory of asphalt concrete mix design High types of flexible pavement are constructed by bining an asphalt cement, often in the peration 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 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. Before 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 displacement under load. Deformation of an asphalt pavement can occur in three ways, two unsatisfactory and one desirable. Plastic deformation XX 大 學(xué) 學(xué)生畢業(yè)設(shè)計(jì) 第 3頁(yè) 共 12 頁(yè) 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 e 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 pavements 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 probably 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 tirepavement friction factor for control and safety. The texture of the 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 bination which provides a skid resistant roadway. Design procedures which yield paving mixtures embodying all these properties are not available. Sound pavements are constructed where materials and methods are selected by using timetested tests and specifications and engineering judgments along with a socalled design method. The final requirement for any pavement is one of economy. Economy, again, cannot be measured directly, since true economy only begin
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