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1、毕业论文（外文翻译）（2012届）学院名称 土木与水利工程学院 专 业 （班 级） 土木工程七班 姓 名 （学 号） 李 小 润（20083650） 指 导 教 师 扈 惠 敏 系（教研室）负责人 方 诗 圣 13PavementHighway pavements are divided into two main categories: rigitand flexible. The wearing surfaceof a rigid pavement is usually constructed of Portland cement concrete such that it acts li
2、ke a beam over any irregularities in the underlying supporting material. The wearing surface of flexible pavements, on the other hand, is usually constructed of bituminous material such that they remain in contact with the underlying material even when minor irregularities occur.Flexible pavements u
3、sually consist of a bituminous surface underlaid with a layer of granular material and a layer of a suitable mixture of coarse and fine materials. Coarse aggregates Fine aggregatesTraffic loads are transferred by the wearing surface to the underlying supporting materials through the interlocking of
4、aggregates, the frictionaleffect of the granular materials, and the cohesion of the fine materials.Flexible pavements are further divided into three subgroups: high type, intermediate type, and low type. High-type pavements have wearing surfaces that adequately support the expected traffic load with
5、out visible distress due to fatigue and are not susceptible to weather conditions. Intermediate-type pavements have wearing surfaces that range from surface treated to those with qualities just below that of high-type pavements. Low-type pavements are used mainly for low-cost roads and have wearing
6、surfaces that range from untreated to loose natural materials to surface-treated earth. The components of a flexible pavement include the subgradeor prepared roadbed, the subbase, basecourse, and the surface course (Fig.11.1). Upper surface courseMiddle surface course Lower surface course The perfor
7、mance of the pavement depends on the satisfactory performance of each component, which requires proper evaluation of the properties of each component separately. The subgrade is usually the natural material located along the horizontal alignment of the pavement and serves as the foundation of the pa
8、vement structure. The subgrademay also consist of a layer of selected borrow materials, well compacted to prescribedspecifications.Compacting plant Compaction device Compactness It may be necessary to treat the subgrade material to achieve certain strength properties required for the type of pavemen
9、t being constructed.Located immediately above the subgrade, the subbase component consists of a superior quality to that which generally is used for subgrade construction. The requirements for subbase materials are usually given in terms of the gradation, plastic characteristics, and strength. When
10、the quality of the subgrade material meets the requirements of the subbase material, the subbase component may be omitted. In cases where suitable subbase material is not readily available ,the available material can be treated with other materials to achieve the necessary properties. This process o
11、f treating soils to improve their engineering properties is know as stabilization. The base course lies immediately above the subbase. It is placed immediately above the subgrade if a subbase course is not used. This course usually consists of granular materials such as crushed stone, crushed or unc
12、rushed. The specifications for base course materials usually include stricter requirements than those for subbase materials, particularly with respect to their plasticity, gradation, and strength. Materials that do not have the required properties can be used as base materials if they are properly s
13、tabilized with Portland cement, asphalt, or lime .In some cases, high-quality base course materials may also be treated with asphalt or Portland cement to improve the stiffness characteristics of heavy-duty pavementsThe surface course is the upper course of the road pavement and is constructed immed
14、iately above the base course. The surface course in flexible pavement usually consists of a mixture of mineral aggregates and asphaltic materials. It should be capable of withstanding high tire pressures, resisting the abrasive forces due to traffic, providing a skid-resistant driving surface, and p
15、reventing the penetration of surface water into the underlying layers. The thickness of the wearing surface can vary from 3 in. to more than 6 in.（inch，英寸，2.54cm） , depending on the expected traffic on the pavement. It was shown that the quality of the surface course of a flexible pavement depends on the mix design of the asphalt concrete used. Rigid highway pavements usually are constructed to carry heavy traffic loads, although they have been used for residential and local roads. Properly designed an
