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 1 Pavement Highway 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
2、acts like 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 pav
3、ements usually 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 aggregates Traffic loads are transferred by the wearing surface to the underlying supporting materials through the interlo
4、cking of 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
5、 load without 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 hav
6、e wearing 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 course Middle surface course Lower surface course
7、 The performance 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 foundatio
8、n of the pavement 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 typ
9、e of pavement being constructed. 2 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
10、strength. When 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.
11、 This process of 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,
12、 crushed or uncrushed. 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
13、 are properly stabilized 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 c
14、onstructed immediately 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 drivin
15、g surface, and preventing 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
16、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 and constructed rigid pavements have long service lives and usually are less
17、expensive to maintain than the flexible pavements. The Portland cement concrete commonly used for rigid pavements consists of Portland cement, coarse aggregate, fine aggregate, and water. Steel reinforcing rods may or may not be used, depending on the type of pavement being constructed. Rigid highwa
18、y pavements be divided into three general type: plain concrete pavements, simply reinforced concrete pavements, and continuously reinforced concrete pavement. The definition of each pavement type is related to the amount of reinforcement used. Plain concrete pavement has no temperature steel or dowels for load transfer.
