道路工程(路桥)毕业设计外文文献翻译.docx

道路工程(路桥)毕业设计外文文献翻译 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 consid ered here. Asphalt products are used to produce flexibl e pavements for highways and airports. The term “fl exible” 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 provid es they key to the design approach which must be used for successful flexibl e pavement structures. The flexibl e pavement classification may be further broken d own into high and l ow types, the type usually depending on whether a solid or liquid asphalt product is used. The l ow types of pavement are mad e with the cutback, or emulsion, liquid products and are very widely used throughout this country. Descriptive terminology has been devel oped in various sections of the country to the extent that one pavement type may have several names. However, the general process foll owed in construction is similar for most l ow-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 all owed to mix, forming the pavement. The high type of asphalt pavements is made with asphalt cements of some sel ected penetration grad e. Fig. ?1 A mod ern asphalt concrete highway. Should er striping is used as a safely feature. Fig. ?2 Asphalt concrete at the San Francisco International Airport. They are used when high wheel l oads 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 combining an asphalt cement, often in the penetration grad e 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 d etail in later chapter. Each of the constituent parts mentioned has a particular function in the asphalt mixture, and mix proportioning or d esign is the process of ensuring that no function is negl ected. Before these individual functions are examined, however, the criteria for pavement success and failure should be consid ered so that d esign objectives can be established. A successful fl exible pavement must have several particular properties. First, it must be stable, that is to resistant to permanent displacement under l oad. Deformation of an asphalt pavement can occur in three ways, two unsatisfactory and one desirable. Plastic d eformation of a pavement failure and which is to be avoid ed if possible. Compressive deformation of the pavement results in a dimensional change in the pavement, and with this change come a l oss of resiliency and usually a d egree of roughness. This deformation is less serious than the one just described, but it, too, leads to pavement failure. The desirabl e type of deformation is an elastic one, which actually is beneficial to flexibl e 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 fl exible pavements transmit l oads to the subgrad e without significant bridging action, and so a dry firm base is absolutely essential. Rapidly moving vehicl es d epend on the tire-pavement 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 sel ect the asphalt material and aggregates combination which provid es 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 time-tested tests and specifications and engineering judgments al ong with a so-call ed design method. The final requirement for any pavement is one of economy. Economy, again, cannot 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 record ed. 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 or requirements. The functions of the aggregates is to carry the l oad imposed on the pavement, and this is accomplished by frictional resistance and interl ocking 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 texture is desired, this may not be available in some l ocalities. Dense mixtures are obtained by using aggregates that are either naturally or artificially “well grad ed”. This means that the fine aggregate serves to fill the voids in the coarser aggregates. In addition to affecting density and therefore strength characteristics, the grading also influences workability. When an excess of coarse aggregate is used, the mix becomes harsh and hard to work. When an excess of mineral filler is used, the mixes become gummy and difficult to manage. The asphalt cement in the fl exibl e pavement is used to bind the aggregate particl es together and to waterproof the pavements. Obtaining the proper asphalt content is extremely important and bears a significant influence on all the items marking a successful pavement. A chief objective of all the design methods which have been devel oped is to arrive at the best asphalt content for a particular combination of aggregates. 3 . Mix design principl es Certain fundamental principles underlie the design procedures that have been developed. Before these procedures can be properly studied or applied, some consid eration of these principles is necessary. Asphalt pavements are composed of aggregates, asphalt cement, and voids. Consid ering the aggregate alone, all the space between particles is void space. The volume of aggregate voids depends on grading and can vary widely. When the asphalt cement is ad ded, a portion of these aggregate voids is fill ed and a final air-void volume is retained. The retention of this air-void volume is very important to the characteristics of the mixture. The term air-void volume is used, since these voids are weightless and are usually expressed as a percentage of the total volume of the compacted mixture. An asphalt pavement carries the applied load by particl e friction and interlock. If the particl es are pushed apart for any reason , then the pavement stability is d estroyed. This factor indicates that certainly no more asphalt shoul d be ad ded than the aggregate voids can readily hold. However ,asphalt cement is susceptible to volume change and the pavement is subject to further compaction under use. If the pavement has no air voids when placed, or if it loses them under traffic, then the expanding asphalt will overfl ow in a condition known as bleeding. The l oss of asphalt cement through bl eeding weakens the pavement and also reduces surface friction, making the roadway hazard ous. Fig. ?3 Cross section of an asphalt concrete pavement showing the aggregate framework bound together by asphalt cement. The need for a minimum air-void volume (usually 2 or 3 per cent ) has been established. In addition, a maximum air-void volume of 5 to 7 per cent shoul d not be exceed. An excess of air voids promotes raveling of the pavement and also permits water to enter and speed up the deteriorating processes. Also, in the presence of excess air the asphalt cement hard ens and ages with an accompanying loss of durability and resiliency. The air-void volume of the mix is determined by the d egree of compaction as well as by the asphalt content. For a given asphalt content, a lightly compacted mix will have a large voids volume and a l ower d ensity and a greater strength will result. In the laboratory, the compaction is controlled by using a specified hammer and regulating the number of bl ows and the energy per blow. In the fiel d, the compaction and the air voids are more difficult to control and tests must be made no specimens taken from the compacted pavement to cheek on the d egree of compaction being obtained. Traffic further compact the pavement, and all owance must be mad e for this in the design. A systematic checking of the pavement over an extend ed period is needed to given factual information for a particular mix. A change in density of several per cent is not unusual, however. Asphalt content has been discussed in connection with various facets of the ix design problem. It is a very important factor in the mix design and has a bearing an all the characteristics ld a successful pavement: stability, skid resistance, durability, and economy. As has been mentioned, the various design procedures are intended to provid e a means for selecting the asphalt content . These tests will be consid ered in detail in a future chapter ,but the relationship between asphalt content and the measurable properties of stability, unit weight, and air voids will be discussed here. Fig.4 Variations in stability, unit weight, and air-void content with asphalt cement content. If the gradation and type of aggregate, the degree of compaction, and the type of asphalt cement are controll ed, then the strength varies in a predictable manner. The strength will increase up to some optimum asphalt content and then decrease with further additions. The pattern of strength variation will be different when the other mix factors are changed, and so only a typical pattern can be predicted prior to actual testing. Unit weight varies in the same manner as strength when all other variabl e are controll ed. It will reach some peak value at an asphalt content near that determined from the strength curve and then fall off with further additions. As already mentioned, the air-void volume will vary with asphalt content. However, the manner of variation is different in that increased asphalt content will d ecrease air-void volume to some minimum value which is approached asymptotically. With still greater additions of asphalt material the particles of aggregate are only pushed apart and no change occurs in air-void volume. In summary, certain principles involving aggregate gradation, air-void volume, asphalt content, and compaction mist be understood before proceeding to actual mix d esign. The proper design based on these principl es will result in sound pavements. If these principles are overl ooked, the pavement may fail by one or more of the recognized modes of failure: shoving, rutting, corrugating, becoming slick when the max is too rich; raveling, cracking, h aving low durability when the mix is too l ean. It should be again emphasized that the strength of flexible is, more accurately, a stability and d oes not indicate any ability to bridge weak points in the subgrade by beam strength. No asphalt mixture can be successful unless it rests on top of a properly designed and constructed base structure. This fact, that the surface is no better than the base, must be continually in the minds of those concerned with any aspect of fl exible pavement work. 译文： 沥青混合料的应用、理论和原则 1、应用 沥青材料如今在建筑行业广泛使用。沥青最常见的应用是作为的沥青路面的粘结剂使用。然而，这一点必须在这里予以介绍。 沥青产品常用于生产公路和机场柔性路面。所谓“柔性”是用来区分与硅酸盐水泥制成的路面，它被列为刚性路面，也就是这些路面具有刚性强度。这个区别很重要，因为它提出了成功进行柔性路面结构设计的方法的关键。 柔性路面的分类可进一步细分为高、低的类别，分类通常取决于是否有使用固体或液体沥青产品。低类型路面结构类型通过减少沥青用量或使用乳化剂、液体沥青，是非常广泛的应用在全国范围内。在全国的范围内各地区已开发各自的描述性术语，一个路面类型可能有好几个名字。但是，一般对大多数低型路面其施工方法确是相似，可描述为沥青产品通常单独或其混合结构应用于行车道，形成路面。 高级沥青路面用经过选择的具有好的渗透性的沥青混凝土制成。 图1 现代沥青混凝土公路路肩设置路标线具有安全地特点 图2 旧金山国际机场沥青混凝土跑道 它们被用于重荷载和大交通量道路，因此，人们会进行特殊的结构设计。2、沥青混凝土设计原理 高等级柔性路面是用沥青混凝土建造而成，通常根据集料的85%-100%通过率将其分为三种类型。这三种分别为粗集料、细集料和矿粉。这些将在后面的章节中进行详细讨论。 沥青混合料的每一个组成部分都有特定的功能，混合料配合比设计是确保没有功能被忽略的过程。然而，在这些个别功能检查之前，对于路面的成功和失败的标准应该考虑，这样路面的设计目标才能确定。 一个成功的柔性路面必须有几个特定的属性。首先，它必须是稳定的，即抵抗负荷下的永久位移。沥青路面变形的可能发生在三种方式，二个是不理想的形变，一个是可以接受的。塑性变形对路面来说是要尽量避免的失败。路面的压缩变形导致的路面铺装的尺寸变化，这种变化将引起路面弹性和粗糙度的损失。这种变形没有刚刚描述的那种那么严重，但它也同样导致路面破坏。理想类型的变形是一种弹性变形，这实际上有利于柔性路面，并对于其长寿命是十分必要的。 路面应该耐用并能够保护路基。沥青混凝土是受环境的影响的，因此设计必须降低对气候敏感性。一个耐用的路面要不开裂或拥包才能保护路基。我们必须记住，柔性路面将荷载直接传至路基，所以坚实的基础是绝对必要的。 快速移动的车辆依靠的轮胎路面摩擦力实现控制和保证安全。路面表面纹理必须保证足够的防滑性否则将产生不安全的后果。设计过程通过沥青材料的选择和集料的组合设计提供了防滑路面。 设计程序放弃铺面结合料所有这些表面特性都无法使用。合理的路面建造所需的材料和方法是经过使用时间考验和规范和工程判断和在一起所称的设计方法选定。 对于任何路面最后一个要求是经济性。经济性不能一开始就确定，准确的经济是从开始建设直到路面整个寿命期的成本。然而，如果对于路面稳定，耐久，安全性的要求都达到一个合理的安全系数，那么对经济的最佳利益或许已经实现。 考虑到路面的这些要求，可通过检查各组成部分的功能如何有助于现在已经 确定的目标或要求。沥青混凝土功能是承担路面上施加的负荷，这是由混合料各材料之间相互咬合和摩擦阻力实现。也就是沥青路面的承载能力与路面的表面纹理（尤其是细集料）和密度或者混合料的“密实度”相关，表面结构随集料的不同而不同，虽然理想的表面具有粗糙纹理，但在有些情况下却不能实现。密级配混合物通过使用自然或人为的连续级配集料得到。这意味着细骨料的存在填补了粗骨料的空隙。这除了影响混合料的密度和强度特性之外，也影响施工性能。当粗骨料使用过量时，混合料将变得坚硬而且难以施工；当矿物填料使用过多时，混合料将变得较软，影响使用性能。 柔性路面中的沥青胶结材料用于将集料粘结在一起并充当防水材料。选取适当的沥青含量是非常重要的，它对于成功的路面在项目的整个评分过程中具有重要的影响。设计的首要目标是对于特定的集料组合确定沥青的最佳用量。 3 、混合料配合比设计原则 某些基本原则被制定为设计程序的基础程序。在这些步骤之前，进行某些原则的的研究或应用是很有必要的。 沥青路面由集料、沥青胶结料和空隙组成。对于单独的集料颗粒而言，它的周围都是空隙空间，寂寥的空隙率和集料分级有关系并会在很大的范围内变化。当沥青用量增加时，一部分集料的空隙将被填充，最后的空气空隙将得到保留。这部分保留的空气空隙对于混合料的特性是非常重要的。因为这些空隙没有质量，因而常以体积计算，并通常作为混合料的压实总体积百分数表示。 沥青路面通过集料颗粒的摩擦和自锁能力承载外加荷载。如果颗粒由于某种原因被挤出，那么路面的稳定性将遭到破坏，这是由于混合料中没有添加足够的沥青来有效地约束集料间的空隙的因素。然而，沥青混凝土对空隙体积的变化时十分敏感的，路面将根据使用情况进一步被压实。如果路面修筑时没有预留空隙，或者在交通荷载下空隙被挤压，然后多余的沥青将有条件溢出，这被称作泛油。泛油的沥青路面既减小路面厚度，也降低表面摩擦能力，使道路变得危险。 图3沥青混凝土路面横截面显示了沥青胶结材料将集料骨架约束在一起 已经规定了一个最小的空隙率（通常是2%到3%），除此之外最大的空隙率（5%到7%）也不能被超过。过大的空隙率将加快路面的剥落速度，并会让水进入混合料内部加速路面的损坏速度。此外，过量的空气的存在将导致沥青混凝土硬化，并伴随路面的耐久性和弹性，降低路面使用年限。 混合料的空隙率由路面的压实度和沥青用量决定。对于给定的沥青用量，轻轻压实结构将有较大的空隙体积和较低的密度和更大的强度。在实验室，压实控制通过使用指定的击实锤和确定的打击数和每击能量。在现场，压实度和空隙率更加难以控制和测试，没有试验的混合料必须从压实后的的路面检查已经确定的压实程度。交通对路面的进一步压缩限度必须进行设计，对一个特殊混合料的实际资料需要对路面在较长时间内实行系统的检查。然而，密度在百分之几的变化是很常见的。 我们已经讨论了沥青用量与设计的多方面有关，它是混合料设