道路工程外文文献翻译沥青混合料的应用、理论和原则

1、外文文献翻译原文：asphalt mixtures-applications, theory and principles1 . applicationsasphalt 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 considered here.asphalt products

2、 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 because it provides they key to th

3、e 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 pavement are made with the cutba

4、ck, 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 construction is similar for most low-

5、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 selected penetration grade. fig. 1 a

6、 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 asp

7、halt concrete mix designhigh 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 groups are coarse aggregates, fine aggregates, and mineral filler.

8、 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 criteri

9、a 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 occ

10、ur in three ways, two unsatisfactory and one desirable. plastic deformation 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 come a loss of resiliency and usually a degree of ro

11、ughness. 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 p

12、rotection 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 th

13、e 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 pavement surfaces must be such that an adequate skid resistance is developed or unsafe conditi

14、ons 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 all these properties are not available. sound pavements are constructed where materials and method

15、s 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, cannot be measured directly, since true economy only begins with construction cost and is not fully de

16、terminable 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 interests of economy have probably been served as well.with these requirements in mind, the functions

17、 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 on the pavement, and this is accomplished by frictional resistance and interlocking between the i

18、ndividual 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

19、is desired, this may not be available in some localities. dense mixtures are obtained by using aggregates that are either naturally or artificially “well graded”. this means that the fine aggregate serves to fill the voids in the coarser aggregates. in addition to affecting density and therefore str

20、ength 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 flexible pavement is used to bind the

21、 aggregate particles 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 developed is to arrive at the best

22、asphalt content for a particular combination of aggregates.3 . mix design principlescertain fundamental principles underlie the design procedures that have been developed. before these procedures can be properly studied or applied, some consideration of these principles is necessary. asphalt pavemen

23、ts are composed of aggregates, asphalt cement, and voids. considering 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 added, a portion of these aggregate voids is filled and a final a

24、ir-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 car

25、ries the applied load by particle friction and interlock. if the particles are pushed apart for any reason , then the pavement stability is destroyed. this factor indicates that certainly no more asphalt should be added than the aggregate voids can readily hold. however ,asphalt cement is susceptibl

26、e 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 overflow in a condition known as bleeding. the loss of asphalt cement through bleeding weakens the pavement

27、 and also reduces surface friction, making the roadway hazardous. 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-v

28、oid volume of 5 to 7 per cent should 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 hardens and ages with an accompanying loss of durability and r

29、esiliency.the air-void volume of the mix is determined by the degree 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 lower density and a greater strength will result. in the laboratory, the compaction is contr

30、olled by using a specified hammer and regulating the number of blows and the energy per blow. in the field, 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 degree of compaction being obtained. traffi

31、c further compact the pavement, and allowance must be made for this in the design. a systematic checking of the pavement over an extended 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 discu

32、ssed 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 intend

33、ed to provide a means for selecting the asphalt content . these tests will be considered 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 weig

34、ht, 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 controlled, then the strength varies in a predictable manner. the strength will increase up to some optimum asphalt content and then decrease with

35、 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 variable are controlled. it will reach some peak val

36、ue 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 decrease air-void volume to so

37、me 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 compactio

38、n mist be understood before proceeding to actual mix design. the proper design based on these principles will result in sound pavements. if these principles are overlooked, the pavement may fail by one or more of the recognized modes of failure: shoving, rutting, corrugating, becoming slick when the

39、 max is too rich; raveling, cracking, having low durability when the mix is too lean. it should be again emphasized that the strength of flexible is, more accurately, a stability and does not indicate any ability to bridge weak points in the subgrade by beam strength. no asphalt mixture can be succe

40、ssful 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 flexible 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

41、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

42、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

43、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

44、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

45、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 、