XX大学 学生毕业设计
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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 considered here.
Asphalt products 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 the 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 cutback, 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-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. https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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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 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.
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 https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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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 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 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 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 methods 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
determinable 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 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 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 https://www.doczj.com/doc/1f1266801.html,XX大学
学生毕业设计
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texture 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 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 flexible pavement is used to bind the 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
asphalt content for a particular combination of aggregates.
3 . Mix design principles
Certain 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 pavements 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 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 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 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 overflow in a condition known as
bleeding. The loss of asphalt cement through bleeding weakens the pavement and also
reduces surface friction, making the roadway hazardous. https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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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 volum
e 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 resiliency.
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 controlled 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. Traffic 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 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 provide a means for
selecting the asphalt content . These tests will be considered in detail in a future chapter ,but https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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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 controlled, 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 variable are controlled.
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 decrease air-void
volume to some minimum value which is approached asymptotically. With still greater
additions of asphalt materia
l 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 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 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 https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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and does 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 flexible pavement work. https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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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
https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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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https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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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。 https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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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计中的一个重
要因素决定着着路面的所有特征稳定性防滑性耐久性和经济性。正如已
经提到的各种设计方法都是选择沥青含量的一种手段这些细节将在未来的章
节的考虑但沥青含量和一些性能特性如稳定性、单位重量和空隙率之间的
关系将在这里讨论。 https://www.doczj.com/doc/1f1266801.html,XX大学 学生毕业设计
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图4.稳定性、密度、空隙率和沥青用量之间的关系图
如果集料的级配压实度沥青种类得到控制那么强度的变化方式是可以
预测的。强度将随沥青用量接近最佳用量增长随着沥青用量的进一步增加强
度将逐渐降低。混合料的强度曲线将随着其他组分的改变而有所不同因此在试
验之前只能预测一种标准的曲线。
当所有其他因素都保持不变时强度和密度的变化有一定联系。强度随沥青
用量的增加达到一个峰值并随沥青用量的继续增加逐渐降低。
正如已经提到的空气空隙体积会随沥青含量变化。然而变化的方式不同
的
是增加沥青含量将减少空气孔洞体积并使之逐渐接近最低值随着沥青用量
的持续增加集料颗粒将彼此脱离而空气空隙体积将保持不变。
总之某些原则比如集料级配空隙率沥青
用量压实度等理解之后再进行
实际的配合比设计。正确设计以这些原则为基础将会有合理的路面。如果这些
原则被忽视这个道路可能会失败并伴随多种病害推移、车辙、波浪当路
面过厚时会变得光滑剥落、开裂耐久性降低当混合料总量过少时。
应该再次强调的是更准确地说柔性强度稳定的并不表示路基强度薄弱点
任何能力。任何一种沥青混合料都是通过一个正确的设计并将其建造为结构物的
基础上才能算做成功。这一事实说明面层和基层一样重要必须不断地关注柔
性路面的发展方面。 https://www.doczj.com/doc/1f1266801.html,