毕业论文外文翻译-混凝土的耐久性

1、Durability of concreteBesides its ability to sustain loads, concrete is also required to be durable .The durability of concrete can be defined as its resistance to deterioration resulting from external and internal causes. The external causes include the effects of environmental and service conditio

2、ns to which concrete is subjected, such as weathering, particularly chlorides and sulphates, in the constituent materials, interaction between the constituent materials, such as alkali-aggregate reaction, volume changes, absorption and permeability. In order to produce a durable concrete, care shoul

3、d be taken to select suitable constituent materials. It is also important that mix contains adequate quantities of materials in proportions suitable for producing a homogeneous and fully compacted concrete mass.Weathering Deterioration of concrete by weathering is usually brought about by the disrup

4、tive action of alternate freezing and thawing of free water within the concrete and expansion and contraction of the concrete, under restraint, resulting from variations in temperature and alternate wetting and drying. Damage to concrete from freezing and thawing arises from the expansion of pore wa

5、ter during freezing; in a condition of restraint, if repeated a sufficient number of times, this results in the development of hydraulic pressure capable of disrupting concrete. Road Krebs and slabs, dams and reservoirs are very susceptible are very susceptible to frost action. The resistance of con

6、crete to freezing and thawing can be improved by increasing its impermeability. This can be achieved by using a mix with the lowest possible water-cement ratio compatible with sufficient workability for placing and compacting into a homogeneous mass. Durability can be further improved by using air e

7、ntrainment, an air content of 3 to 6 per cent of the volume of concrete normally being adequate for most applications. The use of air entrained concrete is particularly useful for roads where salts are used for deicing.Chemical Attackin general, concrete has a low resistance to chemical attack.There

8、 are several chemical agents which react with concrete but the most common forms of attack are those associated with leaching, carbonation, chlorides and sulphates. Chemical agents essentially react with certain compounds of the hardened cement paste and the resistance of concrete to chemical attack

9、 therefore can be affected by the type of cement used. The resistance to chemical attack improves with increased impermeability.WearThe main causes of wear of concrete are the cavitation effects of fast-moving water, abrasive material in water, wind blasting and attrition and impact of traffic. Cert

10、ain conditions of hydraulic flow result in the formation of cavities between the flowing water and the concrete surface .These cavities are usually filled with water vapor charged with extraordinarily high energy and repeated contact with the concrete surface results in the formation of pits and hol

11、es, Known an cavitation erosion. Since even a good-quality concrete will not be able to resist this kind of deterioration, the best remedy is therefore the elimination of cavitation by producing smooth hydraulic flow. Where necessary, the critical areas may be lined with materials having greater res

12、istance to cavitation erosion.In general, the resistance of concrete to erosion and abrasion increases with increase in strength. The use of a hard and tough aggregate tends to improve concrete resistance to wear.Alkali-Aggregate ReactionsCertain natural aggregates react chemically with the alkalis

13、present in Portland cement. When this happens these aggregates expand or swell resulting in cracking and disintegration of concrete.Volume ChangesPrincipal factors responsible for volume changes are the chemical combination of water and cement and the subsequent drying of concrete, variations in tem

14、perature and alternate wetting and drying. When a change in volume is resisted by internal or external forces this can produce cracking, The greater the imposed restraint, the more severe the cracking. The presence of cracks in concrete reduces its resistance to the action of leaching, corrosion of

15、reinforcement, attack by sulphates and other chemicals, alkali-aggregate reaction and freezing and thawing, all of which may lead to disruption of concrete. Severe cracking can lead to complete disintegration of the concrete surface particularly when this is accompanied by alternate expansion and co

16、ntraction. Volume changes can be minimized by using suitable constituent materials and mix proportions having due regard to the size of structure. Adequate moist curing is also essential to minimize the effects of any volume changes.Permeability and AbsorptionPermeability refers to the ease with whi

17、ch water can pass through the concrete. This should not be confused with the absorption property of concrete and the two are not necessarily related. Absorption may be defined as the ability of concrete to draw water into its voids. Low permeability is an important requirement for hydraulic structur

18、es and in some cases water tightness of concrete may be considered to be more significant than strength although, other conditions being equal, concrete of low permeability will also be strong and durable. A concrete which readily absorbs water is susceptible to deterioration. Concrete is inherently

19、 a porous material. This arises from the use of water in excess of that required for the purpose of hydration in order to make the mix sufficiently workable and the difficulty of completely removing all the air from the concrete during compaction. If the voids are interconnected concrete becomes per

20、vious although with normal care concrete is sufficiently impermeable for most purposes. Concrete of low permeability can be obtained by suitable selection of its constituent materials and their proportions followed by careful placing, compaction and curing. In general for a fully compacted concrete,

21、 the permeability decreases with decreasing water-cement ratio. Permeability is affected by both the fineness and the chemical composition of cement. Aggregates of low porosity are preferable when concrete with a low permeability is required. Segregation of the constituent materials during placing c

22、an adversely affect the impermeability of concrete.混凝土的耐久性混凝土除了承受荷载之外，还需要有一定的耐久性。混凝土的耐久性可能被定义为混凝土对于内外原因引起的劣化的抵抗能力。外部原因包括混凝土受环境和使用条件的影响，如风化，化学作用和磨损。内部原因是组成材料中的盐，特别是氯盐和硫酸盐，与组成材料之间的相互作用，如碱骨料反应，体积变化，吸收和渗透性。为了生产具有耐久性的混凝土，应注意选择合适的组成材料。混合物中包含充足的按比例配置的材料，能适合于生产出均匀的并完全压实的混凝土块，这一点也是很重要的。风化作用 因风化产生的混凝土劣化，通常是由混

23、凝土中自由水的交替冻融和在约束条件下因温度变化及干湿交替所引起的混凝土的膨胀和收缩所引起的。混凝土因冻融引起的破坏是由结冰后孔隙水的膨胀造成的；在某一约束条件下，如果重复足够多次，这就会导致液压的发展，从而引起混凝土破坏。路缘石，混凝土路面，大坝和水库都很容易受到冰冻作用。混凝土的抗冻性，可以用增强其抗渗性来提高。在和易性满足条件的前提下，以最低的水灰比来制作混凝土，放至均质体中并压实。耐久性可以通过使用引气剂而进一步提高，通常空气含量占混凝土体积的3%6%即可胜任大部分应用。引气混凝土的使用，尤其对需用盐除冰的道路非常有用。化学侵蚀 一般而言,混凝土的抗化学侵蚀能力很低. 有很多种化学物质会

24、与混凝土发生反应，但最常见的形式与淋滤作用，碳化，氯化物和硫酸盐有关。化学物质本质上是与某些水泥石化合物发生反应。因此，混凝土的抗化学侵蚀能力与所使用的水泥种类有关。抗化学侵蚀能力随抗渗性的提高而改善。磨损 混凝土磨损的主要原因有高速水流所产生的气蚀效应，水中有磨蚀作用的物质，疾风，交通的摩擦和碰撞。在一定的条件下，水力流导致水流和混凝土表面之间形成空洞。这些空洞通常被高能水汽所填满，水汽反复与混凝土表面接触，形成凹坑和洞，这就是大家知道的空蚀。因为即使是优质的混凝土也无法抵挡这种恶化，因此，最好的应对措施是通过形成顺畅的水力流来消除空蚀。必要时，可在关键区域放置更好的抗空蚀材料。一般来说，混

25、凝土的抗腐蚀和抗磨损能力随它的强度的增大而增大。使用强硬的骨料有助于提高混凝土抗磨强度。碱骨料反应某些天然骨料和普通硅酸盐水泥中的碱发生化学反应。这时，这些骨料就会膨胀，从而导致混凝土开裂和剥蚀。体积变化 体积变化的主要因素是水和水泥的化合作用，以及随后的混凝土干燥（收缩），温度变化和干湿交替。当体积变化受到内力或外力的反抗，则会引起开裂。施加的约束越大，开裂越严重裂缝的存在降低了混凝土对淋滤作用，钢筋锈蚀，硫酸盐及其他化学物质侵蚀，碱骨料反应和冻融的抵抗能力，所有这些都可能导致混凝土的破坏。严重的开裂会导致混凝土表面完全瓦解，尤其是此时还伴随着交替的膨胀和收缩。使用合适的材料和合理配合比并充

26、分考虑到结构的大小，这样可实现体积变化的减小。充分的湿养护对减少体积变化的影响也是必不可少的。渗透性和吸收性渗透性是指水可以很容易地通过混凝土。这不应该与混凝土吸收性混淆，二者没有必然的关系。吸收性可被定义为混凝土吸水到它孔洞里的能力。低渗透性是水工建筑物中的一个重要要求，在某些情况下,会认为混凝土的水密性比强度更重要，即使其他条件相同，混凝土的低渗透性也要很强很耐久。如果混凝土容易吸收水分，那么它将很容易劣化。混凝土本身是一种多孔材料。这是因为要水化来使混合物充分拌合并能够使用，但所使用的水超过了水化所需要的水；而且在混凝土压实过程中很难将空气全部排出。如果孔洞是相互贯通的，那么混凝土就变成

27、可渗透的了，即使经过常规处理后混凝土在大多数场合下可以不透水。低渗透混凝土可以通过选择适当的组成材料和配合比,随后小心的浇筑、压实和养护来获得。一般来说，对于完全压实的混凝土,其渗透率随水灰比的减小而降低。渗透率受到水泥细度和化学成分的影响。当需要低渗透混凝土的时候，选择低孔隙率的骨料较好。浇筑时组成材料的离析会对混凝土的抗渗性产生不利影响。Durability of building MaterialsSome building materials are likely to last as long as their building does whereas others will re

28、quire periodic replacement. In life-cycle costing, the cost of such replacement is taken into account, but it is a matter of opinion whether the choice of a material should be based on its initial cost or its life-cycle cost. Some materials-for example, glazed tile and stainless steel sheet-are extr

29、emely durable; once installed in a new building, they may not require renewal during its entire life. Other materials, such as paint and galvanized steel sheet, will need renewal several times during its life. Is it then cheaper to use galvanized steel or stainless steel for the rain gutters? Is it

30、cheaper to use glazed tiles or painted plaster? In estimating a building on present cost, the maintenance is ignored, or at least not formally considered. In life-cycle costing, the capitalized cost of the maintenance during the entire life of the building is estimated to obtain the total cost. Many

31、 materials that require frequent renewal or maintenance have a far higher life-cycle cost than others cost much more initially, but require no maintenance, Thus, It is likely that stainless-steel gutters and glazed tiles will have a lower life-cycle cost but galvanized-steel gutters and painted plas

32、ter the lower initial cost. High or low temperatures and high or low humilities in themselves do not cause significant damage to building materials, but changes in temperature and humidity do. Thermal expansion and contraction can cause cracks in brittle materials and so can moisture movement. The a

33、lternate and drying that takes place during and after rain can also cause appreciable damage, particularly to materials that absorb some of the water. Some bricks and natural stones contain soluble salts that rain water can bring to the surface, where they form efflorescence. This can usually be rem

34、oved with a brush. Efflorescence may also occur on concrete containing unsuitable aggregates. Most climatic zones experience a substantial number of days when the temperature at night drops below the freezing point (00C or 320F) and rises above it during daytimes. Since ice has a greater volume than

35、 water, these cycles of freezing and thawing can be very damaging to materials that are both porous and brittle. The spectrum of solar radiation includes both infrared (heat) radiation with a longer wavelength and ultraviolet radiation with a shorter wavelength; both overlap with visible light. Heat

36、 radiation can produce overheating of some materials. Thus, bituminous flat roofs are usually covered either with a thin layer of light-colored paint or white stone chips to reflect some of the radiation or with a thicker layer of gravel. Ultraviolet radiation is a major cause of deterioration of ce

37、rtain plastics, and some of these cannot be used if they are to be exposed to sunlight. Sunlight fades certain pigments, mostly those of organic origin and these should not be used externally either in paints or for coloring anodized aluminum. Sunlight is also a major cause of the breakdown of paint

38、 film, which is further accelerated by the thermal movement that occurs. Iron and steel corrode in the presence of moisture by forming rust, the common term for hydrated iron oxide(2Fe203 3H20 ) , unless the climate is extremely dry. The reinforcement in concrete must be protected by an adequate cov

39、er of concrete; if this is insufficient, spalling may occur. Erosion of external walls is caused by wind-driven particles of sand. It occurs comparatively rarely since it requires high wind velocities or the formation of eddies, a supply of sand or dust, and soft material in the wall. The main damag

40、e is to old buildings that contain deteriorating stone or brick. Abrasion is the damage caused by fine solid particles to floor surfaces. Wear is a more complex phenomenon that is caused partly by abrasion, but also by compression and by impact. Carpeting, for example, is frequently damaged more by

41、the permanent impression made by heavy pieces of furniture than by abrasion. It is relatively simple to test abrasion resistance, however, and many machines for testing accelerated wear are simply abrasion-testing machines. Concrete is one of the best floor surfaces for industrial use, and it can be

42、 further improved by using a hard aggregate at least for the surface layer. Cast iron tiles may be appropriate for conditions of extreme wear. Quarry tiles, which are hard-burned, unglazed clay tiles, provide one of the hardest wearing surfaces for commercial and domestic buildings. Tile and stone f

43、loors provide heat storage for passive solar design. Carpeting is used increasingly, both for offices and for homes, because its relative cost has been greatly reduced by modern manufacturing processes that enable the entire floor to be covered wall to wall. Carpet provides a comfortable walking sur

44、face; it is easier to clean than a hard surface; and it is a good thermal insulator and an excellent absorber of impact sound.建筑材料的耐久性一些建筑的建筑材料可能需要维持,而另一些则需要定期更换。在建筑的生命周期中,这种替换是需要考虑的成本,但它是一种观念,一种材料是否应该更换应根据其初始成本和其生命周期成本。在一些材料的例子中,釉面砖和不锈钢极其耐用;一旦安装在新的建筑上,在它们的寿命周期中他们可能不需要被替换。其他材料,如油漆和镀锌钢板,则需要多次被替换。那么使用

45、镀锌钢或不锈钢雨水槽便宜还是使用釉面砖或石膏更便宜?现在在估计基础成本的上,维护往往被忽略,或者至少没有正式考虑。在生命周期成本中, 在整个建筑生命周期内维护建筑的成本估计可以得到的其总成本。许多材料,在其的生命周期中需要频繁的替换或维护的成本远高于其他的一些不需要维护的材料,因此,不锈钢水槽和釉面砖很可能将有一个较低的生命周期成本,但镀锌钢水槽和石膏初始成本越低。环境温度的高低和湿度的高低本身不会造成重大损害,但温度和湿度的变化。热膨胀和冷收缩会引起水分子的运动导致在脆性材料上出现裂缝。在下雨前后干燥和湿润的轮流交替也能造成明显的损害,尤其是材料吸收一些水后。一些天然石材和砖块中含有可溶性盐

46、,雨水导致石材和砖表面风化形成一些可以被刷除的粉尘。风化也可能出现在包含不合适的骨料的混凝土中。大多数气候区域大多数晚上的气温低于冰点温度（00C或320F）高于它在白天的温度。由于冰的体积比水的体积更大,这些周期冻结和解冻的特性对多孔可脆性材料的损害很大。太阳辐射的光谱包括较长波长的红外线(热)辐射和较短波长的紫外线辐射;两个波重叠区域是可见光。热辐射能产生过热的一些材料。因此,沥青平屋顶通常覆盖有一层薄薄的浅色漆或白色的石屑,以反射一些辐射或厚砾石层。紫外线辐射是某些塑料的恶化的主要原因,其中一些不能使用,如果他们要暴露在阳光下。太阳光能致使某些颜料消失,主要是有机起源和这些不应使用外部油

47、漆或着色阳极电镀铝。阳光也是漆膜的击穿的主要原因, 进一步加快了所发生的热运动铁和钢腐蚀在潮湿所形成的锈,水合氧化铁的常见术语(2Fe203 3H20),除非气候非常干燥。混凝土中的钢筋混凝土必须有一个适当的保护盖,如果不能保证,混凝土可能会发生剥落。外墙的腐蚀是由风力驱动沙子引起的。它相对很少发生因为它需要高风速度或漩涡的形成,供应的沙子或灰尘和在墙上的软材料。主要的破坏，是包含不断恶化的石头或砖砌成的老建筑物。磨损是地板表面的固体微粒所造成的损害。磨损是一个更复杂的现象,部分是由磨损引起的,但也受压缩的影响。例如地毯,经常损坏更永久的印象由沉重的家具比磨损。测试耐磨性相对比较简单,然而,许

48、多机器测试加速穿耐磨试验机器。混凝土通常被当做是一种最好的抹面材料使用,它可以进一步提高材料表面硬度。铸铁瓷砖可能适合极端条件。采石场瓷砖,用烈火烧硬的,未上釉的陶瓦、提供最难的穿着为商业和国内建筑表面。磁砖和石材地板为被动式太阳能设计提供热存储。地毯越来越多的使用于办公室和家庭,因为其相对现代制造过程成本大大降低了, 使整个地板覆盖墙到墙。地毯表面提供了一个舒适的步行面;比硬表面更容易清洁;它是一个很好的热绝缘和一个优秀的声音吸收器。五分钟搞定5000字毕业论文外文翻译，你想要的工具都在这里!在科研过程中阅读翻译外文文献是一个非常重要的环节，许多领域高水平的文献都是外文文献，借鉴一些外文文献

49、翻译的经验是非常必要的。由于特殊原因我翻译外文文献的机会比较多，慢慢地就发现了外文文献翻译过程中的三大利器：Google“翻译”频道、金山词霸（完整版本）和CNKI“翻译助手。具体操作过程如下： 1.先打开金山词霸自动取词功能，然后阅读文献； 2.遇到无法理解的长句时，可以交给Google处理，处理后的结果猛一看，不堪入目，可是经过大脑的再处理后句子的意思基本就明了了； 3.如果通过Google仍然无法理解，感觉就是不同，那肯定是对其中某个“常用单词”理解有误，因为某些单词看似很简单，但是在文献中有特殊的意思，这时就可以通过CNKI的“翻译助手”来查询相关单词的意思，由于CNKI的单词意思都是来源与大量的文献，所以它的吻合率很高。 另外，在翻译过程中最好以“段落”或者“长句”作为翻译的基本单位