畢業(yè)論文外文翻譯-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載之外，還需要有一定的耐久性?；炷恋哪途眯钥赡鼙欢x為混凝土對(duì)于內(nèi)外原因引起的劣化的抵抗能力。外部原因包括混凝土受環(huán)境和使用條件的影響，如風(fēng)化，化學(xué)作用和磨損。內(nèi)部原因是組成材料中的鹽，特別是氯鹽和硫酸鹽，與組成材料之間的相互作用，如堿骨料反應(yīng)，體積變化，吸收和滲透性。為了生產(chǎn)具有耐久性的混凝土，應(yīng)注意選擇合適的組成材料?；旌衔镏邪渥愕陌幢壤渲玫牟牧?，能適合于生產(chǎn)出均勻的并完全壓實(shí)的混凝土塊，這一點(diǎn)也是很重要的。風(fēng)化作用 因風(fēng)化產(chǎn)生的混凝土劣化，通常是由混

23、凝土中自由水的交替凍融和在約束條件下因溫度變化及干濕交替所引起的混凝土的膨脹和收縮所引起的。混凝土因凍融引起的破壞是由結(jié)冰后孔隙水的膨脹造成的；在某一約束條件下，如果重復(fù)足夠多次，這就會(huì)導(dǎo)致液壓的發(fā)展，從而引起混凝土破壞。路緣石，混凝土路面，大壩和水庫(kù)都很容易受到冰凍作用?；炷恋目箖鲂裕梢杂迷鰪?qiáng)其抗?jié)B性來(lái)提高。在和易性滿足條件的前提下，以最低的水灰比來(lái)制作混凝土，放至均質(zhì)體中并壓實(shí)。耐久性可以通過(guò)使用引氣劑而進(jìn)一步提高，通?？諝夂空蓟炷馏w積的3%6%即可勝任大部分應(yīng)用。引氣混凝土的使用，尤其對(duì)需用鹽除冰的道路非常有用?；瘜W(xué)侵蝕 一般而言,混凝土的抗化學(xué)侵蝕能力很低. 有很多種化學(xué)物質(zhì)會(huì)

24、與混凝土發(fā)生反應(yīng)，但最常見(jiàn)的形式與淋濾作用，碳化，氯化物和硫酸鹽有關(guān)。化學(xué)物質(zhì)本質(zhì)上是與某些水泥石化合物發(fā)生反應(yīng)。因此，混凝土的抗化學(xué)侵蝕能力與所使用的水泥種類有關(guān)?？够瘜W(xué)侵蝕能力隨抗?jié)B性的提高而改善。磨損 混凝土磨損的主要原因有高速水流所產(chǎn)生的氣蝕效應(yīng)，水中有磨蝕作用的物質(zhì)，疾風(fēng)，交通的摩擦和碰撞。在一定的條件下，水力流導(dǎo)致水流和混凝土表面之間形成空洞。這些空洞通常被高能水汽所填滿，水汽反復(fù)與混凝土表面接觸，形成凹坑和洞，這就是大家知道的空蝕。因?yàn)榧词故莾?yōu)質(zhì)的混凝土也無(wú)法抵擋這種惡化，因此，最好的應(yīng)對(duì)措施是通過(guò)形成順暢的水力流來(lái)消除空蝕。必要時(shí)，可在關(guān)鍵區(qū)域放置更好的抗空蝕材料。一般來(lái)說(shuō)，混

25、凝土的抗腐蝕和抗磨損能力隨它的強(qiáng)度的增大而增大。使用強(qiáng)硬的骨料有助于提高混凝土抗磨強(qiáng)度。堿骨料反應(yīng)某些天然骨料和普通硅酸鹽水泥中的堿發(fā)生化學(xué)反應(yīng)。這時(shí)，這些骨料就會(huì)膨脹，從而導(dǎo)致混凝土開(kāi)裂和剝蝕。體積變化 體積變化的主要因素是水和水泥的化合作用，以及隨后的混凝土干燥（收縮），溫度變化和干濕交替。當(dāng)體積變化受到內(nèi)力或外力的反抗，則會(huì)引起開(kāi)裂。施加的約束越大，開(kāi)裂越嚴(yán)重裂縫的存在降低了混凝土對(duì)淋濾作用，鋼筋銹蝕，硫酸鹽及其他化學(xué)物質(zhì)侵蝕，堿骨料反應(yīng)和凍融的抵抗能力，所有這些都可能導(dǎo)致混凝土的破壞。嚴(yán)重的開(kāi)裂會(huì)導(dǎo)致混凝土表面完全瓦解，尤其是此時(shí)還伴隨著交替的膨脹和收縮。使用合適的材料和合理配合比并充

26、分考慮到結(jié)構(gòu)的大小，這樣可實(shí)現(xiàn)體積變化的減小。充分的濕養(yǎng)護(hù)對(duì)減少體積變化的影響也是必不可少的。滲透性和吸收性滲透性是指水可以很容易地通過(guò)混凝土。這不應(yīng)該與混凝土吸收性混淆，二者沒(méi)有必然的關(guān)系。吸收性可被定義為混凝土吸水到它孔洞里的能力。低滲透性是水工建筑物中的一個(gè)重要要求，在某些情況下,會(huì)認(rèn)為混凝土的水密性比強(qiáng)度更重要，即使其他條件相同，混凝土的低滲透性也要很強(qiáng)很耐久。如果混凝土容易吸收水分，那么它將很容易劣化?；炷帘旧硎且环N多孔材料。這是因?yàn)橐瘉?lái)使混合物充分拌合并能夠使用，但所使用的水超過(guò)了水化所需要的水；而且在混凝土壓實(shí)過(guò)程中很難將空氣全部排出。如果孔洞是相互貫通的，那么混凝土就變成

27、可滲透的了，即使經(jīng)過(guò)常規(guī)處理后混凝土在大多數(shù)場(chǎng)合下可以不透水。低滲透混凝土可以通過(guò)選擇適當(dāng)?shù)慕M成材料和配合比,隨后小心的澆筑、壓實(shí)和養(yǎng)護(hù)來(lái)獲得。一般來(lái)說(shuō)，對(duì)于完全壓實(shí)的混凝土,其滲透率隨水灰比的減小而降低。滲透率受到水泥細(xì)度和化學(xué)成分的影響。當(dāng)需要低滲透混凝土的時(shí)候，選擇低孔隙率的骨料較好。澆筑時(shí)組成材料的離析會(huì)對(duì)混凝土的抗?jié)B性產(chǎn)生不利影響。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維持,而另一些則需要定期更換。在建筑的生命周期中,這種替換是需要考慮的成本,但它是一種觀念,一種材料是否應(yīng)該更換應(yīng)根據(jù)其初始成本和其生命周期成本。在一些材料的例子中,釉面磚和不銹鋼極其耐用;一旦安裝在新的建筑上,在它們的壽命周期中他們可能不需要被替換。其他材料,如油漆和鍍鋅鋼板,則需要多次被替換。那么使用

45、鍍鋅鋼或不銹鋼雨水槽便宜還是使用釉面磚或石膏更便宜?現(xiàn)在在估計(jì)基礎(chǔ)成本的上,維護(hù)往往被忽略,或者至少?zèng)]有正式考慮。在生命周期成本中, 在整個(gè)建筑生命周期內(nèi)維護(hù)建筑的成本估計(jì)可以得到的其總成本。許多材料,在其的生命周期中需要頻繁的替換或維護(hù)的成本遠(yuǎn)高于其他的一些不需要維護(hù)的材料,因此,不銹鋼水槽和釉面磚很可能將有一個(gè)較低的生命周期成本,但鍍鋅鋼水槽和石膏初始成本越低。環(huán)境溫度的高低和濕度的高低本身不會(huì)造成重大損害,但溫度和濕度的變化。熱膨脹和冷收縮會(huì)引起水分子的運(yùn)動(dòng)導(dǎo)致在脆性材料上出現(xiàn)裂縫。在下雨前后干燥和濕潤(rùn)的輪流交替也能造成明顯的損害,尤其是材料吸收一些水后。一些天然石材和磚塊中含有可溶性鹽

46、,雨水導(dǎo)致石材和磚表面風(fēng)化形成一些可以被刷除的粉塵。風(fēng)化也可能出現(xiàn)在包含不合適的骨料的混凝土中。大多數(shù)氣候區(qū)域大多數(shù)晚上的氣溫低于冰點(diǎn)溫度（00C或320F）高于它在白天的溫度。由于冰的體積比水的體積更大,這些周期凍結(jié)和解凍的特性對(duì)多孔可脆性材料的損害很大。太陽(yáng)輻射的光譜包括較長(zhǎng)波長(zhǎng)的紅外線(熱)輻射和較短波長(zhǎng)的紫外線輻射;兩個(gè)波重疊區(qū)域是可見(jiàn)光。熱輻射能產(chǎn)生過(guò)熱的一些材料。因此,瀝青平屋頂通常覆蓋有一層薄薄的淺色漆或白色的石屑,以反射一些輻射或厚礫石層。紫外線輻射是某些塑料的惡化的主要原因,其中一些不能使用,如果他們要暴露在陽(yáng)光下。太陽(yáng)光能致使某些顏料消失,主要是有機(jī)起源和這些不應(yīng)使用外部油

47、漆或著色陽(yáng)極電鍍鋁。陽(yáng)光也是漆膜的擊穿的主要原因, 進(jìn)一步加快了所發(fā)生的熱運(yùn)動(dòng)鐵和鋼腐蝕在潮濕所形成的銹,水合氧化鐵的常見(jiàn)術(shù)語(yǔ)(2Fe203 3H20),除非氣候非常干燥?；炷林械匿摻罨炷帘仨氂幸粋€(gè)適當(dāng)?shù)谋Ｗo(hù)蓋,如果不能保證,混凝土可能會(huì)發(fā)生剝落。外墻的腐蝕是由風(fēng)力驅(qū)動(dòng)沙子引起的。它相對(duì)很少發(fā)生因?yàn)樗枰唢L(fēng)速度或漩渦的形成,供應(yīng)的沙子或灰塵和在墻上的軟材料。主要的破壞，是包含不斷惡化的石頭或磚砌成的老建筑物。磨損是地板表面的固體微粒所造成的損害。磨損是一個(gè)更復(fù)雜的現(xiàn)象,部分是由磨損引起的,但也受壓縮的影響。例如地毯,經(jīng)常損壞更永久的印象由沉重的家具比磨損。測(cè)試耐磨性相對(duì)比較簡(jiǎn)單,然而,許

48、多機(jī)器測(cè)試加速穿耐磨試驗(yàn)機(jī)器?；炷镣ǔ１划?dāng)做是一種最好的抹面材料使用,它可以進(jìn)一步提高材料表面硬度。鑄鐵瓷磚可能適合極端條件。采石場(chǎng)瓷磚,用烈火燒硬的,未上釉的陶瓦、提供最難的穿著為商業(yè)和國(guó)內(nèi)建筑表面。磁磚和石材地板為被動(dòng)式太陽(yáng)能設(shè)計(jì)提供熱存儲(chǔ)。地毯越來(lái)越多的使用于辦公室和家庭,因?yàn)槠湎鄬?duì)現(xiàn)代制造過(guò)程成本大大降低了, 使整個(gè)地板覆蓋墻到墻。地毯表面提供了一個(gè)舒適的步行面;比硬表面更容易清潔;它是一個(gè)很好的熱絕緣和一個(gè)優(yōu)秀的聲音吸收器。五分鐘搞定5000字畢業(yè)論文外文翻譯，你想要的工具都在這里!在科研過(guò)程中閱讀翻譯外文文獻(xiàn)是一個(gè)非常重要的環(huán)節(jié)，許多領(lǐng)域高水平的文獻(xiàn)都是外文文獻(xiàn)，借鑒一些外文文獻(xiàn)

49、翻譯的經(jīng)驗(yàn)是非常必要的。由于特殊原因我翻譯外文文獻(xiàn)的機(jī)會(huì)比較多，慢慢地就發(fā)現(xiàn)了外文文獻(xiàn)翻譯過(guò)程中的三大利器：Google“翻譯”頻道、金山詞霸（完整版本）和CNKI“翻譯助手。具體操作過(guò)程如下： 1.先打開(kāi)金山詞霸自動(dòng)取詞功能，然后閱讀文獻(xiàn)； 2.遇到無(wú)法理解的長(zhǎng)句時(shí)，可以交給Google處理，處理后的結(jié)果猛一看，不堪入目，可是經(jīng)過(guò)大腦的再處理后句子的意思基本就明了了； 3.如果通過(guò)Google仍然無(wú)法理解，感覺(jué)就是不同，那肯定是對(duì)其中某個(gè)“常用單詞”理解有誤，因?yàn)槟承﹩卧~看似很簡(jiǎn)單，但是在文獻(xiàn)中有特殊的意思，這時(shí)就可以通過(guò)CNKI的“翻譯助手”來(lái)查詢相關(guān)單詞的意思，由于CNKI的單詞意思都是來(lái)源與大量的文獻(xiàn)，所以它的吻合率很高。 另外，在翻譯過(guò)程中最好以“段落”或者“長(zhǎng)句”作為翻譯的基本單位