土木工程专业英语unit1课件(3)

1、Unit1(3) Durability of Concrete 混凝土耐久性 Why These Happen?At present, more and more destructive cases of engineering due to lack of durability not insufficient strength under all kinds of serious conditions and many new questions companying with the development of concrete technology make people pay a

2、ttention to the durability of concrete. 目前，在各种严峻环境条件下新问题伴随着许多混凝土技术发展而出现，越来越多的由于缺乏耐久性而不是强度不足的工程破坏实例引起了人们对混凝土耐久性的关注。The idea of which concrete should be designed according to durability instead of strength was accepted widely.耐久性设计代替强度设计的观点越来越广泛被人们所接受。lackinginadquatedeficientattach importance tolay e

3、mphasis onthink highly ofvalue/emphasizereplacetake the place ofin place ofsubsitute forThe durability of concrete can be defined as its resistance to deterioration resulting from external and internal causes.混凝土的耐久性被定义为混凝土对于外部、内部原因引起劣化的抵抗能力。deterioration：劣化、恶化、退化 degradationv.deteriorate: degenerat

4、e/worsenThe external causes include the effects of environmental and service conditions to which concrete is subjected, such as weathering, chemical actions and wear. 外部原因包括混凝土所受的环境和使用条件的影响，如风化，化学作用和磨损。be subjected to:易受.影响/ 受到. be susceptible to/be liable to/be apt toconsistcomprisebe composed ofbe

5、 made up of The internal causes are the effects of salts, particularly chlorides and sulphates in the constituent materials, interaction between the constituent materials, such as alkali aggregate reaction, volume changes, absorption and permeability.内部原因是组成材料中盐的影响，特别是氯化物和硫酸盐，与组成材料之间的相互作用。如碱骨料反映，体积变

6、化，吸水性和渗透性。be absorbed inconcentrate onbe immersed inbe occupied inIn order to produce a durable concrete care should be taken to select suitable constituent materials.为了生产高耐久性的混凝土，人们应该注意选择合适的组成材料。 It is also important that the mix contains adequate quantities of materials in proportions suitable for

7、 producing a homogeneous and fully compacted concrete mass.为生产均匀致密的混凝土，使各组成材料配比得当，这一点也是非常重要的。in proportion：按比例、与.相称in proportion to:Each mans pay will be in proportion to his work每个人的报酬将与其工作成比例be fit forbe suited tobe suitable for Deterioration of concrete by weathering is usually brought about by t

8、he disruptive action of alternate freezing and thawing of free water within the concrete and expansion and contraction of the concrete, under restraint, resulting from variation in temperature and alternate wetting and drying.因风化产生的混凝土劣化通常是由混凝土内部自由水的冻融交替, 在抑制作用下因温度变化和干湿交替引起的混凝土的膨胀、收缩所导致的。Weathering(

9、风化作用)lead toresult ingive rise to Damage to concrete from freezing and thawing arise from the expansion of pore water during freezing, in a condition of restraint, if prepared a sufficient number of times, these results in the development of hydraulic pressure capable of disrupting concrete. Road ke

10、rbs and slabs, dams and reservoirs are very susceptible to frost actions. 混凝土因冻融引起的破坏是由孔隙水的膨胀造成的，在一个特定条件的限制下，如果冻融循环足够的次数，水压力的发展有可能导致破坏混凝土。路肩和石板路，水坝和水库是非常容易遭受冻胀作用的结构。result fromroot in The resistance of concrete to freezing and thawing can be improved by increasing its impermeability.混凝土耐冻融的能力可以通过提高其

11、抗渗透性来改善。 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 homogenous mass. 这可以通过采用尽可能低的水灰比来达到，但是必须具有经浇筑和捣实成内均匀体所需要的和易性。Durability can be further improved by using air entrainment, an air content o

12、f 3 to 6 percent 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.混凝土的耐久性可以通过采用引气剂进一步改善，通常3%-6%混凝土体积的含气量，可以满足大多数应用的要求。引气混凝土的使用尤其对需要用盐除冰的道路上非常有用。Chemical attack（化学侵蚀）In general,

13、 concrete has a low resistance to chemical attack. 一般情况下，混凝土具有较低的耐化学侵蚀能力。There are several chemical agents, which react with concrete, but the most common forms of attack are those associated with leaching, carbonation, chlorides and sulphates. 很多化学制剂会与混凝土发生反应，但最常见的形式与溶析作用，碳化作用和氯化物，硫酸盐有关。generally s

14、peakingbe related tobe connected withconcerning Chemical agents essentially react with certain compounds of the hardened cement paste and the type of cement used. 化学制剂主要与硬化水泥浆体的某种成分发生反应，因此，混凝土的耐化学侵蚀能力通常与所使用的水泥种类有关。The resistance to chemical attack improves with increased impermeability（不渗透性、抗渗性）.混凝土

15、的耐化学侵蚀能力随着抗渗性的增强而明显改善。Wear （磨损）The main causes of wear of concrete are cavitation effects of fast-moving water, abrasive material in water, wind blasting and attrition and impact of traffic.混凝土磨损的主要原因有高速水流所产生的气蚀效应，水中的磨损物质，风沙袭击和磨耗以及交通的影响。 Certain conditions of hydraulic flow result in the formation o

16、f cavities between the flowing water and the concrete surface.一定条件下的水压流量会导致流动的水和混凝土表面之间空隙的形成。n.wear/abrasionv. attrite/abrade 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 an

17、d holes, known as cavitation erosion. 这些空隙通常被有超高能量的水蒸气充满，由于与混凝土表面频繁接触，就导致了孔和洞的形成，称为气蚀。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

18、 areas may be lined with materials having greater resistance to cavitation erosion.即使质量很好的混凝土也无法抗拒这种劣化，因此，最好的补救方法是通过制造光滑的液压流来消除气穴。如有必要，关键部位可以用有更好的耐气蚀材料作为内衬。removeclear upwipe offeven thougheven ifIn general, the resistance of concrete to erosion and abrasion increases with increase in strength. The

19、use of a hard and tough aggregate tends to improve concrete resistance to wear.一般情况下，混凝土的耐侵蚀性和抗磨损能力随着强度的增大而增大。使用坚硬和坚韧的骨料有助于提高混凝土的耐磨损性。 Alkali aggregate reactionsCertain natural aggregate react chemically with the alkalis present in Portland cement. When this happens these aggregates expand or swell

20、resulting in cracking and disintegration of concrete.某些天然的骨料与普通硅酸盐水泥中的碱发生化学反应。当这种反应发生的时候，这些骨料扩大或膨胀，导致混凝土的开裂和破碎。breakdowncollapsecrashcrushVolume change （体积的改变） Principal factors responsible for volume changes are the chemical combination of water and cement and the subsequent drying of concrete, var

21、iations in temperature and alternate wetting and drying.体积改变的主要因素是水和水泥的化学结合、随之而来的混凝土干燥以及温度的变异和干湿交替。When change in volume is resisted by internal or external forces, this can produce cracking, the greater the imposed restraint, the more severe the cracking.当混凝土体积的改变被内部或外部力抑制时，这将会产生裂缝，越是抑制，裂缝就越严重。The

22、presence of cracks in concrete reduces its resistance to the action of leaching, corrosion of reinforcement, attack by sulphates and other chemicals, alkali-aggregate reaction, corrosion of reinforcement, attack by sulphates and other chemicals, alkali-aggregate reaction and freezing and thawing，all

23、 of which may lead to disruption of concrete.混凝土中裂缝的存在降低了它对溶析、钢筋锈蚀、硫酸盐和其他化学物质侵蚀、碱骨料反应和冻融损伤的抵抗力，从而导致混凝土破坏。Severe cracking can lead to complete disintegration of the concrete surface particularly when this is accompanied by alternate expansion and contraction.特别是当伴有交替的膨胀和收缩的时候，严重的裂缝能导致混凝土彻底破碎。Volume c

24、hanges can be minimized by using suitable constituent materials and mix proportions having due regard to(充分考虑) the size of structure. Adequate moist is also essential to minimize the effects of any volume changes.体积的改变可以通过合适的材料组分以及结构尺寸有关的配合比来减小。适当的湿度也能减小体积变化。take full account oftake full considerati

25、on ofbe indispensable toreduceabatedepletedwindlePermeability and Absorption (吸水性和渗透性)Permeability refers to the ease with which can pass through the concrete. This should not be confused with(混淆) the absorption property of concrete and the two are not necessarily related. 渗透性是指水透过混凝土的难易程度，不能与混凝土的吸水

26、性相混淆，二者没有必然的联系。Absorption can be defined as the ability of concrete to draw water into its voids.吸水性可被定义为混凝土汲取水分进入孔洞的能力。Low permeability is an important requirement for hydraulic structures and in some cases water tightness of concrete may be considered to be more significant than strength although, 对于水工结构，低渗透性是一个很重要的要求，在某些情况下，可以认为混凝土的不渗透水性比强度更为重要。 other conditions being equal,concrete of low permeability will also be strong and durable. A concrete which readily absorbs water is susceptible to deterioration.其他条件相同的情况下，混凝土的低渗透性将会使其更耐久。容易吸收水分的混凝土更容易劣化。be known asbe ident