土木工程專業(yè)英語lesson 4 Volume Changes of Concrete

1、LESSON 4Volume Changes of ConcreteConcrete undergoes volume changes during hardening. If it loses moisture by evaporation. it shrinks, but if the concrete hardens in water, it expands. The causes of the volume changes in concrete can be attributed to changes in moisture content, chemical reaction of

2、 the cement with water， variation in temperature， and applied load.混凝土在硬化過程中產(chǎn)生了體積的變化。如果由于蒸發(fā)失去水分，它會(huì)縮小，但如果混凝土在水中變硬，它會(huì)膨脹?；炷馏w積變化的原因可以歸咎于水含量的變化，水泥與水的化學(xué)反響和所承受的荷載。Undergo vt. 經(jīng)歷，遭受，忍受Evaporation n. 蒸發(fā)(作用Shrinkage n. 收縮ShrinkageThe change in the volume of drying concrete is not equal to the volume of water

3、 removed. The evaporation of free water causes little or no shrinkage. As concrete continues to dry, water evaporates and the volume of the restrained cement paste changes, causing concrete to shrink, probably due to the capillary tension that develops in the water remaining in concrete. Emptying of

4、 the capillaries causes a loss of water without shrinkage. But once the absorbed water is removed, shrinkage occurs參考譯文枯燥中的混凝土體積的變化不等于失去水分的體積。自由水分的蒸發(fā)作用導(dǎo)致很少或沒有收縮。隨著混凝土繼續(xù)枯燥，導(dǎo)致混凝土收縮的水蒸發(fā)和有限的水泥漿體積的變化可能應(yīng)歸于在混凝土中的剩余的水中開展的毛細(xì)管張力。排空毛細(xì)管造成水喪失不會(huì)收縮。但是一旦喪失所吸收的水分，收縮產(chǎn)生了。capillary a. 毛細(xì)作用的moisture content 含水量，含濕度cemen

5、t paste 水泥漿the capillary tension 毛細(xì)管張力，微張力Shrinkage1Many factors influence the shrinkage of concrete caused by the variations in moisture conditions 1Cement and water content. The more cement or water content in the concrete mix. the greater the shrinkage 2Composition and fineness of cement. High-ea

6、rly-strength and lowheat cements show more shrinkage than normal Portland cement. The finer the cement, the greater is the expansion under moist conditions參考譯文1 許多因素影響混凝土中由水分條件變化引起的收縮。1、 水泥和含水量。混凝土混合物中的水泥和含水量越多，收縮越大。2、水泥成分和細(xì)度?？煊菜嗪偷蜔崴啾绕胀ü杷猁}水泥表現(xiàn)更多的收縮。水泥越細(xì)，在潮濕條件下的膨脹越大。 Shrinkage 3Type，amount，and grad

7、ation of aggregate. The smaller the size of aggregate particles, the greater is the shrinkage. The greater the aggregate content, the smaller is the shrinkage4Ambient conditions, moisture, and temperature. Concrete specimens subjected to moist conditions undergo an expansion of 200 to 30010-4, but i

8、f they are left to dry in air, they shrink. High temperature speeds the evaporation of water and, consequently, increases shrinkage參考譯文3、骨料的品種, 數(shù)量和級(jí)配。骨料粒子越小，收縮越大。骨料含量越大，收縮越小。4、環(huán)境條件、水分和溫度。潮濕條件下混凝土試樣會(huì)膨脹 200 到 300 10-4，但如果在枯燥空氣中就會(huì)縮小。高溫加速了水蒸發(fā)，從而增加了收縮。gradation of aggregate 骨料級(jí)配Ambient a周圍的；n. 周圍環(huán)境Specim

9、en n樣品，樣本，試樣 Shrinkage5Admixtures Admixtures that increase the water requirement of concrete increase. the shrinkage value6Size and shape of specimen. As shrinkage takes place in a reinforced concrete member, tension stresses develop in the concrete, and equal compressive stresses develop in the ste

10、el. These stresses are added to those developed by the loading action. Therefore, cracks may develop in concrete when a high percentage of steel is used. Proper distribution of reinforcement, by producing better distribution of tensile stresses in concrete， can reduce differential internal stresses

11、參考譯文 5、添加劑。添加劑增加，需水量增加，收縮等值。6、 試件的大小和形狀。像鋼筋混凝土構(gòu)件產(chǎn)生收縮那樣，張拉應(yīng)力 在混凝土中產(chǎn)生，而等量的壓應(yīng)力作用在鋼筋上。這些壓力將與荷載作用產(chǎn)生的壓力疊加。因此，當(dāng)混凝土中使用高百分比鋼筋時(shí)裂縫可能發(fā)育。通過在混凝土中產(chǎn)生更好的拉伸應(yīng)力的分布，適當(dāng)分布的鋼筋，可以減少不同的內(nèi)應(yīng)力。 Shrinkage The values of final shrinkage for ordinary concrete vary between 200 and 70010-6For normalweight concrete, a value of 30010-6

12、may be used. The British Code CPll0 gives a value of 50010-6，which represents an unrestrained shrinkage of 1.5mm in 3m length in thin, plain concrete sections. If the member is restrained, a tensile stress of about 10Nmm2(1400psi) arises. If concrete is kept moist for a certain period after setting,

13、 shrinkage is reduced; therefore, it is important to cure the concrete for a period of no fewer than 7 days參考譯文普通混凝土的最終收縮值在200 到700 10-6之間變化。對(duì)常規(guī)混凝土，可使用300 10-6。英國混凝土標(biāo)準(zhǔn) CP110 給出值 500 10-6，其表達(dá)的是3米長(zhǎng)無鋼混凝土有1.5 mm的自然收縮 。 如果構(gòu)件受限，張拉應(yīng)力上升約 10N/mm2(1400psi)。如果澆筑后混凝土保持濕潤(rùn)一段時(shí)間，收縮減少； 因此，養(yǎng)護(hù)混凝土不少于 7 天是很重要的。The Briti

14、sh Code CP110 英國混凝土標(biāo)準(zhǔn)CP110Shrinkage Exposure of concrete to wind increases the shrinkage rate on the upwind side. Shrinkage causes an increase in the deflection of structural members, which in turn increases with time. Symmetrical reinforcement in the concrete section may prevent curvature and defle

15、ction due to shrinkage Generally, concrete shrinks at a high rate during the initial period of hardening, but at later stages the rate diminishes gradually. It can be said that 15 to 30 of the shrinkage value occurs in 2 weeks，40 % to 80 % occurs in 1 month. and 70to 85 occurs in l year參考譯文 暴露于風(fēng)中的混凝

16、土迎風(fēng)一側(cè)的收縮率增加。收縮導(dǎo)致的結(jié)構(gòu)構(gòu)件翹曲隨時(shí)間增加而增加。混凝土構(gòu)件的對(duì)稱加固可以防止由收縮引起的彎曲和撓度。 一般來說，混凝土在硬化初期將以高速率收縮，但后期逐漸減小?？梢哉f收縮值的 15%至 30%發(fā)生在 2 星期內(nèi)，40 % 至 80 % 發(fā)生在 1 個(gè)月內(nèi)，70%至 85%發(fā)生在 l年內(nèi)。 Expansion due to Rise in TemperatureConcrete expands with increasing temperature and contracts with decreasing temperature. The coefficient of ther

17、mal expansion of concrete varies between 4 and 710-6 per degree Fahrenheit. An average value of 5510-6 per degree Fahrenheit (1210-6 per degree Celsius) can be used for ordinary concrete參考譯文 混凝土隨溫度上升膨脹并溫度下降而收縮。混凝土的熱膨脹系數(shù)在4 至 7 10-6 每華氏度之間變化。普通混凝土可采用平均值 5.5 10-6 每華氏度 12 10-6 每攝氏度。 The coefficient of t

18、hermal expansion of concrete 混凝土熱膨脹系數(shù)Expansion due to Rise in TemperatureThe B. S. Code suggests a value of 10-5 per degree Celsius. This value represents a change of length of 10mm in a 30m member subjected to a change in temperature of 33 If the member is restrained and unreinforced. a stress of a

19、bout 7Nmm2(1000 psi) may develop參考譯文 B.S.法規(guī)建議 10-5 每攝氏度。這一數(shù)值代表長(zhǎng)度 30 米構(gòu)件承受 33 溫度變化有 10 毫米的變化。如果該構(gòu)件受限且無鋼筋，可能有 7N/mm2(1000 psi的應(yīng)力。 The BS Code 英國標(biāo)準(zhǔn)標(biāo)準(zhǔn)Expansion due to Rise in Temperature In long reinforced concrete structures, expansion joints must be provided at lengths of 100 to 200 ft (30 to 60m). Th

20、e width of the expansion joint is about 1 in(25mm)Concrete is not a good conductor of heat, whereas steel is a good one. The ability of concrete to carry load is not much affected by temperature參考譯文 長(zhǎng)的鋼筋混凝土結(jié)構(gòu)，必須在 100 到 200 英尺 30 到 60 米 的長(zhǎng)度上設(shè)置伸縮縫。伸縮縫的寬度是約 1 英寸(25mm)。 混凝土是不良導(dǎo)體熱，而鋼材是。混凝土的負(fù)載能力不太受溫度影響。 t

21、he expansion joint 伸縮縫 CreepConcrete is an elastoplastic material, and beginning with small stresses, plastic strains develop in addition to elastic ones. Under sustained load, plastic deformation continues to develop over a period that may last for years. Such deformation increases at a high rate d

22、uring the first 4 months after application of the load. This slow plastic deformation under constant stress is called creep參考譯文 混凝土是一種彈塑性材料，從小的應(yīng)力開始，除彈性應(yīng)變外塑性應(yīng)變亦開展。在持續(xù)荷載下, 塑性變形持續(xù)開展可能會(huì)持續(xù)多年。這種變形在負(fù)載后的頭 4 個(gè)月期間內(nèi)以高速率增加。這種在恒定壓力下緩慢的塑性變形稱為蠕變。 Creep n. 徐變, 蠕變 Creep Fig41 shows a concrete cylinder that is loaded

23、. The instantaneous deformation is 1, which is equal to the stress divided by the modulus of elasticity. If the same stress is kept for a period of time, an additional strain 2，due to creep effect, can be recorded. If load is then released, the elastic strain, 1, will be recovered, in addition to so

24、me creep strain. The final permanent plastic strain，3，will be left, as shown in Fig41In this case 3=(1一) 2，where is the ratio of the recovered creep strain to the total creep strain參考譯文 Fig.4.1 顯示加載的混凝土圓柱。瞬時(shí)變形是 1，其等于應(yīng)力除以彈性模量。如果一段時(shí)間內(nèi)保持相同的壓力，可以記錄到源自蠕變效應(yīng)的額外應(yīng)力2。如果負(fù)載被釋放，除塑性應(yīng)變外，彈性應(yīng)變1將被復(fù)原。最終的永久塑性應(yīng)變3會(huì)被留下，如F

25、ig.4.1 所示。這里3=(1-)2，為復(fù)原的蠕變與總?cè)渥冎取?Creep The ratio ranges between 0.1 and 0.2The magnitude of creep recovery varies with the previous creep and depends appreciably upon the period of the sustained load. Creep recovery rate will be less if the loading period is increased, probably due to the hardening

26、 of concrete while in a deformed condition 參考譯文比率在 0.1 和 0.2之間。蠕變的規(guī)模隨以前的蠕變變化并明顯取決于持續(xù)負(fù)載的期間。如果加載期間增加，蠕變恢復(fù)率將會(huì)減少，這可能緣于混凝土在變形條件下時(shí)硬化。 CreepCreepThe ultimate magnitude of creep varies between 0.210-6 and 210-6 per unit stress (1 bin.2) per unit length. A value of 110-6 can be used in practice. The ratio of

27、 creep strain to elastic strain may be as high as 4Creep takes place in the hardened cement matrix around the strong aggregate. It may be attributed to slippage along planes within the crystal lattice, internal stresses caused by changes in the crystal lattice, and gradual loss of water from the cem

28、ent gel in the concrete參考譯文蠕變的最終量級(jí)在0.2 10-6 和 2 10-6 每單位應(yīng)力 1 b/in.2單位長(zhǎng)度之間。在實(shí)踐中，可以使用 1 10-6 的值。蠕變應(yīng)變，彈性應(yīng)變的比例可能高達(dá) 4。蠕變?cè)趶?qiáng)骨料周圍已硬化的水泥基質(zhì)中發(fā)生。它可能歸因于沿晶格內(nèi)位面的滑動(dòng)，由晶格改變引起的內(nèi)部應(yīng)力，混凝土中水泥凝膠水分的逐步喪失。 crystal lattice 晶體點(diǎn)陣，晶格cement gel 水泥凝膠體 CreepThe different factors that affect the creep of concrete can be summarized as

29、 follows 1The level of stress 2Creep increases with an increase of stress in specimens made from concrete of the same strength and with the same duration of load 2Duration of loading. Creep increases with the loading period. About 80 of the creep occurs within the first 4 months；90 Occurs after abou

30、t 2 years參考譯文 影響混凝土蠕變的不同因素可以歸納如下。1、應(yīng)力水平。2 對(duì)相同強(qiáng)度混凝土制成的試件及相同的負(fù)載期限，蠕變隨應(yīng)力的增加而增加。2、加載的持續(xù)的時(shí)間。蠕變隨加載期間增加。大約 80%的蠕變出現(xiàn)在頭 4個(gè)月 ；90%發(fā)生在隨后大約 2 年內(nèi)。 Creep 3Strength and age of concrete. Creep tends to be smaller if concrete is loaded at a late age. Also, creep of 2000 psi-(14Nmm2)strength concrete is about 1.4110-6

31、 whereas that of 4000 psi-(28Nmm2)strength concrete is about 0.810-6 per unit stress and length of time4Ambient conditions. Creep is reduced with an increase in the humidity of the ambient air5Rate of loading. Creep increases with an increase in the rate of loading when followed by prolonged loading

32、參考譯文3、 強(qiáng)度和混凝土的年齡。如果混凝土晚期加載蠕變趨于更小。此外，2000 psi (14N/mm2) 強(qiáng)度混凝土約為 1.41 10-6，而4000 psi (28N/mm2) 強(qiáng)度混凝土約為0.8 10-6每單位應(yīng)力和時(shí)間長(zhǎng)度。4、環(huán)境條件。增加周圍空氣的濕度蠕變會(huì)減少。5、負(fù)荷率。蠕變隨長(zhǎng)時(shí)間加載率增加而增加。 Creep 6. Percentage and distribution of steel reinforcement in a reinforced concrete member. Creep tends to be smaller for higher proport

33、ion or better distribution of steel 7. Size of the concrete mass. Creep decreases with an increase in the size of the tested specimen 8. Type, fineness, and content of cement. The amount of cement greatly affects the final creep of concrete, as cement creeps about 15 times as much as concrete 參考譯文6、

34、 鋼筋混凝土構(gòu)件中鋼筋的分布與百分比。鋼筋比例越高或分布越好那么蠕變趨于越小。7、混凝土質(zhì)量的大小。蠕變隨試件尺寸的增加而減小。8、品種，細(xì)度和水泥含量。水泥含量極大地影響混凝土最終的蠕變， 因?yàn)樗嗳渥兗s為混凝土的 15倍。 Creep 9Watercement ratio. Creep increases with an increase in the water-cement ratio. 10Type and grading of aggregate. Wellgraded aggregate will produce dense concrete and consequently a

35、 reduction in creep 11Type of curing. High-temperature steam curing of concrete as well as the proper use of a plasticizer will reduce the amount of creep.參考譯文 9、水灰比。蠕變隨水灰比增加而增加。10、骨料類型與級(jí)配。良好級(jí)配的骨料將產(chǎn)生密實(shí)混凝土并因此減少蠕變。11、養(yǎng)護(hù)形式?；炷粮邷卣羝B(yǎng)護(hù)以及增塑劑的正確使用會(huì)減少蠕變量。 Creep Creep develops not only in compression, but als

36、o in tension, bending, and torsionThe ratio of the rate of creep in tension to that in compression will be greater than l in the first 2 weeks, but this ratio decreases over longer periods.參考譯文 蠕變不僅在壓縮情況下產(chǎn)生； 也發(fā)生在張拉、 彎曲、 扭轉(zhuǎn)情況下。張拉與壓縮的蠕變率之比在前 2個(gè)星期將超過 1，不過這一比率會(huì)長(zhǎng)期下降。 CreepCreep in concrete under compress

37、ion has been tested by many investigators. Troxell, Davis， and Raphael measured creep strains periodically for up to 20 years and estimated that of the total creep after 20 years，18 to 35occurred in 2 weeks，30to 70 occurred in 3 months, and 64 to 83 % occurred in 1 year. 參考譯文 許多研究者進(jìn)行了壓縮下混凝土蠕變的測(cè)試。 Troxell、 戴維斯和拉斐爾定期測(cè)量蠕變20 年并估計(jì) 20 年后的總?cè)渥儯?18%至 35%發(fā)生在 2 星期內(nèi)，30%至 70%發(fā)生在 3 個(gè)月內(nèi)。 64%至 83%發(fā)生在 1 年內(nèi)。 Creep For normal concrete loaded after 28 days, Cr=0.13t， wher