外文翻譯--混凝土的收縮

1、<p><b>　　科技資料原文</b></p><p>　　Shrinkage of Concrete</p><p>　　When concrete loses moisture by evaporation it shrinks. Shrinkage strains are mdependent of the stress conditions in

2、the concrete. If restrained, shrinkage strains can cause cracking of concrete and will generally cause the deflection of structural members to increase with time. The calculation of stress and deformations due to shrinka

3、ge is deferred until Chapter 10.</p><p>　　A curve showing the increase in shrinkage strain with time appears inFig.2.21. The shrinkage occurs at a decreasing rate with time appeard in shrinkage strains vary

4、greatly, being generally in the range 0.0002 to 0.0006 but sometime as much as 0.0010.</p><p>　　Fig.2.21. Typical shrinkage curve for concrete</p><p>　　Shrinkage is to a large extent a reversibl

5、e phenomenon. If the concrete is saturated with water after it has shrunk, it will expand to almost its original volume. Thus alternating dry and wet conditions will cause alternating volume changes of concrete. This phe

6、nomenon is partly responsible for the fluctuating deflections of structures (e.g. concrete bridges) exposed to seasonal changes each year.</p><p>　　As a rule, concrete that exhibits a high creep also display

7、s high shrinkage. Thus the magnitude of the shrinkage strain depends on the composition of the concrete and on the environment in much the same way as discussed previously for creep.</p><p>　　Both the ACI Co

8、mmittee 2092.26 and the CEB-FIP2.27 have proposed empirical methods for the estimation of shrinkage strains. The former approach is described blow.</p><p>　　According to ACI Committee 2092.26 for normal weig

9、ht, sand lightweight concrete (using both moist and steam ouring and types I and III cement), the unrestrained shrinkage strain at any time t is given by</p><p>　　Where the coefficients are given below.</

10、p><p>　　Ultimate shrinkage strain, </p><p>　　The value of can vary widely. In ACI Committee 209 review, was found to be in the range 0.000415 to 0.00107, with mean values of 0.00080 for moist-cure

11、d concrete or 0.00073 for steam-cured concrete. These average values should be assumed only in the absence of more exact date for the concrete to be used.</p><p>　　Time of shrinkage coefficient, St</p>

12、<p>　　At any time after age 7 days, for moist-cured concrete,</p><p><b>　　(2.17a)</b></p><p>　　Where t = time in days from age 7 days</p><p>　　(St=0.46, 0.72, 0.8

13、4, 0.91,and 0.98 for t = 1 month, 3 months, 6months, 1 year, and 5 years, respectively)</p><p>　　or, at any time after age 1 to 3 days for steam-cured concrete,</p><p><b>　　(2.17b)</b&g

14、t;</p><p>　　Where t = time in days from age 3 days</p><p>　　(St=0.35, 0.62, 0.77, 0.87,and 0.97 for t = 1 month, 3 months, 6months, 1 year, and 5 years, respectively)</p><p>　　For s

15、hrinkage considered from greater ages than given above, the difference may be determined use Eq.2.17a or 2.17b for any period after than time. That is shrinkage for moist-cured concrete between, say, 1 month and 1 year w

16、ould be equal to the 7-day to 1-year procedure assumes that the moist-cured concerte hs been cured the shrinkage needs to be multiplied by 1.2; a linear interpolation between 1.2 at 1day and 1.0 abd 1.0 at 7 days may be

17、used.</p><p>　　Relative humidity coefficient, Sh</p><p>　　Sh=1.4-0.01H for 40<H<80% (2.18a)</p><p><b>　　or, </b></p><p>　　Sh=3.0-0.03H for 80&

18、lt;H<100% (2.18b)</p><p>　　Where H = relative humidity in percent</p><p>　　(Sh = 1.00, 0.80, 0.60, 0,for 40, 60, 80, and 100% relative humidity)</p><p>　　Minimum thickness of

19、member coefficient, Sth</p><p>　　Sth = 1.00 for 6 in or less and 0.84 for 9 in (1 in = 25.4mm)</p><p>　　Slump of concrete coefficient, Ss</p><p>　　Ss = 0.97 for 2 in ,1.00 for 2.7 i

20、n, 1.01 for 3in, 1.05 for 4 in, and 1.09 for 5 in (1 in =25.4mm)</p><p>　　Fines coefficient, Sf</p><p>　　Sf =0.86 for 40%, 1.00 for 50%, and 1.04 for 70% fines by weight </p><p>　　A

21、ir content coefficient, Se</p><p>　　Se=0.98 for 4%, 1.00 for 6%, and 1.03 for 10% air</p><p>　　Cement content factor, Sc</p><p>　　Sc=0.87 for376 1b/yd3, 0.95 for564 1b/ yd3 ,1.00 fo

22、r705 1b/yd3 and1.09for 940 1b/yd3(1 1b/yd3=0.593kg/m3)</p><p>　　Example 2.2</p><p>　　Estimate the free shrinkage strain that can be expected to occur in a 9 in (230mm) thick concrete wall from

23、the age of 7 days during a 5-year period at a relative humidity of 60%. The concrete has a slump of 3 in (76mm), a fines content of 34% by weight, a cement content of 600 1b/yd3 (356kg/m3), an air content of 5%, and is m

24、oist cured for 5days after being placed.</p><p><b>　　Solution</b></p><p>　　From Eq.0.16 we have </p><p><b>　　原文翻譯</b></p><p><b>　　混凝土的收縮&l

25、t;/b></p><p>　　當混凝土由蒸發(fā)丟失水分時便產(chǎn)生了收縮現(xiàn)象。 混凝土的收縮是一種自發(fā)的變形，并不依靠作用在混凝土上的外力。因此當收縮變形不能自由進行時，有可能導致混凝土產(chǎn)生裂縫，并且裂縫的數(shù)量隨著時間的增加而增多。在后面的第10章具體介紹收縮產(chǎn)生的變形和裂縫的計算。</p><p>　　圖2.2.1反應了混凝土的收縮隨時間發(fā)展的規(guī)律，早期混凝土的收縮變形速率隨時間的增加

26、變化較快，但是到了后期混凝土的收縮變形和初期相比有很大的不同，收縮的總量一般為（2～5）×10-4，有時達到1×10-3。</p><p>　　圖2.21 混凝土收縮隨時間發(fā)展的規(guī)律</p><p>　　混凝土的體積變形，包括收縮和膨脹兩個方面。如果混凝土在水中硬結時，體積就會增大，因此分別在干、濕環(huán)境中會引起體積的收縮和膨脹。這種現(xiàn)象與結構的環(huán)境變化有很大的關系，（如

27、：混凝土橋梁）很容易受到每年季節(jié)變化。</p><p>　　通?；炷脸尸F(xiàn)收縮和徐變兩種情形。因此混凝土的收縮大小與混凝土的構成及前面介紹的徐變的環(huán)境有關。</p><p>　　ACI2092.26和CEB-FIP2.27早就提出了混凝土的收縮變形的經(jīng)驗公式。公式如下所述。</p><p>　　根據(jù)ACI2092.26給出的重量、集料級配及所有的混凝土強度等級（使用

28、I到III級水泥）在假設沒有外力條件的混凝土收縮變形的時間已給出。</p><p><b>　　系數(shù)由下面給出</b></p><p><b>　　最終的收縮變形</b></p><p>　　值的變化范圍很大。在ACI2092.26提到過，變化范圍為0.000415～0.00107，采用濕養(yǎng)護方法取0.00080，采用蒸氣

29、養(yǎng)護方法取0.00073。平均值常用在缺乏精確的數(shù)據(jù)時被使用。</p><p>　　干燥前的養(yǎng)護時間，St</p><p><b>　　采用濕養(yǎng)護7天后</b></p><p><b>　　(2.17a)</b></p><p>　　t=養(yǎng)護7天后的時間，</p><p>　

30、　(St=0.46, 0.72, 0.84, 0.91,和 0.98 從t = 1 個月, 3個月, 6個月, 1年, 和 5年, 各自取值)</p><p>　　或者, 采用蒸汽養(yǎng)護3天后,</p><p><b>　　(2.17b)</b></p><p>　　t=養(yǎng)護3天后的時間，</p><p>　　(St=0.

31、35, 0.62, 0.77, 0.87,和0.97從 t = 1 個月, 3 個月, 6個月, 1 年，和5年各自取值)</p><p><b>　　濕度條件，Sh</b></p><p>　　Sh=1.4-0.01H for 40<H<80% (2.18a)</p><p><b>　　或者， </b&

32、gt;</p><p>　　Sh=3.0-0.03H for 80<H<100% (2.18b)</p><p>　　H = 濕度的百分比</p><p>　　(Sh = 1.00, 0.80, 0.60, 0,從 40, 60, 80,和100%各自取值)</p><p>　　試件的平均厚度， Sth</p&g

33、t;<p>　　Sth =小于6英尺時取0.84，9英尺時取1.00 (1 英尺 = 25.4mm)</p><p><b>　　塌落度, Ss</b></p><p>　　Ss = 2英尺時取0.97, 2.7英尺時取1.00, 1.01 ，3英尺時取1.01, 4 英尺時取1.05, 5英尺時取1.09 (1 in =25.4mm)</p>

34、;<p><b>　　砂率，Sf</b></p><p>　　Sf =含砂率40%取0.86, 含砂率50%取1.00，含砂率70%取1.04。 </p><p>　　含氣量影響系數(shù), Se</p><p>　　Se= 含氣量 4%時取0.98, 含氣量 6%時取1.00， r含氣量10% 取1.03.</p>&l

35、t;p><b>　　單位水泥量, Sc</b></p><p>　　Sc=376 1b/yd3,取0.87， 564 1b/ yd3,取0.95,705 1b/yd3 取1.00 940 1b/yd3取1.09 (1 1b/yd3=0.593kg/m3)</p><p><b>　　例 2.2</b></p><p&g

36、t;　　假設一片 230mm厚的混凝土墻，處在為7天到5年的期間內(nèi)，相對濕度為60%。 混凝土塌落度為3英尺 (76mm)，混凝土的含沙率為34％，單位水泥量為600 1b/yd3（356 kg/m3）,空氣含量影響系數(shù)為5％，并且在蒸汽養(yǎng)護5天后被使用的。</p><p><b>　　解：</b></p><p><b>　　由2.16例得 </b&