土木工程專業(yè)畢業(yè)設(shè)計外文翻譯

1、<p>　　Building construction concrete crack of prevention and processing</p><p><b>　　Abstract</b></p><p>　　The crack problem of concrete is a widespread existence but again diffi

2、cult in solve of engineering actual problem, this text carried on a study analysis to a little bit familiar crack problem in the concrete engineering, and aim at concrete the circumstance put forward some prevention, pro

3、cessing measure. Keyword:Concrete crack prevention processing</p><p><b>　　Foreword</b></p><p>　　Concrete's ising 1 kind is anticipate by the freestone bone, cement, water and oth

4、er mixture but formation of the in addition material of quality brittleness not and all material.Because the concrete construction transform with oneself, control etc. a series problem, harden model of in the concrete ex

5、istence numerous tiny hole, spirit cave and tiny crack, is exactly because these beginning start blemish of existence just make the concrete present one some not and all the characteristic of qualit</p><p>　

6、　concrete engineering crack problem is ineluctable, also acceptable in certainly of the scope just need to adopt valid of measure will it endanger degree control at certain of scope inside.The reinforced concrete norm is

7、 also explicit provision:Some structure at place of dissimilarity under the condition allow existence certain the crack of width.But at under construction should as far as possible adopt a valid measure control crack cre

8、ation, make the structure don't appear crack possibly or as f</p><p>　　durable of the rust eclipse influence concrete of reinforcing bar, under the function of the water pressure dint would creation the

9、water power split crack influence concrete of loading dint etc..Concrete stem the Suo be main with water ash of the concrete ratio, the dosage of the composition, cement of cement, gather to anticipate of the dosage of t

10、he property and dosage, in addition etc. relevant. Main prevention measure:While being to choose to use the constringency quantity smaller cement, g</p><p>　　constringency, therefore creation cracked.The inf

11、luence concrete Su constringency open the main factor of crack to have water ash ratio, concrete of condense time, environment temperature, wind velocity, relative humidity……etc.. Main prevention measure:One is choose to

12、 use stem the Suo value smaller higher Huo sour salt of the earlier period strength or common the Huo sour brine mire.Two is strict the control water ash ratio, the Chan add to efficiently reduce water to increment the c

13、ollapse of </p><p>　　just degree, and prop up firm, and make the foundation be subjected to dint even.Three is keep concrete from sprinkle infusing the foundation in the process is soak by water.Four is time

14、 that template tore down to can't be too early, and want to notice to dismantle a mold order of sequence.Five is at jelly soil top take to establish template to notice to adopt certain of prevention measure. 4.Temper

15、ature crack and prevention Temperature crack much the occurrence is in big surface or difference i</p><p>　　parallelism, crack along long side cent the segment appear, in the center more airtight.Crack width

16、 the size be different, be subjected to temperature variety influence more obvious, winter compare breadth, summer more narrow.The concrete temperature crack that the heat inflation cause is usually in the center the thi

17、ck both ends be thin, but cold Suo crack of thick thin variety not too obvious.The emergence of the this kind crack will cause the rust eclipse of reinforcing bar, the carbonization</p><p>　　Building constru

18、ction concrete crack of prevention and processing</p><p><b>　　Abstract</b></p><p>　　The crack problem of concrete is a widespread existence but again difficult in solve of engineerin

19、g actual problem, this text carried on a study analysis to a little bit familiar crack problem in the concrete engineering, and aim at concrete the circumstance put forward some prevention, processing measure. Keyword:Co

20、ncrete crack prevention processing</p><p><b>　　Foreword</b></p><p>　　Concrete's ising 1 kind is anticipate by the freestone bone, cement, water and other mixture but formation of

21、 the in addition material of quality brittleness not and all material.Because the concrete construction transform with oneself, control etc. a series problem, harden model of in the concrete existence numerous tiny hole,

22、 spirit cave and tiny crack, is exactly because these beginning start blemish of existence just make the concrete present one some not and all the characteristic of qualit</p><p>　　concrete engineering crack

23、 problem is ineluctable, also acceptable in certainly of the scope just need to adopt valid of measure will it endanger degree control at certain of scope inside.The reinforced concrete norm is also explicit provision:So

24、me structure at place of dissimilarity under the condition allow existence certain the crack of width.But at under construction should as far as possible adopt a valid measure control crack creation, make the structure d

25、on't appear crack possibly or as f</p><p>　　durable of the rust eclipse influence concrete of reinforcing bar, under the function of the water pressure dint would creation the water power split crack inf

26、luence concrete of loading dint etc..Concrete stem the Suo be main with water ash of the concrete ratio, the dosage of the composition, cement of cement, gather to anticipate of the dosage of the property and dosage, in

27、addition etc. relevant. Main prevention measure:While being to choose to use the constringency quantity smaller cement, g</p><p>　　constringency, therefore creation cracked.The influence concrete Su constrin

28、gency open the main factor of crack to have water ash ratio, concrete of condense time, environment temperature, wind velocity, relative humidity……etc.. Main prevention measure:One is choose to use stem the Suo value sma

29、ller higher Huo sour salt of the earlier period strength or common the Huo sour brine mire.Two is strict the control water ash ratio, the Chan add to efficiently reduce water to increment the collapse of </p><

30、p>　　just degree, and prop up firm, and make the foundation be subjected to dint even.Three is keep concrete from sprinkle infusing the foundation in the process is soak by water.Four is time that template tore down to

31、 can't be too early, and want to notice to dismantle a mold order of sequence.Five is at jelly soil top take to establish template to notice to adopt certain of prevention measure. 4.Temperature crack and prevention

32、Temperature crack much the occurrence is in big surface or difference i</p><p>　　parallelism, crack along long side cent the segment appear, in the center more airtight.Crack width the size be different, be

33、subjected to temperature variety influence more obvious, winter compare breadth, summer more narrow.The concrete temperature crack that the heat inflation cause is usually in the center the thick both ends be thin, but c

34、old Suo crack of thick thin variety not too obvious.The emergence of the this kind crack will cause the rust eclipse of reinforcing bar, the carbonization</p><p>　　Tu2 Shua.13 is to strengthen concrete to pr

35、otect, the concrete after sprinkle build use moist grass Lian in time, hemp slice's etc. overlay, and attention sprinkle water to protect, appropriate extension protect time, assurance the concrete surface be slow-mo

36、ving cool off.At the cold season, concrete surface should constitution heat preservation measure, in order to prevent cold wave assault.14 is the allocation be a little amount in the concrete of reinforcing bar perhaps a

37、dd fiber material con</p><p>　　Crack processing</p><p>　　The emergence of the crack not only would influence structure of whole with just degree, return will cause the rust eclipse of reinforcin

38、g bar, acceleration concrete of carbonization, lower durable and anti- of concrete tired, anti- Shen ability.Therefore according to the property of crack and concrete circumstance we want differentiation to treat, in tim

39、e processing, with assurance building of safety usage. The repair measure of the concrete crack is main to have the following some method:Surfa</p><p>　　polymer cement sand syrup. 2, the structure reinforce

40、a method When the crack influence arrive concrete structure of function, will consideration adopt to reinforce a method to carry on processing to the concrete structure.The structure reinforce medium in common use main h

41、ave the following a few method:The piece of enlargement concrete structure in every aspect accumulate, outside the Cape department of the Gou piece pack type steel, adoption prepare should the dint method reinforce, glue

42、 to st</p><p>　　the composition, at concrete inner part formation the intelligence type imitate to living from heal nerve network system, be the concrete appear crack secrete a parts of liquid Xin fiber can

43、make the crack re- heal.</p><p>　　Conclusion</p><p>　　The crack is widespread in the concrete structure existence of a kind of phenomenon, it of emergence not only will lower the anti- Shen of b

44、uilding ability, influence building of usage function, and will cause the rust eclipse of reinforcing bar, the carbonization of concrete, lower the durable of material, influence building of loading ability, so want to c

45、arry on to the concrete crack earnest research, differentiation treat, adoption reasonable of the method carry on processing, and at under c</p><p>　　From《CANADIAN JOURNAL OF CIVIL ENGINEERING》</p>&l

46、t;p>　　建筑施工混凝土裂縫的預防與處理</p><p>　　混凝土的裂縫問題是一個普遍存在而又難于解決的工程實際問題，本文對混 凝土工程中常見的一些裂縫問題進行了探討分析，并針對具體情況提出了一些預 防、處理措施。 關(guān)鍵詞：混凝土 裂縫 預防 處理 前言 混凝土是一種由砂石骨料、水泥、水及其他外加材料混合而形成的非均質(zhì)脆 性材料。由于混凝土施工和本身變形、約束等一系列問題，硬化成型的混凝土中 存在著眾多

47、的微孔隙、氣穴和微裂縫，正是由于這些初始缺陷的存在才使混凝土 呈現(xiàn)出一些非均質(zhì)的特性。微裂縫通常是一種無害裂縫，對混凝土的承重、防滲 及其他一些使用功能不產(chǎn)生危害。但是在混凝土受到荷載、溫差等作用之后，微 裂縫就會不斷的擴展和連通，最終形成我們?nèi)庋劭梢姷暮暧^裂縫，也就是混凝土 工程中常說的裂縫。 混凝土建筑和構(gòu)件通常都是帶縫工作的，由于裂縫的存在和發(fā)展通常會使內(nèi) 部的鋼筋等材料產(chǎn)生腐蝕，降低鋼筋混凝土材料的承載能力、耐久性及抗?jié)B能力，

48、影響建筑物的外觀、使用壽命，嚴重者將會威脅到人們的生命和財產(chǎn)安全。很多 工程的失事都是由于裂縫的不穩(wěn)定發(fā)展所致。近代科學研究和大量的混凝土工程 實踐證明，在混凝土工程中裂縫問題是不可避免的，在一定的范圍內(nèi)也是可以接</p><p>　　干縮裂縫多出現(xiàn)在混凝土養(yǎng)護結(jié)束后的一段時間或是混凝土澆筑完畢后的一 周左右。水泥漿中水分的蒸發(fā)會產(chǎn)生干縮，且這種收縮是不可逆的。干縮裂縫的 產(chǎn)生主要是由于混凝土內(nèi)外水分蒸發(fā)程度不同

49、而導致變形不同的結(jié)果：混凝土受 外部條件的影響，表面水分損失過快，變形較大，內(nèi)部濕度變化較小變形較小， 較大的表面干縮變形受到混凝土內(nèi)部約束，產(chǎn)生較大拉應力而產(chǎn)生裂縫。相對濕 度越低，水泥漿體干縮越大，干縮裂縫越易產(chǎn)生。干縮裂縫多為表面性的平行線 狀或網(wǎng)狀淺細裂縫，寬度多在0.05-0.2mm之間，大體積混凝土中平面部位多見， 較薄的梁板中多沿其短向分布。干縮裂縫通常會影響混凝土的抗?jié)B性，引起鋼筋 的銹蝕影響混凝土的耐久性，在水壓力的作

50、用下會產(chǎn)生水力劈裂影響混凝土的承 載力等等?；炷粮煽s主要和混凝土的水灰比、水泥的成分、水泥的用量、集料 的性質(zhì)和用量、外加劑的用量等有關(guān)。 主要預防措施：一是選用收縮量較小的水泥，一般采用中低熱水泥和粉煤灰 水泥，降低水泥的用量。二是混凝土的干縮受水灰比的影響較大，水灰比越大， 干縮越大，因此在混凝土配合比設(shè)計中應盡量控制好水灰比的選用，同時摻加合 適的減水劑。三是嚴格控制混</p><p>　　少水泥及水的用

51、量。三是澆筑混凝土之前，將基層和模板澆水均勻濕透。四是及 時覆蓋塑料薄膜或者潮濕的草墊、麻片等，保持混凝土終凝前表面濕潤，或者在 混凝土表面噴灑養(yǎng)護劑等進行養(yǎng)護。五是在高溫和大風天氣要設(shè)置遮陽和擋風設(shè) 施，及時養(yǎng)護。 3.沉陷裂縫及預防 沉陷裂縫的產(chǎn)生是由于結(jié)構(gòu)地基土質(zhì)不勻、松軟或回填土不實或浸水而造成 不均勻沉降所致；或者因為模板剛度不足，模板支撐間距過大或支撐底部松動等 導致，特別是在冬季，模板支撐在凍土上，凍土化凍后產(chǎn)生不均勻沉降

52、，致使混 凝土結(jié)構(gòu)產(chǎn)生裂縫。此類裂縫多為深進或貫穿性裂縫，其走向與沉陷情況有關(guān)， 一般沿與地面垂直或呈30°-45°角方向發(fā)展，較大的沉陷裂縫，往往有一定的錯 位，裂縫寬度往往與沉降量成正比關(guān)系。裂縫寬度受溫度變化的影響較小。地基 變形穩(wěn)定之后，沉陷裂縫也基本趨于穩(wěn)定。 主要預防措施：一是對松軟土、回填土地基在上部結(jié)構(gòu)施工前應進行必要的 夯實和加固。二是保證模板有足夠的強度和剛度，且支撐牢固，并使地基受力均 勻。三是

53、防止混凝土澆灌過程中地基被水浸泡。四是模板拆除的時間不能太早， 且要注意拆模的先后次序。 五是在凍土上搭設(shè)模板時要注意采取一定</p><p>　　尺寸較大的結(jié)構(gòu)，裂縫多平行于短邊；深入和貫穿性的溫度裂縫一般與短邊方向 平行或接近平行，裂縫沿著長邊分段出現(xiàn)，中間較密。裂縫寬度大小不一，受溫 度變化影響較為明顯，冬季較寬，夏季較窄。高溫膨脹引起的混凝土溫度裂縫是 通常中間粗兩端細，而冷縮裂縫的粗細變化不太明顯。此種

54、裂縫的出現(xiàn)會引起鋼 筋的銹蝕，混凝土的碳化，降低混凝土的抗凍融、抗疲勞及抗?jié)B能力等。 主要預防措施：一是盡量選用低熱或中熱水泥，如礦渣水泥、粉煤灰水泥等。 二是減少水泥用量，將水泥用量盡量控制在450kg/m3以下。三是降低水灰比，一 般混凝土的水灰比控制在0.6以下。四是改善骨料級配，摻加粉煤灰或高效減水劑 等來減少水泥用量，降低水化熱。五是改善混凝土的攪拌加工工藝，降低混凝土 的澆筑溫度。六是在混凝土中摻加一定量的具有減水、增塑、緩

55、凝等作用的外加 劑，改善混凝土拌合物的流動性、保水性，降低水化熱，推遲熱峰的出現(xiàn)時間。 七是高溫季節(jié)澆筑時可以采用搭設(shè)遮陽板等輔助措施控制混凝土的溫升，降低澆 筑混凝土的溫度。八是大體積混凝土的溫度應力與結(jié)構(gòu)尺寸相關(guān)，混凝土結(jié)構(gòu)尺 寸越大，溫度應力越大，因此要合理安排施工工序，分層、分塊澆筑</p><p>　　和低堿或無堿的外加劑。三是選用合適的摻和料抑制堿骨料反應。 由于混凝土澆筑、振搗不良或者是鋼筋保護層較

56、薄，有害物質(zhì)進入混凝土使 鋼筋產(chǎn)生銹蝕，銹蝕的鋼筋體積膨脹，導致混凝土脹裂，此種類型的裂縫多為縱 向裂縫，沿鋼筋的位置出現(xiàn)。通常的預防措施有：一是保證鋼筋保護層的厚度。 二是混凝土級配要良好。三是混凝土澆注要振搗密實。四是鋼筋表層涂刷防腐涂 料。 裂縫處理 裂縫的出現(xiàn)不但會影響結(jié)構(gòu)的整體性和剛度，還會引起鋼筋的銹蝕、加速混 凝土的碳化、降低混凝土的耐久性和抗疲勞、抗?jié)B能力。因此根據(jù)裂縫的性質(zhì)和 具體情況我們要區(qū)別對待、及時處理，以保證建

57、筑物的安全使用。 混凝土裂縫的修補措施主要有以下一些方法：表面修補法，灌漿、嵌縫封堵 法，結(jié)構(gòu)加固法，混凝土置換法，電化學防護法以及仿生自愈合法。 表面修補法是一種簡單、常見的修補方法，它主要適用于穩(wěn)定和對結(jié)構(gòu)承載 能力沒有影響的表面裂縫以及深進裂縫的處理。通常的處理措施是在裂縫的表面 涂抹水泥漿、環(huán)氧膠泥或在混凝土表面涂刷油漆、瀝青等防腐材料，在防護的同 時為了防止混凝土受各種作用的影響繼續(xù)開裂，通?？梢圆捎迷诹芽p的表面粘貼 玻璃纖維

58、布等措施。 1、灌</p><p>　　射混凝土補強加固。 3、混凝土置換法 混凝土置換法是處理嚴重損壞混凝土的一種有效方法，此方法是先將損壞的 混凝土剔除，然后再置換入新的混凝土或其他材料。常用的置換材料有：普通混 凝土或水泥砂漿、聚合物或改性聚合物混凝土或砂漿。 4、電化學防護法 電化學防腐是利用施加電場在介質(zhì)中的電化學作用，改變混凝土或鋼筋混凝 土所處的環(huán)境狀態(tài)，鈍化鋼筋，以達到防腐的目的。陰極防護法、氯鹽

59、提取法、 堿性復原法是化學防護法中常用而有效的三種方法。這種方法的優(yōu)點是防護方法 受環(huán)境因素的影響較小，適用鋼筋、混凝土的長期防腐，既可用于已裂結(jié)構(gòu)也可 用于新建結(jié)構(gòu)。 5、仿生自愈合法 仿生自愈合法是一種新的裂縫處理方法，它模仿生物組織對受創(chuàng)傷部位自動 分泌某種物質(zhì)，而使創(chuàng)傷部位得到愈合的機能，在混凝土的傳統(tǒng)成分中加入某些 特殊成分（如含粘結(jié)劑的液芯纖維或膠囊），在混凝土內(nèi)部形成智能型仿生自愈 合神經(jīng)網(wǎng)絡系統(tǒng)，當混凝土出現(xiàn)裂縫時分泌出

60、部分液芯纖維可使裂縫重新愈合。 結(jié) 論 裂縫是混凝土結(jié)構(gòu)中普遍存在的一種現(xiàn)象，它的出現(xiàn)不僅會降低建筑物的抗 滲能力，影響建筑物的使用功能，而且會引起鋼筋的銹蝕，混凝土的碳化，降低 材料</p><p>　　出自《加拿大土木工程學報》本文由左左涂涂右右貢獻</p><p>　　Building construction concrete crack of prevention and pro

61、cessing</p><p><b>　　Abstract</b></p><p>　　The crack problem of concrete is a widespread existence but again difficult in solve of engineering actual problem, this text carried on a s

62、tudy analysis to a little bit familiar crack problem in the concrete engineering, and aim at concrete the circumstance put forward some prevention, processing measure. Keyword:Concrete crack prevention processing</p&g

63、t;<p><b>　　Foreword</b></p><p>　　Concrete's ising 1 kind is anticipate by the freestone bone, cement, water and other mixture but formation of the in addition material of quality britt

64、leness not and all material.Because the concrete construction transform with oneself, control etc. a series problem, harden model of in the concrete existence numerous tiny hole, spirit cave and tiny crack, is exactly be

65、cause these beginning start blemish of existence just make the concrete present one some not and all the characteristic of qualit</p><p>　　concrete engineering crack problem is ineluctable, also acceptable i

66、n certainly of the scope just need to adopt valid of measure will it endanger degree control at certain of scope inside.The reinforced concrete norm is also explicit provision:Some structure at place of dissimilarity und

67、er the condition allow existence certain the crack of width.But at under construction should as far as possible adopt a valid measure control crack creation, make the structure don't appear crack possibly or as f<

68、/p><p>　　durable of the rust eclipse influence concrete of reinforcing bar, under the function of the water pressure dint would creation the water power split crack influence concrete of loading dint etc..Concr

69、ete stem the Suo be main with water ash of the concrete ratio, the dosage of the composition, cement of cement, gather to anticipate of the dosage of the property and dosage, in addition etc. relevant. Main prevention me

70、asure:While being to choose to use the constringency quantity smaller cement, g</p><p>　　constringency, therefore creation cracked.The influence concrete Su constringency open the main factor of crack to hav

71、e water ash ratio, concrete of condense time, environment temperature, wind velocity, relative humidity……etc.. Main prevention measure:One is choose to use stem the Suo value smaller higher Huo sour salt of the earlier p

72、eriod strength or common the Huo sour brine mire.Two is strict the control water ash ratio, the Chan add to efficiently reduce water to increment the collapse of </p><p>　　just degree, and prop up firm, and

73、make the foundation be subjected to dint even.Three is keep concrete from sprinkle infusing the foundation in the process is soak by water.Four is time that template tore down to can't be too early, and want to notic

74、e to dismantle a mold order of sequence.Five is at jelly soil top take to establish template to notice to adopt certain of prevention measure. 4.Temperature crack and prevention Temperature crack much the occurrence is i

75、n big surface or difference i</p><p>　　parallelism, crack along long side cent the segment appear, in the center more airtight.Crack width the size be different, be subjected to temperature variety influence

76、 more obvious, winter compare breadth, summer more narrow.The concrete temperature crack that the heat inflation cause is usually in the center the thick both ends be thin, but cold Suo crack of thick thin variety not to

77、o obvious.The emergence of the this kind crack will cause the rust eclipse of reinforcing bar, the carbonization</p><p>　　Tu2 Shua.13 is to strengthen concrete to protect, the concrete after sprinkle build u

78、se moist grass Lian in time, hemp slice's etc. overlay, and attention sprinkle water to protect, appropriate extension protect time, assurance the concrete surface be slow-moving cool off.At the cold season, concrete

79、 surface should constitution heat preservation measure, in order to prevent cold wave assault.14 is the allocation be a little amount in the concrete of reinforcing bar perhaps add fiber material con</p><p>

80、　　Crack processing</p><p>　　The emergence of the crack not only would influence structure of whole with just degree, return will cause the rust eclipse of reinforcing bar, acceleration concrete of carbonizat

81、ion, lower durable and anti- of concrete tired, anti- Shen ability.Therefore according to the property of crack and concrete circumstance we want differentiation to treat, in time processing, with assurance building of s

82、afety usage. The repair measure of the concrete crack is main to have the following some method:Surfa</p><p>　　polymer cement sand syrup. 2, the structure reinforce a method When the crack influence arrive c

83、oncrete structure of function, will consideration adopt to reinforce a method to carry on processing to the concrete structure.The structure reinforce medium in common use main have the following a few method:The piece o

84、f enlargement concrete structure in every aspect accumulate, outside the Cape department of the Gou piece pack type steel, adoption prepare should the dint method reinforce, glue to st</p><p>　　the compositi

85、on, at concrete inner part formation the intelligence type imitate to living from heal nerve network system, be the concrete appear crack secrete a parts of liquid Xin fiber can make the crack re- heal.</p><p&

86、gt;　　Conclusion</p><p>　　The crack is widespread in the concrete structure existence of a kind of phenomenon, it of emergence not only will lower the anti- Shen of building ability, influence building of usa

87、ge function, and will cause the rust eclipse of reinforcing bar, the carbonization of concrete, lower the durable of material, influence building of loading ability, so want to carry on to the concrete crack earnest rese

88、arch, differentiation treat, adoption reasonable of the method carry on processing, and at under c</p><p>　　From《CANADIAN JOURNAL OF CIVIL ENGINEERING》</p><p>　　建筑施工混凝土裂縫的預防與處理</p><p&

89、gt;　　混凝土的裂縫問題是一個普遍存在而又難于解決的工程實際問題，本文對混 凝土工程中常見的一些裂縫問題進行了探討分析，并針對具體情況提出了一些預 防、處理措施。 關(guān)鍵詞：混凝土 裂縫 預防 處理 前言 混凝土是一種由砂石骨料、水泥、水及其他外加材料混合而形成的非均質(zhì)脆 性材料。由于混凝土施工和本身變形、約束等一系列問題，硬化成型的混凝土中 存在著眾多的微孔隙、氣穴和微裂縫，正是由于這些初始缺陷的存在才使混凝土 呈現(xiàn)出一些非均質(zhì)的特性

90、。微裂縫通常是一種無害裂縫，對混凝土的承重、防滲 及其他一些使用功能不產(chǎn)生危害。但是在混凝土受到荷載、溫差等作用之后，微 裂縫就會不斷的擴展和連通，最終形成我們?nèi)庋劭梢姷暮暧^裂縫，也就是混凝土 工程中常說的裂縫。 混凝土建筑和構(gòu)件通常都是帶縫工作的，由于裂縫的存在和發(fā)展通常會使內(nèi) 部的鋼筋等材料產(chǎn)生腐蝕，降低鋼筋混凝土材料的承載能力、耐久性及抗?jié)B能力， 影響建筑物的外觀、使用壽命，嚴重者將會威脅到人們的生命和財產(chǎn)安全。很多 工程的失事都

91、是由于裂縫的不穩(wěn)定發(fā)展所致。近代科學研究和大量的混凝土工程 實踐證明，在混凝土工程中裂縫問題是不可避免的，在一定的范圍內(nèi)也是可以接</p><p>　　干縮裂縫多出現(xiàn)在混凝土養(yǎng)護結(jié)束后的一段時間或是混凝土澆筑完畢后的一 周左右。水泥漿中水分的蒸發(fā)會產(chǎn)生干縮，且這種收縮是不可逆的。干縮裂縫的 產(chǎn)生主要是由于混凝土內(nèi)外水分蒸發(fā)程度不同而導致變形不同的結(jié)果：混凝土受 外部條件的影響，表面水分損失過快，變形較大，內(nèi)部濕度

92、變化較小變形較小， 較大的表面干縮變形受到混凝土內(nèi)部約束，產(chǎn)生較大拉應力而產(chǎn)生裂縫。相對濕 度越低，水泥漿體干縮越大，干縮裂縫越易產(chǎn)生。干縮裂縫多為表面性的平行線 狀或網(wǎng)狀淺細裂縫，寬度多在0.05-0.2mm之間，大體積混凝土中平面部位多見， 較薄的梁板中多沿其短向分布。干縮裂縫通常會影響混凝土的抗?jié)B性，引起鋼筋 的銹蝕影響混凝土的耐久性，在水壓力的作用下會產(chǎn)生水力劈裂影響混凝土的承 載力等等。混凝土干縮主要和混凝土的水灰比、水泥的成

93、分、水泥的用量、集料 的性質(zhì)和用量、外加劑的用量等有關(guān)。 主要預防措施：一是選用收縮量較小的水泥，一般采用中低熱水泥和粉煤灰 水泥，降低水泥的用量。二是混凝土的干縮受水灰比的影響較大，水灰比越大， 干縮越大，因此在混凝土配合比設(shè)計中應盡量控制好水灰比的選用，同時摻加合 適的減水劑。三是嚴格控制混</p><p>　　少水泥及水的用量。三是澆筑混凝土之前，將基層和模板澆水均勻濕透。四是及 時覆蓋塑料薄膜或者潮濕的草

94、墊、麻片等，保持混凝土終凝前表面濕潤，或者在 混凝土表面噴灑養(yǎng)護劑等進行養(yǎng)護。五是在高溫和大風天氣要設(shè)置遮陽和擋風設(shè) 施，及時養(yǎng)護。 3.沉陷裂縫及預防 沉陷裂縫的產(chǎn)生是由于結(jié)構(gòu)地基土質(zhì)不勻、松軟或回填土不實或浸水而造成 不均勻沉降所致；或者因為模板剛度不足，模板支撐間距過大或支撐底部松動等 導致，特別是在冬季，模板支撐在凍土上，凍土化凍后產(chǎn)生不均勻沉降，致使混 凝土結(jié)構(gòu)產(chǎn)生裂縫。此類裂縫多為深進或貫穿性裂縫，其走向與沉陷情況有關(guān)， 一

95、般沿與地面垂直或呈30°-45°角方向發(fā)展，較大的沉陷裂縫，往往有一定的錯 位，裂縫寬度往往與沉降量成正比關(guān)系。裂縫寬度受溫度變化的影響較小。地基 變形穩(wěn)定之后，沉陷裂縫也基本趨于穩(wěn)定。 主要預防措施：一是對松軟土、回填土地基在上部結(jié)構(gòu)施工前應進行必要的 夯實和加固。二是保證模板有足夠的強度和剛度，且支撐牢固，并使地基受力均 勻。三是防止混凝土澆灌過程中地基被水浸泡。四是模板拆除的時間不能太早， 且要注意拆模的先后次

96、序。 五是在凍土上搭設(shè)模板時要注意采取一定</p><p>　　尺寸較大的結(jié)構(gòu)，裂縫多平行于短邊；深入和貫穿性的溫度裂縫一般與短邊方向 平行或接近平行，裂縫沿著長邊分段出現(xiàn)，中間較密。裂縫寬度大小不一，受溫 度變化影響較為明顯，冬季較寬，夏季較窄。高溫膨脹引起的混凝土溫度裂縫是 通常中間粗兩端細，而冷縮裂縫的粗細變化不太明顯。此種裂縫的出現(xiàn)會引起鋼 筋的銹蝕，混凝土的碳化，降低混凝土的抗凍融、抗疲勞及抗?jié)B能力等。

97、 主要預防措施：一是盡量選用低熱或中熱水泥，如礦渣水泥、粉煤灰水泥等。 二是減少水泥用量，將水泥用量盡量控制在450kg/m3以下。三是降低水灰比，一 般混凝土的水灰比控制在0.6以下。四是改善骨料級配，摻加粉煤灰或高效減水劑 等來減少水泥用量，降低水化熱。五是改善混凝土的攪拌加工工藝，降低混凝土 的澆筑溫度。六是在混凝土中摻加一定量的具有減水、增塑、緩凝等作用的外加 劑，改善混凝土拌合物的流動性、保水性，降低水化熱，推遲熱峰的出現(xiàn)時間