徐新-橋梁混凝土裂縫產生的原因和處理措施(共18頁)

1、精選優(yōu)質文檔-傾情為你奉上畢 業(yè) 論 文 論文題目： 橋梁混凝土裂縫產生的原因和處理措施 系 部： 公 路 工 程 系 專業(yè)名稱： 道路橋梁工程技術 班 級： 08213 學 號： 24 姓 名： 徐 新 指導教師： 李 永 成 完成時間： 2011 年 5 月 12 日專心-專注-專業(yè)目 錄橋梁混凝土裂縫產生的原因和處理措施摘要：在橋梁建設使用過程中，因出現裂縫而影響工程質量甚至導致橋梁垮塌的現象也屢見不鮮。本文闡述了混凝土橋梁裂縫的種類，從荷載、溫度變化、地基變形等5個方面介紹了混凝土裂縫的成因，提出了相應的預防措施，同時給出了一些裂縫處理方法。關鍵詞：橋梁混凝土裂縫、原因、措施前言隨著我

2、國交通基礎建設的高速發(fā)展，各地興建了大量的混凝土橋梁。在橋梁建造和使用的過程中，由于混凝土裂縫而影響工程質量甚至造成坍塌事故的案例屢見不鮮?；炷灵_裂可以說是“常發(fā)病”和“多發(fā)病”，嚴重影響了橋梁的使用性能，也經常困擾著橋梁工程技術人員。要想控制橋梁混凝土裂縫的產生，提高工程質量，就必須了解其成因。下面本文就對橋梁裂縫的產生原因做一分析，并提出一些對裂縫的預防措施和處理方法。1 橋梁混凝土裂縫產生的原因1.1 荷載引起的裂縫荷載引起的裂縫可以分為直接應力裂縫和次應力裂縫。1.1.1直接應力裂縫直接應力裂縫是指外荷載引起的直接應力產生的裂縫。裂縫產生的原因有：(1)設計計算階段的結構設計不合理，

3、受力假設與實際受力不符，安全系數不夠，不考慮施工的可能性，構造處理不當。(2)施工階段中不加限制的堆放施工機具、材料；隨意翻身、起吊、運輸、安裝；不按設計圖紙施工，擅自更改結構施工順序等。(3)使用階段時超出設計荷載的重型車輛過橋；受車輛、船舶的接觸、撞擊；發(fā)生地震、爆炸等。1.1.2 次應力裂縫次應力裂縫是指由外荷載引起的次生應力產生的裂縫，其產生的原因可歸納為一下幾個方面：(1)在設計荷載作用下，由于結構物的實際工作狀態(tài)同常規(guī)計算有出入或計算不考慮，從而在某些部位引起次應力導致結構開裂。例如兩鉸拱橋拱腳設計時常采用布置“X”形鋼筋、同時消減該處斷面尺寸的辦法設計鉸，理論算該處不會存在彎矩，

4、但實際該鉸仍然能夠抗彎，以致出現裂縫而導致鋼筋銹蝕。(2)橋梁結構中經常需要鑿槽、升洞、設置牛腿等，在常規(guī)計算中難以用準確的圖式進行模擬計算，一般根據經驗設置受力鋼筋。研究表明，受力構件挖空后，力流將產生繞射現象，在空洞附近密集，產生巨大的集中應力。在長跨預應力連續(xù)梁中，經常在跨內根據截面內力需要截斷鋼束，設置錨頭，而在錨固斷面附近經?？梢钥吹搅芽p。因此，在這些結構的轉角處或構件形狀突變處、受力鋼筋截面處容易出現裂縫。實際工程中次應力是產生荷載裂縫的最常見原因。次應力裂縫多屬于張拉、劈裂、剪切性質。在設計上，應盡量避免結構突變（或截面突變），當不能同時避免時，應作局部處理，如做成圓角或倒角，同

5、時加強構造配筋，轉角處配置斜向鋼筋，對于較大空洞有條件時可以在周邊設置護邊角鋼。1.2 收縮引起的裂縫1.2.1 塑性收縮混凝土澆筑后4h5h左右，水泥水化反應劇烈，分子鏈逐漸形成，出現泌水和水分急劇蒸發(fā)，混凝土失水收縮，同時骨料因自重下沉，而此時混凝土尚未硬化，稱為塑性收縮。在骨料下沉過程中若受到鋼筋阻擋，便形成沿鋼筋方向的裂縫，在構件豎向變截面處如T梁、箱梁腹板與頂板交接處，因硬化前沉實不均勻將發(fā)生表面的順腹板方向裂縫。(1)干縮：混凝土結硬以后，隨著表面水分逐漸蒸發(fā)，溫度逐漸降低，混凝土體積減小，稱為干縮。因混凝土表面水分損失快，內部損失慢，因此產生表面收縮快，內部收縮慢的不均勻收縮，導

6、致混凝土表面承受拉力，產生收縮裂縫。(2)自生收縮：混凝土在硬化工程中，水泥和水發(fā)生水化反應，這種收縮與外界溫度無關，并可以是正的（即收縮，如普通硅酸鹽水泥混凝土），也可以是負的（即膨脹，如礦渣水泥混凝土與粉煤灰混凝土）。(3)碳化收縮：大氣中的二氧化碳和水泥中的水化物發(fā)生化學反應引起的收縮變形。1.3 地基變形引起的裂縫(1)地質勘探精度不夠、試驗資料不準?？辈靾蟾娌荒艹浞址从硨嶋H地質情況是造成地基不均勻沉降的主要原因。(2)地基地質差異太大。(3)結構荷載差異太大。在地質情況比較一致的情況下，各部分基礎荷載差異太大時，有可能引起不均勻沉降。(4)結構基礎類型差別大。同一聯橋梁中混合使用不同

7、基礎，如擴大基礎和樁基礎，或雖采用同一種基礎，但是基底標高差異太大，也可能引起地基不均勻沉降。(5)分期建造的基礎。在原有的橋梁附近新建橋梁時，如分期修建的高速公路左右半幅橋梁，新建橋梁荷載或基礎處理時引起地基土重新固結，均可能對原有橋梁基礎造成較大沉降。(6)地基凍脹。(7)橋梁基礎置于滑坡體、溶洞或活動斷層等不良地質時，可能造成不均勻沉降。(8)橋梁建成以后，原有地基條件變化。大多數天然地基和人工地基浸水后，尤其是素填土、黃土、膨脹土等特殊地基土、土體強度遇水下降，壓縮變形加大。1.4 原材料質量引起的裂縫混凝土主要由水泥、砂、骨料、拌合用水及外加劑等組成，配置混凝土時所采用的材料不合格，

8、可能導致結構出現裂縫。(1)水泥質量不合格、受潮或過期會造成混凝土強度不夠，并導致混凝土開裂。(2)砂石含泥量超過規(guī)定，不僅降低混凝土強度和抗?jié)B性，還會是混凝土干燥時產生不規(guī)則的網狀裂縫。砂石的級配差，或砂石顆粒過細，用這種材料拌制的混凝土常造成側面裂縫。堿骨料反應，骨料中含有的活性硅化物質與堿性物質相遇，水、硅反應會產生膨脹的膠質，吸水后體積變大，造成局部膨脹和拉應力，則構件產生爆裂狀裂縫，在潮濕的地方較為多見。(3)拌合用水及外加劑 拌合用水或外加劑中氯化物等雜志含量較高時對鋼筋銹蝕有較大的影響。采用海水或堿泉水拌制混凝土，或采用含堿的外加劑，都可能對堿骨料反應有影響。(4)用于結構的鋼筋

9、已經銹蝕 植入結構體中的鋼筋已經有銹斑或銹蝕，造成鋼筋表面氧化膜破壞，在保護層厚度不足的情況下，空氣侵入到混凝土內部，鋼筋中的鐵離子與侵入到砼中的氧氣和水發(fā)生反應，其銹蝕物體積比原來增長越24倍，從而使周圍砼產生膨脹應力，導致保護層開裂、剝離，沿鋼筋縱向產生裂縫，并有銹跡滲透到砼表面。1.5 溫度變化引起的裂縫 (1)年溫差 由于四季溫度不斷變化，但變化相對緩慢，對橋梁結構的影響主要是導致橋梁的縱向位移，一般可通過橋面伸縮縫、支座位移、設置柔性墩等構造措施來調節(jié)，只有結構位移受到限制時才會引起溫度裂縫的產生，例如拱橋、剛架橋等。(2)日照橋面板、主梁或橋墩側面受到太陽暴曬后，溫度明顯高于其他部

10、位，溫度梯度呈非線性分布。由于受到自身約束作用，導致局部拉應力過大，出現裂縫。日照和下述驟然降溫是導致結構溫度裂縫的最常見原因。(3)驟然降溫 突降大雨、預冷空氣侵襲、日落等可導致外表面溫度突然下降，但結構內部溫度變化相對較慢而產生溫度梯度。日照和驟然降溫內力計算時可采用設計規(guī)范或參考實橋資料進行，混凝土彈模不考慮折減。(4)水化熱 出現在施工過程中，大體積混凝土（厚度超過2m）澆筑之后由于水泥水化放熱，導致內部溫度很高，內外溫度差太大，導致表面出現裂縫。(5)蒸汽養(yǎng)護或冬季施工施工措施不當，砼驟冷驟熱，內外溫度不均，易出現裂縫。(6)預制T梁之間橫隔板安裝時，支座預埋鋼板與調平鋼板焊接時，若

11、焊接不當，鐵件附近混凝土容易燒傷開裂。小結：水泥混凝土裂縫產生的原因當然遠不止這些，在這里就不一一贅述了。下面我們根據以上原因給出相應的裂縫預防措施和處理方法。2 預防裂縫的措施2.1 干縮裂縫的預防(1)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。(2)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計中應盡量控制好水灰比的選用，同時摻加合適的減水劑。(3)嚴格控制混凝土攪拌和施工中的配合比，混凝土的用水量絕對不能大于配合比設計所給定的用水量。(4)加強混凝土的早期養(yǎng)護，并適當延長混凝土的養(yǎng)護時間。冬季施工時要適當延長混凝土保溫覆蓋時間，并

12、涂刷養(yǎng)護劑養(yǎng)護。(5)嚴格按照設計要求在混凝土結構中設置合適的收縮縫。2.2 塑性收縮裂縫的預防(1)選用干縮值較小早期強度較高的硅酸鹽或普通硅酸鹽水泥。(2)嚴格控制水灰比，摻加高效減水劑來增加混凝土的坍落度和和易性，減少水泥及水的用量。(3)澆筑混凝土之前，將基層和模板澆水均勻濕透。(4)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。(5)在高溫和大風天氣要設置遮陽和擋風設施，及時養(yǎng)護。2.3 沉陷裂縫的預防(1)對松軟土、填土地基在上部結構施工前應進行必要的夯實和加固。(2)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

13、。(3)防止混凝土澆灌過程中地基被水浸泡。(4)模板拆除的時間不能太早，且要注意拆模的先后次序。(5)在凍土上搭設模板時要注意采取一定的預防措施。2.4 溫度裂縫的預防措施(1)盡量選用低熱或中熱水泥，如礦渣水泥、粉煤灰水泥等。(2)減少水泥用量,將水泥用量盡量控制在450kg/m3以下。(3)降低水灰比，一般混凝土的水灰比控制在0.6以下。(4)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。(5)改善混凝土的攪拌加工工藝，在傳統的三冷技術的基礎上采用二次風冷新工藝，降低混凝土的澆筑溫度。(6)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

14、性、保水性，降低水化熱，推遲熱峰的出現時間。(7)高溫季節(jié)澆筑時可以采用搭設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。(8)大體積混凝土的溫度應力與結構尺寸相關，混凝土結構尺寸越大，溫度應力越大，因此要合理安排施工工序，分層、分塊澆筑，以利于散熱，減小約束。(9)在大體積混凝土內部設置冷卻管道，通冷水或者冷氣冷卻，減小混凝土的內外溫差。(10)加強混凝土溫度的監(jiān)控，及時采取冷卻、保護措施。(11)預留溫度收縮縫。(12)減小約束，澆筑混凝土前宜在基巖和老混凝土上鋪設5mm左右的砂墊層或使用瀝青等材料涂刷。(13)加強混凝土養(yǎng)護，混凝土澆筑后，及時用濕潤的草簾、麻片等覆蓋，并注意灑

15、水養(yǎng)護，適當延長養(yǎng)護時間，保證混凝土表面緩慢冷卻。在寒冷季節(jié)，混凝土表面應設置保溫措施，以防止寒潮襲擊。(14)混凝土中配置少量的鋼筋或者摻入纖維材料將混凝土的溫度裂縫控制在一定的范圍之內。3 裂縫的處理措施一般性表面細小裂縫，可將裂縫部位清洗干凈，干燥后用環(huán)氧漿液灌縫或表面涂刷封閉；裂縫較大時，可將裂縫鑿成八字形凹槽、洗凈濕潤，刷一層水泥漿，用1：2水泥砂漿分層壓實抹光后用環(huán)氧膠泥嵌補。3.1 墩、柱側面裂縫墩、柱側面裂縫一般發(fā)生在距頂面50cm的范圍內，當裂縫未形成環(huán)狀時，可用環(huán)氧樹脂進行灌注來封閉裂縫；當裂縫形成環(huán)狀裂縫，且深度達到箍筋或超過箍筋時，應將裂縫以上部分鑿除重新澆筑；當裂縫深

16、度未達到箍筋位置時，可用環(huán)氧樹脂進行灌注封閉裂縫。3.2 梁板及橋面鋪裝出現的裂縫對于梁、板上表面出現的收縮裂縫，一般均較細，由于梁、板上還有一層混凝土橋面鋪裝，可不進行處理。對于水泥混凝土橋而鋪裝上出現的裂縫無需處理，原因是現行設計均在水泥混凝土鋪裝上加鋪瀝青混凝土。而在鋪瀝青混凝土之前通常要做防水層或噴灑粘層油，這此措施能夠將裂縫封堵住，起到很好的防水作用。對于梁板側而出現的裂縫，可以采用“壁可法”（該法是利用注入器橡膠管的壓力300KN/，保持低壓持續(xù)灌注。通過橡膠管的收縫自動完成注漿。該法可灌注的最小裂縫寬度為0 . 02 mm ）灌注來封閉裂縫，以防止雨水滲入腐蝕鋼筋及發(fā)生堿骨料反應

17、而降低橋梁的承載能力。3.3 其他特殊裂縫(1)拆模后發(fā)現的裂縫，一般性表面細小裂縫，可將裂縫部位清洗干凈，干燥后用環(huán)氧漿液灌縫或表面涂刷封閉；裂縫較大時，可將裂縫鑿成八字形凹槽、洗凈濕潤，刷一層水泥漿，用1：2水泥砂漿分層壓實抹光后用環(huán)氧膠泥嵌補。(2)對影響結構整體，防水防滲要求的結構裂縫，應根據裂縫寬度、深度情況，采用水泥壓力灌漿、化學灌漿的方法修補，或表面封閉與注漿同時使用；明顯降低結構剛度，承載力和嚴重裂縫，應根據情況，采用預應力加固或用鋼筋混凝土圍套、鋼套箍或結構膠粘貼劑貼鋼板加固等方法。結束語鋼筋混凝土構造物裂縫往往造成許多困擾，輕則影響結構物外觀，重則危及構造物安全。文中分析了

18、產生裂縫的多方面原因，實際存在的原因當然不止這些。因此，嚴格按照國家有關規(guī)范、技術標準進行設計、施工和監(jiān)理，是保證橋梁結構安全耐用的前提和基礎。另外，在運營管理過程中，進一步加強巡查和管理，及時發(fā)現和處理問題，也是相當重要的環(huán)節(jié)。參 考 文 獻1侯耀華.混凝土橋梁施工裂縫的成因及防治對策.陜西建筑 2010/11 2李春鵬，陳宇，高金生.淺談橋梁裂縫產生的原因.吉林交通科技 2008/02 3邱嘉宏.淺議溫度荷載與橋梁混凝土裂縫的控制.汕頭科技 2006/04 4辛登云.常規(guī)混凝土梁裂縫原因的分析.石家莊聯合技術職業(yè)學院學術研究 2006/04 5段莉麗.橋梁裂縫產生原因分析及整治方案.太原鐵

19、道科技 2009/02譯文CONTENTS Introduction 1 1 Cracks in Concrete Bridge 1 Loading induced crack 1.1 1 1.1.1 Direct stress fracture 1 2 secondary stress crack 1.1.2 2 1.2 cracks caused by shrinkage 1.2.1 Plastic Shrinkage 2 Cracks caused by foundation deformation 1.3 3 1.4 The quality of raw materials cause

20、d by cracks 4 Cracks caused by temperature changes 1.5 4 Preventive measures 2 5 crack 2.1 Shrinkage Cracks 5 Prevention of plastic shrinkage cracks 2.2 5 2.3 Settlement Cracks 6 2.4 6 preventive measures temperature cracks Treatment measures 3 7 Crack 3.1 pier, column 7, the side cracks 3.2 Beam an

21、d Deck 7 cracks appear 3.3 Other special crack 8 Conclusion 8 8 References   Causes of cracks in concrete bridge And treatment measures Abstract: The use of the bridge construction process, due to cracks and even affect the quality of the project led to bridge collapse phenomenon is also not un

22、common. This paper describes the types of cracks in concrete bridge, from the load, temperature changes, ground deformation 5 introduces the causes of concrete cracks, the corresponding preventive measures, and gives some crack approach. Keywords: bridge concrete cracks, causes, measures Preface Wit

23、h China's rapid development of transport infrastructure, built around a large number of concrete bridges. The bridge construction and use of the process, the concrete cracks caused by affecting the quality of the project or even collapse is not uncommon. Concrete cracking can be said to be "

24、;regular onset" and "frequently-occurring disease," a serious impact on the bridge performance, and often troubled bridge engineering and technical personnel. To control the bridge concrete cracks, improve project quality, we must understand its causes. The following article on the ca

25、uses of cracks in the bridge do an analysis and some of the cracks in the preventive measures and treatment. 1 Bridge Concrete Cracks Loading induced crack 1.1 Load induced cracks can be divided into direct and secondary stress fracture stress fracture. 1.1.1 Direct stress fracture Direct stress fra

26、cture is caused by direct external load stress cracks. Cracks are: (1) design phase of design and calculation of unreasonable force Shouli Bu Fu assumptions and the actual safety factor is not enough, does not consider the possibility of construction, construction handled properly. (2) the construct

27、ion phase of unrestricted stacked construction machinery, materials; free to stand up, lifting, transportation, installation; do not follow the construction design drawings, construction sequence and other unauthorized changes to the structure. (3) the use of load beyond the design stage of heavy ve

28、hicles crossing the bridge; by vehicles, ships of contact, impact; earthquakes, explosions and so on. 1.1.2 secondary stress fracture Secondary stress fracture is caused by the external load secondary stress cracks, the causes can be summarized as following aspects: (1) the design loads, the structu

29、re of the actual working conditions differ with the conventional calculations, or calculations do not take into account, which in some parts of the structure caused by the secondary stress lead to cracking. For example, two-hinged arch bridge design layout often use "X"-shaped bar, where t

30、he section size at the same time reducing design hinge approach, theoretical calculation moment there does not exist, but the actual bending of the hinges still, resulting in cracks and lead to reinforcement corrosion. (2) bridge structures often need to gouges or holes, set the bracket so difficult

31、 in the conventional calculation for an accurate simulation of schema, the general rule of thumb to set the reinforced. The results show that hollowing out the force components, the power flow will produce diffraction phenomenon in the vicinity of hole density, resulting in huge concentration of str

32、ess. In the long-span prestressed concrete continuous, often in a cross-section of internal forces according to need to cut the steel beams, set the anchor head, and in the anchoring section can often be seen near the crack. Therefore, in the corner of these structures or structural mutations at the

33、 shape, the reinforced section was prone to cracks. The secondary stress of the actual project is to produce the most common cause of fracture load. Times are mostly tensile stress cracks, splitting, shear properties. In the design, structural breaks should be avoided (or section mutant), when can n

34、ot be avoided, should be handled locally, such as made of rounded or chamfered, while strengthening the structural reinforcement, diagonal corner reinforcement configuration, for more large hole in the surrounding conditions can be set to protect edge angle. 1.2 contraction cracks 1.2.1 Plastic Shri

35、nkage 4h 5h after pouring concrete around the cement hydration reaction of intense molecular chain gradually formed, there bleeding and rapid evaporation of moisture, concrete shrinkage water loss, and aggregate sinking due to weight, but this time has not yet hardened concrete, known as plasticity

36、contraction. In the aggregate, if the process of being reinforced sink blocked, then the direction of the formation of cracks along the reinforcement in the vertical component, such as T at the variable section beam, box girder webs and roof junction, due to pragmatic and uneven hardening will occur

37、 before the surface The cracks along the web direction. (1) Shrinkage: Concrete Results hard then, as the gradual evaporation of surface water temperature decreased gradually reduce the volume of concrete, known as shrinkage. Water loss due to the concrete surface faster, the internal loss of slow,

38、resulting in rapid contraction of the surface, uneven contraction of the internal contraction of slow, leading to the concrete surface under tension, resulting in shrinkage cracks. (2) autogenous shrinkage: the hardening of concrete engineering, cement and water, hydration occurs, this contraction h

39、as nothing to do with the outside temperature, and can be positive (ie, contraction, such as ordinary portland cement concrete), it can be negative (ie expansion, such as slag cement concrete and fly ash concrete.) (3) carbonation shrinkage: the atmosphere of carbon dioxide and cement hydrates in th

40、e chemical reaction caused by shrinkage. Cracks caused by foundation deformation 1.3 (1) lack of precision of geological exploration, test data are not allowed. Investigation report does not adequately reflect the actual geological conditions are the main reasons causing uneven settlement of foundat

41、ion. (2) are too different geological foundation. (3) structural loads are too different. More consistent in the case of geological conditions, each part of the foundation loads are too different, there is likely to cause differential settlement. (4) Structural basis of type big difference. Bridge i

42、n the same mix together different bases, such as the expansion base and foundation, or while using the same basis, but differences in substrate elevation is too large may also cause uneven settlement of foundation. (5) the construction of the foundation stage. Near the new bridge in the original bri

43、dge, such as stage construction of the highway about half frame bridge, new bridge based on processing load or caused by soil re-consolidation of the existing bridge foundation are likely to lead to a greater settlement. (6) foundation frost heaving. (7) bridge placed on the basis of landslides, cav

44、e or other adverse geological active fault may cause differential settlement. (8) bridges are completed, the original foundation changes. Most of the natural ground and artificial ground after immersion in water, especially in plain fill, loess, expansive soil, and other special soil, soil strength

45、decreased with water, deformation increased. 1.4 The quality of raw materials caused by cracks Concrete mainly by the cement, sand, aggregate, mixing water and additives and other components, configuration, materials used in concrete when the failure may result in structural cracks. (1) substandard

46、quality of cement, damp or expired will cause concrete strength is not enough, and lead to concrete cracking. (2) exceeds the aggregate amount of mud, not only reduces the strength and impermeability of concrete, but also the concrete resulting in irregular mesh dry cracks. Difference between the gr

47、ading of sand and gravel, or sand particles too small, concrete mixing this material often causes cracks in the side. Alkali - aggregate reaction, silica aggregate containing the active material and alkaline substances meet, water, silicon produce expansion of the glial reaction, after absorbing wat

48、er became larger, resulting in local swelling and tensile stress, the components have burst-like cracks are more common in damp places. (3) mixing water and additives or the additives in the mixing water with higher levels of chloride and other magazines have greater when the impact of steel corrosi

49、on. Alkaline spring water mixing with sea water or concrete, or the use of alkaline admixture, are likely to alkali - aggregate reaction affected. (4) has been used for the reinforcement corrosion of steel bars embedded in the structure has rust spots or corrosion, resulting in damage to the steel s

50、urface oxide film, in the case of insufficient thickness of protective layer, the air intrusion into the concrete inside the iron bar and the intrusion into the concrete in the reaction of oxygen and water, the corrosion properties than the original volume growth of 2 to 4 times more, so that the co

51、ncrete around the expansion stress generated, leading to protective layer cracking, peeling, cracks along the longitudinal steel, and rust penetrate into the concrete surface. Cracks caused by temperature changes of 1.5 (1) the temperature in temperature due to changing seasons, but the change is re

52、latively slow, on bridge structure is mainly caused vertical displacement of the bridge, usually through the bridge deck expansion joints, bearing displacement, set flexible measures to regulate piers and other structures, Only limited structural displacement only when the cracks caused by temperatu

53、re, such as bridge, just bridging. (2) sun decks, the main beam or pier side by sun exposure, the temperature was higher than other parts of the distribution of the temperature gradient is nonlinear. Due to its own restraints, resulting in excessive local tensile stress, cracks. The following is a s

54、udden drop in sunshine and temperatures cause cracks in the structure of the most common cause. (3) The sudden drop in dump heavy rain, pre-invasion of cold air, the outer surface of the sun and so can lead to a sudden drop in temperature, but the relatively slow temperature changes within the struc

55、ture resulting from the temperature gradient. Sunshine and the sudden drop in temperature when the internal force calculation can be real bridge design specifications or reference data, without considering the reduction of concrete elastic modulus. (4) heat of hydration in the construction process,

56、mass concrete (thickness of more than 2m) after pouring the cement hydration heat, causing the internal temperature is high, both inside and outside temperature difference is too large, resulting in surface cracks. (5) Construction of steam curing or inappropriate measures winter construction, concr

57、ete cold and heat, the temperature inside and outside the uneven, prone to cracks. (6) pre-T beams installed between the diaphragm, bearing embedded steel plate welded with leveling, if welded properly, iron burns near the concrete easier to crack. Summary: Cracks in concrete of course, far more tha

58、n these, not one by one go into details here. According to the above reasons we have given below the corresponding fracture prevention measures and treatment. 2 measures to prevent fractures 2.1 Prevention of shrinkage cracks (1) use a smaller contraction of cement, commonly used in low-heat cement and fly ash cement, reducing the amount of cement. (2) shrinkage of concrete influenced by the water-cement ratio, the