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毕 业 论 文
论文题目： 桥梁混凝土裂缝产生的原因和处理措施
系 部：
公 路 工 程 系
专业名称：
道路桥梁工程技术 班 级： 08213 学 号： 24
姓 名：
徐 新
指导教师：
李 永 成完成时间： 2011 年 5 月 12 日
目 录
前言..............................................................1 1 桥梁混凝土裂缝产生的原因........................................1 1.1 荷载引起的裂缝.............................................1 1.1.1直接应力裂缝..........................................1 1.1.2 次应力裂缝...........................................2 1.2 收缩引起的裂缝.............................................2 1.2.1 塑性收缩.............................................2 1.3 地基变形引起的裂缝.........................................3 1.4 原材料质量引起的裂缝.......................................4 1.5 温度变化引起的裂缝.........................................4 2 预防裂缝的措施..................................................5 2.1 干缩裂缝的预防.............................................5 2.2 塑性收缩裂缝的预防.........................................5 2.3 沉陷裂缝的预防.............................................6 2.4 温度裂缝的预防措施.........................................6 3 裂缝的处理措施..................................................7 3.1 墩、柱侧面裂缝.............................................7 3.2 梁板及桥面铺装出现的裂缝...................................7 3.3 其他特殊裂缝...............................................8 结束语............................................................8 参 考 文 献.......................................................8 译文..............................................................9 1
桥梁混凝土裂缝产生的原因
和处理措施
摘要：在桥梁建设使用过程中，因出现裂缝而影响工程质量甚至导致桥梁垮塌的现象也屡见不鲜。本文阐述了混凝土桥梁裂缝的种类，从荷载、温度变化、地基变形等5个方面介绍了混凝土裂缝的成因，提出了相应的预防措施，同时给出了一些裂缝处理方法。关键词：桥梁混凝土裂缝、原因、措施
前言
随着我国交通基础建设的高速发展，各地兴建了大量的混凝土桥梁。在桥梁建造和使用的过程中，由于混凝土裂缝而影响工程质量甚至造成坍塌事故的案例屡见不鲜。混凝土开裂可以说是“常发病”和“多发病”，严重影响了桥梁的使用性能，也经常困扰着桥梁工程技术人员。要想控制桥梁混凝土裂缝的产生，提高工程质量，就必须了解其成因。下面本文就对桥梁裂缝的产生原因做一分析，并提出一些对裂缝的预防措施和处理方法。桥梁混凝土裂缝产生的原因
1.1 荷载引起的裂缝
荷载引起的裂缝可以分为直接应力裂缝和次应力裂缝。
1.1.1直接应力裂缝
直接应力裂缝是指外荷载引起的直接应力产生的裂缝。裂缝产生的原因有：(1)设计计算阶段的结构设计不合理，受力假设与实际受力不符，安全系数不够，不考虑施工的可能性，构造处理不当。
(2)施工阶段中不加限制的堆放施工机具、材料；随意翻身、起吊、运输、安装；不按设计图纸施工，擅自更改结构施工顺序等。
(3)使用阶段时超出设计荷载的重型车辆过桥；受车辆、船舶的接触、撞击；发生地震、爆炸等。
1.1.2 次应力裂缝
次应力裂缝是指由外荷载引起的次生应力产生的裂缝，其产生的原因可归纳为一下几个方面：
(1)在设计荷载作用下，由于结构物的实际工作状态同常规计算有出入或计算不考虑，从而在某些部位引起次应力导致结构开裂。例如两铰拱桥拱脚设计时常采用布置“X”形钢筋、同时消减该处断面尺寸的办法设计铰，理论算该处不会存在弯矩，但实际该铰仍然能够抗弯，以致出现裂缝而导致钢筋锈蚀。
(2)桥梁结构中经常需要凿槽、升洞、设置牛腿等，在常规计算中难以用准确的图式进行模拟计算，一般根据经验设置受力钢筋。研究表明，受力构件挖空后，力流将产生绕射现象，在空洞附近密集，产生巨大的集中应力。在长跨预应力连续梁中，经常在跨内根据截面内力需要截断钢束，设置锚头，而在锚固断面附近经常可以看到裂缝。因此，在这些结构的转角处或构件形状突变处、受力钢筋截面处容易出现裂缝。
实际工程中次应力是产生荷载裂缝的最常见原因。次应力裂缝多属于张拉、劈裂、剪切性质。在设计上，应尽量避免结构突变（或截面突变），当不能同时避免时，应作局部处理，如做成圆角或倒角，同时加强构造配筋，转角处配置斜向钢筋，对于较大空洞有条件时可以在周边设置护边角钢。
1.2 收缩引起的裂缝
1.2.1 塑性收缩
混凝土浇筑后4h~5h左右，水泥水化反应剧烈，分子链逐渐形成，出现泌水和水分急剧蒸发，混凝土失水收缩，同时骨料因自重下沉，而此时混凝土尚未硬化，称为塑性收缩。在骨料下沉过程中若受到钢筋阻挡，便形成沿钢筋方向的裂缝，在构件竖向变截面处如T梁、箱梁腹板与顶板交接处，因硬化前沉实不均匀将发生表面的顺腹板方向裂缝。
(1)干缩：混凝土结硬以后，随着表面水分逐渐蒸发，温度逐渐降低，混凝土体积减小，称为干缩。因混凝土表面水分损失快，内部损失慢，因此产生表面收缩快，内部收缩慢的不均匀收缩，导致混凝土表面承受拉力，产生收缩裂缝。
(2)自生收缩：混凝土在硬化工程中，水泥和水发生水化反应，这种收缩与外界温度无关，并可以是正的（即收缩，如普通硅酸盐水泥混凝土），也可以是负的（即膨胀，如矿渣水泥混凝土与粉煤灰混凝土）。
(3)碳化收缩：大气中的二氧化碳和水泥中的水化物发生化学反应引起的收缩变形。
1.3 地基变形引起的裂缝
(1)地质勘探精度不够、试验资料不准。勘察报告不能充分反映实际地质情况是造成地基不均匀沉降的主要原因。
(2)地基地质差异太大。
(3)结构荷载差异太大。在地质情况比较一致的情况下，各部分基础荷载差异太大时，有可能引起不均匀沉降。
(4)结构基础类型差别大。同一联桥梁中混合使用不同基础，如扩大基础和桩基础，或虽采用同一种基础，但是基底标高差异太大，也可能引起地基不均匀沉降。
(5)分期建造的基础。在原有的桥梁附近新建桥梁时，如分期修建的高速公路左右半幅桥梁，新建桥梁荷载或基础处理时引起地基土重新固结，均可能对原有桥梁基础造成较大沉降。
(6)地基冻胀。
(7)桥梁基础置于滑坡体、溶洞或活动断层等不良地质时，可能造成不均匀沉降。
(8)桥梁建成以后，原有地基条件变化。大多数天然地基和人工地基浸水后，尤其是素填土、黄土、膨胀土等特殊地基土、土体强度遇水下降，压缩变形加大。
1.4 原材料质量引起的裂缝
混凝土主要由水泥、砂、骨料、拌合用水及外加剂等组成，配置混凝土时所采用的材料不合格，可能导致结构出现裂缝。
(1)水泥质量不合格、受潮或过期会造成混凝土强度不够，并导致混凝土开裂。
(2)砂石含泥量超过规定，不仅降低混凝土强度和抗渗性，还会是混凝土干燥时产生不规则的网状裂缝。砂石的级配差，或砂石颗粒过细，用这种材料拌制的混凝土常造成侧面裂缝。碱—骨料反应，骨料中含有的活性硅化物质与碱性物质相遇，水、硅反应会产生膨胀的胶质，吸水后体积变大，造成局部膨胀和拉应力，则构件产生爆裂状裂缝，在潮湿的地方较为多见。
(3)拌合用水及外加剂 拌合用水或外加剂中氯化物等杂志含量较高时对钢筋锈蚀有较大的影响。采用海水或碱泉水拌制混凝土，或采用含碱的外加剂，都可能对碱—骨料反应有影响。
(4)用于结构的钢筋已经锈蚀 植入结构体中的钢筋已经有锈斑或锈蚀，造成钢筋表面氧化膜破坏，在保护层厚度不足的情况下，空气侵入到混凝土内部，钢筋中的铁离子与侵入到砼中的氧气和水发生反应，其锈蚀物体积比原来增长越2~4倍，从而使周围砼产生膨胀应力，导致保护层开裂、剥离，沿钢筋纵向产生裂缝，并有锈迹渗透到砼表面。
1.5 温度变化引起的裂缝
(1)年温差 由于四季温度不断变化，但变化相对缓慢，对桥梁结构的影响主要是导致桥梁的纵向位移，一般可通过桥面伸缩缝、支座位移、设置柔性墩等构造措施来调节，只有结构位移受到限制时才会引起温度裂缝的产生，例如拱桥、刚架桥等。
(2)日照桥面板、主梁或桥墩侧面受到太阳暴晒后，温度明显高于其他部位，温度梯度呈非线性分布。由于受到自身约束作用，导致局部拉应力过大，出现裂缝。日照和下述骤然降温是导致结构温度裂缝的最常见原因。
(3)骤然降温 突降大雨、预冷空气侵袭、日落等可导致外表面温度突然
下降，但结构内部温度变化相对较慢而产生温度梯度。日照和骤然降温内力计算时可采用设计规范或参考实桥资料进行，混凝土弹模不考虑折减。
(4)水化热 出现在施工过程中，大体积混凝土（厚度超过2m）浇筑之后由于水泥水化放热，导致内部温度很高，内外温度差太大，导致表面出现裂缝。
(5)蒸汽养护或冬季施工施工措施不当，砼骤冷骤热，内外温度不均，易出现裂缝。
(6)预制T梁之间横隔板安装时，支座预埋钢板与调平钢板焊接时，若焊接不当，铁件附近混凝土容易烧伤开裂。
小结：水泥混凝土裂缝产生的原因当然远不止这些，在这里就不一一赘述了。下面我们根据以上原因给出相应的裂缝预防措施和处理方法。预防裂缝的措施
2.1 干缩裂缝的预防
(1)选用收缩量较小的水泥，一般采用中低热水泥和粉煤灰水泥，降低水泥的用量。
(2)混凝土的干缩受水灰比的影响较大，水灰比越大,干缩越大，因此在混凝土配合比设计中应尽量控制好水灰比的选用，同时掺加合适的减水剂。
(3)严格控制混凝土搅拌和施工中的配合比，混凝土的用水量绝对不能大于配合比设计所给定的用水量。
(4)加强混凝土的早期养护，并适当延长混凝土的养护时间。冬季施工时要适当延长混凝土保温覆盖时间，并涂刷养护剂养护。
(5)严格按照设计要求在混凝土结构中设置合适的收缩缝。
2.2 塑性收缩裂缝的预防
(1)选用干缩值较小早期强度较高的硅酸盐或普通硅酸盐水泥。
(2)严格控制水灰比，掺加高效减水剂来增加混凝土的坍落度和和易性，减少水泥及水的用量。
(3)浇筑混凝土之前，将基层和模板浇水均匀湿透。
(4)及时覆盖塑料薄膜或者潮湿的草垫、麻片等，保持混凝土终凝前表面湿润，或者在混凝土表面喷洒养护剂等进行养护。
(5)在高温和大风天气要设置遮阳和挡风设施，及时养护。
2.3 沉陷裂缝的预防
(1)对松软土、填土地基在上部结构施工前应进行必要的夯实和加固。(2)保证模板有足够的强度和刚度，且支撑牢固，并使地基受力均匀。(3)防止混凝土浇灌过程中地基被水浸泡。
(4)模板拆除的时间不能太早，且要注意拆模的先后次序。(5)在冻土上搭设模板时要注意采取一定的预防措施。
2.4 温度裂缝的预防措施
(1)尽量选用低热或中热水泥，如矿渣水泥、粉煤灰水泥等。(2)减少水泥用量,将水泥用量尽量控制在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)改善骨料级配，掺加粉煤灰或高效减水剂等来减少水泥用量,降低水化热。
(5)改善混凝土的搅拌加工工艺，在传统的三冷技术的基础上采用二次风冷新工艺，降低混凝土的浇筑温度。
(6)在混凝土中掺加一定量的具有减水、增塑、缓凝等作用的外加剂，改善混凝土拌合物的流动性、保水性，降低水化热，推迟热峰的出现时间。
(7)高温季节浇筑时可以采用搭设遮阳板等辅助措施控制混凝土的温升，降低浇筑混凝土的温度。
(8)大体积混凝土的温度应力与结构尺寸相关，混凝土结构尺寸越大，温度应力越大，因此要合理安排施工工序，分层、分块浇筑，以利于散热，减小约束。
(9)在大体积混凝土内部设置冷却管道，通冷水或者冷气冷却，减小混凝土的内外温差。
(10)加强混凝土温度的监控，及时采取冷却、保护措施。(11)预留温度收缩缝。
(12)减小约束，浇筑混凝土前宜在基岩和老混凝土上铺设5mm左右的砂垫层或使用沥青等材料涂刷。
(13)加强混凝土养护，混凝土浇筑后，及时用湿润的草帘、麻片等覆盖，并注意洒水养护，适当延长养护时间，保证混凝土表面缓慢冷却。在寒冷季节，混凝土表面应设置保温措施，以防止寒潮袭击。
(14)混凝土中配置少量的钢筋或者掺入纤维材料将混凝土的温度裂缝控制在一定的范围之内。裂缝的处理措施
一般性表面细小裂缝，可将裂缝部位清洗干净，干燥后用环氧浆液灌缝或表面涂刷封闭；裂缝较大时，可将裂缝凿成八字形凹槽、洗净湿润，刷一层水泥浆，用1：2水泥砂浆分层压实抹光后用环氧胶泥嵌补。
3.1 墩、柱侧面裂缝
墩、柱侧面裂缝一般发生在距顶面50cm的范围内，当裂缝未形成环状时，可用环氧树脂进行灌注来封闭裂缝；当裂缝形成环状裂缝，且深度达到箍筋或超过箍筋时，应将裂缝以上部分凿除重新浇筑；当裂缝深度未达到箍筋位置时，可用环氧树脂进行灌注封闭裂缝。
3.2 梁板及桥面铺装出现的裂缝
对于梁、板上表面出现的收缩裂缝，一般均较细，由于梁、板上还有一层混凝土桥面铺装，可不进行处理。对于水泥混凝土桥而铺装上出现的裂缝无需处理，原因是现行设计均在水泥混凝土铺装上加铺沥青混凝土。而在铺沥青混 7
凝土之前通常要做防水层或喷洒粘层油，这此措施能够将裂缝封堵住，起到很好的防水作用。
对于梁板侧而出现的裂缝，可以采用“壁可法”（该法是利用注入器橡胶管的压力300KN/㎡，保持低压持续灌注。通过橡胶管的收缝自动完成注浆。该法可灌注的最小裂缝宽度为0.02 mm）灌注来封闭裂缝，以防止雨水渗入腐蚀钢筋及发生碱骨料反应而降低桥梁的承载能力。
3.3 其他特殊裂缝
(1)拆模后发现的裂缝，一般性表面细小裂缝，可将裂缝部位清洗干净，干燥后用环氧浆液灌缝或表面涂刷封闭；裂缝较大时，可将裂缝凿成八字形凹槽、洗净湿润，刷一层水泥浆，用1：2水泥砂浆分层压实抹光后用环氧胶泥嵌补。
(2)对影响结构整体，防水防渗要求的结构裂缝，应根据裂缝宽度、深度情况，采用水泥压力灌浆、化学灌浆的方法修补，或表面封闭与注浆同时使用；明显降低结构刚度，承载力和严重裂缝，应根据情况，采用预应力加固或用钢筋混凝土围套、钢套箍或结构胶粘贴剂贴钢板加固等方法。
结束语
钢筋混凝土构造物裂缝往往造成许多困扰，轻则影响结构物外观，重则危及构造物安全。文中分析了产生裂缝的多方面原因，实际存在的原因当然不止这些。因此，严格按照国家有关规范、技术标准进行设计、施工和监理，是保证桥梁结构安全耐用的前提和基础。另外，在运营管理过程中，进一步加强巡查和管理，及时发现和处理问题，也是相当重要的环节。
参 考 文 献
[1]侯耀华.混凝土桥梁施工裂缝的成因及防治对策.陕西建筑 2010/11 [2]李春鹏，陈宇，高金生.浅谈桥梁裂缝产生的原因.吉林交通科技
2008/02 [3]邱嘉宏.浅议温度荷载与桥梁混凝土裂缝的控制.汕头科技 2006/04 [4]辛登云.常规混凝土梁裂缝原因的分析.石家庄联合技术职业学院学术研究 2006/04 [5]段莉丽.桥梁裂缝产生原因分析及整治方案.太原铁道科技 2009/02 译文
CONTENTS
Introduction 1 Cracks in Concrete Bridge 1 Loading induced crack 1.1 1 1.1.1 Direct stre fracture 1 2 secondary stre 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 caused 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 and 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 proce, due to cracks and even affect the quality of the project led to bridge collapse phenomenon is also not uncommon.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
With China's rapid development of transport infrastructure, built around a large number of concrete bridges.The bridge construction and use of the proce, the concrete cracks caused by affecting the quality of the project or even collapse is not uncommon.Concrete cracking can be said to be “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 causes of cracks in the bridge do an analysis and some of the cracks in the preventive measures and treatment.Bridge Concrete Cracks Loading induced crack 1.1
Load induced cracks can be divided into direct and secondary stre fracture stre fracture.1.1.1 Direct stre fracture
Direct stre fracture is caused by direct external load stre cracks.Cracks are:
(1)design phase of design and calculation of unreasonable force Shouli Bu Fu aumptions and the actual safety factor is not enough, does not consider the poibility of construction, construction handled properly.(2)the construction 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 vehicles croing the bridge;by vehicles, ships of contact, impact;earthquakes, explosions and so on.1.1.2 secondary stre fracture
Secondary stre fracture is caused by the external load secondary stre cracks, the causes can be summarized as following aspects:
(1)the design loads, the structure 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 stre lead to cracking.For example, two-hinged arch bridge design layout often use “X”-shaped bar, where the 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 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
stre.In the long-span prestreed concrete continuous, often in a cro-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 shape, the reinforced section was prone to cracks.The secondary stre of the actual project is to produce the most common cause of fracture load.Times are mostly tensile stre cracks, splitting, shear properties.In the design, structural breaks should be avoided(or section mutant), when can not 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 Shrinkage
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 lo, and aggregate sinking due to weight, but this time has not yet hardened concrete, known as plasticity contraction.In the aggregate, if the proce 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 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 lo due to the concrete surface faster, the internal lo of slow, 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 has 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 the 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 foundation.(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 in 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 bridge, such as stage construction of the highway about half frame bridge, new bridge based on proceing 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, cave 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, loe, expansive soil, and other special soil, soil strength 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 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 grading of sand and gravel, or sand particles too small, concrete mixing this material often causes cracks in the side.Alkaliaggregate 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 surface oxide film, in the case of insufficient thickne 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 concrete around the expansion stre 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 relatively 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 temperature, 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 exceive local tensile stre, cracks.The following is a sudden 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 structure 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 proce, ma concrete(thickne 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, concrete 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 than 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 greater the water-cement ratio, the greater the shrinkage, so the concrete mix design should try to control the selection of water-cement ratio, while adding the appropriate reduction agent.(3)strictly control the concrete mixing and construction in the mix, the water consumption of concrete mix design must not be greater than the given amount of water.(4)to strengthen the early curing of concrete and appropriate to extend the concrete curing time.Winter construction thermal insulation of concrete cover to be extended time and brushing curing agent curing.(5)in strict accordance with the design requirements set in the proper concrete contraction joint.2.2 Prevention of plastic shrinkage cracks
(1)selection of high early strength and shrinkage value is small or ordinary Portland cement.(2)strictly control the water-cement ratio, adding superplasticizer to increase slump and workability of concrete, reduce the amount of cement and water.(3)Prior to pouring concrete, water will be evenly wet the gra roots and templates.(4)timely coverage of plastic film or damp straw, hemp and other films to keep wet concrete surface before the final setting, or curing agent in the sprayed concrete surface for conservation.(5)at high temperatures and windy weather to set the sun and wind facilities, and timely maintenance.2.3 Subsidence Cracks
(1)of the soft soil, filling the upper structure of the foundation neceary before construction compaction and reinforcement.(2)ensure that the template has sufficient strength and stiffne, and the solid support, and to the foundation in good condition.(3)to prevent the proce of concrete pouring foundations were immersed in water.(4)the time the template is not removed too early, and pay attention to the order form removal.(5)puts up a template in the permafrost to take some time to pay attention to preventive measures.2.4 The preventive measures temperature cracks
(1)try to use low heat or in the hot cement, such as slag cement, fly ash and cement.(2)reduce the amount of cement, will try to control the amount of cement in the 450kg/m3 below.(3)reduce the water-cement ratio, the general control of the concrete water-cement ratio of 0.6 or le.(4)to improve the aggregate gradation, fly ash or high water reducing agent to reduce the amount of cement to reduce heat of hydration.(5)to improve the concrete mixing proce, in the traditional three-technology based on cold air cooling with the second new technology, reduce the temperature of the concrete pouring.(6)in concrete by adding a certain amount of water, plasticizer, such as the role of retarding admixture to improve the flow of fresh concrete, water retention, reduce heat of hydration, thermal spike delay the emergence of time.(7)can be used when pouring the hot season erection of sun visor and other auxiliary measures to control the concrete temperature rise, reducing the temperature of pouring concrete.(8)the temperature of ma concrete structure size-related stre, the larger the size of concrete structure, the greater the thermal stre, so to arrange the construction proce, hierarchical, block casting, to facilitate cooling, reducing
the constraints.(9)set in ma concrete internal cooling pipes, through water or air cooling, reducing the temperature difference between inside and outside the concrete.(10)to strengthen concrete temperature monitoring, timely cooling, protective measures.(11)reserved for temperature contraction joints.(12)reduce constraints, before pouring concrete in the basement and the old concrete should be laid on the sand cushion of about 5mm or use of asphalt and other materials brushing.(13)to strengthen the concrete curing, concrete pouring, the timely use of wet straw mat, linen strips, cover, and pay attention to watering conservation, appropriate to extend the curing time, ensure the concrete surface of the slow cooling.In the cold season, the concrete surface insulation measures should be set to prevent the cold wave attack.(14)of reinforced concrete in the configuration or the incorporation of a small amount of fiber to concrete crack control the temperature within a certain range.measures to deal with crack
General surface of small cracks, crack area can be cleaned, dried epoxy grout pouring or brushing the surface closed;crack is large, can be eight-shaped crack hewn groove, wet wash, brush a layer of cement pulp, layered with a 1:2 cement mortar trowel compacted clay embedded with epoxy after the meeting.3.1 pier, column side of the crack
Pier, column side of the crack generally occurs in the range of 50cm from the top, when the crack does not form a ring, can be used to close the cracks in epoxy resin infusion;When cracks form a ring cracks, and the depth of stirrups or more stirrups when the crack should be chiseled above the part of the re-casting;when the crack depth does not meet the stirrup position, can be used by pouring epoxy sealed cracks.3.2 Deck Slab and cracks appear
For the beam, the shrinkage cracks in the surface of the board, are generally smaller, due to beam, plate a layer of concrete pavement, do not be proceed.Cement concrete pavement for the bridge and the cracks appear without treatment, because the current design are in the cement concrete pavement overlay on asphalt concrete.In the shop is usually done before the asphalt concrete or spray adhesive layer, waterproof layer of oil, which measures the ability to crack the sealed block, play a good waterproof.For the slab cracks in the side and there can be a “wall to Law”(the Act is the use of rubber tubing injector preure 300KN / ㎡, maintain low preure infusion.Through the rubber tube closed automatically grouting joints.This method can be The minimum crack width perfusion 0.02 mm)infusion to close the cracks to prevent water infiltration and corrosion of reinforced alkali-aggregate reaction and reduce the occurrence of the carrying capacity of the bridge.3.3 Other special crack
(1)found that the cracks form removal and general surface, small cracks, fracture site can be cleaned, dried epoxy grout pouring or brushing the surface closed;crack is large, may be hewn figure eight concave fracture tank, wet wash, brush a layer of cement, with cement mortar 1:2 layer after compaction trowel mortar embedded with epoxy fill.(2)of the whole structure, the structural requirements of water seepage cracks, should be based on crack width and depth of the situation, the use of cement preure grouting, chemical grouting method of repair, or surface sealing and grouting the same time;significantly lower structural stiffne, load force and serious cracks, should be under the circumstances, the use of reinforced or prestreed reinforced concrete encircling, steel hoop or structural adhesive patch affixed to steel reinforcement and other methods.Conclusion
Cracks in reinforced concrete structures is often caused many problems, ranging from the appearance of structures, while in endangering the safety structures.This paper analyzes the cracks in a number of reasons, the actual reason, of course there's more.Thus, in strict accordance with the relevant national standards, technical standards for design, construction and supervision is to ensure safe and durable bridge structure and foundation of the premise.In addition, operation and management proce, to further strengthen the inspection and management, detect and deal with the problem, are very important aspects.References
[1] Murphy.Concrete bridge construction and Countermeasures of Cracks.Shaanxi Construction 2010/11
[2] Li Chunpeng, Chen Yu, Jinsheng high.On the causes of cracks in the bridge.Jilin Science and Technology 2008/02 Traffic
[3] Qiu Jiahong.On the load and temperature control of the bridge concrete cracks.Shantou Technology 2006/04
[4] Xin Dengyun.Conventional concrete beam analysis of the causes.Shijiazhuang Vocational Institute of Technology academic research combined 2006/04
[5] above Lily.Cause of the cracks of the bridge and remediation programs.Taiyuan Railway Technology 2009/02
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