外文翻译--论建筑工程中混凝土裂缝的预防与处理.docx

中文5153字附录A 论建筑工程中混凝土裂缝的预防与处理作者：阿西夫哈米德摘 要：混凝土裂缝是建筑工程中普遍存在的一种不良现象，它直接影响到混凝土结构的使用功能和耐久性。对建筑工程中一些常见的混凝土裂缝进行了分类探讨，并对具体情况提出了一些预防和处理措施。关键词：混凝土；裂缝；预防；处理1 前言建筑工程施工中，如果混凝土构件出现裂缝，就会影响混凝土构件的刚度和建筑物结构的整体抵抗能力，即使裂缝的出现不会导致混凝土构件的破坏或建筑物的倒塌，也会影响到建筑外观，当裂缝宽度超出一定限度时，也会造成钢筋锈蚀，影响结构构件的耐久性能。本文介绍混凝土工程施工中几种常见裂缝的预防、控制方法及裂缝的处理措施，对混凝土工程的施工有一定的参考价值。2 常见裂缝分类混凝土裂缝产生的原因是多方面的，情况较为复杂，综合因素较多。对于某种裂缝的出现，人们很难给予一个准确明晰的原因分析。工程实践证明，裂缝形成的原因主要来自三个方面：变形、荷载以及不均匀沉降。一般由温差、收缩、不均匀沉降等引起的变形赞成的裂缝约占80%，荷载等造成的约占20%，当然还需要考虑其综合原因。根据这些主要影响因素，人们常把混凝土裂缝归纳为收缩裂缝、温度裂缝、沉降裂缝、徐变裂缝、应力裂缝和施工裂缝等几大类。3 常见裂缝分析及预防3.1混凝土塑性收缩裂缝及预防塑性收缩是指混凝土在凝结前期。表面因失水过快而产生的收缩。一般在干热和大风天气裂缝较为常见，形状多为中间宽、两端细、互不连贯且长短不一，较长的裂缝可达2m3m，宽度可达0.5cm，严重影响混凝土的抗渗性和耐久性。主要预防措施：一是选用干缩值较小、早期强度较高的硅酸盐或普通硅酸盐水泥。二是严格控制水灰比，在保证混凝土施工所需坍落度和和易性的前提下尽量减少水的用量，必要时掺入减水剂。三是浇筑混凝土之前，将基层和模板均匀浇水湿透。四是及时覆盖握料薄膜或者潮湿的草垫、麻片等，保持混凝土凝结前表面湿润，或者在混凝土表面喷洒养护剂等进行养护。3.2 沉陷裂缝及预防沉陷裂缝的产生主要是由于结构地基浸水、土质不匀或回填土不密实等原因引起不均匀沉降所致；另外在混凝士硬化过程中由于模板刚度不足或支撑底部不牢固也会引起沉陷裂缝。主要预防措施：一是在结构施工前，保证地基处理质量。原地基土必须密实、均匀，并达到设计要求的承载能力；回填土严格按规范规定分层夯实，达到设计要求的压实系数。二是在基坑或地基周围做好防护措施，防止地基被水浸泡。三是保证模板有足够的强度和刚度。在支撑底部加设垫板保证支撑牢固。并使地基受力均匀。四是模板拆除的时间不能过早，且要注意拆模的先后次序。五是在结构自重不同或建筑物层高不同的相邻部位设置后浇带，待相邻结构沉降基本趋于稳定后再浇筑。3.3 温度裂缝及预防温度裂缝的走向无一定规律，通常纵横交错，深浅不一。长短边比例较大的梁板结构，裂缝多平行于短边，沿着长边分段出现，中间较密、较宽。裂缝的宽度受温度变化影响较大，冬季较宽，夏季较窄。此种裂缝的出现会引起钢筋的锈蚀和内部混凝土的碳化，严重影响其使用功能和耐久性。主要预防措施：一是尽量选用低热或中熟水泥，如矿渣水泥、粉煤灰水泥等。二是在保证混凝土强度的前提下。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。三是在保证混凝土和易性和满足施工需要的前提下，降低水灰比。四是改善混凝土的制作工艺，降低混凝土的浇筑温度。五是在混凝土中掺加一定量的缓凝剂，推迟热峰的出现时间。六是加强混凝土温度的监控，及时采取冷却或保温措施，减小混凝土的内外温差。七是加强混凝土养护，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。八是混凝土中配置少量的小规格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。3.4 化学反应引起的裂缝及预防化学反应引起的裂缝一般在钢筋混凝土结构中分为碱骨料反应裂缝和钢筋锈蚀裂缝两种。建筑工程中限于混凝土的构成，在其拌和后会产生一些碱性离子，这些离子与某些活性骨料发生化学反应并吸收周围环境中的水分而膨胀，造成混凝土酥松、胀裂。这种裂缝一般出现在混凝土结构使用期间，一旦出现很难补救，因此应在施工中采取有效措施进行预防。主要的预防措施有：一是选用碱活性小的砂石骨料。二是选用低碱水泥和无碱外加剂。三是选用能抑制碱骨料反应的掺和料。由于钢筋混凝土结构施工不良引起的钢筋保护层薄、露筋、蜂窝、麻面等不利现象，使得有害物质与外露钢筋或穿过混凝土与内部钢筋产生反应而锈蚀，锈蚀的钢筋体积膨胀，导致混凝土胀裂，此种类型的裂缝一般沿钢筋的位置出现。通常的预防措施；一是在浇筑混凝土前，严格检查钢筋保护层，保证其厚度满足设计要求，同时确保钢筋绑扎牢固且位置准确，避免振捣混凝土时钢筋移位而露筋。二是采用级配较好的砂石骨料配制混凝土。三是混凝土浇筑要振捣密实。四是拆模后及时处理混凝土的夹渣、蜂窝和麻面现象。4 常见裂缝处理方法4.1 表面修补法表面修补法是一种简单、常见的修补方法，它主要适用于稳定和对结构承载能力没有影响的表面裂缝以及深迸裂缝的处理。通常的处理措施是在裂缝的表面涂抹水泥浆、环氧胶泥或在混凝土表面涂刷油漆、沥青等防腐材料，在防护的同时为了防止混凝土受各种作用的影响继续开裂，采用在裂缝的表面粘贴玻璃纤维布的方法，当混凝土表面裂缝数量较多，分布面较广时，常采用增加一层水泥砂浆或细石混凝土整体面层的方法处理，同时整体面层内宜配置双向钢丝网。4.2 混凝土置换法混凝土置换法是处理严重损坏混凝土的一种有效方法，此方法是先将损坏的混凝土剔除干净、润湿，然后涂刷结合层，最后再置换入新的高一级标号混凝土或其他材料。常用的置换材料有：普通混凝土、水泥砂浆、聚合物或改性聚合物混凝土或砂浆。4.3 结构加固法当裂缝影响到混凝土结构的性能时，就要考虑采取加固法对混凝土结构进行处理。结构加固中常用的主要有以下几种方法：在构件上外包型钢、粘贴钢板加固；在构件上增设支撑点加固；在构件上施加预应力加固等。4.4 灌浆、嵌缝封堵法灌浆法主要适用于对结构整体性有影响或有防渗要求的混凝土裂缝的修补，它是利用压力设备将胶结材料压人混凝土的裂缝中，胶结材料硬化后与混凝土形成一个整体，从而起到封堵加固的目的。常用的胶结材料有水泥浆、环氧树脂、甲基丙烯酸酯、聚氨酯等化学材料。嵌缝法是裂缝封堵中最常用的一种方法，它通常是沿裂缝凿槽，在槽中嵌填塑性或刚性止水材料。以达到封闭裂缝的目的。常用的塑性材料有聚氯乙烯胶泥、塑料油膏、丁基橡胶等等；常用的刚性止水材料为聚合物水泥砂浆。5 裂缝的控制措施5.1 收缩（干缩）裂缝的控制收缩（干缩）裂缝的控制主要在于控制湿度的变化，使结构、构件具有相对稳定的湿度。加强混凝土的早期养护，混凝土浇筑完后，裸露表面应及时用草垫、草袋或塑料薄膜覆盖，并洒水湿润养护。在气温高、湿度低、风速大的天气应及早覆盖、喷水雾养护，并适当延长养护时间。加强混凝土表面的抹压，但应注意避免过分抹压。采用密封保水方法，在混凝土表面喷养护剂或覆盖塑料薄膜，使水分不易蒸发，或采用其他养活空气流动（如设挡风墙、罩）、延缓表面水分蒸发的办法。预应力构件应及时张拉，避免长期堆放。适当选择配合比，避免水灰比、水泥用量、砂率过大、严格控制砂、石的含泥量，避免使用粉砂，以提高混凝土抗拉强度。构件长期露天堆放时，应继续适当洒水或覆盖养护，以便有较长的保湿养护时间，特别是薄壁构件，应放在阴凉的地方覆盖堆放。5.2 温度裂缝的控制防止混凝土内部约束引起的表面温度裂缝，一般采用控制混凝土表面与外界或内部的温差的方法，使其小于25。常用控制措施是：对加热养护的构件，应采用缓慢升降温，使升降温度不大于10/h，并注意缓慢揭盖、脱模，避免表面温度应力过大；对大体积结构，当混凝土与外界温差较大时，应采用保温养护，适当处长拆模时间，使温差控制在25以内。预防结构受外部约束引起的混凝土温度裂缝，一般可采取以下几方面的技术措施：1、选用低热或中热水泥（如矿渣水泥、抗硫酸盐水泥、粉煤灰水泥）配制混凝土；在混凝土中掺加粉煤灰或减水剂；利用后期（90d、180d）强度以降低水泥用量和温升；在基础内预埋冷却水管，通入循环冷水，将水化热导出；在厚度大、少筋、大体积混凝土中，掺入20%以下块石吸热，并可节省混凝土用量。2、避开炎热天气及夜间浇筑混凝土。采用低温水拌制混凝土，对砂石进行冷水雾降温，或设置简易遮阳装置，以降低混凝土拌合物温度。同时采用薄层浇筑混凝土，每层厚度不大于30cm，加快热量散发，并使热量分布均匀。3、做好混凝土的保温、保湿养护，缓慢降温，充分发挥徐变特性，削减温度应力；夏季避免曝晒，冬季保温覆盖。采取长时间养护，规定合理的拆模时间，充分发挥混凝土的“应力松弛效应”；混凝土拆模后，及时回填土，避免结构侧面长期暴露。4、大体积基础采取分层分块浇筑，合理设置施工缝，在适宜位置浇缝，以加快散热；在岩石地基或厚混凝土垫层上浇筑大体积混凝土，应在垫层上放置滑动层（平面浇沥青玛蹄脂，铺砂或铺设卷材），垂直面放置缓冲层（贴聚乙烯泡沫塑料），以消除嵌固作用，释放约束应力。5、选择良好级配的粗骨料，严格控制其含泥量；加强混凝土振捣，提高混凝土密实性和抗拉强度；在基础内设置必要的温度配筋；在接缝部位，适当增大配筋率，设暗梁，以减轻边缘效应，提高抗拉强度；同时加强混凝土早期养护，提高早期抗拉强度和弹性模量。6、避免降温与干缩共同作用导致的应力叠加；在混凝土中掺加水泥用量5%-10%的VEA混凝土微膨胀剂，以抵消由于干缩和降温引起的混凝土收缩，控制混凝土开裂。7、采取“双控计算”措施，即在浇筑混凝土前按施工条件和拟采取的防裂控制措施，计算可能产生的最大降温收缩拉应力，当发现超过计算龄期的混凝土抗拉强度时，调整所采取的措施使应力控制在允许范围内；混凝土浇筑后，应根据实测温度和温度升降曲线，计算每阶段降温时混凝土累计拉应力，当其大于该龄期的混凝土抗拉极限强度时，应采取保温养护措施，使各阶段降温时混凝土的累计拉应力小于该龄期混凝土允许的抗拉强度，以控制裂缝出现。由于混凝土裂缝产生的原因较为复杂，应根据具体情况和条件，采取其中一种或数种措施。5.3 沉降裂缝的控制沉降裂缝主要在混凝土表面沿水平钢筋通长方向出现，分布面比较广，一般在拆模后3d-7d出现，其主要原因在于，若混凝土浇捣时，骨料颗粒下沉，水泥浆上浮，受到钢筋或埋件或大骨料的阻挡，造成混凝土分离。在工程施工中，一般采取的措施为：在混凝土施工时应注意布点下料的位置尽量要少；振捣下层钢筋时可轻轻地对上部钢筋进行振动，尽量减少上部钢筋粘带水泥浆；浇筑混凝土以前可对钢筋及模板用水湿润，降低钢筋及模板的温度；夏季混凝土浇筑尽量选在早晨或晚间温度较凉爽时；施工时应严格控制钢筋的保护层厚度。5.4 徐变裂缝的控制适当加大端头截面高度，配置承受水平力钢筋、放射式配筋或弯起构造筋（弯起方向平等于主拉应力）。压低预应力筋弯起角度，减少非预压区；支撑节点采用微动连接，如采用螺栓连接，预留孔内设橡胶垫圈、柔性连接等，以削减约束应力；构件吊装前应有一个较长的堆放时间，吊车梁的最后固定尽可能晚些（徐变3个月可达60%，4个月基本稳定，半年徐变可完成70%-80%），使徐变变形在吊装前（或固定前）完成大部分，此时混凝土具有较长龄期，强度也较高；预应力混凝土构件不要过早放张，以减少收缩徐变变形，提高抗裂能力；加大端头支承垫板，改进压力分布层，减少应力集中。5.5 施工裂缝的控制木模板浇水湿透，防止胀模将混凝土拉裂。采用翻转脱模时应平稳，防止剧烈冲击和振动，并应在平整坚实的铺砂地面上进行；预应力构件预留孔时管芯要平直，混凝土浇筑后定时（15min左右）转动钢管，抽管时间以手压混凝土表面不显印痕为宜，抽管时应平稳缓慢；胎模应选用有效的隔离剂，起模前先用斤顶均匀松动，再平缓起吊；构件堆放要按支承受力状态设置垫木，重叠堆放时，支点应保持在一条直线上，同时做好标记，避免板、梁、柱构件反放；运输中，构件之间设置垫木并互相绑牢，防止晃动碰撞；屋架、柱等大型构件吊装，应按规定设置吊点；吊装屋架等侧向刚度差的构件时，应用脚手架横向加固，并设牵引绳，防止吊装过程中晃动、碰撞；混凝土冬期施工在掺加氯盐早强剂，同时也应掺加亚硝酸钠阻锈剂（为水泥质量的1%-2%）；滑动模板应确保安装尺寸和质量，施工中若因某种原因停滑时间过长，应松开模板后再滑升，以防止拉裂混凝土。6 结论建筑工程中混凝土裂缝种类较多，而且是普遍存在的一种现象，它的出现不仅会影响建筑物的外观，还会影响建筑物的使用功能和耐久性，严重者将会威胁到人们的生命和财产安全，因此要根据不同的部位、形态以及严重程度对混凝土裂缝进行认真分析，采用合理的方法进行处理，并在施工中采取各种有效的预防措施来预防裂缝的出现和发展，保证建筑物和构件安全、稳定的工作。附录B外文文献On the prevention and treatment of cracks in concrete in the construction worksBy Asif Hameed Abstract：Concrete cracks a bad phenomenon is common in construction projects, it directly affects the use of function and durability of concrete structures. Classification of some common concrete cracks in the building works, and the specific circumstances of prevention and treatment measures.Keywords: concrete; cracks; prevention; processing1. ForewordBuilding construction, concrete structures, cracks, it will affect the stiffness of the concrete structures and the overall resistance of the structure of the building, even if the cracks do not lead to the destruction of concrete structures or building collapse will affect the exterior of the buildingwhen the crack width exceeds a certain limit, can also cause corrosion, durability of structural elements. This article describes several common cracks in the concrete construction of prevention measures, control methods and cracks on the concrete construction has a certain reference value.2. Common cracks CategoryConcrete cracks are many reasons, the situation is more complicated, more a combination of factors. For some cracks, it is difficult to give an accurate and clear analysis. Engineering practice shows that the main reasons for crack formation from three aspects: deformation, load, and uneven settlement. Generally by the temperature difference, shrinkage, differential settlement cracks caused by the deformation in favor of about 80% load caused about 20%, of course, also need to consider the comprehensive reason. Based on these main factors, often concrete cracks summarized shrinkage cracks, temperature cracks, settlement cracks, creep cracks, stress cracks and construction cracks in several categories.3. Common fracture analysis and prevention3.1 Plastic shrinkage cracks and preventionPlastic shrinkage of concrete in the condensation of pre-Surface due to excessive water loss and shrinkage. General more common in the dry and hot and windy weather cracks, the shape of the wide in the middle, both ends of the thin, non-coherent and of varying lengths, long cracks up to 2m-3m, width up to 0.5cm, seriously affect the resistance of concrete permeability and durability.The main preventive measures: First, make use of the shrinkage value is smaller, higher early strength portland or portland cement. Second, strict control of the water-cement ratio, to minimize the amount of water to ensure the concrete construction of the required slump and workability under the premise, if necessary, mixed with superplasticizer. Third, prior to pouring concrete, grass-roots and templates uniform watering wet. Timely coverage of the grip material film or wet straw mats, hemp films and so on, to keep the concrete setting the front surface moist, or sprayed on the concrete surface with the conservation agent for conservation.3.2 Subsidence cracks and preventionSubsidence cracks in the main is due to the flooding of the structure foundation, soil is uneven or not compacting the backfill caused uneven settlement due. In addition, Concrete hardening process due to the stiffness is insufficient or does not firmly support the bottom of the template will cause subsidence cracks.The main preventive measures: First, the structure of the pre-construction, to ensure the quality of ground treatment. The original foundation soil must be dense, uniform, carrying capacity and to achieve the design requirements; backfill compaction in layers in strict accordance with the specification, design requirements compaction factor. The second is to do a good job in the pit or foundation around the protective measures to prevent the foundations were immersed in water. Is to ensure that the template of sufficient strength and stiffness. Support additional at the bottom of the plate to ensure a solid support. And the foundation force uniform. The fourth template removed prematurely, and to pay attention to the priorities of form removal. Fifth, it is poured band structure weight or different buildings storey adjacent parts of the set, to be adjacent to the structure of the settlement basically tends to stabilize and then pouring.3.3 Temperature cracks and PreventionThe trend of temperature crack a certain regularity, usually criss-cross, shades. The larger the proportion of long and short sides of the slab structure, cracks parallel to the short side along the long edge segments appear, in the middle more dense and wide. The width of the cracks by temperature changes, winter, wide, narrow summer. The emergence of such cracks will cause reinforcement corrosion and internal concrete carbonation, and seriously affect its function and durability.The main preventive measures: First, try to use low heat or cooked cement, slag cement, fly ash cement. Second, under the premise of ensuring the strength of concrete. Improve the aggregate gradation, fly ash or superplasticizer to reduce the amount of cement. Third, to ensure the workability of concrete and meet the construction needs of the premise, lower water-cement ratio. Is to improve the production process of concrete, reduce the temperature of concrete pouring. Is mixed with a certain amount of concrete retarders, delayed the emergence of the thermal peak time. Is to strengthen the concrete temperature monitoring, and to take timely cooling or insulation measures, reducing the temperature difference between inside and outside of the concrete. 7 is to strengthen the concrete curing, pouring concrete, timely cover with wet straw mat, linen piece, and note the sprinkler maintenance, appropriate to extend the curing time. Eight is to configure a small amount of the small size reinforced concrete or mixed fiber material to control the temperature cracks of the concrete within a certain range.3.4 Chemical reaction caused by cracks and PreventionAlkali aggregate reaction cracks and steel corrosion cracks in two kinds of cracks caused by the chemical reaction is generally divided into the reinforced concrete structure.Construction works is limited to the composition of the concrete, after mixing some alkaline ions, these ions react chemically with some of the reactive aggregate expansion and to absorb the moisture in the surrounding environment, resulting in shortening of concrete, Splitting. Such cracks generally appear in the concrete structure during the event difficult to remedy, and should therefore take effective measures to prevent construction. The main preventive measures are: First, the choice of the alkali reactivity of small gravel aggregate. Second, the selection of low-alkali cement and alkali-free admixture. The third is optional and can inhibit the admixture of alkali aggregate reaction.Adverse phenomenon due to the reinforced protection of reinforced concrete structures during construction caused by bad thin, exposed tendons, cellular, pockmarked face, making the hazardous substances and exposed reinforcement through the concrete and internal reinforcement to react to rust, corrosion of reinforced volume expansion, resulting in concrete spalling, cracks of this type generally along the reinforced positions. The usual precautionary measures; First, before pouring concrete, strict inspection of reinforced protective layer to ensure that its thickness to meet design requirements, while ensuring a solid steel banding, and accurate position, to avoid the reinforced vibrated concrete shift and exposed tendons. Second, using the class with a good gravel aggregate concrete prepared. Vibration compacting concrete pouring. Timely processing of the concrete after form removal slag, cellular, and Ma surface phenomenon.4 Common cracks approach4.1 Surface repair methodSurface repair method is a simple, common repair method is mainly applied to the processing of stability and no effect on the structure carrying capacity of surface cracks and deep into the cracks. The usual treatment measures in the cracks in the surface of smear grout, epoxy mortar or concrete surface brushing paint, asphalt and other anti-corrosion materials, continue to crack in order to prevent the concrete role in protection while using crack surface paste of glass fiber cloth, when the concrete surface cracks in larger quantities, the distribution of the surface of a wider, often used to add a layer of cement mortar or fine aggregate concrete method of the overall surface treatment, while the overall surface should configure two-way steel mesh.4.2 Concrete replacement methodConcrete replacement method is an effective way to deal with serious damage to the concrete, this method is removed clean, the first damage to the concrete, wetting, and then brushing the binding layer, and finally replacement into the new high-level grade concrete or other materials. Replacement material: ordinary concrete, cement mortar, polymer or modified polymer concrete or mortar.4.3 Structural reinforcementWhen the cracks affect the performance of concrete structures, it is necessary to consider taking a reinforced concrete structure processing. Structural reinforcement commonly used mainly in the following ways: outsourcing steel components, paste, steel reinforcement; additional support points on the component reinforcement; prestressed reinforcement in the component.4.4 Grouting, caulking block methodGrouting method applies to the structural integrity of the influential or the repair of concrete cracks in the impermeable requirements, it is the use of pressure equipment will cementing material pressure concrete cracks cementing material hardened with concrete to form a whole, and thus play blocking the purpose of reinforcement. Commonly used in the cementing material grout, epoxy, methacrylate, polyurethane and other chemical materials.The caulking is the most commonly used crack block, it usually gouges along the cracks, filling them with plastic or rigid sealing material in the slot. In order to achieve the purpose of closed cracks. Commonly used plastic material PVC clay, plastic ointment, butyl rubber, etc.; rigid sealing material of polymer cement mortar.5. Crack control measures5.1 Contraction (shrinkage) cracks in the controlContraction (shrinkage) cracks in the control is to control the humidity changes, the structure of the component has a relatively stable humidity.To strengthen the early curing of concrete, concrete pouring after the exposed surface with straw mats, straw bags or plastic mulch, and watering moist conservation. Should try to cover in the high-temperature, low humidity, wind speed, weather, spray mist conservation, and appropriate to extend the curing time. To strengthen the concrete surface of the wiping pressure, but it should be taken to avoid excessive wiping pressure.Seal water sprayed on the concrete surface curing agent or covering of plastic film, so that water can not evaporate, or to use other way to feed air flow (such as set up a wind wall, cover), slow down the evaporation of surface moisture. Prestressed component, to avoid piling up long-term tension. Proper mixing ratio, to avoid water-cement ratio, the amount of cement, sand ratio is too large, and strictly control the sand, stone, clay content, avoid the use of silt, in order to improve the tensile strength of concrete. Component of long-term open-air pile up should continue to be the proper watering or covering conservation, to longer moisture conservation, especially thin-walled structures, should be a cool place to cover stacked.5.2 Temperature control of the cracksPrevent the surface temperature cracks in the concrete caused by internal constraints, the general control of the concrete surface with the outside world or the internal temperature difference, it is less than 25 . Commonly used control measures are: the components of the heat conservation, the slow heating and cooling, lift a temperature not greater than 10 C / h, and pay attention to slow Uncovery, mold release, to avoid the surface temperature of the stress is too large; bulk structure, when concrete and the outside temperature difference, heat conservation, proper removal time by the Director, the temperature control at 25 or less.Prevention of structural concrete temperature cracking caused by external constraints, the general technical measures can be taken to the following aspec