混凝土施工裂缝原因及防治外文翻译

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1、外文翻译资料Construction cracks in concrete causes and preventionConstruction cracks in concrete, causes and preventionConstruction cracks of concrete reason for the external and internal. The initial mainly refers to the internal defects of concrete in early concrete, its internal hardening process will

2、exist numerous micro-pores, air-pocket and micro cracks, External refers to the load reason: temperature crack, dry shrinkage effect etc. In these, can produce various forms of concrete cracks. To grasp the construction process of raw materials, in pouring process configuration of progress and thick

3、ness, grasp timely maintenance work well, which can avoid concrete cracks.A, The cause of the tear1.The initial defects of concreteConcrete is composed of cement, sand aggregate, mixed with water and other materials and formation of heterogeneity brittle materials. In the beginning, because hardened

4、 concrete construction and deformation, a series of problems, such as constraint in the concrete shape sclerosis will exist numerous micro-pores, air-pocket and micro cracks of concrete that usually called initial defects. Micro cracks is usually a cracks in the concrete, bearing, and some other fun

5、ction not harm. But under load, temperature of concrete, shrinkage and function, micro cracks will be expanded and connectivity, and finally form the visible cracks of concrete, macroscopic crack, said it was the use of concrete structure, properties and durability of adverse effects.2.The load fact

6、orDue to the tensile strength of concrete structure or structures, small as a part of the external effects of stress than concrete tensile strength, will crack. Therefore, the concrete in the load and the load, can produce a crack. To load the crack, can produce by reasonable design and construction

7、 to prevent. For the load of crack, due to reasons, it is hard to handle and prevent. The more common than load factors have temperature, dry shrinkage, settling contraction deformation, plastic shrinkage deformation, etc, in these function, can make concrete inside tensile stress.3.Big volume concr

8、ete crack formation reasonsMassive concrete cracking reasons can be divided into two types: one is the structural cracks, is caused by external load, 2 it is material of crack is not caused by the changes of deformation and temperature stress and is mainly composed of concretes shrinkage. This artic

9、le mainly discussed type materials. One specific reasons are as follows:The temperature stress caused by fracture (temperature crack) temperature cracks in the main reason is caused by temperature difference. Temperature can be divided into three types: early concrete pouring, produce large amounts

10、of the hydration heat, due to the concrete is a poor conductor of heat accumulation in concrete, the hydration heat to send out, often make internal temperatures rise, concrete and reinforced concrete surface temperature for outdoor environment temperature, it is formed, the temperature and temperat

11、ure inside of condensate in early concrete tensile stress when more than concrete compressive strength, will cause cracking in concrete, In addition, in the dismantling formwork, surface temperature and reduce the temperature caused by fast, and will cause cracking. When the concrete temperature, ma

12、ximum heat radiates to the minimum temperature, temperature, or use them with the highest temperature difference is the internal temperature, These three temperature will produce temperature crack. In these three temperature, is mainly caused by hydration heat and the temperature.Shrinkage crack con

13、traction there are many causes, including drying shrinkage, plastic shrinkage, shrinkage, carbonation contraction, etc. Here mainly introduces drying shrinkage and plastic shrinkage.After drying shrinkage of concrete sclerosis, in dry environment, the water concrete to the loss caused by inside extr

14、oversion, concrete the shrinkage deformation cracks.The plastic shrinkage of cement and concrete in the activity of higher temperature, or in low water-cement condition exacerbate cause craze. When the concrete surface water obviously decreased, lactation evaporation of water cannot get the timely s

15、upplements, then concrete is still in a state of plastic, by a concrete surface tension, uneven distribution will appear the cracks of concrete cracks, and further intensify the moisture inside body, and further expansion crackSecond, the measures to prevent cracksFrom the above analysis, the crack

16、is mainly caused by temperature difference and contraction, so in order to prevent the cracks of, will maximize reduce temperature and reduce the shrinkage of concrete, specific measures as follows.1. Optimizing raw materials(1)Cement. The cement should be chosen according to the engineering propert

17、ies, construction condition, climate and other technical requirements, comprehensive consideration, to meet the strength and durability of concrete design requirements. When the choice should be labeled with cement concrete design match the label. For full strength of cement, cement, cement save fro

18、m the label for concrete label 1.5 to 2 times as appropriate.(2) aggregate. (a) coarse aggregate. The coarse aggregate concrete rubble is close-grained, must have the enough strength, hard to expand the coarse aggregate size. To ensure the concrete pouring dao close-grained, coarse aggregate maximum

19、 diameter less than the minimum size of the structural sections 1/4, also not greater than the minimum distance between steel net for thickness 3/4, in 10 centimeters and concrete, allowing adopts maximum diameter 1 1/2 of the aggregate number, but it shall not exceed 25%. (b) fine aggregate. Sand p

20、article gradation of technical properties of concrete influence, requests the porosity and total surface area small, small need total surface on the surface of the gravel package will reduce quantity of cement slurry, can reduce the dosage of cement hydration heat, reduce to prevent cracks. On the o

21、ther hand is to control the hydraulic sand, the content of 5% in concrete, the contraction deformation, the hydraulic and larger crack, fine aggregate to use clean in the sand.(3) admixtures. (a) water-reducing agent. Jianshuiji belongs to the surface active substances, is a kind of cement dispersan

22、t. Its main function of improving concrete workability, reduce the consumption of concrete mixture, reduce water-cement ratio increases, and improve the liquidity of concrete strength of concrete or keep in concrete cement strength must decrease, while the water-cement ratio, the dosage of cement to

23、 prevent cracking is reduced. (b) retarder. Retarder is delaying the role of concrete exothermic peak time, 2 it is to improve workability, and reduce the loss of collapsbillity. (c) air-entraining agent. In the application of concrete air-entraining agent for improving the concrete workability, can

24、 pump, improving the concrete durability is very favorable. In a certain extent increase anti-cracking performance of concrete.(4) mass concrete chooses raw materials should pay attention to the following: The coarse aggregate gradation, appropriate USES continuous fine aggregate ZhongSha should be

25、adopted. Admixtures appropriate USES retarder, water-reducer, Admixtures appropriate USES fly ash, slag powder etc. In mass concrete strength of concrete and the slump and the requirements of the premise, should improve mixing and aggregate content, in order to reduce the dosage of cement concrete a

26、lone. Should try to choose cement hydration heat low, setting time is long, the cement, low thermal Portland cement slag silicate cement, cement, slag dam Portland cement, coal ash Portland cement, volcanic gray Portland cement, etc.However, the slag cement hydration heat low water cement ratio of c

27、hromatography in other large, casting lots of water surface layer. This phenomenon is not only affect lactation water, also influence the construction speed and quality of construction. Because the water gathered in separation between the two casting concrete surface layer, change, and water-cement

28、ratio in the water and took out some of the mortar, thus forming a layer of interlining content, destroyed the cohesive force of concrete and holistic. The size of the water concrete lactation with water water, water, lactation; And with the temperature, water separation of time with temperature com

29、pletely and shortening, In addition, also with the composition and fineness of cement. Therefore, in selecting slag cement should be chosen when the varieties, and lactation shall be adding water-reducing agent in concrete, to reduce the consumption. During construction, should be in water or mixing

30、 some tomography uniform rolling cement casting in water, with 3-degrees vibration compaction, continue again after a concrete casting.2.the reasonable construction method(1) The concrete mixing and transportation. (a) white, accurate grasp of concrete proportion, especially the strict control of wa

31、ter consumption, the determination of sand. Records of every block water cement, sand and gravel, specific quantity, the application must be accurate to scale, by mixing. Good control of concrete slump and general shoulds not be too big, in 120 20 mm. To minimize the mouth 3 concrete temperature. (b

32、) concrete mixing in a storehouse after good transport process, to prevent to produce separation, lactation water, mortar loss should shorten transportation time, concrete loading not too full.(2)Concrete pouring and open mode. Pouring process may be close-grained, vibration to vibration time should

33、 be uniform in surface functional plasma advisable, uniform spacing, vibrating force scope affected overlap 1/2 advisable, after casting, compaction, surface must, in order to prevent the surface crack. Try to avoid in the solar radiation, high time due to the needs of the project if pouring in summ

34、er construction, avoid noon pouring temperature period, try to arrange at night. Time should be removed, according to air temperature and strength. In the actual temperature curing of the concrete conditions of strength, strength design of concrete center and 75%, the lowest temperature control surf

35、ace in 25 degrees Celsius, expected the concrete surface temperature drop more than 9 degrees Celsius above does not allow removed.(3) Do surface insulation protection of mass concrete temperature crack, is mainly caused by excessive temperature. Concrete pouring, due to internal heat faster, more s

36、urface temperature will form the internal and external surface by internal restraint, contraction, but the tensile stress, not more than usually have small tensile strength and the concrete cracks. But if the air raid, or by excessive ventilation cooling, make the surface temperature will easily lea

37、d to excessive temperature crack in the concrete, and so on, especially after dismantling formwork, low season in the immediate surface protection. To prevent excessive temperature crack, cause surface. In addition, the average day temperature in 2 3d consecutive decline not less than 6 8 degrees Ce

38、lsius, 28d age concrete surface must surface within the protection.(4) Of the mass concrete casting:Construction scheme, besides should satisfy each place of concrete in early before a new concrete are covered and rammed finished outside, still should consider structure size, steel pipe, buries the

39、bolts and leave, concrete and hydration heat supply, the influence of factors such as the commonly used method has the following kinds: Comprehensive stratified:In the first layer after pouring all comprehensive casting, casting back second, should make the first layer of concrete yet, so early, con

40、tinuous casting until completion by far. Using this scheme, applicable to the general structure of planar size shoulds not be too big, when construction from the short side began to push along the long side, is more appropriate. When necessary, can be divided into two sections from middle to both en

41、ds to or from the middle and construction.Section 2 layer:Concrete casting, starting from scratch, casting a certain distance to the second floor, so after pouring in other layers on casting. Due to the total number of layers, therefore, after the first layer top pouring concrete yet at the end of t

42、he beginning of the second period, and can turn from layered casting. This scheme is applicable to units within the time required, the supply of concrete less like the first option on that. This scheme is applicable to structure is too big and thickness of large area or length. Incline stratified:Re

43、quirements of slope not greater than cant 1/3, applicable to greatly exceed the length of the structure of the thickness of the three times. From the bottom layer of concrete casting, gradually move.3.maintenance measuresMaintenance of mass concrete construction is a vital work. Maintain proper main

44、tenance is mainly to control temperature and humidity, temperature, promote concrete outside the normal development of the strength of concrete and prevent the cracks of concrete and development. According to the specific circumstances of should as far as possible much maintenance period of time, af

45、ter dismantling formwork should immediately, covering protection to prevent recent climate, sudden cold temperature, prevent and control in early concrete cracks and medium. The massive concrete curing, not only to satisfy the need that still should increase by artificial temperature control, due to

46、 temperature caused by deformation of the concrete cracking. After the completion of the concrete curing time to keep the concrete surface spraying maintenance, such as reducing often humid heat outside pour cans, and prevent dry crack and promote the stable growth of concrete strength. In general 1

47、8h 12 after pouring in immediately start maintenance, maintenance time not less than 28d or design age.4 CooledIf in the high-temperature seasonal construction, should be in early general refrigeration adopted to reduce the water temperature, but the peak of concrete, water cannot too long, for a lo

48、ng time can cause excessive temperature range of temperature stress caused by large. In order to cut inside and outside, still should temperature in summer jiamoqiuchu undertake metaphase is cooled by water, river, general middle water lasted about two months. Later, water is made concrete cylindric

49、al blocks the necessary measures to juncture grouting, generally USES water and cooling water through the combination scheme.Third, the conclusionConcrete crack, especially large volume concrete crack is currently scholars and engineering is an important problem of attention, through the above analy

50、sis, the material of mass concrete crack is mainly composed of temperature stress and concretes shrinkage, the author thinks carefully select material, and in the use of reasonable construction method, can effectively prevent the cracks.混凝土施工裂缝原因及防治混凝土施工裂缝原因不外乎外因和内因。内因主要指混凝土的初始缺陷：在混凝土初期硬化过程中，其内部会存在众

51、多的微孔隙、气穴和微裂缝；外因是指非荷载原因：温度裂缝、干缩作用等。在这些作用下，混凝土会产生各种形式的裂缝。施工过程中要掌握好原材料的配置，在浇筑过程中把握好进度和厚度，及时做好养护工作，这样就可尽量避免混凝土裂缝了。一、裂缝产生原因1.混凝土的初始缺陷混凝土是一种由砂石骨料、水泥、水及其他外加材料混合而形成的非均质脆性材料。在混凝土硬化初期，由于混凝土的施工和本身变形、约束等一系列问题，硬化成型的混凝土中会存在众多微孔隙、气穴和微裂缝，通常把这称作混凝土的初始缺陷。微裂缝通常是一种无害裂缝，对混凝土的承重、防渗及其他一些使用功能不会产生危害。但是混凝土在受到荷载、温度、收缩等作用下，微裂缝

52、就会不断扩展和连通，最终形成肉眼可见的宏观裂缝，也就是混凝土工程中常说的裂缝，这会对混凝土结构的使用性能和耐久性产生不利的影响。2.非荷载因素由于混凝土的抗拉强度很小，当结构或构件的某一部分由于外部作用产生的拉应力大于混凝土的抗拉强度时，就会出现裂缝。因此，混凝土在荷载与非荷载作用下，都可以产生裂缝。对于荷载产生的裂缝，可以通过合理设计与施工来防止。而对于非荷载产生的裂缝，由于原因复杂，则很难处理和防止。一般常见的非荷载因素有温度作用、干缩作用、沉降收缩变形、塑性收缩变形作用等，在这些作用下，都会使混凝土内部产生拉应力。3. 大体积混凝土裂缝形成的原因大体积混凝土裂缝产生的原因可分为两类：一是

53、结构型裂缝，是由外荷载引起的；二是材料型裂缝，是由非受力变形变化引起的，主要是由温度应力和混凝土的收缩引起的。本文主要探讨材料型裂缝。其中具体原因如下：温度应力引起裂缝（温度裂缝） 目前温度裂缝产生主要原因是由温差造成的。温差可分为以下三种：混凝土浇注初期，产生大量的水化热，由于混凝土是热的不良导体，水化热积聚在混凝土内部不易散发，常使混凝土内部温度上升，而混凝土表面温度为室外环境温度，这就形成了内外温差，这种内外温差在混凝土凝结初期产生的拉应力当超过混凝土抗压强度时，就会导致混凝土裂缝；另外，在拆模前后，表面温度降低很快，造成了温度陡降，也会导致裂缝的产生；当混凝土内部达到最高温度后，热量逐

54、渐散发而达到使用温度或最低温度，它们与最高温度的差值就是内部温差；这三种温差都会产生温度裂缝。在这三种温差中，较为主要是由水化热引起的内外温差。收缩引起裂缝 收缩有很多种，包括干燥收缩、塑性收缩、自身收缩、碳化收缩等等。这里主要介绍干燥收缩和塑性收缩。燥收缩 混凝土硬化后，在干燥的环境下，混凝土内部的水分不断向外散失，引起混凝土由外向内的干缩变形裂缝。塑性收缩 在水泥活性大、混凝土温度较高，或在水灰比较低的条件下会加剧引起开裂。因为这时混凝土的泌水明显减少，表面蒸发的水分不能及时得到补充，这时混凝土尚处于塑性状态，稍微受到一点拉力，混凝土的表面就会出现分布不均匀的裂缝，出现裂缝以后，混凝土体内

55、的水分蒸发进一步加大，于是裂缝进一步扩展二、防止裂缝的措施由以上分析，裂缝主要是由温差和收缩引起，所以为了防止裂缝的产生，就要最大限度地降低温差和减小混凝土的收缩，具体措施如下。1.优选原材料(1)水泥。水泥的选用应根据工程性质、施工条件、气候环境及其他技术要求，综合考虑，以达到满足混凝土设计强度和耐久性的要求。选择水泥标号时应与混凝土的设计标号相匹配。为充分发挥水泥的强度、节约水泥，一般取水泥标号为混凝土标号的1.52倍为宜。(2)骨料。(a)粗骨料。碎石是混凝土中的粗骨料，必须密实坚硬具有足够的强度，尽量扩大粗骨料的粒径。为保证混凝土浇捣密实，粗骨料的最大粒径不大于结构断面最小尺寸的1/4

56、，同时不得大于钢筋间最小净距的3/4，对于厚度在10厘米及以下的混凝土，可允许采用最大粒径达1/2的骨料，但其数量不得超过25%。(b)细骨料。砂的颗粒级配影响混凝土的技术性质，既要求空隙率小又要求总表面积小，总表面小需要包裹砂子表面的水泥浆量也就减少，可以减少水泥用量，降低水化热，对防止裂缝有利。另一方面也要控制砂的含泥量，一般混凝土中其含量5%，含泥量越大，收缩变形越大，裂缝就越大，因此细骨料尽量用干净的中粗砂。(3)外加剂。(a)减水剂。减水剂属于表面活性物质，是一种水泥分散剂。它的主要作用改善混凝土的和易性，减少混凝土混合物的用水量，降低水灰比，增大混凝土的流动性，提高混凝土强度或在保

57、持混凝土一定强度时减少水泥用量，而水灰比的降低，水泥用量的减少对防止开裂是十分有利的。(b)缓凝剂。缓凝剂的作用一是延缓混凝土放热峰值出现的时间，二是改善和易性，减少运输过程中的塌落度损失。(c)引气剂。引气剂在混凝土的应用对改善混凝土的和易性、可泵性、提高混凝土耐久性能十分有利。在一定程度上增大混凝土的抗裂性能。(4)大体积混凝土所选用的原材料应注意以下几点： 粗骨料宜采用连续级配，细骨料宜采用中砂。 外加剂宜采用缓凝剂、减水剂；掺合料宜采用粉煤灰、矿渣粉等。 大体积混凝土在保证混凝土强度及坍落度要求的前提下，应提高掺合料及骨料的含量，以降低单方混凝土的水泥用量。 水泥应尽量选用水化热低、凝

58、结时间长的水泥，优先采用中热硅酸盐水泥、低热矿渣硅酸盐水泥、大坝水泥、矿渣硅酸盐水泥、粉煤灰硅酸盐水泥、火山灰质硅酸盐水泥等。 但是，水化热低的矿渣水泥的析水性比其它水泥大，在浇筑层表面有大量水析出。这种泌水现象，不仅影响施工速度，同时影响施工质量。因析出的水聚集在上下两浇筑层表面间，使混凝土水灰比改变，而在掏水时又带走了一些砂浆，这样便形成了一层含水量多的夹层，破坏了混凝土的粘结力和整体性。混凝土泌水性的大小与用水量有关，用水量多，泌水性大；且与温度高低有关，水完全析出的时间随温度的提高而缩短；此外，还与水泥的成分和细度有关。所以，在选用矿渣水泥时应尽量选择泌水性的品种，并应在混凝土中掺入减

59、水剂，以降低用水量。在施工中，应及时排出析水或拌制一些干硬性混凝土均匀浇筑在析水处，用振捣器振实后，再继续浇筑上一层混凝土。2.采用合理的施工方法(1)混凝土的拌制和运输。(a)拌合混凝土时，要准确掌握配合比，特别是严格控制用水量，测定砂的含水量。记录每一次拦制用水、水泥、砂、碎石的具体数量，各挡砂石料都必须通过磅秤，准确后才能拌制。控制好混凝土坍落度，一般不宜过大在12020毫米即可。要尽量降低混凝土拌合物出机口温度。(b)混凝土拌好后在出仓运输过程中，要防止产生分离、泌水、砂浆流失等现象，应缩短运输时间，混凝土装卸不可过满。(2)混凝土浇筑和拆模。浇注过程中要进行振捣方可密实，振捣时间应均

60、匀一致以表面泛浆为宜，间距要均匀，以振捣力波及范围重叠二分之一为宜，浇注完毕后，表面要压实、抹平，以防止表面裂缝。尽量避开在太阳辐射较高的时间浇注，若由于工程需要在夏季施工，则尽量避开正午高温时段，浇注尽量安排在夜间进行。拆模时间应根据气温和强度情况而定。混凝土在实际温度养护的条件下，强度达到设计强度的75%以上，混凝土中心与表面最低温度控制在25以内，预计拆模后混凝土表面温降不超过9以上允许拆模。(3)做好表面隔热保护 大体积混凝土的温度裂缝，主要是由内外温差过大引起的。混凝土浇注后，由于内部较表面散热快，会形成内外温差，表面收缩受内部约束产生拉应力，但是这种拉应力通常很小，不至于超过混凝土

61、的抗拉强度而产生裂缝。但是如果此时受到冷空气的袭击，或者过分通风散热，使表面温度降温过大就很容易导致裂缝的产生，所以在混凝土在拆模后，特别是低温季节，在拆模后立即采取表面保护。防止表面降温过大，引起裂缝。另外，当日平均气温在23d内连续下降不小于68时，28d龄期内混凝土表面必须进行表面保护。（4）体积混凝土的浇筑： 浇筑方案，除应满足每一处混凝土在初凝以前就被上一层新混凝土覆盖并捣实完毕外，还应考虑结构大小、钢筋疏密、预埋管道和地脚螺栓的留设、混凝土供应情况以及水化热等因素的影响，常采用的方法有以下几种： 全面分层： 即在第一层全面浇筑全部浇筑完毕后，再回头浇筑第二层，此时应使第一层混凝土还

62、未初凝，如此逐层连续浇筑，直至完工为止。采用这种方案，适用于结构的平面尺寸一般不宜太大，施工时从短边开始，沿长边推进比较合适。必要时可分成两段，从中间向两端或从两端向中间同时进行浇筑。 分段分层： 混凝土浇筑时，先从底层开始，浇筑至一定距离后浇筑第二层，如此依次向前浇筑其他各层。由于总的层数较多，所以浇筑到顶后，第一层末端的混凝土还未初凝，又可以从第二段依次分层浇筑。这种方案适用于单位时间内要求供应的混凝土较少，不象第一种方案那样集中。这种方案适用于结构物厚度不太大而面积或长度较大的工程。 斜面分层： 要求斜面的坡度不大于1/3，适用于结构的长度大大超过厚度3倍的情况。混凝土从浇筑层下端开始，

63、逐渐上移。3.养护措施养护是大体积混凝土施工中一项十分关键的工作。养护主要是保持适宜的温度和湿度，以便控制混凝土内外温差，促进混凝土强度的正常发展及防止混凝土裂缝的产生和发展。根据工程的具体情况，应尽可能多养护一段时间，拆模后应立即覆盖保护，同时预防近期骤冷气候影响，以控制内外温差，防止混凝土早期和中期裂缝。大体积混凝土的养护，不仅要满足增长的需要，还应通过人工的温度控制，防止因温度变形引起混凝土的开裂。 养护 混凝土浇注完毕后，应及时洒水养护以保持混凝土表面经常湿润，这样既减少外界高温倒罐，又防止干缩裂缝的发生，促进混凝土强度的稳定增长。一般在浇注完毕后1218h内立即开始养护，连续养护时间

64、不少于28d或设计龄期。4. 通水冷却 若是在高温季节施工，则要在初期采用通制冷水来降低混凝土最高温度峰值，但注意，通水时间不能过长，因为时间过长会造成降温幅度过大而引起较大的温度应力。为了削减内外温差，还应在夏末秋初进行中期通水冷却，中期通水一般采用河水，通水历时两个月左右。后期通水是使混凝土柱状块达到接缝灌浆的必要措施，一般采用通河水和通制冷水相结合的方案。三、结束语混凝土裂缝特别是大体积混凝土的开裂是目前学者和工程界关注的一个重要问题，通过以上分析可知，大体积混凝土的材料型裂缝主要是由温度应力和混凝土的收缩引起的，笔者认为精心选择原材料，并在施工中采用合理的方法，能有效的防止裂缝的发生。