浅谈在大体积混凝土施工中如何预防裂缝的出现.doc

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浅谈在大体积混凝土施工中如何预防裂缝的出现
Discuss how to prevent the cracks in mass concrete construction appear

混凝土在现代工程建设中占有重要方位。而在今天，混凝土的裂缝较为广泛，在桥梁工程中裂缝几乎无所不在。虽然我们在施工中采用各种方法，小心谨慎，但裂缝仍然时有出现。究其原因，我们对混凝土温度应力的改动注重不可是其间之一。　
Concrete occupies an important position in modern engineering construction. Today， concrete cracks is more extensive， cracks in the bridge project is almost ubiquitous。 Although we used various methods in the construction, be careful， but the cracks still appear。 Investigate its reason, we focus on concrete temperature stress changes is one of the meantime.
　在大体积混凝土施工中，因为水泥化热、缩短应力等多种要素发生的混凝土规划裂缝会影响建筑的耐久能功用和力学功用。因此，本文从描写、施工、温控等方面下手,谈谈大体积混凝土施工中应采用的避免方法.一、裂缝发生的首要要素
In mass concrete construction, because ShuiNiHua hot, reduced stress and other elements of cracks in concrete planning affects the durability of buildings can function and mechanical function。 Therefore, this article from the aspects of description, construction， temperature control, etc, talk about should be adopted to avoid in the mass concrete construction method。 The primary elements of a， cracks
　　大体积混凝土规划发生裂缝是由多种要素一同效果构成的，总结起来首要有以下几种：　
Planning of mass concrete crack is formed by a variety of elements together with the effect, to sum up top has the following kinds:
　（一）应力缩短裂缝、混凝土在逐渐散热和硬化过程中,其体积会相应缩短。因为混凝土会受到外界捆绑，体积内发生相应的缩短应力，当缩短应力大于混凝土极抗拉强度时,就会发生缩短裂缝.缩短的首要影响要素是混凝土中的用水量和水泥用量，用水量和水泥用量越高，混凝土缩短就越大。选用的水泥品种不一样，其干缩、缩短的量的量也不一样，一般中低热水泥和粉煤灰水泥的缩短量较小.　
(a) stress is gradually shortened cracks， concrete cooling and hardening process， the volume will be reduced。 Because concrete is tied to the outside world， corresponding shortened stress occurs in the volume， when the reduced stress more than concrete tensile strength， shorten the fracture occurs. Shorten the primary influence factors is water use of concrete and cement dosage, water consumption and the higher the dosage of cement， concrete to shorten。 Choose different varieties of cement， dry shrinkage, reduce the amount of the amount is different also， generally in low thermal cement and small amount of fly ash cement。本文为互联网收集，请勿用作商业用途个人收集整理,勿做商业用途
　（二）温度裂缝。水泥在水化过程中要开释一定的热量,而大体积混凝土规划断面较厚，表面系数相对较小一般需要一次整体浇筑。此时，混凝土龄期短，抗拉强度较低，当温度发生的表面拉应力逾越混凝土极限抗拉强度时，则表面发生裂缝。　
（2） the temperature cracks. In the hydration process of cement to justify a certain quantity of heat, and mass concrete planning section thicker, relatively small surface coefficient generally requires a casting as a whole. At this time, the concrete age is short， low tensile strength， surface tensile stress occurs when the temperature beyond the ultimate tensile strength of concrete, the surface crack。
　（三）沉降缩短裂缝.因为地基地质不匀、松软或回填土不实或浸水而构成不均匀沉降所形成的，或许因为模板刚度缺少，模板支撑间隔过大或支撑底部松动等致使,尤其是冬季，模板支撑在冻土上，冻土化冻后发生不均匀沉降，致使混凝土规划发生裂缝。此类裂缝多为深进或贯穿性裂缝，裂缝一般呈梭形，其走向与沉陷情况有关。一般沿与地上垂直或呈30－45度角方向，展开较大的沉陷裂缝，往往有一定的错位，裂缝宽度往往与沉降量成正比联络。裂缝宽度0。3－0。4mm,受温度改动的影响较小。地基变形安稳之后，沉陷裂缝也底子趋于安稳。　
（3) subsidence shorten fracture。 Because geological not divide evenly， soft or backfill soil foundation is not solid or flooding， constitute, formed by the uneven settlement of perhaps because templates lack of stiffness, loose at the bottom of the formwork support spacing is too large， or support such causes, especially in winter, the template support on permafrost， uneven settlement in the aftermath of the thaw of permafrost, cracks occur in concrete planning。 Such cracks for more deep into or perfoliate crack， crack generally fusiform， its trends and subsidence. Generally along the vertical with the ground or in 30 to 45 degree Angle direction, a larger settlement crack, tend to have certain dislocation， fracture width is proportional to the settlement often contact。 Crack width 0。3 0。4 mm， less affected by temperature changes。 After foundation deformation and stability， settlement cracks foundation also tend to be safe。个人收集整理，勿做商业用途文档为个人收集整理，来源于网络
　（四）材料裂缝。亦称安定性裂缝,表现为龟裂，首要是因为水泥安定性不合格或骨猜中混量过多而致使.　
（4） the material fracture. Also known as crack stability， performance for cracks， first because the cement stability unqualified or bone guess mix amount and cause too much。
　二、裂缝对混凝土规划物的危害　
Second, the harm of cracks of concrete planning
　温度裂缝的走向一般无一定规矩、大面积规划裂缝常纵横交错；如梁板类长度标准较大的规划，裂缝多平行于短边；深化和贯穿性的温度缝一般与短边方向平行或靠近平行,裂缝沿着长边分段出现,中间较密.裂缝宽度大小不一，受温度改动影响较为显着，冬季较宽，夏天较窄.高温胀大致使的混凝土温度裂缝一般是中间粗两端细，而冷缩裂缝的粗细改动不太显着，此种裂缝的出现会致使钢筋的锈蚀，混凝土的碳化，降低混凝土的抗冻、抗疲劳，会降低建筑物的抗渗才干,影响建筑物的运用功用,会致使钢筋的锈蚀,降低材料的耐久性，影响建筑的承载才干。
Temperature cracks in general no certain rules， the direction of the large area planning cracks often crisscross； Such as beam slab length standard planning, more cracks parallel to the short edge； Deepening and penetrability of general and short of the temperature of the seam direction parallel or near parallel， cracks appear along the long side section， middle is close。 Crack width sizes and affected by the temperature changes more significant, and winter with wider and narrower in the summer. High-temperature swelling causes of concrete temperature crack is commonly on both ends of the middle coarse fine, the cold crack thickness change is not significant, the cracking of this cause the corrosion of the reinforcing steel， concrete carbonation， reduce the concrete frost resistance， fatigue resistance, can reduce the structure of the anti—permeability ability， the influence of building use function, cause the corrosion of the reinforcing steel bar, and reduce the durability of the materials affect the load-carrying ability construction.个人收集整理，勿做商业用途个人收集整理,勿做商业用途
　　三、温度的控制和避免裂缝的方法　　为了避免裂缝，减轻温度应力可以从控制温度和改善捆绑条件两个方面着手。
Three, temperature control and avoid method in order to avoid cracks and reducing temperature stress from temperature control and improvement of the bound condition of two aspects。
　　控制温度的方法如下：　
Temperature control method is as follows:
　（一）选用改善骨料级配，用干硬性混凝土,掺混合料，加引气剂或塑化剂等方法以减少混凝土中的水泥用量；　
（a) choose to improve the aggregate grading, with dry concrete， mixing the mixture, adding air-entraining agent and plasticizer and other methods to reduce the dosage of cement in concrete；
　（二）拌合混凝土时加水或用水将碎石冷却以降低混凝土的浇筑温度;　　（三)热天浇筑混凝土时减少浇筑厚度,运用浇筑层面散热;　　（四）在混凝土中埋设水管,通入冷水降温；　
(2） mixing concrete and water or use water cooling to reduce the pouring temperature of concrete rubble; （3) the hot weather when pouring concrete to reduce the thickness of the casting， using the casting level heat dissipation; （4) embedded in the concrete pipe, ventilation with cold water to cool；
　（五）规矩合理的拆模时辰，气温骤降时进行表面保温，避免混凝土表面发生急剧的温度梯度;　
（5) rules and reasonable die hour， when the temperature drop surface heat preservation， avoid concrete surface temperature gradient sharply；
　（六）施工中长时辰显露的混凝土浇筑块表面或薄壁规划，在严寒时节采用保温方法；
（6） the construction long hour show of the surface of the concrete pouring piece or thin walled planning， in the cold season heat preservation method;
　　改善捆绑条件的方法是：
Improve bound condition is：
　　1、合理地分缝分块;　　2、避免基础过大高低；　　3、合理的安排施工工序，避免过大的高差和周围面长时辰显露；
1, reasonable joint block； 2, avoid too high; 3, reasonable arrangement of construction process, to avoid excessive elevation difference and the surrounding surface exposed long time;
　　此外，改善混凝土的功用,前进抗裂才干,加强保护，避免表面干缩，格外是保证混凝土的质量对避免裂缝是十分重要，应格外注重避免发生贯穿裂缝，出现后要恢复其规划的整体性是十分困难的,因此施工中应以避免贯穿性裂缝的发生为主。　
In addition， improve the function of the concrete, crack resistance ability, strengthen protection， avoid surface drying shrinkage， especially to guarantee the quality of concrete to prevent cracks is very important, should be particularly pay attention to avoid cracks, to recover after the onset of the integrity of planning is very difficult, so should give priority to in order to avoid the happening of the perfoliate crack during construction。
　在混凝土的施工中，为了前进模板的周转率，往往需要新浇筑的混凝土尽早拆模.当混凝土温度高于气温时应适当考虑拆模时辰，避免致使混凝土表面的早期裂缝。新浇筑早期拆模，在表面致使很大的拉应力，出现“温度冲击"表象。在混凝土浇筑前期，因为水化热的宣布，表面致使相当大的拉应力，此时表面温度亦较气温为高，此时撤消模板，表面温度骤降，一定致使温度梯度，然后在表面附加一拉应力，与水化热应力迭加，再加上混凝土干缩，表面的拉应力抵达很大的数值，就有致使裂缝的危险，但如果在撤消模板后及时在表面掩盖一轻型保温材料，如泡沫海棉等,关于避免混凝土表面发生过大的拉应力，具有显着的效果。加筋对大体积混凝土的温度应力影响很小,因为大体积混凝土的含筋率极低.仅仅对一般钢筋混凝土有影响。在温度不太高及应力低于屈服极限的条件下,钢的各项功用是安稳的，而与应力情况、时辰及温度无关。钢的线胀系数与混凝土线胀系数相差很小，在温度改动时两者间只发生很小的内应力。加筋后规划内的裂缝一般就变得数目多、间隔小、宽度与深度较小了.而且如果钢筋的直径细而间隔密时，对前进混凝土抗裂性的效果较好。混凝土和钢筋混凝土规划的表面常常会发生细而浅的裂缝，其间大多数归于干缩裂缝。虽然这种裂缝一般都较浅，但它对规划的强度和耐久性仍有一定的影响。　本文为互联网收集，请勿用作商业用途个人收集整理，勿做商业用途
In concrete construction, in order to forward the template turnover， often requiring new pouring concrete open mold as soon as possible. When the concrete temperature is higher than the temperature should be due consideration form removal time， avoid the early cracks on the surface of the concrete. New pouring early, dismantle causes great tension stress in the surface, a ”temperature shock”。 Announced in the early stage of the concrete pouring, because of hydration heat， the surface cause considerable tensile stress, the surface temperature is the temperature is high， so cancel the template surface temperature, must cause temperature gradient， and then attach a tensile stress at the surface, and the stress superposition and hydration heat and shrinkage of concrete, the tensile stress on the surface of the arrived in large Numbers, we run the risk of causing crack, but if after cancel the template in a timely manner on the surface cover a lightweight thermal insulation material, such as foam sponge, about avoiding excessive tensile stress in the concrete surface， has a significant effect。 Reinforcement effect on the temperature stress of mass concrete is very small， because of the mass concrete reinforcement ratio is extremely low。 Only have an effect on general reinforced concrete。 Without too much in temperature and stress below the yield limit of the conditions， the use of steel is stable, and has nothing to do with stress condition, time and temperature。 Linear expansion coefficient of linear expansion coefficient of steel and concrete is very small， when the temperature changes occurs only between a small internal stress。 After reinforcement in the planning generally become more than the number of cracks, and smaller spacing is small， width and depth. Interval and if the diameter of steel thin and dense, the concrete crack resistance effect is better. The surface of the concrete and reinforced concrete planning often thin and shallow cracks， during which most of the cracks due to drying shrinkage。 Although this kind of cracks are generally shallow， but its strength and durability for planning still has certain influence.文档为个人收集整理，来源于网络文档为个人收集整理，来源于网络
　以上对混凝土的施工温度与裂缝之间的联络进行了理论和实习上的开端评论,虽然学术界关于混凝土裂缝的成因和计算方法有不一样的理论,但关于具体的避免和改善方法定见仍是比较共同，一同在实习中的运用效果也是比较好的，具体施工中要靠我们多调查、多比较，出现疑问后多分析、多总结,联络多种避免处置方法，混凝土的裂缝是彻底可以避免。
Above on the construction of concrete temperature and cracks in the contact between the theory and practice on the beginning of a comment, though the academia about the cause of concrete crack and calculation method is not the same theory, but the specific method to avoid and improve mindset is still relatively common, in practice the application effect is good, the construction of concrete depends on our investigation and comparison, in doubt after analysis and summary, contact a variety of avoid disposal method， the concrete cracks can be prevented thoroughly.文档为个人收集整理，来源于网络个人收集整理，勿做商业用途