混凝土工程裂缝的研究毕业论文.doc

混凝土工程裂缝的研究

摘要
  混凝土是一种非均匀值脆性材料，由骨料、水泥石以及其中的气体和水组成。在温度和湿度变化的条件下，硬化并产生体积变化，由于各种材料变化不一致，互相约束而产生初始应力，造成在混凝土内出现微裂缝。这种微裂缝的分布不规则且不连贯，在荷载或应力作用下，裂缝开始扩展，并逐渐互相贯通，从而出现较大的肉眼可见的裂缝，成为宏观裂缝。
  开裂发生的原因可能是原材料的选取与配合比的选择不当、施工方法和措施有误、建筑物所处的条件的影响以及结构不合理等。混凝土所产生的温度收缩、干燥收缩、不均匀沉降、结构应力集中等都可能或导致混凝土开裂。在实际工程中，往往是各种因素多重作用引起混凝土开裂。宽度小于或等于0.05mm的裂缝通常对使用功能无大的危害，叫做无害裂缝；而结构物的有害裂缝不仅会降低力学性能和承载力，而且直接影响结构耐久性，缩短使用寿命。施工中应采用措施式结构尽量不出现裂缝，或减少裂缝的数量和宽度，特别是避免出现有害裂缝。国内外对裂缝宽度都有相应的规定，如我国的CCES01—2004《混凝土结构耐久性设计与施工指南》，对钢筋混凝土结构的最大允许裂缝宽度就明确规定干湿交替和冻融环境下的一般构件为0.2mm；水中和土中环境为0.3mm。混凝土由各种收缩引起的裂缝问题一直是混凝土结构物裂缝控制的重点和难点。

Summary
  Concrete is a brittle material non-uniform value, the aggregate, cement, and one of the gas and water composition.Changes in temperature and humidity conditions, the hardening and produce volume changes due to changes in various materials are inconsistent with each other constraints arising from the initial stress, resulting in micro-cracks in the concrete.This irregular distribution of micro-cracks and not coherent, in the load or stress, the cracks began to expand, and gradually through each other, thus a greater visible cracks become macroscopic cracks.
   Cracking reasons of the occurrence may be the selection of raw materials and the design of the improper selection, construction methods and measures in the wrong, building the condition the influence and unreasonable structure and so on. Concrete temperature shrinkage, produced by drying shrinkage, the uneven settlement, the structure stress concentration may or lead to concrete cracking. In practical projects, often is the various factors of concrete cracking caused by multiple roles. Width of less than or equal to 0.05 mm to use function of crack usually no harmful, called harmless crack; The structures and the harmful cracks will not only reduce the mechanical properties and the bearing capacity, but also directly affecting the structure durability, shorten service life. Construction should be adopted measures type structure try not to crack, or reduce the number of cracks and width, especially avoid harmful cracks. To crack width at home and abroad have corresponding provisions, such as China's CCES01-2004 "concrete structure durability design and construction guide", the biggest of reinforced concrete structure allows the crack width is specific provision alternating wet and freeze-thaw environment of general component is 0.2 mm; The water and soil environment of 0.3 mm. Concrete by all sorts of the shrinking the cracks of the concrete structures is always the crack control of the key and difficult.