混凝土工程裂縫的研究

摘要
  混凝土是一種非均勻值脆性材料，由骨料、水泥石以及其中的氣體和水組成。在溫度和濕度變化的條件下，硬化并產(chǎn)生體積變化，由于各種材料變化不一致，互相約束而產(chǎn)生初始應(yīng)力，造成在混凝土內(nèi)出現(xiàn)微裂縫。這種微裂縫的分布不規(guī)則且不連貫，在荷載或應(yīng)力作用下，裂縫開始擴展，并逐漸互相貫通，從而出現(xiàn)較大的肉眼可見的裂縫，成為宏觀裂縫。
  開裂發(fā)生的原因可能是原材料的選取與配合比的選擇不當、施工方法和措施有誤、建筑物所處的條件的影響以及結(jié)構(gòu)不合理等?；炷了a(chǎn)生的溫度收縮、干燥收縮、不均勻沉降、結(jié)構(gòu)應(yīng)力集中等都可能或?qū)е禄炷灵_裂。在實際工程中，往往是各種因素多重作用引起混凝土開裂。寬度小于或等于0.05mm的裂縫通常對使用功能無大的危害，叫做無害裂縫；而結(jié)構(gòu)物的有害裂縫不僅會降低力學性能和承載力，而且直接影響結(jié)構(gòu)耐久性，縮短使用壽命。施工中應(yīng)采用措施式結(jié)構(gòu)盡量不出現(xiàn)裂縫，或減少裂縫的數(shù)量和寬度，特別是避免出現(xiàn)有害裂縫。國內(nèi)外對裂縫寬度都有相應(yīng)的規(guī)定，如我國的CCES01—2004《混凝土結(jié)構(gòu)耐久性設(shè)計與施工指南》，對鋼筋混凝土結(jié)構(gòu)的最大允許裂縫寬度就明確規(guī)定干濕交替和凍融環(huán)境下的一般構(gòu)件為0.2mm；水中和土中環(huán)境為0.3mm?；炷劣筛鞣N收縮引起的裂縫問題一直是混凝土結(jié)構(gòu)物裂縫控制的重點和難點。

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.