专业英语论文英语部分.doc

Concrete structural cracks common problem analysis Pick to: our national economic growth, drive the construction of rapid and sustainable development. Because of the materials widely concrete, lower price, high compressive strength, can be pouring into various shapes, and fiery good, not easy weathering resistance, maintenance cost low, become today the world building structure is the most widely used as one of the building materials. With the birth of concrete products, because its construction is convenient shortcut, stable performance, reliable quality, low labor strength, high production efficiency, and at the same time can reduce the noise, environmental protection etc comprehensive advantages, but also the concrete pushed to a peak. This paper industrial building concrete structural cracks are analyzed, and various problems in actual construction process summarize experience and proposed solutions. Keywords: concrete structure, Crack causes, Preventive measures Industrial building concrete structural cracks is extremely common phenomena, among which more to several reinforced concrete members. Practice proves that the concrete structure and a considerable portion cracks can be through the design method and construction measures to overcome, the paper common easily neglected problems which the causes of cracks is concluded, and puts forward some corresponding preventive measures. 1 common concrete cracks cause analysis Concrete is a kind of tensile ability very low brittle material, especially industrial architecture in construction and expansion projects, in use process, and when something changes in temperature, humidity, rolling mill vibration, foundation uneven settlement, extremely easy cracks. In recent years, with the architectural technology, building materials, construction technology development and testing methods of progress, not only their physical properties, and importance values its chemical properties. Such as AAR JianJiLiao reaction and chemical medium erosion can make concrete structural cracks, reduce early concrete strength. 1.1 material quality Material quality problem caused by fracture relatively common reason is cement, sand, stone, quality is bad. Bitter engineering by using these unqualified material will lead to shoddy school construction. so said only the good quality of materials, engineering quality will fundamentally guaranteed. 1.2 deformation of foundation In reinforced concrete structure, cause craze main reason is uneven settlement. Fracture of the size, shape, direction decision and the deformation of foundation, due to the deformation of foundation stress is opposite bigger, make the cracks are generally GuanChuanXing. 1.3 construction technology Construction craft emphasize the following: (1) moisture to evaporate, cement stones, and concrete shrinkage is usually leads to the concrete cracks important reasons. (2) the coagu-flocculation soil is a kind of man-made hybrid material, its good quality is an important symbol of after molding and uniformity of concrete close-grained degree. Therefore concrete mixing, transportation, water, vibration compaction each procedure of any defects and omissions, are likely to make of cracks is directly or indirectly causes. (3) template tectonic undeserved, leaking, leakage pulp, bracing rigidity insufficiency, the support of the foundation sink, tear open mould and so on are likely to cause cracking. The construction process, rebar surface pollution, concrete cover too big or too small to irrigate collision of reinforced make its shift etc are likely to cause crack. (4) concrete curing, especially in early maintenance quality and cracks close relationship. Early surface drying can make its internal and external temperature bigger more easily cracks. 1.4 structure by a reciated Structure by jose after cracks of many factors, construction and use are likely to crack. For example, tear open mode early quake-hit early or method is undeserved, component stacking, transportation, hoisting the cushion block or hoisting position of undeserved, construction overload and tension stress value too may both cracks. Which is the most common reinforced concrete beam, plate subjected to bending, in use loads tend to appear different degree of cracks. Common reinforced concrete members under the 30% a 40% of design load, it is possible to crack, naked eye generally cannot detect, while component of limit fracture load are in design load of 1.5 times above. In so usually reinforced concrete members are allowed in crack work (such crack some literature called harmless crack). In reinforced concrete design specification, different conditions stipulated crack maximum width 0.2 a nun. For those 0.3 of crack width surpasses codes, and dont allow the cracks of the components should be deems harmful cracks, need to be careful analysis, handled cautiously. 1.5 designed structure Structure component sections mutation or open hole, leave slot because of stress concentration, Tectonic processes improper cast-in-situ girder in second beams place if not put aside a additional stirrups or additional crane steel structure and various factors such as sewing not set properly are easy to cause the cracking. 1.6 humidity deformation cracks Ordinary concrete in air scleroma, volume happens contraction, which produced inside the component tensile stress, in early concrete strength is low, concrete shrinkage is the largest. Therefore, if the component early maintenance is bad, the susceptible shrinkage crack. This kind of cracks in cast-in-situ shear wall, and pools bottom, the wall of engineering structure is most common. 1.7 creep cracks Structural components in stress, except under the action of transient elastic deformation outside, its deformation value with the extension of time and increase the phenomenon is called creep deformation. It is documented subjected to bending due to creep deformation function, its long-term deformation value can increase 2 3 times, because deformation increase and make pull area concrete under tensile stress, causing cracks appear. Pre-stressed beam for creep produces more stress losses, reduced the structure anti-cracking performance. This kind of crack inthe subjected to bending pull area, the characteristics and the bear loads cracks are the same. 1.8 construction Because construction causes cracks appear many factors. Like concrete structure maintenance bad or curing time enough; Water-cement ratio of excessive, cement or admixture addition amount too big, Stir enough time, vibrating false; Rebar surface pollution, cover too small or too big, Any lien construction joints and does not press formulary processing, Late prophase concrete construction disturbance, Component inside and outside temperature, fails to take effective measures, In the construction of unfavorable climates, and barely construction; Winter construction without adopting anti-freeze measures, etc. 2, prevention measures 2.1 material selection (1) the cement: should choose the hydration heat low cement, verboten safety unqualified cement. (2) the coarse aggregate: appropriate USES rough surface, quality of a material is solid of stone. The gradation is good, porosity small, no alkaline reactions, Hazardous materials and clay content do not exceed the specified. (3) fine aggregate: appropriate is used with thicker grain, pore is lesser, hydraulic lower ZhongSha. (4) outside admixtures: appropriate USES jianshuiji etc admixtures, in order to improve the working performance and reduce consumption of concrete, reduce shrinkage. 2.2 ingredients, (1) proportioning design: using low water-cement ratio, low consumption, to reduce concretes shrinkage. (2) prohibit any increase water dosage. (3) prepared concrete measurement shall be accurate, it must be strictly controlled water-cement ratio and dosage of cement, mix uniformly, segregation of concrete must mix again, and then watered. 2.3 reinforcement Reinforced configured should strictly according to construction drawing construction, especially attention the following each point: (1) from plastic hinge area ductility consider reinforced varieties, specifications, quantity of change, the substitution, must consider to component crack-resistance influence, accomplish strength weak beam. (2) reinforced location should correctly. Cover that is too small or may result in the concrete cracking, reinforced spacing between too easy cause reinforced concrete cracking. 2.4 template engineering Reinforced concrete structure crack prevention, the template engineering should notice the following each point: (1) template tectonic want reasonable, in order to prevent the template each rods between different deformation caused concrete cracks. (2) formwork and scaffold must have plenty of stiffness, prevent construction load (especially the dynamic loads) under the action of excessive cause craze, template deformation. (3) reasonable time of the mould, and master down time of the mould too early, should guarantee the early age concrete not damaged or craze. But also cannot too late, try not to miss concrete hydration heat peak. 2.5 concrete pouring (1) concrete pouring should prevent segregation, should be uniform, appeared ofnon-vibrating moderately. (2) strengthening the concrete early curing time. In the high temperature, lower humidity or wind speed big condition, more should be early on water-jet curing. When water conservation have difficulty, or can guarantee that its full moisture, can be made cover preservation etc method. 2.6 construction technology (1) strengthening the foundation of examination and inspection work, excavation after survey and design units promptly notify the present acceptance. Of more complex foundation, and the design in excavation shall require investigation fill after drilling, when out when have an adverse geological condition, you must first to its reinforcement, and experience collect, conducted only after next construction. (2) excavation base slot, keep its original structure not disturbance. Reasonable arrangement of the construction sequence. Adjacent structures and buildings in relatively recently, the general thing spacing shall first construction deep foundation excavation, in order to prevent the damage already built foundation. In the modern construction process, reinforced concrete enginee