Cracksinreinforcedconcretestructures,analysisofthecausesandprevention_5158

1、Cracks in reinforced concrete structures, analysis of the causes and preventionAbstract: In the civil engineering field of reinforced concrete structures, a very common problem is the quality of cracks in the structure of the problem, and there is growing number of trends, which has affected normal

2、life and production, and troubled by a large number of engineering and technical personnel and management personnel It is an urgent need to address technical problems.Keywords: concrete cracks to prevent0 IntroductionUnder external loads due to structuraldamage and collapse from the beginning of cra

3、ck propagation, so people tend to produce a fracture of the destruction of buildings in fear is understandable. As early as 1932, the former Professor Su Lianmou strength theory of reinforced concrete, pointed out that as a normal reinforced concrete flexural damage to the state is reinforced by the

4、 tension zone to reach the yield strength, flexural compression zone of the compressive strength of concrete to reach this state known as the carrying capacity limit state. The state of the whole process is accompanied by the increasing load, cracks appeared (reinforcement stress is only 40 60MPa),

5、crack propagation, plastic compression zone of the continuous development, ultimately achieving completely destroyed. At this point damage load is often cracks when the load 3 to 5 times, so many large reinforced concrete structures, only the weight more than 30% of the limit load in this condition

6、of reinforced concrete structure with a slight crack is completely normal , the structure is safe, fear is unnecessary.From the modern science of concrete work on the research and proved a lot of concrete work, concrete, structural cracks are inevitable, cracks that people can accept a kind of mater

7、ial properties, but how to harmful levels of control in a valid range. Because a variety of materials used in concrete is composed of a mixture, and because is a kind of brittle materials, influenced by temperature, pressure and under the influence of external forces, there is the possibility of cra

8、cks. While, after cracks appeared, we must analyze what is harmful to crack cracks, which are harmless cracks, an analysis of the causes and harmful to the formation of cracks in how to deal with.A type of reinforced concrete structures,cracks and seepage, leakage causesReinforced concrete seepage,

9、leakage ismainly due to its mixture vibrated in the process of watering and vibrator vibration leakage arising from non-dense honeycomb-like pores or gaps in the external water pressure under the influence, resulting in seepage and leakage phenomenon.At the same time, the design of reasons, such as

10、structure, form size, force, tectonic factors such as ill- considered and lead to reinforced concrete structure, seepage, leakage phenomenon. The actual situation from the past, reinforced concrete, cracks can be divided into the following: concrete mixture precondensation of settlement cracks and s

11、hrinkage cracks; thermal stresscracks in concrete; self-stress cracks in concrete; concrete underexternal and the impact of crack load.The direct cause of cracks in two2.1 The increase in shrinkage and hydration heat since the late 70s (1978 1979) of concrete construction technology in China has cre

12、ated an enormous progress - premixed concrete technology. From the past dry hard, low mobility, on-site mixing of concrete mixing shift focus to shift large pumping liquidity pouring, cement consumption increased, water-cement ratio increased, the rate of increase in sand, aggregate size decreased,

13、increased water consumption due to problems such shrinkage and hydration heat increases.2.2 The strength grade of concrete is rising structural strength grade of concrete is rising, but there are many structural inappropriate choice of the high strength grade. Customary that: 'The higher the int

14、ensity level greater safety on the high not to low, to improve strength grade did not harm'. Is sometimes convenient to accommodate the construction, using high-strength concrete, which is a misleading label led to an increase of cement, cement consumption increased, water consumption increased,

15、 fine aggregate and coarse aggregate diameter is too small, sand and so the rate is too large to hydration heat and shrinkageIncrease .2.3 Structural constraints of stress growing structure, increasing the size increases, the increasing complexity of structure, super-long super-thick and ultra-struc

16、ture of a statically indeterminate structure is frequently used and using in-situ construction, this structure forms a significant binding effect, for a variety of deformation would inevitably lead to greater restraint stress.2.4 The negative effect of admixture admixture admixture, and a wide range

17、 of indicators of lack of hydration only the intensity of heat and shrinkage effects of long-term experimental data (at least one year), some experimental data are not strict, there are many additives serious increase in shrinkage deformation, and some even reduce durability. Reposted elsewhere in t

18、he paper for free download http:/2.5 ignore the structural constraints in both domestic and international structural design of steel structures often overlooked the importance of constructive and thus often cracks. Structural design of the binding nature of the structure is often overlooked, failing

19、 to make use 'of anti-and release' of the design principles, the lack of appropriate design and construction specifications, a point of order.2.6 Conservation of improper methods at present in the concrete construction of the basic conservation techniques used in the past followed a simple m

20、ethod, which has been far from meeting the larger pumping concrete shrinkage deformation temperature requirements.2.7 Performance of concrete under tensile cracks in the resistance of this area are due to lack of concrete tensile properties (tensile strength and ultimate tensile) arise from non-grad

21、ed materials in this regard is sparse.3 precautionsBy this analysis, there are cracks in engineering can be a large part of the means by design, construction and means to overcome.3.1 Material selection Cement: should use a lower heat of hydration of cement, is strictly prohibited the use of substan

22、dard cement stability. coarse aggregate: suitably rough surfacetexture of hard stone, level with good porosity is small, non-alkaline reaction; harmful substances and clay content does not exceed the prescribed. fine aggregate: coarse particles is preferred, the gap smaller, lower clay content in th

23、e sand. foreign admixture material:water-reducing agent and other additives should be adopted to improve the working performance of concrete, reduce water consumption and reduce shrinkage.3.2 Ingredients mix design: should beused with low water-cement ratio, low water consumption, to reduce the amou

24、nt of cement. the prohibition of arbitrary increase in cement consumption. when preparing concrete measures should be accurate, it is necessary to strictly control the water-cement ratio and cement dosage, mixing evenly, segregation of the concrete must be re-mix, before it is poured.3.3 The configu

25、ration of reinforcement steel shall be in strict accordance with the construction drawings, particular attention should be paid to the following points:reinforced varieties, specifications, quantity changes, alternative, we must consider the impact of crack resistance of the component.reinforced the

26、 position correctly, protective layer is too large or too small may lead to concrete cracking, reinforcement spacing is too large, it can lead reinforced concrete between the cracks.3.4 Template Project prevention of cracks in reinforced concrete structure in the template project should pay attentio

27、n to the following points: the template structure should bereasonable, in order to prevent the template between the deformation of the pole pieces of concrete cracks caused by the different. templatesand stents have enough stiffness to prevent the construction of load (especially the dynamic load) u

28、nder the action of the template deformation caused by too much crack. a reasonable opportunity to master the form removal, form removal too early, should ensure that early-age cracking of concrete without damaging or not, but it can not be too late, try not to miss the peak heat of hydration of conc

29、rete, that is, do not miss the best time for conservation intervention.3.5 concrete pouring concrete pouring should be to prevent the segregation phenomenon, vibrator should be uniform, moderate. to strengthen concrete in the early conservation, and appropriate to extend the conservation time, high

30、temperature and low humidity or wind speed conditions, but should an early stage fountain maintenance, there are difficulties in watering maintenance, or when time does not guarantee their full wet , can be used covering materials, methods such as moisture.3.6 designed and constructed buildingwhen t

31、he plane selection using the functional requirements are met under the premise of seeking simple, planar complex of buildings, prone to distortions caused by additional stress in the wall and floor cracks.rational arrangement of vertical and horizontal walls, vertical wall openings should be as smal

32、l as possible. control of tall buildings ina ratio, the less tall than the overall stiffness of the greater ability to adjust the uneven settlement of the stronger. reasonable to adjustthe load-bearing structure of the various parts of the force, thereby making load distributed evenly to prevent the

33、 excessive concentration of force. to reduce the uneven foundation settlement, in addition to the aforementioned measures, in the basic design that could be taken to adjust the basis of the buried depth of the foundations of a different calculation of the intensity and using different methods such a

34、s cushion thickness to adjust the foundation of the non-uniform deformation.appropriate strengthening of the basis of a rigidity and strength.layers set ring beam, structural columns, can increase the integrity of the building to improve brick masonry shear, tensile strength, prevent or reduce the c

35、racks, even if there is a crack, but also to prevent its further development. correctly set up settlement joint. Settlement joint selection of the location and Aperture should be appropriate, construction should be reasonable, its structure can be stitched and set up. limit expansion joint spacing.

36、Shape of the complex, uneven foundation settlement value of large buildings should be strictly controlled, the same can also be stitched, and other structures and uses. part of the sill masonry should be strengthened. On the lower part of the large bay windows, should set the reinforced concrete beams, in order to adapt to the deformation of bay windows to prevent the windowsill Department produced vertical cracks. Reposted elsewhere in the paper for free download http:/3.7 Construction Technology strengthening the foundation of the inspection and acceptance work, and post-excavation shall p