(1) multi-story brick-concrete structure;
(2) Small high-rise cast-in-place reinforced concrete short-leg shear wall structure;
(3) High-rise cast-in-place reinforced concrete shear wall structure;
(4) Multi-layer cast-in-place reinforced concrete frame structure.
Cracks in cast-in-place reinforced concrete floors are common in residential buildings, but relatively few in commercial buildings and public buildings. From the perspective of hierarchical distribution, most cracks have nothing to do with hierarchy, and only a few projects show a decreasing trend in hierarchy.
Second, structural floor cracks generally appear one after another after the structural capping for half a year. If reinforcement measures are not taken in time, the cracks will continue to develop in 1 to 2 years.
Three. Location and characteristics of cracks
(1) The cracks in the cast-in-place reinforced concrete floor are mostly distributed on the floor of the room where the corner of the external wall is located. Cracks are generally inclined at 45, and sometimes two cracks appear in one corner at the same time, and the cracks basically run through from top to bottom.
(2) There are some cracks in the embedding position of the wire tube in the board.
(3) The floor cracks of individual projects are perpendicular to the direction of slab span or irregularly distributed.
Four. Cause analysis of cracks Through the comparative analysis of various influencing factors, we think that:
(1) Cracks in cast-in-place reinforced concrete floors are mainly caused by temperature deformation and shrinkage deformation of concrete. Reinforced concrete beams, columns, walls, slabs and other components are in the same atmospheric environment. When the temperature and humidity of the environment change, the concrete of these components will produce temperature deformation and shrinkage deformation accordingly. Due to the difference of body shape, the ratio of volume to surface area of plate is small, and the shrinkage deformation of plate in horizontal direction is generally ahead of (or greater than) that of beam, column and wall, resulting in tensile stress in plate and internal stress in beam.
On the other hand, under the influence of the outside air temperature, the external longitudinal wall and gable wall experience the repeated action of thermal expansion and cold contraction, and their combined temperature difference will produce greater principal tensile stress on the floor along the outside corner of the room.
The above two forces are superimposed to form the most unfavorable state for the plate. When the tensile stress in the slab exceeds the tensile strength of concrete and the deformation of the slab is greater than the ultimate tensile strength of reinforced concrete, cracks will occur in the slab.
The location of cracks depends on two factors, one is constraint and the other is tensile capacity. For the floor, the position of the greatest constraint is at the four corners, because the beam or wall at the corner has the greatest stiffness and the greatest constraint on the floor. At the same time, due to the influence of external temperature, the floor is the part with the largest shrinkage deformation along the corner of the external wall. Generally speaking, the steel bars in the slab are arranged parallel to the two adjacent edges of the slab, that is, the tensile capacity in the direction of the angular bisector is the weakest. Therefore, most of the cracks in the slab appear at the corner of the external wall, which is 45 oblique and radial.
Question 2: What are the causes of floor cracks? The problem of floor cracks was a professional problem at that time, and some people say that concrete cracks are a big problem that puzzles the engineering community now. There are dozens of factors leading to concrete cracks. General floor cracks are mainly due to concrete molding.
The plastic shrinkage cracking in the process is mainly related to the water loss rate of concrete surface, partly due to the influence of early load, formwork deformation, excessive vibration, excessive slump, on-site water addition and other factors.
The answer to the above question is like this. You can compare which one you belong to.
Question 3: What are the causes of cracks in concrete floors? 1. Causes of cracks in cast-in-place concrete floor slab (cover):
Let's take a look at the cracking of cast-in-place concrete floor (cover):
1) The crack is at the corner of the cast-in-place slab, which forms an angle of about 45 with the edge of the cast-in-place slab and develops obliquely;
2) Cracks develop approximately linearly in the span of cast-in-place slab;
3) The crack develops approximately in a straight line at the edge of the cast-in-place slab;
4) It is purely irregular cracks, and then analyze the causes of cracks in cast-in-place concrete floor (cover):
(1) Concrete: At present, commercial concrete is widely used. There should be no problem with commercial concrete from regular manufacturers, but it is not impossible, and it needs to be inspected. The factors affecting cracking are mixture ratio, water-cement ratio, cement variety, strength grade, cement dosage, coarse aggregate dosage and particle size, powder admixture and admixture.
(2) Design:
1) The plane shrinkage cracks of buildings often appear in the weak parts where the shrinkage stress is concentrated. In architectural design, only the architectural function is paid attention to, while the structural problems are ignored. For example, if the building plane is irregular and no strengthening measures are taken in the structural design, temperature stress and shrinkage stress concentration are easy to occur at the concave-convex corner, which leads to floor cracking.
2) The spacing between the steel bars of the reinforced slab is too large, especially the steel bars resisting negative bending moment on the slab surface are not long enough to set Z, which leads to cracks near the slab edge along the end of negative bending moment steel bars. However, at the corner of the building, the two-way slab is bidirectional due to shrinkage, and because there are not enough structural steel bars with Z, 450 inclined cracks appear.
3) The stress of the reinforced concrete member with floor thickness is shared by the steel bar and the concrete. If the cast-in-place concrete floor is too thin, the stiffness of the floor will inevitably decrease, and the stress of the tensile reinforcement and the compressed concrete will increase, so the floor will crack.
4) The PVC pipe buried in the floor is thin, so the section where the PVC pipe is buried in the floor is greatly weakened, while the middle part of the floor generally has only one layer of reinforcement, which is easy to cause cracks along the PVC pipe. For example, we find that the long cracks in the middle of the floor often pass through the lamp holder.
Question 4: Causes of concrete floor cracks ... There are many reasons for concrete cracks, but they can be summarized as follows:
(1) concrete shrinkage
Shrinkage is a main characteristic of concrete, which has a great influence on the performance of concrete. Once the microcracks caused by shrinkage develop, they may cause cracking, deformation and even destruction of the structure.
⑵ Temperature stress
The cement in concrete releases a lot of heat in the hydration reaction, which heats the concrete and forms a certain temperature difference with the outside air temperature, thus generating temperature stress. Its size is related to the temperature difference, and directly affects the concrete cracking and crack width. (3) insufficient reinforcement
From practice, it is observed that there are more cracks in concrete structures with large reinforcement spacing and small reinforcement ratio, and there are more cracks in unreinforced concrete than in reinforced concrete.
(4) Concrete materials and mix proportion
Improper mix design directly affects the tensile strength of concrete and is the cause of concrete cracking. Improper mixing ratio refers to excessive cement dosage, high water-cement ratio, improper sand content, poor aggregate type, improper selection of additives, etc. These factors are interrelated.
Relevant test data show that when the water consumption is constant, the shrinkage of concrete increases by 5% for every increase of cement consumption 10%; When the dosage of cement is constant, the strength of concrete decreases by 20% and the bonding force between concrete and reinforcement decreases by 10% with each increase of water consumption.
5] Curing conditions
Maintenance is an important means to make concrete harden normally. Curing conditions have an important influence on the appearance of cracks. Under the standard curing conditions, the concrete will harden normally and will not crack, but it is only suitable for making test blocks or prefabricated members in factories, and it is impossible for on-site construction. However, it must be noted that the closer the field concrete curing is to the standard conditions, the less likely the concrete will crack.
[6] Construction quality
In concrete pouring construction, uneven vibration, vibration leakage or excessive vibration will cause concrete segregation and poor compactness, which will reduce the overall strength of the structure. When the air bubbles in concrete cannot be completely eliminated, air bubble cracks will appear on the surface of steel bars, which will reduce the bonding force between concrete and steel bars. If the steel bar is subjected to excessive vibration, the cement slurry will be dense around the steel bar, which will also greatly reduce the bonding force.
These factors will make concrete shrink greatly, which will lead to the rapid expansion of micro-cracks in concrete and the formation of macro-cracks.
Question 5: What is the reason for the floor cracking of the new house? Go to the Housing Authority to find someone with appraisal qualifications and find someone with development. If not, just 123 15. . . What floor are you on? Maybe the geology is bad, but the quality of the project is not good. See if there is such a thing downstairs and upstairs, and identify it together if there is. . .
Question 6: What are the causes of cracks in concrete floors?
1) The crack is at the corner of the cast-in-place slab, which forms an angle of about 45 with the edge of the cast-in-place slab and develops obliquely;
2) Cracks develop approximately linearly in the span of cast-in-place slab;
3) The crack develops approximately in a straight line at the edge of the cast-in-place slab;
4) It is purely irregular cracks, and then analyze the causes of cracks in cast-in-place concrete floor (cover):
Question 7: I don't think what is said upstairs is quite right. If it is a negative reinforcement problem, the crack should appear along the beam.
I think your situation may be a specific problem. For example, concrete will shrink too much due to improper maintenance, and cracks will occur along the diagonal. Is it because of the high temperature after pouring and insufficient water conservation?
Seek adoption
Question 8: There were many cracks in the floor when the house was repossessed. It doesn't matter what the reason is, as long as the whole cement floor doesn't leak. This is normal.
Question 9: What are the possible causes of cracks in cast-in-place reinforced concrete floors? 1, the reason of floor concrete strength;
2. The reason of floor thickness; 3. The configuration of negative reinforcement at the top of the slab, such as spacing and thickness of protective layer (the reason why negative reinforcement deviates downward when stepping on construction);
4. In the construction, there are cases of sinking formwork and early installation (the concrete age has not yet arrived, and the upper floor is constructed by early formwork removal and early installation).
5. Shrinkage cracks caused by temperature;
Question 10: What are the common causes of cracks in cast-in-place slabs? At present, the phenomenon of deformation and crack of cast-in-place concrete floor slab in reinforced concrete civil buildings is more common, which has become a hot issue of commercial housing quality disputes and complaints. Not only does it affect the use function and damage the appearance, but it also destroys the whole structure, reduces its stiffness, causes corrosion of steel bars, and affects durability and strength. Based on the concrete engineering practice and long-term comparative observation in the laboratory, this paper discusses the causes of cracks in cast-in-place concrete floor slab and the construction control measures. ! The reason of concrete floor crack! . 1. 1 material factor (1) cement varieties. The shrinkage value of different kinds of cement depends on the content of C3A, SO3, gypsum and the fineness of cement. Generally speaking, the cement with high C3A content and fine fineness has large shrinkage. Cement with insufficient gypsum content has great shrinkage, while SO3 content has significant influence on soil shrinkage in the mixed zone. (2) Diversity of mixed materials. Its type, content and specific surface area are the main factors affecting the drying shrinkage of cement. The specific surface area of fly ash is the smallest, and the drying shrinkage of concrete decreases with the increase of fly ash content. (3) Aggregate varieties. The shrinkage of concrete decreases with the whitening of aggregate content and the increase of elastic modulus of aggregate, and increases with the increase of clay content in aggregate. (4) Concrete mix proportion. Under the condition of certain raw materials, the mixing ratio of concrete has great influence on shrinkage, including unit water consumption, unit cement consumption, water cement ratio, sand ratio and mortar ratio. The shrinkage of concrete mainly depends on the unit water consumption and cement consumption, and the influence of water consumption is greater than that of cement consumption. Under a certain water consumption, the shrinkage of concrete increases with the increase of cement consumption, and the area increases slightly; At a certain water-cement ratio, the shrinkage of concrete increases obviously with the increase of water-cement ratio; Under the same mix proportion, the drying shrinkage of concrete increases with the increase of sand ratio, but the increase is small. (5) Types and dosage factors of additives. Adding chemical additives will increase the shrinkage of concrete to varying degrees. Adding water reducer is used to improve the workability of concrete. When the slump increases, the shrinkage of concrete mixed with water reducer is slightly larger than that of concrete without water reducer. When water reducer is used to reduce water, improve strength or save cement, the shrinkage of concrete mixed with water reducer is close to or smaller than that of concrete without water reducer. The shrinkage of concrete mixed with calcium chloride early strength agent is obviously higher than that of concrete without calcium chloride, and it increases exponentially with the increase of calcium chloride content. However, the shrinkage of concrete mixed with triethanolamine and sodium chloride is larger than that without triethanolamine, but the increase is smaller than that mixed with calcium chloride early strength agent. 1.2 construction factors (l) preparation and pouring of concrete (1) uneven mixing of additives leads to large loss of additives, which cannot give full play to its role. (2) The concrete mixing time is insufficient. 3 thick. The temperature of fine aggregate and mixed water bin is too high, which makes the pouring temperature too high. (4) The mixing and transportation time is too long, which causes the concrete mixture to segregate, secrete water and sink. (5) Pumping concrete, due to high liquidity requirements, the amount of cement and water is too large. ⑤ Unreasonable pouring sequence leads to "cold joint" in construction or improper treatment of construction joints. (3) Too fast pouring speed, insufficient tamping or excessive vibration cause concrete segregation and bleeding, forming a mortar layer with more cement content on the surface. (3) The reinforced concrete is disturbed before the final setting. (3) In the process of concrete pouring, the negative reinforcement of the floor is not well protected, which reduces the effective height of the section. ④ The concrete cover is too thin or the aggregate of the cover is too little. (2) Formwork construction factors ① Due to the insufficient stiffness of floor formwork support, the difference of beam-slab support stiffness or the excessive deflection of formwork, the subsidence deformation of formwork support is too large. (2) During the construction process, excessive vibration will produce multiple instantaneous relative displacements at the parts where the support stiffness changes. (3) The concrete will be dismantled, frozen or vibrated prematurely before hardening. (4) the template slurry leakage, water seepage. (3) Concrete curing factors ① The untimely curing causes premature dehydration at the initial stage of concrete curing, which leads to concrete shrinkage. (2) Insufficient post-curing will aggravate the carbonation of concrete and cause carbonation shrinkage. (3) Early concrete curing is frozen. (4) After the floor construction is completed, at the initial stage of concrete final setting, construction machines and materials are concentrated, or the next working procedure is constructed too early, resulting in large construction load and vibration and cracks. 1.3 surrounding medium factors ① The lower the relative humidity of air, the greater the shrinkage of concrete. ② The shrinkage of concrete increases with the increase of air temperature. (3) Long-term exposure to wind and sun will also increase the shrinkage of concrete. 2. 1 general example two general examples and experimental analysis of floor cracks Through observing a large number of engineering examples, the author found that concrete ...