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How to control the quality of municipal sewer project

Author: PengShun From: www.yourpaper.net Posted: 2010-06-24 13:17:03 Read:
Abstract: with the development of society and economy, the concrete project of domestic construction engineering volume increasing, concrete is one of the most widely used construction materials.Many of the causes of concrete cracks, which is a common problem.From the general theory and many years of field experience, causes and prevention measures of concrete cracks are simply discussed.
Keywords: cracks; causes; prevention of
Concrete is a kind of aggregate, cement, water and other external material made of a mixture of heterogeneous brittle materials.Due to a series of problems of concrete construction, its deformation and restraint, the concrete crack is the most common engineering industrial engineering problems.Light makes internal reinforced materials such as corrosive, reduce the carrying capacity of reinforced concrete, durability, serious threat to people's life, property.Therefore, how to take effective measures to prevent and reduce the cracking of concrete, is a problem that deserves attention.
1 major causes of cracks in concrete,
1.1 human factor
Cracks caused by improper design.For the pursuit of the appearance of the building style, the building surface there are many concave convex, concave from stress concentration lead to cracks.Some long building, it is prone to expansion crack.In addition, because the bearing plate design thickness is too small, the stiffness decreases, the tensile reinforcement and the compressive stress increase of plate, the plate penetrating cracks appear.
The crack ratio design of concrete caused by improper fit.Concrete mix the improper design will directly affect the tensile strength of concrete, is an important cause of the cracking of concrete.Mix properly refers to the excessive amount of cement, water cement ratio, sand ratio, aggregate, inappropriate species selection improper poor admixture.
Curing condition of concrete is not good cracks.Concrete curing is important means to normal hardening of concrete, has the key effect of curing condition on crack.
The improper use of cracks of concrete material.Such as the use of lead to higher shrinkage of slag cement, rapid hardening cement, low-heat cement and cement grade is low or high water cement ratio Junyi cracks.
The construction method is not standard will lead to cracks in the concrete.Concrete pouring, vibrating uneven, or leakage of vibration, vibration and so on, will cause the concrete segregation, density difference, reduce the overall strength of structures.Cannot be completely excluded inside the bubble concrete, reinforced surface bubbles will reduce bond of concrete and steel.Reinforced if subject to excessive vibration, the cement slurry in the reinforced around the dense, will greatly reduce the cohesive force.
The 1.2 objective reasons
The cracks caused by temperature stress.The main cause of the temperature cracks are caused by temperature difference.
The shrinkage crack.There are many kinds including shrinkage, dry shrinkage, plastic shrinkage, autogenous shrinkage, carbonation shrinkage etc..Because the concrete characteristics, concrete in the hardening process, the water evaporation, the volume decreases gradually, and shrinkage, according to the mechanics analysis, the boards around the restraint of bearing, not stretch.When the plate constraint caused by concrete shrinkage stress exceeds a certain level, must cause the cast-in-place board crack, stress concentration areas are often crack sites.
Due to the development of cement industry, in order to improve the strength of cement, manufacturers often through finely ground cement clinker, resulting in cement specific surface area is increased greatly, volume stability is worse and worse.In addition, with the widespread use of commercial concrete manufacturers, aggregate quality decreased obviously, especially the pumping agent, easy to cause the concrete early-age plastic shrinkage cracks and the late shrinkage crack.
The load induced crack.Reinforced concrete structures under load, crack due to deformation, according to the component category, mechanical property and force, deformation and crack of different shapes.2, crack prevention measures of
Ratio of
2.1 control material
To ensure the concrete in good working condition, should as far as possible to reduce the unit water use of concrete, three low "(low sand ratio, low slump, low water binder ratio (two), mixed with superplasticizer and high performance air entraining agent), a high (high fly ash volume)" design criteria, to produce high strength, high toughness, shot, low heat and high tension value of the anti-crack concrete.
In the actual construction mix ratio, should be adjusted appropriately according to the specific circumstances of the time.First of all, should be based on the heat of hydration of cement, water, shrinkage, specific surface area and other properties of reasonable selection of cement and amount; second, strict control of water used in concrete, and try to control the concrete slurry, enhance the viscosity of cement mortar, reduce aggregate settlement, give full play to role of skeleton of sand, stone, reduce excess mixing water; again is the sand content strictly control the concrete aggregate, optimizing aggregate distribution: finally, in high temperature season construction, strictly control the temperature of various raw materials, especially cement temperature, to prevent the crack of the concrete is also very important.
2.2 control of construction process
The improvement of mixing process.The two feed stone enveloped with cement or mortar coating technology, can effectively prevent water accumulation in the cement mortar and stones of the interface, the interface transition layer of dense hardened structure, bonding force, so as to improve the strength of concrete 10 or save cement 5 , and further reduce the heat of hydration and crack.To improve the concrete mixing process, using two air-cooled technology based on three cold on the technologies of traditional, reduce the temperature of the concrete pouring.
The strict control of casting process.The reasonable arrangement of construction procedure, layer, block placement, to facilitate cooling, reducing constraints.The pouring of concrete, two vibration in before the final setting, may be excluded from the concrete due to bleeding, in space and water stone, horizontal bars formed in the lower part, improve the adhesive force and tensile strength, and reduce the internal cracks and pores, improve crack resistance.In the season of high temperature pump, suitable for cooling with warm grass bag covering pipelines, in order to reduce the temperature of casting.
To pay attention to the maintenance after placement.The curing of concrete is mainly to maintain the proper temperature and humidity conditions.Insulation can reduce the thermal diffusion on the surface of concrete, reduce the temperature difference in concrete surface, prevent surface cracks.After pouring concrete, timely coverage with wet straw, hemp, and pay attention to water conservation, prolonging the curing time, ensure the concrete surface slow cooling.In the cold season, the concrete surface heat preservation measures should be provided, in order to prevent the cold wave attack.In order to ensure the concrete in early as little as possible shrinkage, early maintenance work in the new pouring concrete is particularly important, moist curing mainly to control component, for large volume concrete, conditional to use water or water curing, curing time is L4 ~ 28 days.
2.3 from the design calculation, structure angle control
The crack is allowed, in the structural design, inspection, especially for concrete members subjected to tensile cracks area should attach great importance to, should consider standard load and permanent load, conversion for testing the maximum crack width allowable value; relative to control other cracks, structure should be used to meet the strength and stability, security the requirements, must be checked.The current structure engineering toward the development of large-scale, complex, the designed strength grade of concrete to the development of C40 ~ C60, designers pay more attention to the structure safety, control of deformation cracks of ill-considered, design personnel should be based on the aspects such as; the foundation, static, dynamic load, environmental factors, the durability of the structure to control the crack.
Strict construction control of concrete mixture ratio, according to the concrete strength grade and quality inspection and workability of concrete requirements determine the mixture ratio, strict control of water / cement ratio and cement content, requires supervision strict supervision and control.Good quality, choose good gradation gravel, sand control particle size and content, appropriate to reduce the void ratio to reduce concrete shrinkage, thus strengthening the cracking strength of concrete.
3, the
The emergence and development of crack control, is an indispensable and important link in construction, although the cause and calculation method of concrete cracks in academic circles have different opinions on the theory, but the prevention and improvement measures is still relatively uniform.Crack control should be scientific requirements of crack control is within the allowable range, focus on preventing cracks, and from the design, construction, use of common efforts, combined with a variety of prevention and treatment measures.To strictly implement the rules, regulations, the concrete crack is completely controlled by the.The problem of concrete crack is a comprehensive problem, the structure cracks, should give height to take seriously, root causes of accurate grasp of the emergence, development, and take corresponding measures from the design, construction, prevent and control the occurrence and development of cracks to.
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