Concrete crack treatment.Txt（砼裂缝处理.txt）

Concrete crack treatment.Txt（砼裂缝处理.txt） Concrete crack treatment.Txt(砼裂缝处理.txt) - Abstract: This paper analyzes the causes of concrete cracks, in order to ensure the effectiveness and durability of cast-in-place concrete, in addition to rational design, must improve the level of construction technology, the cracks will not only affect the structural integrity and stiffness, can also cause & reinforcement corrosion, carbonation, accelerated the decline of concrete durability and the anti fatigue and anti permeability ability. Therefore, according to the nature and specific situation of cracks, we should treat them differently and deal with them in a timely manner. To ensure the safe use of buildings. Key words: concrete; cast-in-place; cracks; quality Concrete, referred to as "concrete", refers to a composite material consisting of cementitious material that combines the aggregate into a whole. Generally speaking the term refers to the use of concrete cement as cementitious material, sand and stone as aggregate, and water (with or without admixtures and additives) according to a certain proportion, concrete mixing, molding, curing and, also known as ordinary concrete. It is widely used in civil engineering. According to the function, there are mainly structural concrete, thermal insulation concrete, decorative concrete, waterproof concrete, refractory concrete, hydraulic concrete, marine concrete, road concrete, anti radiation concrete, etc.. According to the construction process, there are mainly. Centrifugal concrete, vacuum concrete, grouting concrete, shotcrete, roller compacted concrete, extruded concrete, pumping concrete, etc.. According to the reinforcement way, there are: Plain (i.e. non reinforced) concrete, reinforced concrete, steel wire mesh cement, fiber concrete, prestressed concrete and so on. According to the workability of concrete mix, dry concrete, semi dry concrete, plastic concrete, flowing concrete, high flowing concrete, flowing concrete, etc.. 1 causes of concrete cracks There are many reasons for concrete cracks, but the basic reason is that the tensile stress in concrete exceeds the tensile strength of concrete. It can be attributed to three reasons, such as temperature and humidity change, excessive deformation caused by external load and improper construction method. Specific types are; (1) cracks caused by dry shrinkage of cement. The cracks appear on the surface of the concrete and are relatively small. Cement is a hydraulic material, with dry shrinkage, in the early stages of hardening, if inadequate maintenance, resulting in insufficient moisture, may cause cracks. (2) the change of temperature difference is caused by thermal expansion and cold contraction effect. This kind of crack usually appears in the environment or area with larger temperature difference or larger length, but not in the proper part. (3) cracks caused by stress concentration. This kind of crack usually appears at the Yin and Yang corner of the concrete slab or the support seat. It is due to the negative bending moment of the steel plate, the lack of reinforcement or the coarse steel bars and the excessive spacing. (4) the cracks caused by overloading and excessive deformation are caused by improper use. This kind of crack usually occurs in the tension zone of concrete flexural members. (5) cracks caused by tensile force. In the process of tensioning the prestressed reinforced concrete members, cracks may occur if the control is not good. This kind of crack usually appears at the end of the prestressed component or the upper surface corner of the plate. (6) cracks caused by uneven settlement. The uneven settlement of foundation caused by the foundation or beam, beams and other components of tension is too large and crack. (7) during construction, during the initial stage of concrete construction, cracks will occur because of the vibration, deformation or displacement of the formwork. (8) cracks due to premature loading. The construction for formwork early strength of concrete does not meet the design requirements and early loading. Cause the component to overload and crack. (9) the cracks in the construction joints may occur when the construction joints are not properly handled. (10) the concrete prefabricated component in the process of demoulding, transporting, stacking and lifting, causes the compression region of the component in the tension state for various reasons, and may cause the component to crack. 2 cracks caused by concrete damage Concrete is a multi component composite under conditions of temperature and humidity variations. Harden and produce volume deformation. Due to the inconsistent deformation of various materials, the initial stress is produced by mutual restraint, which results in the microscopic cracks which are not visible between the aggregate and the cement bond or the cement itself. The micro crack distribution is irregular, incoherent, but under load or further temperature changes, maintenance is not in place under the condition of dry shrinkage, cracks began to expand, and gradually connected with each other, thus visible cracks become larger, macro cracks, serious floor joints under formation and this has become harmful cracks. Such cracks will cause serious damage to the bearing capacity of the structure, fire resistance, impermeability, corrosion resistance of steel reinforcement, chemical resistance and other durability. Chemical erosion, freeze-thaw, carbonation, steel corrosion and alkali aggregate reaction, Will destroy the concrete structure. In addition to the influence of the concrete properties of the concrete, cracks are an important factor affecting the occurrence or progression of these damage effects. From the general structure of formwork to decoration was completed after 2 to 3 months, some large projects also inter annual construction. When the air CO2, SO2 gas and rain will enter along the cracks of concrete, rebar corrosion accelerate, accelerate the alkali aggregate reaction and carbonization rate; caused a decline in durability and shorten the life of the use of the building. 3 concrete cracks, cracks, treatment measures The main measures for repairing concrete cracks are as follows: surface repair method, grouting method, embedded plugging method, and structural strengthening method. Concrete replacement method, electrochemical protection method and bionic self-healing method. 3.1 surface repair Surface repair is a simple and common method of repair. It is mainly applied to the surface cracks which are stable and have no influence on the carrying capacity of the structure and the treatment of deep penetration cracks. Treatment is usually a surface in crack daubery cement slurry, epoxy mortar or concrete in the paint, brushing the surface of asphalt anticorrosion material, the protection at the same time in order to prevent the impact of various concrete action to crack, usually used in fracture surface bonded glass fiber cloth and other measures can. 3.2 grouting and plugging method The grouting method is mainly applied to the whole structure have influence or have cracks in concrete anti-seepage requirement of repair, it is make use of pressure equipments of cracks in the concrete cement material pressure, cement hardening and concrete to form a whole, thus reinforce the purpose of cementing materials are commonly used cement, epoxy resin, methyl acrylate, polyurethane and other chemical materials. Sealing method is one of the most commonly used method of crack closure, it is usually along the crack gouge, filling plastic or rigid water material embedded in the groove, in order to achieve the purpose of crack closure. Commonly used plastic materials are PVC cement, plastic ointment, Ding Ji rubber, etc.; the commonly used rigid water stop material is polymer cement mortar. 3.3 structure strengthening method When the cracks affect the performance of concrete structures, it is necessary to consider the reinforcement method to deal with concrete structures. The main methods used in structural reinforcement are as follows: increase the section area of concrete structure. In the angle of the component, the wrapped steel is strengthened by the prestressing method, the bonding steel plate is strengthened, the fulcrum reinforcement is added, and the shotcrete reinforcement is strengthened. 3.4 concrete replacement method Concrete replacement method is an effective way to deal with serious damage to concrete. The method is to remove the damaged concrete first and then replace the new concrete or other materials. Commonly used replacement materials are: ordinary concrete or cement mortar, polymer or modified polymer concrete or mortar. 3.5 electrochemical protection Electrochemical corrosion protection is to change the environmental conditions of concrete or reinforced concrete by electrochemical action of applied electric field in medium. Passivation of steel bars to achieve the purpose of corrosion protection. Cathodic protection, chloride extraction and alkaline recovery are three commonly used and effective methods in chemical protection. The advantage of this method is that the protection method is less affected by environmental factors. It is suitable for long-term corrosion protection of steel bars and concrete. It can be used either for cracked structures or for new structures. 3.6 bionic self-healing method Bionic self-healing crack processing method is a new, mimicking the biological tissue of wound automatically secrete a certain material to wound get healing of function, adding some special components in the traditional group of concrete points (such as containing adhesive liquid core fiber or capsule), the formation of intelligent bionic self-healing combined neural network system in the concrete, when the concrete cracks secrete a liquid core fiber can make the crack healing again. (free paper net www.mianfeilunwen.com)