Common causes of concrete cracks and Prevention.doc

Common causes of concrete cracks and PreventionAbstract Concrete Cracks in the engineering construction is an extremely common phenomenon, it also affected the emergence of the quality of construction, the author directed at a specific course of construction of several concrete cracks appear in the phenomenon, the main analysis of the emergence This was the main reason cracks as well as its preventive measures. Key words Analysis of concrete crack prevention measures As the reform and opening up and modernization process of accelerating, Chinas construction scale is growing, how to ensure construction quality, and are also increasingly subject to various levels of government and community attention. In a number of engineering quality problems, the phenomenon of concrete cracks is even more prominent, and therefore must be very great importance to the analysis of the causes of concrete cracks and prevention. It should be noted that some cracks in concrete is difficult to avoid, for example, in reinforced concrete beams, in the 30% -40% design loads may be cracking; while cracking when the tensile component of stress is only reinforced steel design stress 7% -10%. Engineering practice in addition to loads caused by the cracks, the more of a concrete shrinkage, temperature, deformation and uneven settlement, leading to cracking. Although some cracks on the use of little harm, but in actual construction, there is a need for its effective control, in particular, to avoid harmful cracks. In this paper, the mass concrete on the basement floor, basement wall of concrete, ground concrete, in-situ concrete floor and roof waterproofing a brief analysis of the fine aggregate concrete cracks in the main, and then raised a number of targeted preventive measures and of our discussion. 1, cracks in mass concrete basement floor of the main reasons and preventive measures Basement slab of mass concrete shrinkage due to temperature stress and under stress, so that the structure, cracks, followed by the main reason for cracks can be seen in this first of temperature and shrinkage deformation, followed by the water-cement ratio concrete and so on, specifically the is the improper selection of cement, hydration heat is too high, the outside air temperature of concrete inside and outside the constraints as well as the influence of cracks in the concrete appeared specific preventive measures have the following four aspects. (A) strictly control the hydration heat To meet design strength requirements and obtain the consent of the premise of the design, concrete mix design strength of 60 days could be considered to reduce the amount of cement, the same time, should choose low-heat cement, reduce the heat of hydration of cement. (B) The Double Mixed techniques to reduce the crack Double Mixed technology, that is (retarding superplasticizer admixture and fly ash), to reduce the amount of cement, and to improve the workability of concrete to improve concrete pumpability. (C) using a certain sequence of pouring In casting, it is necessary to use sub-fixed a slope, thin casting, progressive advance, a reach the peak method, one end of the whole continuous casting. (D) In accordance with the provisions of the work of a reasonable moisture Pound mass concrete poured after the initial setting before the feet with a long scratch Calibrating, after 6 hours of iron rollers on the first few times, and then wood trowel the concrete surface, making false and rub hair twice or more in order to close close water cracks, preventing shrinkage cracks in the surface, about 12-14 hours later, covered by plastic sheeting and straw bag for insulation moisture conservation. Time measurement of concrete in accordance with the provisions of the temperature of each part to ensure that the temperature difference inside and outside of concrete does not exceed 25 . Second, the causes of cracks in the basement wall analysis and preventive measures The main reason for cracks in the basement wall also due to shrinkage caused by, there are two main aspects of specific preventive measures. The first is to not change the total amount of wall reinforcement cases, siding and other cross-section for the level of reinforcement substitution, the original rough into fine steel reinforced large spacing small spacing, thus preventing wall cracks; followed by the wall concrete pouring plate, after at least 7 days before the template removal, and pouring water in the top of the wall set up to conduct a 24-hour non-stop tricking conservation. Third, the main reason for the ground of concrete cracks and prevention measures Uniform settlement (the settlement of the ground are often associated with the main structure of the columns, walls and other settlement inconsistent in their binding sites and thus have a greater crack), temperature and shrinkage deformation. The preventive measures should be first and foremost on the ground and pouring concrete walls, leaving 30mm gap between columns, so that walls, columns and ground settlement independent of each other. Followed by the cushion laid before its next layer of the surface should be moist. General may from time to set up house on the ground stretching joints. Outdoor floor mat should be used to set stretch of concrete joints, the spacing of 30m. Indoor and outdoor ground concrete pads, shall be set up vertical and horizontal shrinkage shrinkage sew seam. Longitudinal contraction joints spacing of 3-6m, transverse contraction joints spacing of 6-12m. Outdoor construction of the ground or hot seasons the ground, contraction joints should adopt the lower limit of pitch. Longitudinal shrinkage of concrete cushion should be done flat head sewn seam or flat head joints stiffened panels. When the cushion when the thickness is more than 150mm, do stand Kuchinui. Transverse contraction joints shall be seam fraud. Flat seam and enterprises should not be placed Kuchinui of sutural separation materials, casting should be close to each other, stand Kuchinui size should be consistent with design requirements, fake slit width 5-20mm, a depth of cushion thickness of 1 / 3, sewn inside the with 1:3 cement mortar filling. Industrial plants, an auditorium, lobby and other large-scale concrete pouring section cushion should partition, partition section should be combined with deformation crack location, different types of buildings and equipment for the ground connection at the location-based division and shall be set vertical, horizontal consistent spacing of contraction joints. Reposted elsewhere in the paper for free download http:/ Fourth, in-situ reinforced concrete floor of the main causes and preventive measures for cracks In-situ reinforced concrete slab cracks are one of the main reasons, concrete water-cement ratio, slump to spend big. Second, the negative reinforcement plate improperly located. Third, poor maintenance of early concrete. Fourth, After the completion of the building (especially the long-vacant commercial buildings) long-term closure of room air relative humidity is too low, concrete shrinkage cracking. This is often ignored. That in normal humidity environment, the concrete shrinkage cracks are very small, and that no further expansion of crack. Concrete surroundings when the relative humidity below 80%, the concrete within the free water evaporation accelerated, thus exacerbating the contraction of the concrete, if this process continues for too long, micro-cracks will be further expanded, which may form a seam pass . 5, the concrete strength even before 1.2N/mm ago, in piling up material on it, puts up bracket. The specific preventive measures are the following five aspects: 1) to strictly control the construction of concrete mix, concrete slump for commodities inspection should be strengthened. 2) In the slab casting process of handing someone ramming protect tendons, and to avoid the phenomenon depresses the occurrence of negative reinforcement. 3) The concrete pouring and templates before the first watering the grass-roots wet, pouring to be taken after the effective conservation measures and meet the following requirements: (1) should be within 12 hours after pouring of concrete to be covered and moisture conservation; ( 2) concrete watering curing time: The use of Portland cement, ordinary Portland cement or slag cement concrete mixing and shall not be less than 7 days, for mixed with retarding admixture or impermeability requirements concrete, shall not be less than 14 days; (3), watering frequency should be able to maintain the concrete in a moist state; (4) using plastic sheeting covering the conservation of concrete, its surface should be covered all of Chang Lu tight and plastic sheeting should be kept within condensate. 4) In a certain time period (usually from the concrete pouring is completed within 2 years) to maintain the relative humidity inside the vacant room and outdoor relative humidity are basically the same and should not be less than 85%, this requirement can be used the method frequently open the window to be realized, areas where conditions permit to spray water on a regular basis to increase humidity better. 5) concrete strength reached 1.2N/mm ago, may not stampede or stockpiled material on which to install the template and the bracket in order to avoid cracks due to vibration and other reasons. 5, roof waterproofing layer of fine aggregate concrete rigid main causes and preventive measures cracking Roof waterproofing layer of fine aggregate concrete rigid main reasons for cracking are about four areas, first, has not established a sub-grid or sub-grid sewn seam to set unreasonable; followed