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Early on Concrete Slab Cracks Analysis and Prevention

Concrete fracturing, crack trend seen after demolition of touch with the threading pipe in the same direction. Early Prevention of Slab 2 technical measures to crack a reasonable selection of raw materials 2.1 1) should be adopted in construction of cement low heat; try to avoid using fine through the thin cement, because the fineness of cement hydration is too thin fast, hydration shrinkage large, easy to crack. 2) The coarse aggregate gradation shall be as near the middle; fine aggregate to use, the sand is appropriate, tests showed that when the fineness modulus of 2.79, 0.318 of the average particle size, coarse sand compared with fineness modulus of 2.12, the average particle size of 0.336 in the sand, each cubic meter of concrete reduces the amount of water 2O ~ 25kg mud can be reduced 28 ~ 35kg, which reduces the temperature rise of concrete and reduce the shrinkage of concrete. 3) sand, stone clay content must be strictly controlled, over the provisions of the shrinkage of concrete will increase, causing decreased tensile strength of concrete, the cracking of concrete is very unfavorable, the general control of stones in the sand content of less than 1, sand control the clay content is less than 2. 2.2 to prevent the concrete surface of the concrete by adding water pumping early volatile agent, retarding long time, such as by routine operations until after the initial setting of concrete, then trowel calendar the old method, the surface of the first l of Cui Jianjun, et al: Early Slab concrete cracks on the Causes and Control 31 5 ~ 6h in water evaporation inside the cracks have formed. This can be completed in the vibrator, while closing pulp hand side, and immediately covered by plastic film, plastic film can be a roll,[link widoczny dla zalogowanych], backward construction method. As gas-tight plastic film, water is not easy footsteps, even if the barrier will be free to form a small space with high humidity on the concrete curing is beneficial. Plastic film is light, easily blown open, it should be heavy pressure side, to prevent blowing. 2.3 Elimination of the disturbance after the initial setting of concrete 1) before the concrete strength to achieve 1.2N/ram not in its pull on the stampede or install mode and support, in the use of composite wood parts should be encrypted template support. 2) before pouring concrete, carefully check the extent of the template securely. Especially for larger span and composite wood parts should be encrypted template support. 3) a reasonable layout of concrete pipes, ducts must be supported in the template rod bracket, eliminating the disturbance of the template. 4) When a low temperature season, built a concrete surface is then covered with plastic film outside the upper layer of straw bags holding 1 to 2,[link widoczny dla zalogowanych], to promote the rapid development of concrete strength, producing a number of test block, the same curing condition to determine the form removal time. References [1] GB50204 - 2002,[link widoczny dla zalogowanych], Concrete Structures Construction Quality Acceptance Is]. [23GBJ107 - 87, inspection and assessment of concrete strength [S]. [33 Chen Guang Chang. Discussion on the problem of concrete cracks [J]. Hebei Engineering College. 2003, (2) :17-20 [43 Huang Shiji. High-rise building facilities TIM]. Guangzhou: South China University Press, 1997. AnalysisoftheCauseofEarlyCrackonConcretePlankasWel1asItsPreventionandCureCUIJian-jun, WANGCheng-jie (CapitalConstructionOffice, HebeiEngineeringandTechnicalCollege, C_,[link widoczny dla zalogowanych], angzhou061001, China) Abstract: Theappearancequality, intensityanddurabilityofconcreteareaffectedbyconcretecrack, whichthenaffectstheservicelifeofbuildings. Inthepaperthecausesofconcreteplankcrackingareana-lyzed, includingplastic, temperature, self-shrinkagedeformation, AARanddisorder. Intheendsomepre-ventivemeasurestocracksareproposed. Keywords: high-rise; concrete; earlycrack; originalcoagulation; preventionandcure (Editor: Guo Shujun)

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