Research On The Early Temperature Cracking Of Underground Super-long Reinforced Concrete Side Wall

After three decades of reform and opening up, especially in the recent ten years, with frequent large-scale construction that large and complex buildings is continuous emerging, underground long side wall of reinforced concrete structure has been widely used. Because of these underground long concrete sidewall structure belonging to the large volume of concrete, concrete in the construction process due to heat of hydration reaction produces a lot of heat of hydration, resulting in non-uniform temperature field inside the concrete structure, the structure of the temperature drop is constrained because of the shrinking process will produce temperature cracks, seriously affecting the durability of the structure of the applicability of the relevant major projects, and even security. Current solutions such as shrinkage joints, back strip and other effects in general and the application have some limitations.In this paper, the Shenzhen Municipal Science and Technology Program(basic research)(JCYJ20130329143859418), on the side wall of reinforced concrete structures underground long early cracking temperature has been systematically studied, and specific work includes the following aspects:From the materials, while ensuring the tensile strength of concrete, concrete mix optimization carried out ash, slag admixtures in different proportions ratio of axial compressive strength, splitting tensile strength test, temperature stress test, flat cracking test. We can get the following conclusions:1, the control effect of fly ash concrete hydration heat much better than ore, and the effect is more pronounced in the early, late effects decreased significantly. Therefore, fly ash can be effectively controlled mass concrete hydration heat, so as to achieve the purpose of control of mass concrete temperature stress in concrete.2, slag early activity than fly ash, mixed with a large volume of concrete early strength slag, slag can make it through the incorporation of fly ash to replace cement due to the loss of that part of the strength.3, the amount of fly ash in concrete incorporation of equal incorporation of slag, the adiabatic temperature rise of concrete smaller, tensile strength values of lager pressure, thus Fly: ore = 1: 1 for optimal incorporation ratio.From a structural standpoint, the contraction joints, back strip, such as the early effects of temperature cracking normal circumstances, put forward to solve the early temperature induced joints cracking program. Basement in Shenzhen, a project as an example, the temperature field with no seams in the side wall, induced joint spacing 20 m, 24 m, 28 m, 32 m and induced joints weakened section rate of 15%, 20%, 25% the stress field, analysis and comparison of the deformation field, the optimum spacing and induced joints weakened section rate. The following conclusions:1,A set structure induced joints can effectively reduce the temperature stress of early prevention of disorder crack generation. Can induce different pitches with varying degrees of lower seam early thermal stress, finite element simulation results in induced joint spacing effect when compared with 24 m 20m, 28 m, 32 m obvious.2,The rate of induced joints can weaken the different sections with varying degrees of reduced temperature stress early, by finite element simulation results, the 20 percent limitation section weakened 15 percent, 25 percent of the fruit of the most obvious.3,It will form a similar circular stress weakening region, the radius is about 3 meters. In the stress weakening region, the more close to the crack, the stress is smaller.In summary, this paper experimental research and practical projects based on the finite element analysis, from materials and structures effectively reduce the adiabatic temperature rise reduce the generation of random cracks for concrete mix optimization, early cracking temperature control provides reference.