Construction scheme design and implementation key

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Construction scheme design and implementation key points of mass concrete in the construction of mass concrete structures, the control of concrete cracks is a very important subject. Due to the large section size of mass concrete structure, the possibility of cracks caused by external load is very small. However, due to the joint action of temperature change caused by hydration heat released by cement in hydration reaction and concrete shrinkage, large temperature stress and shrinkage stress will be generated, which will become the main factor for cracks in mass concrete structure. The construction overview of Kaide building project in Tianjin is as follows: the main building of phase II project has 2 floors underground, the slab thickness of reinforced concrete raft foundation bearing platform is 3.0m, and the plane is 48.80m × 48.80m, and the concrete volume of bearing platform is 6360m3. The underground floor of the shop building is 1, the thickness of the bearing platform is 1.8m, and the amount of concrete is 1817m3. The slab thickness of the bearing platform of the underground garage is 1.0m, the concrete volume is 2319m3, and a post cast strip is set in the middle of the bearing platform. The strength grade of bearing platform concrete is C30, the impermeability grade is P8, and the total amount is 10496m3. The design requirements are to meet the technical requirements of crack free self waterproofing. In this study, ZY expansive concrete is used, the application of ZY expansive concrete is studied, the mix proportion of ZY shrinkage compensating concrete is determined, and effective control measures are taken in the implementation of seamless construction scheme

I. seamless construction scheme design

1 The design mechanism is that the shrinkage compensating concrete mixed with ZY expansion agent is used as the basic material, and the super long concrete structure is continuously poured with reinforcing strip instead of post pouring strip. According to the requirements of seamless design of concrete structure, the floor of the square is divided into blocks: the post pouring belt divides the whole floor into 4 blocks to form 4 pouring units, and the expansion reinforcing belt is set in the block to divide it into 4 blocks, and the whole floor is divided into 16 blocks. After the partition of the bottom plate is determined, the post cast strip and reinforcing strip shall be reserved at the same parts of the wall plate, the top plate and the bottom plate, and the retaining method is the same as that of the bottom plate. The expansion reinforcement bandwidth is 2m, and the dense hole iron wire is set at each side of the edge to be reinforced with steel bars to prevent the concrete outside the reinforcement zone from flowing into the reinforcement zone. When pouring concrete, the concrete outside the belt shall be poured first, and when pouring to the reinforcing belt, the concrete mixed with ZY expansion agent shall be used for construction. Considering that the expansion will reduce the strength, the concrete strength grade of the expansion reinforcement zone should be improved, and the amount of expansion agent should be increased. The purpose of super long seamless structure can be achieved by cyclic construction with this method

2. Shrinkage compensating concrete is shrinkage compensating concrete according to gbj119288 "technical code for application of concrete admixtures", which produces self stress below 0.2 to 0.7MPa

in order to measure the limited expansion rate, the laboratory has carried out the limited expansion rate test of adding ZY to the test piece to verify that the actual addition of ZY can indeed obtain micro expansion, and the amount of ZY has a direct impact on the expansion rate

3. Design of mix proportion selection of concrete materials: 1 Cement: 42.5mpa ordinary portland cement produced by Tangshan cement plant is adopted. 2. sand: Zunhua medium sand is selected, with fineness modulus mx=2.6 ~ 2.8, apparent density of 2.64 g/cubic centimeter, loose density of 1410 kg/cubic meter, and compact density of 1. 90% of synthetic leather is produced in China at 550 kg/cubic meter. 3. Under working conditions, the mud content is ≤ 3%. 3. stone: Jixian stone is selected, with particle size of 5 ~ 31.5mm, continuous grading, crushing index of 8% ~ 9.8%, and silt content ≤ 3%. 4. expansion agent: ZY expansion agent produced by Beijing Zhongyan special materials Co., Ltd. 5. water reducer: Grade II fly ash from Yangliuqing power plant is selected

4. The preparatory measure of adding a small amount of water reducing agent later is that the concrete pouring is in the high temperature season from July to August, which is easy to increase the concrete slump loss and reduce the requirements for concrete workability. In addition, the possible traffic jam during transportation or temporary problems to be handled during construction slow down the pouring and tamping speed, delay the concrete molding time, and increase the concrete slump loss due to the extension of time, resulting in failure to meet the pumping requirements, At this time, it is strictly forbidden to add raw water, but the post mixing method of adding a small amount of fdn2i water reducer for the second time should be adopted to compensate and recover the slump loss of concrete. In the mix proportion, the water reducing dosage of fdn2i is 0.8%, generally the maximum dosage of the water reducing agent is 1%, and it is only considered to be within 0.2% when adding water reducing agent later. The water reducing effect of the later mixing method is significantly higher than that of the first mixing method or the same mixing method at the same dosage, which can compensate for the slump loss. However, it should be noted that any transport vehicle later mixed with water reducing agent should quickly mix for more than 30 revolutions or 1 second. The mixing amount and mixing time shall be implemented by a specially assigned person

5. Concrete mix proportion and pouring measures for basement wall: in the stage of determining the design mix proportion, the measures to reduce the water cement ratio were taken. The development process of the bottom from imitation to self renovation is not satisfactory. Both the plate and the wall plate are c30p8, while the water cement ratio of the bottom plate is 0.47. While the water cement ratio of the wallboard is 0.41, the slump index of the concrete floor is 18 ~ 2, and the resulting carbon emission is 7820 tons 0 cm. The slump index of the wallboard is controlled at 14 ~ 16 cm. The purpose of this measure is to reduce water consumption and concrete shrinkage. In the concrete pouring stage, the secondary vibration process is adopted, that is, the secondary vibration is carried out before the initial setting of the concrete. Avoid cracks caused by settlement shrinkage of concrete. The implementation of these measures is very necessary to control the occurrence of wall cracks. Other aspects of control during pouring are the same as those of the bottom plate

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