The jump bin method was put forward and popularized by Professor Wang Tiemeng, a famous crack control expert in China. Professor Wang put forward the design principle of "anti-radiation". Based on this principle, the skip bin method has a significant effect on reducing cracks in super-long, super-thick and ultra-thin mass concrete. The skip bin method makes full use of the principle of "resistance to release" that concrete is easy to release internal stress before its performance is unstable and it is not completely solidified within 5 ~ 10 days. It divides the building foundation or large-area concrete plane mechanism into several areas, and carries out the construction according to the principle of "block planning, block construction, layered pouring and integral molding". Its mode is the same as checkers, that is, pouring one by one. The interval between two adjacent sections shall not be less than seven days, so as to avoid the strong temperature difference and drying effect at the initial stage of concrete construction, and thus there is no need to leave post-cast strip.
Second, about the jump warehouse method
Jumping bin method construction: the sectional length of bottom plate should not be greater than 40m, and the sectional length of side wall and top plate should not be greater than 16m. Jumping spacing should not be less than 7d, and jumping should be set and handled according to the requirements of construction joints.
The comprehensive technical measures of skip bin method have successfully solved the problem of crack control and seepage control of super-long, super-wide and super-thick mass concrete without joints. The main technologies are as follows: (1) Based on the principle of "combined application of anti-detachment, priority of anti-detachment, priority of anti-detachment", the "skip block" is scientifically divided through analysis, and comprehensive measures of material, structure and construction management are taken to strictly control the early cracks in concrete. (2) Long walls are equipped with small-diameter high-density horizontal reinforcement outside the main reinforcement, and the bottom plate is covered with steel mesh to increase the crack resistance of concrete. (3) Choose low shrinkage cement, optimize concrete mix ratio and strictly control cement dosage, so as to effectively control concrete temperature stress and reduce concrete shrinkage and deformation. (4) Strictly control the silt content and concrete slump of coarse and fine aggregates in concrete raw materials to further improve the tensile strength and ultimate tensile deformation of concrete. (5) Strengthen information construction, and adopt temperature measurement method to realize temperature control. Comprehensive sanitary measures, such as plastic film moisturizing and straw bag insulation, should be taken to backfill and cover the soil as soon as possible, slow down the temperature, give full play to the stress relaxation of concrete and reduce the constraint stress. The theoretical analysis of crack control carried out in this achievement includes strength and deformation analysis. Close contact with engineering practice: the temperature stress of concrete is not linear with the length of structure, and the cracks of super-long structure concrete are controllable. Super-long, super-wide and super-thick mass concrete structures are not provided with deformation joints and post-pouring zones. By using conventional concrete without any expansion agent and adopting the comprehensive technical measures of "pouring in blocks and jumping in warehouses", the harmful concrete cracks can be effectively controlled and the anti-cracking safety of the project can be ensured. Compared with the common construction methods at home and abroad, it is innovative and breaks through the provisions of domestic norms on the allowable spacing of deformation joints of underground long walls.
Three, jump warehouse method construction scheme (taking a garage basement as an example)
(A) the basement structure jump warehouse method construction deployment
1, the overall deployment of the warehouse hopping method.
This project is divided into 6 construction sections and 40 storage areas, with one side of the post-pouring belt in the garage structure design drawing as the construction joint. See Figure 3. 1- 1 "Basement Structure Division and Construction Sequence Diagram" for details of the division and construction sequence. Every time concrete pouring construction inclines to two warehouses, the pouring time interval between adjacent warehouses shall not be less than 7d, and the whole garage basement structure construction shall be completed in turn.
According to the structural design drawings, the main building and the garage are bounded by settlement joints, which are independent of each other and can be constructed independently; The garage is divided into construction sections according to the post-cast strip. The horizontal construction joint of the basement exterior wall shall be 300mm away from the bottom plate or floor, and 3 thick water-stop steel plates shall be added; The horizontal construction joints on the inner wall of the basement are directly left on the upper surface of the foundation slab or floor. The concrete delivery pump (a combination of truck pump and truck-mounted pump) is mainly used for concrete pouring of the bottom plate, and the concrete pouring of each warehouse section is required to be completed at one time as planned.
2, the basement structure construction site layout
See the construction plan of foundation construction stage for the layout of cranes and other machines and tools at the construction site. The crane equipped on site can solve the transportation of steel bars, templates and other materials in the foundation construction stage.
In order to ensure the construction quality, the basement structural reinforcement is processed on site, and the off-site processing mode is eliminated, while the stirrup and slab reinforcement are processed off-site. The site is equipped with 10 steel bar bending machine and 6 steel bar straightening machines to ensure that the needs of basement structure construction are met.
3, labor, turnover materials and equipment organization
The construction period of this project is tight, which requires a large number of all kinds of labor. In the construction stage of cushion and bottom slab, according to the characteristics of large amount of concrete pouring in bottom slab and tight site, combined with the design of post-pouring belt of bottom slab, the foundation and bottom slab are divided into 12 sections. In addition, according to the specific situation of the field project, under the condition of meeting the technical requirements, the construction section can be mastered flexibly, which is conducive to accelerating the construction speed of the basement structure. We should coordinate all aspects of relations in terms of manpower and material resources.
4, the foundation slab jump warehouse construction sequence
In the basement foundation design of the garage, the basement foundation, wallboard and roof are divided into 40 sections with a total of 23 construction joints, with one side of the post-pouring belt as the construction joint. The serial number of each part is detailed and attached to the floor plan. According to the principle that the adjacent warehouses can only be connected into a whole after 7 days and the site schedule, the foundation slab is poured in 12 times.
(2) the basement structure jump warehouse construction measures
1, concrete material control and mix proportion optimization design
The principle of concrete material control and mix design is to improve the tensile and flexural strength as much as possible while ensuring the compressive strength meets the requirements, and at the same time reduce the temperature shrinkage and drying shrinkage of concrete from two aspects: reducing the amount of cement and water.
2, concrete raw material control
According to the investigation and recommendation of the mixing station during this period, the brand and performance of raw materials are tentatively set as follows: the cement variety is P.S.A42.5 ordinary portland cement of Ruby Cement Co., Ltd.; The sand adopts Taian high-quality medium sand; Crushed stone adopts local high-quality crushed stone in Jinan; The waterproofing agent adopts the composite waterproofing agent of Jinan Huajian Building Materials Co., Ltd.; See the test report and photos of crushed stone and waterproof agent below for details.
3. Mix proportion design and concrete performance control
See the table below for the optimal mix proportion of C30 concrete in the garage basement structure. It is required that the slump of pumping concrete is18 2 cm, and the slump of pouring bin surface is17 2 cm, and it has good workability and water retention.
4. Design and construction requirements of construction joints
(1) Use stainless steel wire mesh at the construction joint of the hopper. Weld Ф12 @ 200 steel bars into steel mesh, and then tie stainless steel wire mesh on the steel mesh.
Steel wire mesh is used in the construction joint of warehouse jumping, and the surface of the construction joint is rough, so it is not necessary to cut hair. After cleaning, the second concrete pouring can be carried out, and the concrete pouring at the joint is dense.
(2) At the construction joint, the water-stop steel plate and the original post-cast strip reinforcement (if any) are still set as usual according to the original design, and shall be implemented according to the structural design drawings of this project.
(3) laitance at the construction joints and non-vibrated compacted concrete shall be carefully chiseled. Before pouring concrete at the construction joint, the surface of formwork shall be cleaned, and the concrete and formwork shall be wet. After pouring concrete for construction joints, the maintenance shall be strengthened for at least 14d. Construction joint concrete should adopt multiple light-receiving methods, with a total of not less than three times.
5, wire mesh setting requirements
(1) Cut the steel wire mesh according to the spacing of double steel bars in the structure and the position of the water stop steel plate (on the floor and roof).
(2) Set column reinforcement outside the steel wire mesh. The rebar is HRB400 grade, with a diameter of 12mm and a spacing of 200mm. Installation needs to ensure the verticality of the column, so as to ensure the verticality of the steel wire mesh.
(3) Set up diagonal reinforcement, which is HRB400 grade 12mm with a spacing of 500mm, and the bottom of diagonal reinforcement is welded on the horizontal reinforcement.
(4) Formwork strips are arranged at the top of the bottom plate and the top plate as structural measures to prevent concrete leakage at the top.
5. Key points of construction
(1) The back brace of the fast and easy convergent net must be perpendicular to the net skeleton.
(2) The connecting mesh should be combined with the skeleton tile sleeve, and the mesh lap should be greater than 150mm, and should be supported and fixed. The edge of the convergent net template should be greater than150 mm. ..
(3) In order to prevent concrete leakage at the bottom, before pouring concrete, cement mortar with the same composition as concrete should be poured in advance at the fast closing net with a thickness of about 50 mm..
(4) The slump of precast concrete should be between 140~ 160mm. For concrete with excessive slump, vibrators should not be used to avoid flowing.
(5) When vibrating, the vibrating rod should be more than 450mm away from the steel mesh template, so as to reduce the impact load on the template, ensure the concrete behind the template to be vibrated tightly, and avoid quality problems such as honeycomb.
(6) The excess moisture gathered on the concrete surface during vibrating shall be removed as soon as possible to prevent the excess moisture from flowing down the steel mesh template and washing the corrugated surface.
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