Construction scheme of mass concrete project?

What are the construction schemes for mass concrete projects? The following is an example of Zhong Da Consulting Company for your reference.

I. Overview of the Project:

This project is a modern building integrating business and office apartments. There are 4-storey podium buildings on the ground floor, 24 floors in Block A and 29 floors in Block B, with a total construction area of over 74,500 square meters. The structure type is frame-supported shear wall structure. The basement of this project is a parking lot with fire pool, water pump room, power distribution room and generator room. The first to fourth floors are mainly commercial and office buildings, and the fifth floor is elevator apartments. This project and foundation basement are divided into six working areas according to the post-pouring zone. 1 and 3 areas are raft foundations with a thickness of 1600, and the rest are foundation waterproof boards with a thickness of 400. The design bottom elevation of the bearing platform is -5.2m, C40 impervious concrete is adopted, the impervious grade is 0.8Mpa, and the concrete volume of the whole foundation slab is about 4000m3. Except for Area 2, Area 5 and Area 6, all the others have been poured. This scheme is suitable for the foundation concrete pouring construction in Area 2, Area 5 and Area 6.

Second, the construction preparation work:

The technical requirements of mass concrete construction are relatively high, especially in construction, to prevent temperature stress cracks caused by temperature difference caused by cement hydration heat. Therefore, it is necessary to make full preparations from the aspects of material selection and technical measures to ensure the smooth construction of mass concrete for foundation slab.

1, material selection

This project adopts commercial concrete pouring. The main material requirements are as follows:

(1) Cement: Considering the high hydration heat of ordinary cement, especially when it is applied to mass concrete, a large amount of hydration heat of cement is not easy to dissipate. If the internal temperature of concrete is too high, it will have a large temperature difference with the surface of concrete, thus generating compressive stress in concrete and tensile stress on the surface. When the surface tensile stress exceeds the tensile strength of early concrete, temperature cracks will occur. Therefore, the low hydration heat slag portland cement with the number of 525# was determined. By adding appropriate additives, the performance of concrete can be improved and the impermeability of concrete can be improved.

(2) Coarse aggregate: crushed stone with a particle size of 5-25mm, with a silt content not exceeding 1%. Concrete made of stone with large particle size and good gradation has good workability and high compressive strength, and at the same time, it can reduce water consumption and cement consumption, thus reducing the hydration heat of cement and the temperature rise of concrete.

(3) Fine aggregate: medium sand, with average particle size greater than 0.5 mm and silt content not greater than 5%. Compared with the concrete mixed with fine sand, the concrete mixed with medium-coarse sand with larger average particle size can reduce the water consumption by about 10%, and at the same time reduce the cement consumption accordingly, thus reducing the hydration heat of cement, temperature rise of concrete and concrete shrinkage.

(4) Fly ash: As the pouring method of concrete is pumping, in order to improve the workability of concrete and facilitate pumping, consider adding an appropriate amount of fly ash. According to the specification requirements, when slag portland cement is used to mix mass fly ash concrete, the maximum limit of fly ash replacing cement is 25%. Fly ash is beneficial to the hydration heat and workability of concrete, but the early ultimate tensile value of concrete decreases after adding fly ash, which is not conducive to the impermeability and crack resistance of concrete. Therefore, the content of fly ash should be controlled within 10, and the external mixing method should be adopted, that is, the amount of cement in the mixture ratio should not be reduced. Calculate the dosage of fly ash per cubic meter of concrete according to the requirements of mixture ratio.

(5) Admixtures: There are no specific requirements for the design. Through analysis and comparison and previous experience in other projects, it is found that adding 2kg water reducing agent into concrete per cubic meter can reduce the peak hydration heat, compensate the shrinkage of concrete and improve the crack resistance of concrete. Before pouring commercial concrete, the dosage and performance of concrete admixture shall be reported to the construction unit.

2, concrete mixture ratio

(1) The concrete adopts the commercial concrete supplied by the mixing station, so the concrete mixing station is required to try out the concrete in advance according to the technical requirements put forward on site.

(2) the concrete mixture ratio should be determined by trial matching. This design is based on the relevant technical requirements of the current national Code for Construction and Acceptance of Concrete Structure Engineering, Code for Design of Mix Proportion of Ordinary Concrete and Technical Code for Application of Fly Ash Concrete.

(3) When fly ash is mixed externally, only sand with the same volume is deducted from the sand. In addition, the supply of cement should be considered to meet the construction requirements.

3. Site preparation work

(1) Foundation slab reinforcement, column reinforcement and wall reinforcement shall be completed in sections as soon as possible, and concealed works shall be accepted.

(2) The pits and water accumulation pits on the foundation slab are closed by combined steel formwork, and the non-module parts are closed by wooden formwork.

(3) Copy the elevation of the upper surface of the foundation slab on the column and wall reinforcement, and clearly mark leveling when pouring concrete.

(4) When pouring concrete, the embedded temperature measuring tube, plastic film and straw mat for thermal insulation should be prepared in advance.

(5) The Project Manager Department shall contact the construction unit for good construction electricity utilization to ensure concrete vibrating and construction lighting.

(6) Management personnel, construction personnel, logistics personnel, security personnel, etc. Should be scheduled day and night, stick to their posts, their respective responsibilities, to ensure the smooth progress of continuous concrete pouring.

Three, mass concrete temperature and temperature stress

According to the design requirements, the temperature of the foundation slab concrete is detected; The peak temperature rise at the center of the concrete foundation slab is usually slightly lower than the adiabatic temperature rise. Generally, it is produced about 3 days after concrete pouring, and then it tends to be stable and does not heat up, and gradually begins to cool down. According to the specification, temperature control measures should be taken according to the climatic conditions for mass concrete maintenance, and the surface and internal temperatures of the poured concrete should be measured as needed to control the temperature difference within the design requirements; When the design has no specific requirements, the temperature difference should not exceed 25 degrees; The design of this project has no specific requirements, that is, it shall be implemented in accordance with the specifications. The surface temperature can be controlled by adjusting the thickness of the insulating layer.

Fourthly, mass concrete construction.

1 division of construction section and pouring sequence

Because the foundation slab has been divided into three different areas, and the foundation concrete of area 2 and area 5 with a thickness of 400 mm is cured by normal water spraying, the foundation slab is divided as a natural construction section.

In area 2, concrete is transported by two concrete pump pipes, and poured from two positions at the right post-pouring zone 1/3 of axis ⑾, and poured from the right side of axis 1 1 to the direction of axis 18. The volume of concrete pouring is about 600 cubic meters, and the planned pouring completion time is 20 hours.

Two concrete delivery pumps are used for concrete pouring in Area 6. Erect a shuttle slot between the 1 axis and the B axis to the center of the raft, and then pour it backwards. The other pump is connected from the joint of shaft 3 and shaft S, and placed at the position of shaft H of the raft, and the raft is also poured backwards. The total amount of concrete is about 2000 cubic meters, and the planned time for concrete pouring is 48 hours.

Two concrete delivery pumps are used for concrete pouring in Area 5, with a total concrete volume of about 500 cubic meters, and the planned pouring time is 12 hours.

2, concrete pouring

(1) The concrete is made of commercial concrete, which is transported to the site by concrete truck, and two concrete delivery pumps are used in each area.

(2) When pouring concrete, the pouring process of "fixed points in different areas, one slope, progressive advance and reaching the top at one time" should be adopted. The length of the placing boom of the reinforced concrete pump truck shall determine the pouring area, and each pump truck shall be responsible for the concrete pouring in this area. When pouring, it should be carried out in one place until the design elevation is reached, and the concrete flows forward in a fan shape, and then it is poured continuously on its slope and pushed forward in sequence. This pouring method can better adapt to the pumping process, so that each truck concrete is poured on the slope formed by the previous truck concrete, ensuring that the pouring interval between each layer of concrete does not exceed the specified time. At the same time, it can solve the problem of frequent movement of the pump pipe, and it is also convenient for covering and insulating the poured parts.

(3) When pouring concrete, set 1~2 vibrators at the ash outlet of each pump truck. Because the slump of concrete is relatively large, it can flow obliquely about 1 m in the bottom plate with a thickness of 1.5 m. Two vibrators are mainly responsible for the vibrating compaction of the lower slope, and the other 2~4 vibrators are mainly responsible for the vibrating of the upper concrete.

(4) Due to the large slump of concrete, water will be generated at the lower part of the surface reinforcement, or the concrete at the upper part of the surface reinforcement will produce tiny cracks. In order to prevent such cracks, secondary plastering and compaction measures are taken before the initial setting of concrete and after the pre-settlement of concrete.

(5) Three groups of test blocks are made on site according to each pouring 100 cubic meter (or one machine-team), and the strength of 1 group pressure for 7d and 1 group pressure for 28d are used in technical files; The strength of group L is still 14d.

(6) Waterproof concrete impermeability test block shall not be less than 2 groups per unit project as stipulated in the specification. Considering that the project is not too big, two groups of waterproof concrete impermeability test blocks were taken as required.

5, concrete temperature measurement

(1) When pouring foundation slab concrete, assign special personnel to cooperate with the embedded thermometer. The length of temperature measuring tube is divided into two specifications, and the arrangement of temperature measuring points is shown in Figure 2. The temperature measuring line shall be embedded according to the temperature measuring layout. When the temperature measuring tube is embedded, it should be firmly bound with the steel bar to avoid displacement or damage. Each group has two temperature measuring lines (that is, temperature measuring lines with different lengths), and the upper and lower ends of the lines are marked with adhesive tape, which is convenient for distinguishing the depth. The temperature measuring line shall be wrapped with plastic tape and bound firmly, and the temperature measuring end shall not be affected with damp. The position of the temperature measuring line is marked with a protective wooden frame, which is easy to find after heat preservation.

(2) Equipped with full-time temperature measuring personnel, according to two shifts. Training and technical disclosure should be given to temperature measuring personnel. Temperature measuring personnel should be serious and responsible, and measure the temperature according to the hole on time, and must not omit or resort to deceit. Fill in the temperature measurement records clearly and neatly, and make disclosure during the shift change.

(3) The temperature measurement shall be carried out continuously, once at a time, and the temperature measurement can be stopped only after the concrete strength reaches the specified time and strength and is approved by the technical department.

(4) When measuring the temperature, if the highest temperature inside the concrete differs from the departmental temperature by 25 degrees or the temperature is abnormal, the technical department and the technical director of the project shall be informed in time so as to take timely measures.

6, concrete curing

(1) After concrete pouring and secondary plastering compaction, it shall be covered with heat preservation immediately. First, the concrete surface should be covered with two layers of straw mats, and then covered with a layer of plastic film.

(2) The hydration speed of fresh concrete is fast, and it can be cured after being covered with plastic film, so as to prevent the concrete surface from drying shrinkage cracks due to dehydration, and at the same time, it can also prevent the straw mat from reducing its thermal insulation performance due to moisture absorption.

(3) Column and wall steel dowel is the difficulty of heat preservation, so special attention should be paid to cover tightly to prevent the temperature difference from being large or freezing.

(4) With the consent of the technical department and the technical person in charge of the project, the thermal insulation layer and plastic film can be gradually removed to make the concrete dissipate heat.

Verb (abbreviation of verb) main management measures

1, the raw materials of mixing concrete need to be inspected, and can only be used after they are qualified. At the same time, we should pay attention to the temperature of raw materials to ensure that the temperature of concrete entering the mold is basically close to the theoretical calculation value.

2, in the concrete mixing station by designated personnel with admixture, dosage should be accurate.

3, the commercial concrete on the construction site should be checked by car, determine the slump and temperature of concrete, and check whether the concrete quantity is consistent. At the same time, it is forbidden to temporarily add water to the concrete mixer at the construction site.

4, concrete pouring should be continuous, intermittent time shall not exceed 3~5h, at the same time, the surface temperature of the poured concrete before it is covered by new concrete shall not be lower than the relevant provisions.

5, the test department designated persons responsible for temperature measurement and maintenance management, found that the problem should be promptly reported to the project technical director.

6. Before pouring concrete, the sundries in the base groove should be cleaned up.

7, strengthen the concrete block production and maintenance management, block after ripping timely number and sent to the standard room for maintenance.

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