With a pouring volume of nearly 30000 m3 at a time, Greenland 468 project also set a new record for the pouring volume of concrete in the West.
In addition to causing concrete cracking and water leakage of the bottom plate, it may also cause structural damage to the foundation bottom plate and potential safety hazards.
According to the trial mix results, the final mix proportion of mass concrete is shown in the following table: (III) strictly control the temperature of mass concrete (1) the temperature rise of concrete pouring body based on the molding temperature should not be greater than 50 ℃; (2) The inner surface temperature difference of concrete pouring block (excluding the equivalent temperature of concrete shrinkage) shall not be greater than 25 ℃; (3) The cooling rate of concrete pouring body should not be greater than 2.0 ℃; (4) The temperature difference between the surface of concrete pouring body and the atmosphere should not be greater than 20 ℃.
In order to prevent the sudden drop of the concrete surface temperature caused by rain during the curing period, a layer of colored strip cloth is covered on the gunny bag to achieve both the rain proof effect and the covering and thermal insulation effect.
What is the difficulty of “mass concrete” project? The hydration heat released by mass concrete is very large.
The thickness of each layer of gunny bags is about 2cm, and three layers of gunny bags can meet the thermal insulation requirements.
Share a typical “mass concrete” The concrete pouring volume of the project is nearly 30000 cubic meters, and the floor thickness is 4.6-7.65 meters.
It can be adjusted according to the construction of special parts such as the bottom plate to appropriately slow down the setting time and delay the occurrence of thermal peak; (6) Use Hengke hk-f waterproof agent and Aetna gf-p expansion agent; (7) The use of Aetna xd-f polymer composite fiber can enhance the grip and binding force between reinforcement and cement surface, which is conducive to enhancing the crack resistance of concrete.
At the same time, take measures for thickening and insulation according to the temperature monitoring.
When the internal and external temperature difference and cooling rate of concrete exceed the temperature control index, calculation and analysis shall be carried out, and spare gunny bags shall be covered in time to strengthen thermal insulation..
Through calculation, it is determined that the thickness of thermal insulation material covered on the surface of concrete pouring body is 5.2cm.
In addition, in order to facilitate the water conservation and curing of the concrete, the concrete surface needs to be covered with plastic film.
The pouring range is 118.8 meters from east to west and 83.9 meters from north to south, which is equivalent to filling 25 standard swimming pools at the same time.
The pouring volume of mass concrete for the floor of CD Green Space Center Shufeng 468 super high-rise project is nearly 30000 cubic meters, covering a wide area during pouring, and the pouring volume is huge at one time.
In the face of such a large volume of concrete engineering, what control measures should the project department take (I) using high standard concrete raw materials, the thickness of tower raft is up to 4.6-7.65m, and the one-time pouring volume is large (about 30000 m3).
According to the construction quality requirements, the pouring work is carried out continuously day and night, and the pouring time needs to reach 96 hours.
(2) The use of retarding polycarboxylic acid superplasticizer can delay the peak temperature rise of hydration heat, delay the process of hydration reaction, and control the early hydration reaction speed of concrete, so as to achieve the purpose of controlling the early hydration heat temperature rise.
Therefore, mass concrete engineering not only challenges the construction organization of concrete pouring and the preparation of concrete materials, but also puts forward high requirements for its core technologies – concrete hydration heat control, mass concrete temperature control, concrete crack control and so on.
（2） Optimize the concrete mix proportion (1) reduce the water consumption per cubic meter of concrete and control the maximum cement consumption; Adding high-quality fly ash as admixture plays a positive role in controlling the hydration heat of concrete and improving the volume stability of concrete.
This tall project is the CD Green Space Center Shufeng 468 project, the tallest building in the West.
This product has a high water reduction rate and meets the requirements of the current national standard concrete admixtures (gb8076-2008).
（4） To strengthen the curing, three layers of gunny bags are required for the above-mentioned bottom slab concrete to meet the curing requirements.
The planned construction area is 454000 square meters, and the T1 tower is 468 meters high, with a total of 101 floors.
Special attention should be paid to the control of early hydration heat and concrete volume stability.
With the on-site command of “pouring start”, the concrete rushed out of the pump pipe, 130 concrete tank trucks poured back and forth, and more than 200 construction workers worked in an orderly manner.
The concrete grades of the main tower floor of Shufeng 468 project are C50 and p12 impermeable concrete.
During the actual construction, one layer of gunny bags and one layer of quilt are used for thermal insulation.
For the insulation of concrete side and elevator shaft, take formwork maintenance.
The temperature difference between inside and outside the concrete shall not exceed 15 ℃ after surface curing.
The concrete grade is high, the raft thickness is large, the single pouring volume is large, and the area is large.
In order to ensure the smooth pouring of floor concrete in T1 area of Green Space Center 468 project, higher requirements are put forward for the use of raw materials: (1) low heat cement p.o42 5R； (2) Adopt grade I fly ash; (3) Fine aggregate shall be washed medium coarse machine-made sand with high quality, reasonable gradation, uniform and solid texture, moderate fineness and inactive; (4) Coarse aggregate shall be 5-31.5mm high-quality continuous graded washed gravel; (5) The admixture adopts zjc-01 polycarboxylic acid high-performance water reducer.
Therefore, the release of hydration heat, the temperature difference between inside and outside the concrete, and the cracks on the concrete surface need to be controlled scientifically.
The pouring time needs 96 hours day and night.
What is “mass concrete”? The code for construction of mass concrete stipulates that mass concrete with the minimum geometric size of concrete structure not less than 1m, or concrete that is expected to cause harmful cracks due to temperature change and shrinkage caused by hydration of cementitious materials in concrete, is called mass concrete.
In addition, during construction, another layer of film and a layer of colored strip cloth shall be covered to increase the thermal insulation effect.
The specific curing days shall be subject to temperature monitoring, generally not less than 14 days.
