"By playing checkers on concrete, we can effectively avoid the large temperature difference and shrinkage in the early stage of concrete construction, and there is no need to leave post-cast strip." Lin Qiang, head of the project in Area C of the Southern Headquarters Base of the Fourth Navigation Bureau, proudly introduced to the visitors.
The Southern Headquarters Base Area C Project is located near the Pearl River in Haizhu District, Guangzhou, with a total construction area of more than 200,000 square meters, a total building height of 154.9 meters, 31 floors above ground and 3 floors underground. Among them, the basement area is 37000 square meters, which is equivalent to the size of five standard football fields. The excavation of the foundation pit is 300 meters long and 130 meters wide, which is a super-long and super-wide concrete structure. The winter in Guangzhou is wet and cold, so the project construction not only has to face the impact of humid and cold air, but also has to face the great challenge of "resisting" the temperature stress and shrinkage tension of concrete materials.
The super-long and super-wide concrete structure is prone to deformation and cracks, and it is not feasible to rely solely on the traditional "resistance" method in concrete pouring. After several considerations, the project team took into account the scheme of setting up the post-pouring belt for construction. The post-cast strip is a concrete strip reserved with a certain width and poured after a period of time to prevent the uneven shrinkage or settlement of the reinforced concrete structure itself. However, the super-long concrete structure of the project will lead to too many post-cast strips, which are difficult to clean up in the later stage and prone to cracks, resulting in cracking and seepage of the basement. At this time, the overall construction progress of the basement has been delayed compared with the original plan, so it is urgent to improve the construction efficiency.
Aim at the "pain point" and make precise efforts. Li Jingfeng, the chief engineer of the project, led the technical team to tackle the key problems with the idea of "resisting and releasing simultaneously", "releasing first and then resisting" and "giving priority to resisting", and used the principle of "resisting and releasing" which is easy to release the internal stress of concrete before its performance is not stable and completely solidified in 5 to 10 days, and adopted the "jumping warehouse method" for construction. The basement foundation, wallboard and roof are divided into 21 blocks according to 30 construction joints. According to the block division, one block is poured at an interval.
"Jumping method" pouring not only reduces 1200 meters of post-pouring belt, ensures the integrity of basement floor, but also avoids the cost of construction joint cleaning and expansion reinforcement belt pouring concrete, so we have a good chance to win the chess game. Lin Qiang looked at the construction progress and said with a smile. After accounting, the "jump warehouse method" was adopted to construct the basement floor, which saved nearly 600000 yuan.
However, while everyone is immersed in the joy of solving the problem of super-long and super-wide concrete structure, the continuous high temperature in Guangzhou in summer has brought new problems. Due to the different structures of basement foundation, wallboard and roof, the concrete mix proportion is different, and the continuous high temperature affects the temperature control of concrete center, which brings the potential hidden danger of temperature cracks. "Skipping" the challenge of deformation cracks caused by the internal stress of concrete, how to "adjust" the optimization scheme of concrete mix proportion has become another difficult problem faced by the project.
Under the leadership of Li Jingfeng, the project team adopted the double mixing ratio of "fly ash + mineral powder" for the first time, that is, adding more secondary fly ash and mineral powder to the original concrete mix proportion, so as to reduce the release rate of hydration heat of concrete. After repeated tests, it is found that the new proportioning method can effectively prevent the shrinkage of concrete due to dehydration, increase the compactness of concrete, and save the amount of cement. But Li Jingfeng is well aware of the "delicate" super-long and super-large concrete structure, "matching" is only the first step to complete, "maintenance" is more important. The project team controlled the sectional pouring length of the wall construction within 20 meters, covered the exposed concrete surface with plastic film, and covered the column pier and column cap with felt insulation materials for maintenance, so as to minimize the risk of concrete cracking. The concrete pouring method
like "playing checkers" and the concrete quality control measures of "proportioning" and "curing" make the project not only successfully catch up with the lagging basement concrete pouring progress, but also improve the concrete entity quality and apparent quality by carefully studying the "secret recipe" of concrete construction.
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