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The Workability of Fresh Concrete
Jul 06 , 2021

Fresh concrete is an unset mixture made by mixing cement, sand and coarse aggregate with water. The workability of fresh concrete is a comprehensive index, such as fluidity, pumpability, filling, uniformity, etc. The workability of a concrete mix is the relative ease with which concrete can be placed, compacted and finished without separation or segregation of the individual materials. Workability is not the same thing as consistency. Mixes with the same consistency can have different workabilities, if they are made with different sizes of stone. The smaller the stone the more workable the concrete.


HPC requires fresh concrete to have high fluidity (slump 20cm~25cm) and low fluidity loss over time to meet the technological requirements of centralized mixing, transportation, pumping and pouring of concrete. Even during pouring, the concrete is required to be self-leveling without vibrating, that is, good filling properties. Finally, uniform and stable concrete is obtained. These requirements are difficult to meet with ordinary concrete. Compared with ordinary concrete, the components of HPC are complex, and a variety of admixtures are used in conjunction with superplasticizers (SP), the purpose of which is to adjust performance through these components. One of the most critical technologies is SP and its composition. Single-component SP have a strong dispersing effect on cement slurries, and the water reduction rate is as high as 18 or more, but they cannot meet all the requirements of HPC for workability. Because a single-component SP is difficult to solve the problems of slump loss, segregation and delamination. Therefore, it is necessary to form a composite superplasticizer (CSP) with high-efficiency water reducer, retarder, air-entraining agent, stabilizer, etc. in order to fully meet the requirements of HPC for workability.

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