6. The problem of poor workability of fresh concrete
The working properties of fresh concrete include fluidity, cohesion and water retention. Fluidity refers to the ability of concrete mixture to flow and fill the formwork evenly and densely under the action of its own weight or mechanical vibration. Cohesion refers to the cohesion between the components of the concrete mixture, which can avoid stratification and segregation during the construction process. Water retention refers to the ability of the concrete mixture to retain water, which can avoid bleeding during the construction process. In the actual preparation of concrete, on the one hand, for low-strength concrete, the amount of cementitious materials is not high and the water-binder ratio is large. In addition, the aggregate grading of such concrete is usually poor. The use of PCE with a high water reduction rate to prepare such concrete is prone to segregation and bleeding of the mixture; on the other hand, high-strength concrete prepared by using lower-strength cement, increasing the amount of cementitious materials and reducing the water-binder ratio is prone to high concrete viscosity, poor mixture fluidity and slow flow rate. Therefore, too low or too high viscosity of the concrete mixture will lead to poor concrete working performance, reduce construction quality, and be extremely unfavorable to the mechanical properties and durability of concrete.