Segregation mechanism of concrete mixture

Segregation occurs because concrete is a non-homogeneous material, but only a mixture of different compounds.

The main reason for internal segregation is that the density of the coarse aggregate used is different from the density of the mortar part of the concrete. When strong external forces act on the fresh concrete in the model, these forces can separate the different components of the fresh concrete. Gradually increasing water consumption can eventually lead to internal segregation. The factors that prevent internal segregation are: the bonding and friction between the slurry and aggregate particles, the cohesion and ability of the respective plastic deformations of cement slurry and mortar, and the mutual interference between coarse aggregate particles in fresh concrete. It can be imagined that all these factors also play an important role in the workability of the mix. External segregation occurs when fresh concrete has insufficient cohesion and ability to plastically deform. For example, gradually increasing the coarse aggregate content or reducing water consumption can eventually lead to external segregation. Power can also cause coarse aggregate particles to separate during mixing, transportation and pouring. Therefore, the prevention of segregation is particularly important when concrete must undergo extensive loading, unloading, and transportation, such as truck transportation, chutes, or pumping.

Dynamic factors, such as shock and vibration, are the main causes of the above two kinds of segregation. These factors can overcome the resistance to segregation more quickly than static forces. Therefore, the greater the inertia and the smaller the specific surface area of ​​the coarse aggregate used, the smaller the cohesion of the mixture; the stronger the dynamic factors, the greater the tendency of concrete to segregate.

The direct cause of the separation of various types of particles in a uniformly stirred mixture is that different movements occur between them, resulting in different displacements, such as along the edges of the mixture. When falling down a chute, the surface part of the plastic mixture flows faster than the ground part of the chute, and the part with heavy particles moves faster than the part with light particles, so segregation occurs. However, for dry and hard mixtures that can form an integral movement, this uneven flow can be avoided because the yield shear stress is greater than the shear resistance caused by the friction between the chute bottom and the mixture. </p