How does external vibration affect the segregation of concrete materials?

Choosing to say that external vibration prevents segregation of concrete materials is accurate because vibration can effectively enhance the homogeneity of a concrete mix. When concrete is vibrated, the lighter and finer materials tend to fill the voids between the larger aggregate particles. This action enables the particles to settle more evenly and helps to eliminate air pockets, which can be detrimental to the structural integrity of a concrete element.

Moreover, proper vibration ensures that the heavier aggregates do not sink to the bottom of the mix while the lighter components float to the surface. Instead, it promotes an even distribution, resulting in a tightly compacted and uniform matrix. This is particularly important in achieving a durable and high-quality concrete that can withstand environmental challenges and loading conditions.

In contrast, options suggesting that vibration promotes segregation or enhances the separation of aggregates do not align with the fundamental principles of concrete placement and compaction. External vibration is specifically employed to counteract potential issues of segregation caused by the natural tendency of components to segregate under gravity alone.