What are Concrete Vibration Acceleration and Vibration Duration?

Experimental studies have shown that vibration acceleration significantly affects the reduction of viscosity in concrete mixtures. For general flowable concrete mixtures, compaction begins when the acceleration approaches 0.5g (where g is the gravitational acceleration). As the acceleration increases, the compaction effect improves linearly. However, when the acceleration exceeds 4g, the compaction effect no longer improves.

The selection of appropriate amplitude, vibration frequency, vibration velocity, and vibration acceleration is based on ensuring that the concrete achieves the required density within a specific vibration duration. When the amplitude and vibration frequency are fixed, there is a critical value for the vibration duration required for a concrete mixture of a given fluidity. Below this critical value, the concrete cannot be fully compacted. Above this value, the density of the concrete does not increase significantly, and excessive vibration time can lead to segregation, thereby reducing the quality of the concrete.

In the latest construction specifications for concrete engineering structures, there is no specific time limit for the vibration duration of concrete mixtures. Vibration should stop when:

• The concrete surface shows no significant subsidence.
• A layer of cement paste appears.
• No more air bubbles are observed.

Typically, the vibration duration for concrete mixtures is 20-30 seconds.