The Use of Vibration Frequency

Proper consolidation of fresh concrete is a very important component of quality concrete in any precast plant. Fresh concrete must be properly consolidated, to ensure that both strength and durability are fully realized. Consolidation is also used to eliminate voids and rock pockets, which are gaps in between coarse aggregate that can entrap air between other aggregate, reinforcement or other imbeds. These voids are typically referred to as “honeycomb” due to their distinct appearance and resemblance to a beehive. Honeycomb can severely impact the performance of concrete.

Here at Western Precast, we employ the use of an electric motor with a steel encased, vibrating head. These units are known in the industry as “internal vibrators.” The basic principle of this technology is the use of vibration frequency, generated by the oscillating element inside the steel head, to properly push and space all of the components of concrete into place. The sizing of the steel head is also important, varying by the type of structure being cast, the reinforcing steel congestion, wall thickness and overall size of the structure.

Common practice as to how much time the steel head is inserted into fresh concrete can vary, depending on certain specifications or structural requirements, but a rule of thumb per ACI (American Concrete Institute) is to hold the vibrator approximately 10 seconds per “lift,” or vertical section, while staying behind the trapped air and using an upward motion to release the air. Further, never allow the vibrator to move concrete laterally, since it will cause segregation, and lastly, withdraw the vibrator quickly near the top portion to prevent churning any air back into the top layer.

I alternate our production staff in the consolidation position once per week, so that they’re all trained and can gain experience in the process. We also hold monthly meetings as refresher training for all staff, beyond the standard training for concrete placement and finishing. Further, we provide additional on the spot training as needed to cover any other issues that may arise. The goal is to cover all of the steps and components of proper concrete placement to ensure that we manufacture quality concrete structures.

By/Por: Jorge Rodriguez
Production Manager/ Gerente de Producciόn

Photo/Foto: John Horta

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