Problems associated with over-vibrating concrete

The strength and durability of concrete structure affected greatly by the compaction of concrete. Proper compaction of concrete will produce a dense concrete with low permeability. Reducing the permeability of concrete is essential to prevent the ingress of aggressive chemicals such as chloride and sulfate. The compaction of concrete performed by vibrators. There is a different type of vibrators, such as poker (needle vibrator), screed vibrators, and external vibrators. Sufficient numbers of vibrators should be used to ensure proper vibrating of freshly casted concrete. Also, the vibrator type and size should be suitable. For example, the vibrator size should be smaller than the gap between reinforcement bars. In congested reinforcement, where the inserting of poker vibrator is difficult, external vibrators mounted on forms can be used to ensure proper compacting of concrete. Self-compacting concrete is another solution for members with congested reinforcement. Self-compacting concrete not requiring any mechanical vibration. Self-compacting concrete possesses a high flowability enables the placement of concrete without compaction.

Figure 1

Over compacting of concrete can adversely affect the strength of concrete members. Over compacting of concrete can result in segregation. The heavy aggregates will settle down while the light cement paste will go up due to the over compacting of concrete. This will create a weak concrete. For concrete placed on layer, the upper surface of each layer will form a weak plane, the strength and durability will be significantly reduced. For concrete placed on one lift, the top surface of the concrete will be weak with low abrasion resistance. For roads, this becomes a critical problem to concrete carriageway where its surface is continuously subject to tearing and traction forces exerted by vehicular traffic.