Original paper(Vol.48 No.11 pp.1294)
Influence of low frequency vibration on surface air bubbles and segregation in self-compacting concrete
Ichimiya Kazuo; Idemitu Takashi; Yamasaki Takehiro; Watanabe Akira
Abstract:Generally, air bubbles are easily formed on the surface of concrete products made of self-compacting concrete due to its high viscosity. These bubbles affect unfavorably the appearance and durability. In order to reduce the surface air bubbles, the authors used low frequency vibration. However, vibration applied to the concrete products during compaction, even with a low frequency, causes a segregation of coarse aggregate in the self-compacting concrete.
In this research, the effect of the low frequency vibration on the formation of surface air babbles and the segregation of coarse aggregate were investigated by comparing with cases under the following conditions.
In Case1, compaction was performed without vibration. In Case2, the concrete was filled up while vibration was applied. In Case3, the concrete was vibrated after being filled up.
The conclusions are summarized as follows.
(1) The surface air bubbles decreased as the vibration time after filling up of concrete increased.
(2) In the concrete filled up with vibration, the amount of surface air bubbles and the segregation rate of concrete increased as the filling time increased.
(3) Those amounts were less than those in the other cases.
(4) From these results, an effective casting method of self-compacting concrete, by which the surface air bubbles can be decreased without causing segregation is considered to be filling up with vibration for an adequately short time, and then applying for an appropriate period of time.
Key Words:surface air babbles, self-compacting concrete, concrete product, segregation of coarse aggregate, low frequency vibration