2020 Volume 69 Issue 2 Pages 173-179
SEC method is one type of two-stage-mixing method of concrete. It had been found that SEC concrete produced by this mixing method had reduced bleeding, improved segregation resistance and high flowability under vibration, and improved strength characteristics and durability. Also, the fact that SEC concrete exhibited excellent properties after hardening was related to the bleeding reduction effect of this concrete. Therefore, in order to improve the bleeding characteristics of this concrete, the authors examined the influence of differences in concrete mixing method, procedure of materials charging, and material temperature. As a result, it was found that the bleeding of cement paste, mortar and concrete produced by the SEC (Sand Enveloped with Cement) method were reduced to about 40% compared to the case of normal mixing of the same proportion. The authors proposed a model on the composition of cement particles in concrete, which can explain the reduction of bleeding, the improvement of material segregation resistance and the fluidity under vibration in such fresh concrete in which differ the mixing method. In the future, the authors will plan to clarify the certainty of proposed model produced by this methods such as trying to visualize cement particle structure.
