In this paper, segregation tendency of aggregate particles with different size fractions caused by self-floating or sinking was investigated. After washing analysis of concrete samples picked from every portion in the vertical direction of a prismatic specimen, sieve analyses of fine and coarse aggregates were made and the unit contents of the particles retained on each of sieve series were determined. The segregation tendency in a portion was evaluated by the ratio (Ri) of the unit content to that in the specified mix. If the particle content increases or decreases as compared with the specified one, Ri>1 or Ri<1, and the closer Ri to unity, the milder the tendency.
The subtraction of the ratio in the top portion from that in the bottom portion was adopted as the segregation factor (SA) of the particles for the whole specimen in the height direction. If the content of particles with a certain size fraction is highest in the top portion due to self-floating and decreases down ward, SA<0, and if the content is lowest due to self-sinking and increases downward, SA>0. The higher the absolute value, the more the segregation tendency, and the distribution of the particles corresponding to SA=0 remains unchanged. The conclusions obtained were as follows;
(1) In the top portion of concrete with 25mm maximum particle size, Ri≈1 for the particles with 2.5-5mm size fraction, Ri>1 for those with smaller one than that and Ri<1 for those with larger one. The smaller the size fraction, the higher the ratio. Also, the larger the one, the lower the ratio. In the bottom portion, the opposite trend was more or less observed on the whole.
(2) In the case of concrete with 25mm maximum particle size, SA≈0 for the particles with 2.5-5mm size fraction, SA<0 for those with smaller one than that and SA>0 for those with larger one. The smaller or the larger the size fraction, the higher the absolute value.
(3) Except the particles corresponding to SA=0, the higher the maximum particle size, the slump value, the frequency and the amplitude of vibrator, the higher the segregation tendency.
(4) As the correlation was observed between the segregation indicator of concrete expressed by the ratio relative to the coarse aggregate content and the factor of the particles with each size fraction, the factor could be estimated from the indicator readily. Under the adequate consolidating condition, it was estimated that SA≈0.5 and SA≈-0.2 for the particles with 20-25mm and 0.15-0.3mm size fraction, respectively.
