)l( noitardyhed fo tnuomAm00123the gap between the concrete and the pipe wall, the thickness of the water film was experimentally estimated. The concrete used in the experiment had a slump flow of 50 to 65cm, with the fluidity and material separation resistance increased by adding an admixture (hereinafter “fluid concrete”).The cement used in the experiment was ordinary portland cement with a density of 3.16g/cm3 and a fineness of 3,200cm2/g made by company T. The fine aggregate was a 7:3 mixture of land sand from Kashima, Ibaragi, and that from Shiraoi, Hokkaido, which was adjusted to have a particle size distribution in the standard particle size range (density 2.63g/cm3, water absorption rate 2.00%, F.M.: 2.3). The coarse aggregate was crushed stone 2005 from Ome, Tokyo (density 2.67g/cm3, water absorption rate 1.03%, F.M.:6.77). The admixture was an air-entraining high-range water-reducing agent made by company B which was a complex of polycarboxylate ether-based compound and thickening polymeric compound. It was a recently proposed product capable of providing a high fluidity and separation resistance compatible with high-flow concrete by using the same amount of cement as that in normal concrete, without increasing the amount of powder.In consideration of the feature of the admixture, the mix proportions of the fluid concrete were adjusted to have a water cement ratio of 45%, with the unit water content varied between 160, 165 and 170kg/m3 to achieve a slump flow of about 50cm, 60cm and 65cm, respectively, according to JIS A 1150. Table 1 shows the mix proportions of the concrete specimens. The target air content just after mixing was 4.5±1.5%.12010080604020Concrete in pipes is known to show a tendency in dehydration that the water separated from the concrete does not return to the original state when the load is removed immediately after the dehydration test.This was confirmed in the present experiment where no change was observed in the liquid surface in the measuring cylinder just after the dehydration test when the load acting on the specimen was removed, with the drain pipe inserted beneath the liquid surface as shown in Fig. 3. These suggest that, although the pressure acting on the concrete reaches the W=160kg/m3Underpressure100200300Unloaded1.5MPa2.5MPa3.5MPa500600400Pressurizing time (s)3.1 Materials and mix proportionsFig. 2 shows an example of change over time in the amount of dehydration of the fluid concrete with a unit water content of 160kg/m3, sorted by applied pressure levels. It was found in Fig. 2 that the higher the pressure level, or the longer the pressurizing time, the larger the amount of dehydration was.Mix No.Slump flow （cm）Air content （%）50±560±565±54.5±1.5Table 1 Mix proportions of the concrete specimensWater cement ratio （%）Fine-total aggregate ratio （%）53.753.152.445Fig. 2 Change over time in the amount of dehydrationFig. 3 Liquid surface in the measuring cylinder during and after the dehydration testSpecific weights （kg/m3）Fine Water [W]Cement aggregate [C]160165170356367378─ 3 ─Coarse aggregate Admixture [S]966845937[G]844944960Air entraining aid agent※[Ad]1.071.101.132.852.942.38※100-floud dilution
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