y1y2y3y1= 0.0012x + 0.0944y2= 0.0026x + 0.0830y3= 0.004x + 0.0823y1y3y1= 0.0024x + 0.1129y2= 0.0039x + 0.1091y3= 0.0056x + 0.1111000y3y2y1= 0.0015x + 0.1130y2= 0.0019x + 0.1143y3= 0.0039x + 0.1167■■■■■■■■■■■■■■■■■■maximum level at the pump outlet (pipe inlet) and causes dehydration, creating a thin water film on the pipe wall surface, the amount of dehydration remains the same through to the pipe outlet, with no change in the water film thickness due to the dehydration.The pressure acting on the concrete during pumping is maximum at the pump outlet for an extremely short period of time, which allows an assumption that the amount of dehydration corresponding to the pumping pressure level is the amount of dehydration at t=0 in Fig. 2. As shown in Fig. 2, a linear increase was found in the first 90 seconds of pressurization, with very slight variations in the measurement results. Therefore, the amount of dehydration at t=0 was estimated as the value of the intercept of a linear regression of the measured values in the initial period where the increase was deemed to be linear.Using a pipe viscometer, the concrete specimen in the pressure bleeding container was pressurized to simulate the concrete pumping, with the pressure varied at three levels. The amount of dehydration during pumping was estimated by linear regression, using the data in the area where the increase was linear within the first 90 seconds of pressurization. Fig. 4 shows the estimated change over time in the amount of dehydration during pumping of the concrete with a unit water content W=160, 165 or 170kg/m3, respectively. The estimation results in Fig. 4 showed a similar tendency to that in Fig. 2 where the higher the applied pressure level, or the longer the pressurizing time, the larger the amount of hydration was for each unit water content. However, the intercept of the linear equation representing the relationship between the pressurizing time and the amount of dehydration in the initial period was found to be almost constant for each unit water content, regardless of the level of the applied pressure. The water film thickness on the pipe wall surface was obtained by dividing the amount of dehydration at the intercept with the surface area of the specimen in the pressure vessel. Table 2 shows the estimated water film thickness values. The values were in the range between 0.000116cm to 0.000164cm and very close to each other, depending on the applied pressure level, with only slight differences in the amount of dehydration depending on the unit water content.The experimental equation for the relationship between the water film thickness and the unit water content can be expressed as Equation (7), with a correlation coefficient R=0.918.0.250.200.150.100.050.000.400.350.300.250.200.150.100.050.000.300.250.200.150.100.050.00W160kg/m3W165kg/m3W170kg/m30.017MPa0.022MPa0.026MPa204060Pressurizing time (s)0.022MPa0.026MPa0.028MPa204060Pressurizing time (s)0.010MPa0.020MPa0.025MPa2040Pressurizing time (s)y2R = 0.992R = 0.986R = 0.99480100R = 0.979R = 0.9994R = 0.98880100R = 0.991R = 0.999R = 0.9936080100y13.2 Water film thickness between the pipe wall and the concreteFig. 4 Relationship between the applied pressure level and the amount of dehydrationTable 2 Estimation of the water film thicknessUnit water ─ 4 ─content （kg/m3）160165170Amount of dehydration Stress （MPa）（ml）0.09440.08300.08230.11290.10910.11110.11300.11430.11670.0170.0220.0260.0220.0260.0280.0100.0200.025Water film thickness （cm）0.0001330.0001170.0001160.0001590.0001530.0001560.0001590.0001610.000164
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