obtained by the multiple point method.26)As shown in Table 4, the plastic viscosity values measured by the pipe viscometer were generally close to those by the rotating viscometer. Similar results were found in the yield stress, with slightly smaller values by the pipe viscometer as compared to those by the rotating viscometer.To obtain rheological quantities by using a rotating viscometer requires about 15 minutes for the tests and data analysis and about 2 hours for the image analysis of the fraction of the flow velocity of the specimen in the viscometer at each rotational speed. With a pipe viscometer used, in contrast, experiment values are available in a short period of time, requiring only about 30 minutes for the tests and data analysis. In addition, the pipe viscometer can be purchased at a price one sixth that of the rotating viscometer and is also excellent in portability.The findings obtained within the scope of this experiment can be summarized as follows:(1) A two-layer flow can be applied to the analytical model of a concrete flow in pipes, in place of the liquid friction state conventionally assumed in previous studies for the slip between the concrete and the pipe wall, based on the assumption that a this film of water is present between the concrete and the pipe wall, that a Newtonian flow is caused at the water film area, and that the flow velocity of the contact area between the concrete and the water film is equivalent to the slip velocity of the concrete.(2) When a water film is assumed to be present between the concrete and the pipe wall, the water film thickness can be estimated by the following procedure:1) apply linear regression to the time-dehydration curves for the first 90 seconds of pressurization measured under three different pressure levels by using a pressure bleeding tester specified in the JSCE-F502;2) apply linear regression to the relationship between the pressure level and the amount of dehydration which is estimated for pressure bleeding by means of stress conversion of the pressure gradient obtained by using a pipe viscometer.3) divide the amount of dehydration at each pressure gradient with the surface area of the specimen in the pressure vessel to obtain the water film thickness.(3) With the two-layer flow assumed, the amount of instantaneous dehydration from concrete due to pumping pressure (water film thickness) was found to vary by unit water content, presenting a relationship of y=4×10−6 W-5×10−4 (where y: water film thickness (cm); and W: unit water content (kg/m3)) within the scope of this experiment. The relationship was found to be almost consistent, regardless of the level of the applied pressure.(4) With the relationship between the water film thickness and the unit water content determined beforehand, it will be possible to determine the slip velocity by using the water film thickness (y) corresponding to a desired pumping pressure and then estimate the pump load (pressure gradient) required for the desired amount of pumping by using the flow rate estimation equation.(5) Rheological quantities were determined by solving a set of three simultaneous equations with the pressure gradient and the Bingham fluid flow rate which was obtained by subtracting the flow rate due to slip and the water film flow rate, both based on the estimated water film thickness, from the flow rate measured by the pipe viscometer. The results were found to be generally close to the test results using a rotating viscometer. This suggests the usefulness of the pipe viscometer in the measurement of the rheological quantities of fluid concrete.(6) Both measured flow rates and estimated rheological quantities can be obtained at the same time by using the pipe viscometer.(7) Compared to methods using a rotating viscometer, measurement of rheological quantities using the pipe viscometer requires less time for measurement and no special skills like those required in image analysis.1) Browne, R.D. and Bamforth, P.B., (1977). “Tests to Establish Concrete Pumpability.” ACI Jour., 74 (5), 193-207.2) Houghton, D.L., (1971). “Placing Concrete by Pumping Methods.” ACI Jour., Reported by ACI Committee 304, 68 (5), 327-345.3) Ede, A.N., (1957). “The resistance of concrete pumped through pipelines.” Magazine of Concrete Research, 9 (27), 129-140.4) Tobin, R.E., (1972). “Hydraulic Theory of Concrete Pumping.” ACI Jour., Reported by ACI Committee 304, 69 (8), 505-512.5) Best J.F. and Lane R.O., (1980). “Testing for optimum pumpability of concrete.” Concr. Int., 2 (10), 9-17.6) Yonezawa, T. and Fujiki, E., (1997). “Functionality of Concrete--Part 1: High-Flow Concrete.” JCI Concrete ─ 7 ─5. ConclusionsReferences
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