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The primary objective of this study is to verify if the rheological properties of the lubricating layer obtained from the newly developed tribometer can give a good prediction of the real flow rates of pumped concrete. An equation for the calculation of the flow rates was derived considering the thickness and the rheological properties of the layer. Full-scale pumping tests were performed with pipelines of350 and 548 m (383 and 599 yd) with seven different mixtures. From the test results and the comparison between the measured flow rates and the flow rates calculated from the equation, it was verified that the flow rates of pumped concrete can be accurately predicted before pumping according to the rheological properties of the lubricating layer measured with the tribometer. It was also found that the rheological properties of the lubricating layer remained constant during pumping, whereas the rheological properties of the concrete were found to vary.
Keywords: concrete pumping; concrete pumping test; lubricating layer; prediction; pumping mechanism; rheological properties; tribometer.
INTRODUCTION
There have been many attempts to predict the flow in concrete pumping.1-9 Most of the previous studies have revealed that the lubricating layer is formed near the wall of the pipe and plays a dominant role in facilitating concrete pumping. However, four different hypotheses about the laws for the behavior of the layer have been suggested by researchers: 1) the first law is that the layer has constant friction stress5; 2) the second is that the friction stress of the layer is linearly proportional to the flow speed3,4,9; 3) the third is that the friction stress is only linearly proportional to the normal pressure applied to the layer1,2,4,6; and 4) the fourth is that the friction stress is influenced by both the flow speed and the normal pressure.7
There was a pioneering study10 to quantitatively predict the flow of pumped concrete, in which the second law was adopted and the properties of the lubricating layer were experimentally determined with the tribometer developed by the same authors. It first turned out that if the properties of the layer are found before pumping, the flow rates in the given conditions such as pump pressure, pipe diameter, and length can be very accurately predicted.
Recently, a method to control pumping...