Effect of Lubrication-Layer on Velocity-Profile of Concrete in a Pumping Pipe (2015-01)¶

The rheology of concrete is predominant for the required pressures in a pumping pipe. However, more detailed information is required on the formation and the properties of the lubrication layer near the pipe surface, in order to be able to accurately predict the pressure-discharge relation. By means of experimental research in combination with advanced numerical simulations, the lubrication layer near the surface of the concrete pipe has been studied in this paper. The research confirms the existence and the effects of the lubrication layer on the movement of concrete in a pumping pipe. By means of the particle image velocimetry technique, the velocity profile along the cross section has been accurately determined for different types of concrete. There is no real slip at the surface of the pipe, however the velocity profile steeply grows in a thin layer, called lubrication layer, showing a thickness of about 2 mm. The mortar in this layer, with lower yield stress and lower viscosity than the bulk concrete, is highly sheared. The bulk of the concrete is sheared and/or shows a plug flow, depending on the yield stress of the concrete. The stiffer the concrete, the more important the effect of the lubrication layer on the overall velocity profile. In most cases, the lubrication layer is the dominant effect for pumping of concrete. Shear of the bulk concrete only plays a significant role for more fluid concretes.