Lubrication layer properties during concrete pumping

In order to progress in the understanding of the physical phenomena involved in the pumping process of concrete, we study in this work the properties of the lubrication layer, which forms between the pipe and the bulk material. Using ultrasonic velocity profiler, we measure the thickness of this lubrication layer in the case of real size pumping circuits. Our experimental, analytical and numerical results suggest that, from a rheological point of view, this layer behaves similarly as the constitutive mortar of the pumped concrete. Moreover, this layer thickness does not seem to depend on flow rate. We finally propose a simple analytical relation allowing for a rough estimation of the pumping pressure.