Mechanistic origins of concrete pumping: a comprehensive outlook and way forward

Abstract

The construction of high rise buildings and tunnels has necessitated concrete pumping to long distances. Concrete pumping is a complex physico-chemical process that results in the formation of different layers with distinct characteristics inside the pipe. A thin cement paste/mortar layer formed at the concrete-pipe interface, called the lubrication layer (LL) is considered vital for facilitating concrete pumping. Engineering the pumping process involves understanding the origin, controlling the onset, magnitude and velocity of the LL. However, the formation, evolution, and characteristics of LL are still largely unexplored. This paper presents comprehensive review of the mechanistic origins of LL, its influencing parameters, and the measured data on LL thickness using various techniques till date. It is attempted to find the overall link between the different theories such as shear induced particle migration (SIPM), wall depletion theory etc. in terms of concrete rheology. Further, the paper also provides a fundamental understanding of the different mechanisms involved in the formation of LL, with the help of different theories put forth by researchers in the field of particle rheology. Based on the insights derived from the discussions, recommendations have been made for future research directions in concrete pumping.