Evaluation of pumpability of concrete

Abstract

Current guidelines and practices at construction sites on concrete pumping has not been based on theoretical understanding of pipe flow of fresh concrete. In fact, only the slump value is monitored at construction sites, even-though any single point test is insufficient to represent flow curve properties of fresh concrete. Based on flow curves of concrete and basic rheological properties, a theoretical model for horizontal straight flow has been developed and validated in previous studies. Yet, properties of concrete flow at horizontal and vertical bends, tapered sections and vertical lengths had to be investigated. In this research study, experimental investigations were carried out at two high rise building construction sites which included monitoring rheology of fresh concrete with ICAR plus concrete rheometer and pressure at some points of the concrete pumping pipe line with a pressure transducer and several strain gauges. In the horizontal straight section, theoretical pressure drop based on sheared plus plug flow condition could reasonably estimate the actual pressure drop with a 20% margin. Pressure drop at a horizontal bend was in between 0.5 to 1.7 bar while in a vertical bend it was around 6 bar. Pressure drop in the vertical straight length was equal to the pressure needed to overcome the selfweight only. Hence, concrete pumping pressure could be estimated within 20% margin. Moreover, understanding on the influence of mix design parameters on concrete rheology is much useful for deciding the mix proportions of concrete at the mix design stage. A series of laboratory experiments were conducted at paste and mortar phases of concrete. Correct admixture concentration, increase of w/c ratio, decrease of fine aggregate volume concentration and round shape fine aggregates over angular shape found to be improving the rheological properties and hence the pumpability of concrete.