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Mar . 22, 2024 11:12 Back to list

Pumping of concrete: Understanding a common placement method with lots of challenges

Abstract

Several million cubic meters of concrete are pumped daily, as this technique permits fast concrete placement. Fundamental research has been performed and practical guidelines have been developed to increase the knowledge of concrete behavior in pipes. However, the pumping process and concrete behavior are not fully understood. This paper gives an overview of the current knowledge of concrete pumping. At first, the known physics governing the flow of concrete in pipes are introduced. A series of experimental techniques characterizing concrete flow behavior near a smooth wall to predict pressure-flow rate relationships are discussed, followed by recent developments in the use of numerical simulations of concrete behavior in pipes. The influence of the pumping process on concrete rheology and air-void system is reviewed, and the first developments in active rheology control for concrete pumping are introduced. The last section of this paper gives an overview of open research questions and challenges.

 

Introduction

Nearly a century ago, Max Giese and Fritz Hull came up with the idea to pump concrete [1]. The industry has massively adopted this placement technique as it enables a much quicker delivery of concrete, resulting in faster construction. New records are continually being set in terms of how far and how high concrete can be pumped. The current record height is 621 m, achieved during construction of the China 117 Tower in Tianjin, China, September 2015 [2], exceeding the previous pumping height record of 606 m established while constructing the Burj Khalifa building in Dubai, April 2008 [3].

However, pumping concrete is not a straightforward task and is indeed potentially dangerous, as numerous accidents happen annually due to blocking, blowouts or breaking of the pump or the pipeline. Practical guidelines have been developed for concrete mix design and pressure predictions, based on experience, not only to select the right pump and pipeline system, but also to avoid injuries and casualties [4], [5], [6], [7], [8].

Examples of such guidelines are the ACI 211-P document [7], dealing with proportioning of concrete to ensure pumpability. The main message of this document is to reduce the amount of coarse aggregate, but additional practical recommendations are included to provide guidance for improving pumpability. Another example that provides general guidance are several empirical pumping nomograms for conventional vibrated concrete [8], [9], which helps in predicting pumping pressure and selecting the required pump, as a function of desired flow rate, pipeline diameter, equivalent length of the pipeline and the spread or slump of the concrete. Fig. 1 shows a general schematic of a nomogram, for which one starts on the top vertical axis and moves clockwise through the diagram to obtain pressure on the left horizontal axis. Based on flow rate and pressure, the required pump power can be obtained [9].

During the last two decades, scientific research has focused on the pumping process in an attempt to predict pumpability and pumping pressure. It should be mentioned that research prior to roughly 2000 was mainly focused on pumpability and the surrounding conditions [10], [11], [12], [13], [14], [15]. After the year 2000, potentially caused by the introduction of the poly-carboxylate ethers water-reducing admixtures and the application of rheology to concrete, research shifted to pumping pressure, shear-induced particle migration, and interrelations between rheology and pumping. More recently, with the introduction of 3D concrete printing, more attention is paid to matching the requirements for concrete pumpability with extrudability and layer stability [16], [17].

This paper provides an overview of the concrete pumping research developments. Its purpose is to point the readers to the most relevant concepts and tools so that this contribution can serve as a guidance to further explore the literature. A short overview is given of typical pumps and pipelines (Section 2), followed by the most relevant physical concepts applicable to pumping (Section 3). 4 Testing equipment, 5 Prediction of pumping pressure describe a series of experimental test methods and pumping prediction tools, respectively, while Section 6 focuses on the use of numerical simulations to understanding pumping behavior. 7 Changes in concrete properties induced by pumping, 8 Rheology control discuss the consequences of pumping on key fresh and hardened properties, as well as the latest developments in rheology control to facilitate concrete pumpability. The last section gives an overview of future challenges and research needs.

 

Section snippets

Pumps and pipes

Truck mounted dual piston pumps are commonly used for concrete pumping. Invented in 1931, and with subsequent improvements, these pumps utilize an alternating and synchronized movement of two pistons connected to a valve system to push the concrete through the pipe system [18]. While one piston is pushing the concrete into the pipes, another piston is filled with concrete by suction. A stepwise control of pressure and flow rate is nowadays typically enabled through a remote control system.

Physical concepts of pumping

This section briefly introduces the different physical phenomena that need to be considered to understand the flow of concrete in pipes.

General

The previous section described the flow behavior in pipes, mentioning the importance of the rheological properties and shear-induced particle migration to form the lubrication layer, on the required pumping pressure. From a physics viewpoint, the rheological property that has the largest impact on pumping is viscosity [24], [31], [35]. However, the empirical test method used on site is either the slump or the slump flow, which solely relates to the yield stress. As mentioned in the

General

All testing devices and experimental methods introduced in Section 4 are focused on answering open questions regarding pumpability by investigating some aspects of concrete flow in a pipe: the material characteristics, the lubrication layer composition and thickness, the velocity profile of concrete inside a pipe, and so on. However, as long as a general flow equation such as Buckingham-Reiner is used [35], the pressure loss values are over-estimated. Thus, researchers are beginning to

Numerical simulations

Despite advances in testing equipment and derivation of more specific analytical equations for dense granular suspensions, there are still many unanswered questions with regard to concrete flow behavior in a pipeline. To understand concrete flow behavior in greater depth and to answer some of the open questions, numerical simulations and computer modeling can be of value. Unfortunately, modeling of a concrete mixture in full detail remains a challenging task due to the wide range of particle

Changes in concrete properties induced by pumping

Previous sections discussed how several concrete properties can be used to predict pumping pressures experimentally or numerically. It has also been shown that the lubrication layer, and potentially the bulk concrete, are exposed to extensive shear rates of several 100 s−1 in the lubrication layer and several 10 s−1 in the bulk concrete in case of SCC [20]. In addition, the material is also exposed to high pressure during the process. This section discusses how shear and pressure affect

Rheology control

It is well understood how the rheological properties of fresh concrete can be modified through mix design [97] and further influenced by mixing procedure [98], [99]. However, once mixed, the fresh concrete shows its intrinsic rheological behavior, which is only influenced by initial hydration processes, environmental conditions e.g. temperature, and shearing procedures [100], [101], [102], with no obvious means to actively modify the flow properties if needed. Nevertheless, active adjustment of 

Understanding lubrication layer composition, thickness and properties

Understanding the composition and properties of the lubrication layer is a challenge for a variety of reasons. The viscosity of pumped concrete can dramatically change over small distances near the pipe wall due to the wall-effect and shear-induced particle migration. Since viscosity is largely controlled by the volume fraction of particles, the local viscosity ranges from an estimated 50 Pa s in the bulk concrete to few Pa s in the fine mortar, all the way down to 1 mPa s for the water film

Summary

Despite several million cubic meters of concrete being placed daily by pumping methods, and the fact that concrete has been pumped for nearly a century, a full understanding of this process has not yet been accomplished. It is clear from analytical calculations, experiments, field work and numerical simulations that the formation of a lubrication layer facilitates the flow of concrete in a pipe. This is caused by the geometrical wall effect and shear-induced particle migration of the coarse

Author statement

This reviewer paper was requested by the Editor in chief of Cement and Concrete Research as part of a special edition in conjunction with the ACI Conference on Advances in Concrete Technology and Sustainability.

Dimitri Feys led the effort and composed the team of co-authors: Geert De Schutter, Shirin Fataei, Nicos Martys and Viktor Mechtcherine. As there are no new data and no new findings in the paper, the contributions from the team are the conceptualization, writing, reviewing and editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

Information in 7 Changes in concrete properties induced by pumping, 9.4 Time and shear dependency of concrete properties stem from a project sponsored by the American Concrete Institute's Concrete Research Council (award to Drs. Feys and Riding) and the US Department of Transportation Tier-1 UTC (RE-CAST) at Missouri S&T (a multi-University consortium led by Dr. Khayat).

Part of this paper (mainly 4.4.1 Ultrasonic velocity profiler (UVP), 8 Rheology control, 9.5 Further development of active

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