Experimental Insights into Concrete Flow-Regimes Subject to Shear-Induced Particle Migration (SIPM) during Pumping.

Shirin Fataei,Viktor Mechtcherine,Egor Secrieru

doi:10.3390/ma13051233

Abstract

In this paper, the authors have focused on shear-induced particle migration (SIPM), its effect on concrete flow patterns, and lubricating layer formation during pumping. For this purpose, various volume-fractions ϕ of aggregates were selected. The particle migration was analyzed by applying two methods: sampling hardened concrete exposed to pumping and performing X-ray microcomputed tomography (μCT) and image analysis to determine the thickness of the lubricating layer due to SIPM. The results indicate that the first approach is unsuitable due to the nearly equal molecular density of particles and matrix. The second approach indicated that the actual thickness of the lubricating layer depends on the discharge rate as well as on ϕ and viscosity of concrete bulk; hence, it cannot be defined as a constant parameter for all concrete mixtures. Additionally, the concrete pipe-flow pattern, i.e., plug versus shear flow, was captured and studied while considering pumping pressure and discharge rate. It was concluded that particle migration is essential in the cases of both flowable and very flowable concretes with a high volume-fraction of solids. The changes in rheological properties caused by SIPM are severe enough to influence the definition of the flow pattern as plug or shear and the discharge rate of pumped concrete as well.

Highlights

In concrete rheology, the granular nature of concrete is often neglected when performing rheological investigations or studying flow behavior with respect to various applications
The constitutive mortar with a maximum aggregate size of one mm and the aggregates larger than one mm will be referred to as “mortar” and “aggregates”, respectively. This arrangement was set based on the definition of the lubricating layer in this work, the thin layer formed in the vicinity of the pipe wall during pumping consisting of a fine cementitious mortar with a maximum particle size of 1 mm
The aim of this paper was to capture the formation of the lubricating layer during the pumping of concrete and analyze it with regard to shear-induced particle migration (SIPM)

Summary

Introduction

The granular nature of concrete is often neglected when performing rheological investigations or studying flow behavior with respect to various applications. This being so, it is generally assumed that the concrete’s constituents are uniformly distributed throughout the sampling volume during rheological measurements with wide-gap rheometers [1,2]. Another prominent example is pumping, during which the concrete flow in the pipeline is expected to reach a steady state after an initial critical deformation [3]. The rheological properties of the lubricating layer are considered similar to that of constitutive mortar; its thickness is still in debate, with 2 mm being the most accepted value [6,7,8]

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Conclusion