Estimation of Lubrication Layer Thickness and Composition through Reverse Engineering of Interface Rheometry Tests

Alexis Salinas,Dimitri Feys

doi:10.3390/ma13081799

Abstract

During concrete pumping, a lubrication layer is formed near the pipe wall. Extensive research has been performed on measuring and modeling the properties of this layer and using these values to predict pumping pressures. However, there are numerous discussions in the literature about the composition and thickness of this layer: can it be considered mortar, a micromortar, or is it cement paste? In this paper, possible solutions for the thickness and composition of the lubrication layer are derived from interface rheometry tests. It is assumed that the lubrication layer is composed of one or more concentric layers of paste or micromortar. To accomplish this determination, the rheological properties of the composing paste, mortars with different maximum particle sizes and concrete need to be known. Challenges arising from using different rheometers and from the sensitivity of the paste rheology to shearing are addressed in this contribution. The results show that, mathematically, a single layer of homogeneous paste or mortar with different maximum particle sizes can be responsible for the formation of the lubrication layer. Physically, however, the composing material should contain sand particles to some extent, as particle migration is proportional to the size squared. If the literature results from pumping are applicable to the results obtained in this paper, it seems that the lubrication layer is composed of a mortar with a maximum particle size of around 1 to 2 mm.

Highlights

It is well known from literature that pumping of concrete requires the formation of a lubrication layer [1]
The Krieger-Dougherty equation for relative viscosity [36], and its counterpart for yield stress [37] are fitted on the data, determining φmax, φm, and [η]. φmax stands for the maximum packing density and φm is the percolation threshold: the transition of the material into frictional regime [33,34]. [η] is the intrinsic viscosity, taking particle shape, angularity, and roughness into consideration
Separate values for the intrinsic viscosity were fitted for yield stress and viscosity equations

Summary

Introduction

It is well known from literature that pumping of concrete requires the formation of a lubrication layer [1]. Many studies have been performed to predict pumping pressures of concrete, whether through the use of interface rheometers [1,3,4,5,6,7], the Sliper [8,9,10,11], or by measuring the rheology of concrete and its constituent (micro-) mortar [12,13,14] In the latter case, the thickness of the lubrication layer needs to be known before applying capillary rheometer principles on pipe flow. The lubrication layer thickness is implicitly included in the interface parameters (viscous constant), or in the relationship between pressure loss and flow rate

Methods

Results

Conclusion