Effect of Different Shear Rates on Particle Microstructure of Cementitious Materials in a Wide Gap Vane-in-cup Rheometer.

Mahmoud Eslami Pirharati,Dirk Lowke,Hans-W Krauss,Carsten Schilde

doi:10.3390/ma13092035

Mahmoud Eslami Pirharati, Dirk Lowke + Show 2 more

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https://doi.org/10.3390/ma13092035

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Abstract

Rheological properties of cementitious suspensions are affected not only by their mixture composition but also by process-related factors such as shear history. To enable a model-based description, investigations were carried out on the effect of shear history (shear rate variation over time) on the cement paste agglomeration state. Therefore, a Focused Beam Reflectance Measurement (FBRM) system and a wide gap rheometer were coupled to study the relation between shear history and in-situ chord length distribution simultaneously, indicating particle agglomeration. Hence, the effect of average shear rates (resulting from the applied shear profile), as well as shear rate distribution within the gap (local shear rates) on the particle agglomeration state have been investigated. The rheological properties of cement paste were evaluated with the Reiner–Riwlin approach. Furthermore, the agglomeration state of the particles was compared for different average shear rates and local shear rates at various positions of the FBRM probe. The results show that the median chord length increases in all positions when the average shear rate is decreased, indicating increasing particle agglomeration. Moreover, due to variable local shear rates at different FBRM probe positions, different agglomeration states are observed, resulting from two factors, shear rate dependent particle agglomeration and shear-induced particle migration.

Highlights

The characterization of the rheological properties of cement pastes as a function of different influencing factors, such as mixing intensity, shear history, chemical and physical properties, and microstructure has been in the focus of research within the last decades [1,2,3]
The results revealed a decrease of mean chord length of about 11% at a constant rotational velocity (ω = 400 rpm), indicating a disagglomeration of particles
The main objective of the present contribution is the investigation of the in-situ agglomeration state under different average shear rates and local shear rates

Summary

Introduction

The characterization of the rheological properties of cement pastes as a function of different influencing factors, such as mixing intensity, shear history, chemical and physical properties, and microstructure has been in the focus of research within the last decades [1,2,3]. Shear histories (shear rate variations over time) the rheological properties of cement paste can change significantly [4,5,6,7,8]. Depending on the actual microstructural properties, particle characteristics and mix composition, different types of macro flow behavior of cement paste can be identified, such as shear thinning, linear or shear thickening behavior [1,5]. To enable proper modeling of rheological properties as a function of shear history, in-depth investigations are required to link the shear rate, microstructure, and rheology of cement paste. First results on the relation between the in-situ particle size distribution and the rheological properties of cement paste have been published [1,2,10,11,12,13,14,15]

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