Details
| Original language | English |
|---|---|
| Article number | 139330 |
| Journal | Construction and Building Materials |
| Volume | 457 |
| Early online date | 3 Dec 2024 |
| Publication status | E-pub ahead of print - 3 Dec 2024 |
Abstract
The de-airing of fresh concrete is a crucial step in ensuring sustainable and durable concrete structures. Currently, proper de-airing is ensured by adjusting the fresh concrete consistency i.e. its rheological properties, without any knowledge whether this will actually guarantee sufficient de-airing. The exact relationship between the rheological properties and air bubble dynamics in concrete is not yet understood. In this paper, a detailed study was carried out in which air bubbles of different size and volume were injected in fresh cement suspensions with varying solid volume fractions (i.e. varying rheological behaviour). The air bubbles were visualised by means of X-ray radiography and the rise behaviour was evaluated with image based algorithms. It was found that in more viscous suspensions (i.e. higher particle contents) the bubble speed increases with decreasing suspension viscosity. For suspensions with higher flowability (i.e. less particle content), the inertial forces dominate the viscous forces, with the viscosity playing a subordinate role. The shear rate induced by an ascending air bubble is sufficient to locally reduce the dynamic viscosity of the suspension. In addition, it leads to shear-induced particle migration, with less concentrated regions in the ascending channel. Consequently, subsequent bubbles are influenced by changes of viscosity in this channel, rising faster and having different bubble shapes.
Keywords
- Air bubble rise, Cement suspensions, De-airing, Particle migration, Rheology, X-ray
ASJC Scopus subject areas
- Engineering(all)
- Civil and Structural Engineering
- Engineering(all)
- Building and Construction
- Materials Science(all)
- General Materials Science
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In: Construction and Building Materials, Vol. 457, 139330, 27.12.2024.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Mechanisms of air bubble rise in cement suspensions studied by X-ray analysis
AU - Strybny, Bastian
AU - Link, Julian
AU - Coenen, Max
AU - Vidal, Valérie
AU - Zuber, Marcus
AU - Schack, Tobias
AU - Haist, Michael
N1 - Publisher Copyright: © 2024 The Authors
PY - 2024/12/3
Y1 - 2024/12/3
N2 - The de-airing of fresh concrete is a crucial step in ensuring sustainable and durable concrete structures. Currently, proper de-airing is ensured by adjusting the fresh concrete consistency i.e. its rheological properties, without any knowledge whether this will actually guarantee sufficient de-airing. The exact relationship between the rheological properties and air bubble dynamics in concrete is not yet understood. In this paper, a detailed study was carried out in which air bubbles of different size and volume were injected in fresh cement suspensions with varying solid volume fractions (i.e. varying rheological behaviour). The air bubbles were visualised by means of X-ray radiography and the rise behaviour was evaluated with image based algorithms. It was found that in more viscous suspensions (i.e. higher particle contents) the bubble speed increases with decreasing suspension viscosity. For suspensions with higher flowability (i.e. less particle content), the inertial forces dominate the viscous forces, with the viscosity playing a subordinate role. The shear rate induced by an ascending air bubble is sufficient to locally reduce the dynamic viscosity of the suspension. In addition, it leads to shear-induced particle migration, with less concentrated regions in the ascending channel. Consequently, subsequent bubbles are influenced by changes of viscosity in this channel, rising faster and having different bubble shapes.
AB - The de-airing of fresh concrete is a crucial step in ensuring sustainable and durable concrete structures. Currently, proper de-airing is ensured by adjusting the fresh concrete consistency i.e. its rheological properties, without any knowledge whether this will actually guarantee sufficient de-airing. The exact relationship between the rheological properties and air bubble dynamics in concrete is not yet understood. In this paper, a detailed study was carried out in which air bubbles of different size and volume were injected in fresh cement suspensions with varying solid volume fractions (i.e. varying rheological behaviour). The air bubbles were visualised by means of X-ray radiography and the rise behaviour was evaluated with image based algorithms. It was found that in more viscous suspensions (i.e. higher particle contents) the bubble speed increases with decreasing suspension viscosity. For suspensions with higher flowability (i.e. less particle content), the inertial forces dominate the viscous forces, with the viscosity playing a subordinate role. The shear rate induced by an ascending air bubble is sufficient to locally reduce the dynamic viscosity of the suspension. In addition, it leads to shear-induced particle migration, with less concentrated regions in the ascending channel. Consequently, subsequent bubbles are influenced by changes of viscosity in this channel, rising faster and having different bubble shapes.
KW - Air bubble rise
KW - Cement suspensions
KW - De-airing
KW - Particle migration
KW - Rheology
KW - X-ray
UR - http://www.scopus.com/inward/record.url?scp=85210675861&partnerID=8YFLogxK
U2 - 10.1016/j.conbuildmat.2024.139330
DO - 10.1016/j.conbuildmat.2024.139330
M3 - Article
AN - SCOPUS:85210675861
VL - 457
JO - Construction and Building Materials
JF - Construction and Building Materials
SN - 0950-0618
M1 - 139330
ER -