Details
| Original language | English |
|---|---|
| Article number | 114144 |
| Journal | Journal of Building Engineering |
| Volume | 113 |
| Early online date | 24 Sept 2025 |
| Publication status | Published - 1 Nov 2025 |
Abstract
The durability and mechanical properties of hardened concrete are significantly affected by its porosity. Air voids can be trapped in fresh concrete during placement, particularly when insufficient workability is combined with inadequate processing. The mechanisms by which air bubbles rise in fresh concrete and interact with surrounding aggregates remain largely unknown. This study investigates how the rheological and granulometrical characteristics of fresh concrete affect de-airing behavior. Due to the opacity of concrete, X-ray techniques coupled to digital image analysis were used to study the bubble dynamics and the bubble-aggregate interactions. Concrete is idealised as a mix of glass beads as model aggregates (da ≤ 8 mm) suspended in a cement-water suspension, termed cement paste. The investigation focused on the relationship between the cement paste rheology, the aggregate properties and the speed, shape and trajectory of rising air bubbles. Further the effect of shear history and shear-induced particle migration on bubble rise was also investigated. The results show that the addition of aggregates to pure cement paste significantly alters the de-airing behavior and affects the bubble dynamics. As the bubble volume decreases, the bubble speed decreases. Increasing the aggregate content from 0 vol% to either 30 vol% or 60 vol% also results in a decrease in bubble speed. Small bubbles show minimal variation in rise trajectories across different aggregate volumes and gradings. In contrast, larger bubbles exhibit consistent paths with 30 vol% aggregates, but demonstrate dispersed trajectories at 60 vol%. Shear-induced particle migration depends on the bubble-to-aggregate size ratio. Finally, a dimensionless parameter is introduced that can be used to determine phase separation as a function of the ratio of bubble buoyancy to aggregate inertia. This research improves the understanding of concrete de-airing and is also applicable to other coarse granular suspensions in various industries.
Keywords
- Aggregate grading, Air bubble, Concrete, De-airing, Particle migration, X-ray
ASJC Scopus subject areas
- Engineering(all)
- Architecture
- Engineering(all)
- Civil and Structural Engineering
- Engineering(all)
- Building and Construction
- Engineering(all)
- Safety, Risk, Reliability and Quality
- Engineering(all)
- Mechanics of Materials
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In: Journal of Building Engineering, Vol. 113, 114144, 01.11.2025.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The influence of aggregate content and aggregate grading on the air bubble rise in fresh concrete
AU - Strybny, Bastian
AU - Coenen, Max
AU - Vidal, Valérie
AU - Schack, Tobias
AU - Zuber, Marcus
AU - Haist, Michael
N1 - Publisher Copyright: © 2025 The Authors
PY - 2025/11/1
Y1 - 2025/11/1
N2 - The durability and mechanical properties of hardened concrete are significantly affected by its porosity. Air voids can be trapped in fresh concrete during placement, particularly when insufficient workability is combined with inadequate processing. The mechanisms by which air bubbles rise in fresh concrete and interact with surrounding aggregates remain largely unknown. This study investigates how the rheological and granulometrical characteristics of fresh concrete affect de-airing behavior. Due to the opacity of concrete, X-ray techniques coupled to digital image analysis were used to study the bubble dynamics and the bubble-aggregate interactions. Concrete is idealised as a mix of glass beads as model aggregates (da ≤ 8 mm) suspended in a cement-water suspension, termed cement paste. The investigation focused on the relationship between the cement paste rheology, the aggregate properties and the speed, shape and trajectory of rising air bubbles. Further the effect of shear history and shear-induced particle migration on bubble rise was also investigated. The results show that the addition of aggregates to pure cement paste significantly alters the de-airing behavior and affects the bubble dynamics. As the bubble volume decreases, the bubble speed decreases. Increasing the aggregate content from 0 vol% to either 30 vol% or 60 vol% also results in a decrease in bubble speed. Small bubbles show minimal variation in rise trajectories across different aggregate volumes and gradings. In contrast, larger bubbles exhibit consistent paths with 30 vol% aggregates, but demonstrate dispersed trajectories at 60 vol%. Shear-induced particle migration depends on the bubble-to-aggregate size ratio. Finally, a dimensionless parameter is introduced that can be used to determine phase separation as a function of the ratio of bubble buoyancy to aggregate inertia. This research improves the understanding of concrete de-airing and is also applicable to other coarse granular suspensions in various industries.
AB - The durability and mechanical properties of hardened concrete are significantly affected by its porosity. Air voids can be trapped in fresh concrete during placement, particularly when insufficient workability is combined with inadequate processing. The mechanisms by which air bubbles rise in fresh concrete and interact with surrounding aggregates remain largely unknown. This study investigates how the rheological and granulometrical characteristics of fresh concrete affect de-airing behavior. Due to the opacity of concrete, X-ray techniques coupled to digital image analysis were used to study the bubble dynamics and the bubble-aggregate interactions. Concrete is idealised as a mix of glass beads as model aggregates (da ≤ 8 mm) suspended in a cement-water suspension, termed cement paste. The investigation focused on the relationship between the cement paste rheology, the aggregate properties and the speed, shape and trajectory of rising air bubbles. Further the effect of shear history and shear-induced particle migration on bubble rise was also investigated. The results show that the addition of aggregates to pure cement paste significantly alters the de-airing behavior and affects the bubble dynamics. As the bubble volume decreases, the bubble speed decreases. Increasing the aggregate content from 0 vol% to either 30 vol% or 60 vol% also results in a decrease in bubble speed. Small bubbles show minimal variation in rise trajectories across different aggregate volumes and gradings. In contrast, larger bubbles exhibit consistent paths with 30 vol% aggregates, but demonstrate dispersed trajectories at 60 vol%. Shear-induced particle migration depends on the bubble-to-aggregate size ratio. Finally, a dimensionless parameter is introduced that can be used to determine phase separation as a function of the ratio of bubble buoyancy to aggregate inertia. This research improves the understanding of concrete de-airing and is also applicable to other coarse granular suspensions in various industries.
KW - Aggregate grading
KW - Air bubble
KW - Concrete
KW - De-airing
KW - Particle migration
KW - X-ray
UR - http://www.scopus.com/inward/record.url?scp=105017787529&partnerID=8YFLogxK
U2 - 10.1016/j.jobe.2025.114144
DO - 10.1016/j.jobe.2025.114144
M3 - Article
AN - SCOPUS:105017787529
VL - 113
JO - Journal of Building Engineering
JF - Journal of Building Engineering
M1 - 114144
ER -