Air Entraining Agents
Air Entraining Agents - Related Videos
01:27
Air-entraining Agents
0 Views •
2024
Air-entraining agents improve the durability and workability of concrete in climates with frequent freezing and thawing. These agents prevent cracks by introducing small air bubbles into the mix, creating spaces accommodating water expansion when temperatures drop. The air-entraining agents lower the surface tension of water, forming stable, small air bubbles. This method is more effective than having accidental large voids, as the intentional, smaller, and evenly distributed air voids improve...
01:28
Effects of Air-entrainment in Concrete
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2024
Air entrainment in concrete significantly enhances the material's durability, especially in environments subjected to freeze-thaw cycles. Introducing small air bubbles into the concrete mix acts as internal voids that accommodate the expansion of water when it freezes, thereby alleviating internal stress and preventing structural cracks. This function is crucial in climates with significant freezing and thawing, as it protects the concrete from repeated stresses that could lead to premature...
11:27
Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging
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Cited by 5 •
2016
This protocol describes the preparation and characterization of a dendrimeric magnetic resonance imaging (MRI) contrast agent that carries cyclen-based macrocyclic chelates coordinating paramagnetic gadolinium ions. In a series of MRI experiments in vitro, this agent produced an amplified MRI signal when compared to the commercially available monomeric analogue.
07:12
Circadian Entrainment of Drosophila Melanogaster
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Cited by 1 •
2020
Here, we detail how to synchronize Drosophila to a circadian day. This is the first, and most important step necessary for studying biological rhythms and chronobiology.
07:33
Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice
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Cited by 4 •
2018
We describe the use of optogenetics and electrophysiological recordings for selective manipulations of hippocampal theta oscillations (5-10 Hz) in behaving mice. The efficacy of the rhythm entrainment is monitored using local field potential. A combination of opto- and pharmacogenetic inhibition addresses the efferent readout of hippocampal synchronization.
FAQs
Surfactant molecules reduce the surface tension of the fresh concrete mixture, allowing air to form dispersed voids more readily. They then create protective films around those voids, helping prevent them from merging or escaping before the cement paste hardens. This stabilization produces the consistent internal pore structure needed for the intended durability benefit.
A network of tiny, evenly distributed bubbles provides more consistent space throughout the hardened cement paste for water to expand during freezing. That space helps reduce internal pressure and limits damage from freeze-thaw cycles. If the air system is not properly dispersed, the concrete may not receive the same protective benefit across its structure.
Entrained air creates voids within the hardened concrete, and an excessive amount can reduce the material's compressive strength. Engineering design therefore requires a balance between the air volume needed for freeze-thaw durability and the strength required for the structure. Mixture proportions and quality testing help control this tradeoff.
The admixture is introduced during concrete mixing, when it acts on the fresh cement paste and promotes formation of stabilized air voids. The mixture must then be controlled so the resulting air network remains suitable as the paste hardens. Engineers rely on mixture proportions and quality testing to verify that the intended balance has been achieved.
Engineers should monitor the amount and condition of entrained air while controlling the overall mixture proportions. The goal is to retain enough stabilized void space to support freeze-thaw durability without introducing so much air that compressive strength declines. Quality testing provides evidence that the hardened concrete is likely to meet the intended performance requirements.
They are particularly relevant to concrete structures exposed to freezing conditions, including pavements, bridges, dams, and other durable infrastructure. By providing expansion space for water within the hardened paste, the engineered pore system can reduce freeze-thaw damage. Their use must still be matched to structural strength requirements through proportioning and testing.