Name: aggregate pore states and water uptake
Uploaded: 2024-09-12T16:16:40.000Z
Duration: 1 min 20 s
Channel: JoVE

Die Porosität des Aggregats bezieht sich auf das Volumen der Poren im Aggregat.
Diese Poren variieren in der Größe und sind entweder innerhalb des Aggregats eingeschlossen oder miteinander verbunden und öffnen sich zu seiner Oberfläche, durch die das Wasser oder andere Flüssigkeiten in die Aggregate eindringen können.
Ein gesättigter Oberflächentrockenzustand bedeutet, dass alle Aggregatporen mit Feuchtigkeit gefüllt sind, die Oberfläche jedoch trocken ist.
In der Zwischenzeit weist ein feuchter Zustand auf das Vorhandensein von überschüssiger Feuchtigkeit auf der Oberfläche des gesättigten Aggregats hin.
Wenn Zuschlagstoffe in einem gesättigten oberflächentrockenen Zustand der Luft ausgesetzt werden, verdunstet ein Teil der Feuchtigkeit aus den Poren, was zu einem lufttrockenen Zustand führt.
Beim Trocknen im Ofen verdunstet die gesamte Feuchtigkeit aus den Aggregatporen, was auf einen knochentrockenen Zustand hinweist.
Die Wasseraufnahme wird berechnet als die Differenz in der Masse des Aggregats zwischen dem gesättigten Oberflächentrockenzustand und dem Knochentrockenzustand, ausgedrückt als Prozentsatz der Trockenmasse der Probe.
Schließlich steht das in den Poren der Zuschlagstoffe im Beton absorbierte Wasser nicht zur Verfügung, um Zement zu hydratisieren oder die Verarbeitbarkeit des Betons zu verbessern.
Darüber hinaus kann dieses absorbierte Wasser bei Frost-Tau-Zyklen dazu führen, dass sich das Aggregat auflöst.

porosität und absorption von zuschlagstoffen

Porosity and Absorption of Aggregate

Zuschlagstoffe enthalten Poren unterschiedlicher Größe. Während einige vollständig in den Partikeln eingeschlossen sind, öffnen sich andere zur Oberfläche hin, sodass Wasser eindringen kann. Die Porosität von Zuschlagstoffen ist ein wichtiger Faktor für die Gesamtporosität von Beton, da Zuschlagstoffe etwa drei Viertel des Betonvolumens ausmachen.

Wenn alle Poren in einem Zuschlagstoff mit Wasser gefüllt sind, gilt der Zuschlagstoff als gesättigt und oberflächentrocken. Wenn er an trockener Luft gelassen wird, verdunstet das Wasser, bis der Zuschlagstoff einen lufttrockenen Zustand erreicht. Längeres Trocknen in einem Ofen entfernt die gesamte Feuchtigkeit, was zu einem absolut trockenen oder ofentrockenen Zustand führt.

Die Wasserabsorption, eine kritische Zuschlagstoffeigenschaft, wird durch den Gewichtsverlust einer gesättigten und oberflächentrockenen Probe nach 24-stündiger Ofentrocknung gemessen und als prozentuale Massenabnahme im Verhältnis zur Trockenmasse des Zuschlagstoffs ausgedrückt. Eine realistischere Dauer zur Messung der Wasserabsorption in praktischen Szenarien beträgt jedoch 10 bis 30 Minuten statt 24 Stunden. Diese Anpassung berücksichtigt, dass in realen Bausituationen die tatsächliche Absorption durch Zuschlagstoffe im Mischer geringer ist und auch von der Reihenfolge der Zugabe der Zutaten beeinflusst wird. Darüber hinaus trägt das absorbierte Wasser in den Poren der Zuschlagstoffe möglicherweise nicht zur Hydratation des Zements und zur Verarbeitbarkeit des Betons bei.

Porosität und Absorption von Zuschlagstoffen

Die Porosität des Aggregats bezieht sich auf das Volumen der Poren im Aggregat.
Diese Poren variieren in der Größe und sind entweder innerhalb des Aggregats eingeschlossen oder ...

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JoVE Core

Civil Engineering

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Unit 1

Einheit 1

Aggregates and Water

Gesteinskörnungen und Wasser

KEY TERMS AND CONCEPTS

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aggregate pore states and water uptake

Aggregate contains pores of different sizes, and those pores may be sealed inside the particle or open to the surface. Open pores let water enter the aggregate. Because aggregate makes up about three-quarters of concrete by volume, its porosity strongly affects the porosity of the finished concrete.

Aggregate can also be described by its moisture state. When water fills every pore, the material is saturated and surface-dry. If it sits in dry air, some water evaporates and the aggregate becomes air-dry. After long drying in an oven, no moisture remains, and the sample is bone-dry, or oven-dry.

Water absorption is an important aggregate property. It is measured by finding the weight loss of a saturated, surface-dry sample after it has been oven-dried for 24 hours. The result is reported as a percentage decrease in mass compared with the dry mass of the aggregate.

In practice, a shorter absorption time of about 10 to 30 minutes is often more realistic. In a mixer, aggregates absorb less water than they do in a long drying test, and the result also depends on the order in which materials are added. Water held in aggregate pores may not help cement hydration or improve concrete workability.

Aggregate Pore States and Water Uptake

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moisture content and bulking of aggregate

moisture-content-and-bulking-of-aggregate

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key terms and concepts

Learn how aggregate pores affect concrete, and how saturation, air-dry, and oven-dry states relate to water absorption in construction materials.

Aggregate Pore States and Water Uptake | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

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Aggregate Pore States and Water Uptake

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