Name: concrete voids and strength
Uploaded: 2024-11-07T14:48:30.000Z
Duration: 1 min 12 s
Channel: JoVE

Consider a mass of concrete in which the total volume of voids includes the volume occupied by gel water, capillary pores, and entrapped air, each contributing to the overall porosity of the concrete structure.
The gel, which is the product of cement hydration, is made up of solid substances and water that is either physically retained or adsorbed onto the extensive surface area of the hydrates. The volume of this particular water is the volume of gel water.
It is estimated that one cubic inch of unhydrated cement would need approximately two cubic inches of space for its hydration products upon complete hydration.
Capillary pores are the spaces within the hydrated cement paste that are not occupied by the hydration products, and these pores can either be empty or filled with water.
During the process of mixing concrete, some air often gets trapped within the cement paste.
These entrapped air voids can reach up to 120 mils, which are substantially larger than the capillary voids and can negatively impact the concrete&#39;s strength.

totale holtes in beton

Total Voids in Concrete

Totale holtes in beton omvatten gel watervolume, capillaire poriën en ingesloten lucht. Gelwater (vastgehouden in de cementhydratatie producten) en fysiek ingesloten of geabsorbeerd water zijn belangrijk voor het hydratatieproces. Voor volledige hydratatie wordt geschat dat de ruimte die nodig is voor de producten van een kubieke centimeter cement verdubbelt. Capillaire poriën vormen de onbezette ruimte binnen de gehydrateerde cementpasta, waarbij hun grootte grotendeels wordt beïnvloed door de water-cement verhouding en hydratatiegraad.

Tijdens het mengen van beton treedt een kleine hoeveelheid lucht op, waardoor er holtes ontstaan ​​die aanzienlijk groter kunnen zijn dan capillaire holtes, wat de sterkte van het beton mogelijk verzwakt. Deze luchtholtes variëren in grootte, waarbij de ingesloten holtes tot 3 millimeter groot kunnen zijn, veel groter dan de fijnere capillaire holtes, die variëren van nanometers tot een paar micro meters in diameter. De verdeling van deze capillaire holtes wordt beschouwd als een nauwkeurigere indicator voor het beoordelen van de eigenschappen van gehydrateerde cementpasta dan de totale porositeit.

Luchtholtes, meestal bolvormig, contrasteren met de onregelmatig gevormde capillaire holtes. De impact van deze holtes op beton is aanzienlijk en beïnvloedt de sterkte en permeabiliteit. Om de eigenschappen van het beton te optimaliseren, is het essentieel om het volume en de distributie van deze holtes te begrijpen en te beheersen.

Totale holtes in beton

Consider a mass of concrete in which the total volume of voids includes the volume occupied by gel water, capillary pores, and entrapped air, each ...

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Strength of Concrete

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concrete voids and strength

Concrete voids affect both strength and permeability. They include gel water, capillary pores, and entrapped air. In hydrated cement paste, gel water is held within the cement hydration products. Physically entrapped or adsorbed water also supports the hydration process.

As cement hydrates, the space needed for the products from a cubic centimeter of cement is estimated to double. Capillary pores are the open spaces left inside the hydrated paste. Their size depends mainly on the water-to-cement ratio and the degree of hydration. The pattern of these pores can give a better picture of hydrated cement paste than total porosity alone.

Concrete also traps a small amount of air during mixing. These air voids can be much larger than capillary pores and may weaken concrete strength. Entrapped air voids can reach up to 3 millimeters in size. By comparison, capillary voids range from nanometers to a few micrometers.

Air voids are usually spherical. Capillary voids are more irregular in shape. Because void volume and void distribution affect concrete so strongly, understanding and controlling them helps improve concrete properties.

Concrete Voids and Strength

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total voids in concrete

Concrete voids affect both strength and permeability. They include gel water, capillary pores, and entrapped air. In hydrated cement paste, gel water is held within the cement hydration products. Physically entrapped or adsorbed water also supports the hydration process. As cement hydrates, the space needed for the products from a cubic centimeter of cement is estimated to double. Capillary pores are the open spaces left inside the hydrated paste. Their size depends mainly on the...

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key terms and concepts

Learn how gel water, capillary pores, and entrapped air create voids in concrete and how they affect strength, permeability, and cement hydration.

Concrete Voids and Strength | 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.

civil engineering

Concrete Voids and Strength

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