Name: concrete workability with plasticizers
Uploaded: 2024-11-07T14:48:38.000Z
Duration: 1 min 31 s
Channel: JoVE

Considere hormigonar en lugares de difícil acceso en un molde. Los plastificantes ayudan a que el concreto se compacte por sí solo, mejorando la trabajabilidad con menos agua o cemento.
Los plastificantes comunes incluyen ácidos lignosulfónicos y ácidos carboxílicos hidroxilados, que funcionan como aditivos reductores de agua que pueden reducir el uso de agua entre un 5 y un 15 por ciento en el concreto.
Los agentes tensioactivos de los plastificantes alteran las fuerzas interfaciales entre las fases no mezcladas y se adhieren a las partículas de cemento, impartiendo una carga negativa, fomentando la repulsión y estabilizando su dispersión al tiempo que repelen las burbujas de aire.
La carga negativa induce una capa de moléculas de agua alineadas alrededor de cada partícula, distanciándolas efectivamente.
Por último, se mejora el movimiento de las partículas y se libera agua del sistema agrupado, lo que la hace disponible para facilitar la mezcla y mejorar la trabajabilidad.
Los plastificantes mejoran la dispersión de las partículas de cemento, aumentando el área de superficie para la hidratación. Esta dispersión aumenta la fuerza de la edad temprana en relación con las mezclas sin aditivos.
El impacto de estos aditivos sobre la resistencia es más pronunciado en cementos con bajos niveles de aluminato tricálcico o bajos niveles de álcali.
Antes de usar plastificantes en la construcción, las pruebas son esenciales para identificar problemas como la segregación, el sangrado o la reducción de la trabajabilidad.

plastificantes

Los reductores de agua, o plastificantes, son aditivos químicos que se utilizan en el hormigón para mejorar su resistencia y trabajabilidad. Estos aditivos reducen la relación agua-hormigón sin comprometer la trabajabilidad, reducen el contenido de hormigón manteniendo la misma trabajabilidad o aumentan la trabajabilidad para facilitar la colocación del hormigón en zonas inaccesibles.

Los plastificantes funcionan mediante el uso de agentes tensioactivos para crear fuerzas electrostáticas repulsivas entre las partículas de hormigón. Esta dispersión mejora la trabajabilidad del hormigón y reduce la necesidad de agua de mezclado entre un 5 y un 15 por ciento. A pesar de que ciertos plastificantes retrasan el tiempo de fraguado, la pérdida de trabajabilidad con el tiempo no se reduce necesariamente. Es importante realizar mezclas de prueba para garantizar la compatibilidad con agentes incorporadores de aire, que pueden introducir bolsas de aire que afecten las propiedades finales del hormigón.

Estos aditivos mejoran la resistencia del hormigón, especialmente en las primeras etapas, debido a la hidratación más uniforme del hormigón. Por lo general, son eficaces en todos los tipos de hormigón, con un aumento de resistencia más pronunciado en el cemento con bajo contenido de aluminato tricálcico o álcali. El uso correcto de reductores de agua también puede mejorar la durabilidad del hormigón. Sin embargo, antes de la implementación, es fundamental realizar pruebas para detectar posibles efectos negativos como la segregación o el sangrado para garantizar la viabilidad a largo plazo de la estructura de hormigón.

Plastificantes

Considere hormigonar en lugares de difícil acceso en un molde. Los plastificantes ayudan a que el hormigón se compacte por sí solo, mejorando la trabajabilidad ...

Education

Educación

JoVE Core

Civil Engineering

Ingeniería Civil

Unit 1

Unidad 1

Admixtures

Aditivos

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

Plasticizers

concrete workability with plasticizers

Concrete plasticizers are water-reducing chemical admixtures that improve workability and strength. They help concrete use less water while keeping the same flow, reduce cement content without losing workability, or make mixes easier to place in hard-to-reach areas.

Plasticizers work by using surface-active agents. These agents create repulsive electrostatic forces between cement particles. The particles disperse more evenly, and the concrete needs about 5 to 15 percent less mixing water.

Some plasticizers can delay setting time. Even so, the loss of workability over time is not always reduced. Trial mixes are important to check compatibility with air-entraining agents, which add air pockets that can change the final properties of the concrete.

These admixtures also improve strength, especially early strength, because cement hydrates more uniformly. They are generally effective with all cement types, but the strength gain is often greater in cements with low tricalcium aluminate or low alkali content. When used correctly, water-reducers can also improve durability.

Before using them in a structure, engineers must test for side effects such as segregation or bleeding. Segregation happens when the mix separates, and bleeding is the rise of water to the surface. These checks help confirm that the concrete will perform well over time.

Concrete Workability with Plasticizers

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Calcium Chloride in Concrete Mixes

Calcium chloride is a concrete admixture that speeds up hardening and helps concrete gain early strength faster. It does not always change the setting time itself, but it can reduce the time needed in practice. This makes it useful in cold weather and in rapid repair work where quick heat generation after mixing is helpful. A common amount is 1 to 2 percent of the cement mass. Its effect can be compared with raising the concrete temperature by 11 degrees Fahrenheit. To spread it evenly through...

retarders

Retarders in Concrete Pouring

Retarders are chemical admixtures used in concrete to slow the setting time. They are especially helpful when one pour must follow another after a delay. By keeping the concrete workable for longer, they can help prevent cold joints and support a more cohesive structure. Retarders can also improve the look of exposed aggregate finishes when they are used in the right amount. Their effect on setting time can be checked with a penetration test. Common retarding substances include sugar,...

plasticizers

Concrete plasticizers are water-reducing chemical admixtures that improve workability and strength. They help concrete use less water while keeping the same flow, reduce cement content without losing workability, or make mixes easier to place in hard-to-reach areas. Plasticizers work by using surface-active agents. These agents create repulsive electrostatic forces between cement particles. The particles disperse more evenly, and the concrete needs about 5 to 15 percent less mixing water. <br...

superplasticizers

Superplasticizers for Stronger Concrete Mixes

Superplasticizers are concrete admixtures that make mixes flow better while using less water. They are strong water reducers, so concrete can be easier to place without losing strength. This makes them useful when concrete must reach tight spaces or heavily reinforced areas without mechanical vibration. These admixtures work through sulfonated melamine or naphthalene formaldehyde condensates. These chemicals give cement particles a negative charge. The particles repel each other and spread out...

additives and fillers in concrete

Concrete Fillers That Improve Performance

Concrete fillers and additives help change how cement paste performs. Pozzolans and blast-furnace slag act as additives or admixtures because they react with calcium hydroxide released during cement hydration. Fine fillers are close in fineness to Portland cement and can improve workability, density, and resistance to capillary bleeding or cracking. Some fillers are hydraulic, which means they can react with water, while others take part in harmless reactions inside the cement paste. A key...

waterproofing and anti-bacterial admixtures in concrete

waterproofing-and-anti-bacterial-admixtures-in-concrete

Concrete Water Resistance and Biological Protection

Concrete can absorb water because of capillary action in the pores of its hydrated cement paste. That movement pulls water into the material. Waterproofing admixtures are added to reduce this penetration and help concrete resist water. The effect of a waterproofing admixture depends on the water pressure acting on the concrete. Rain, capillary rise, and hydrostatic pressure in structures made to hold water can all affect performance. These admixtures make concrete hydrophobic, which means they...

key terms and concepts

Learn how plasticizers reduce water use, improve concrete workability, and boost strength. See why trial mixes and compatibility tests matter.

Concrete Workability with Plasticizers | 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 Workability with Plasticizers

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