Name: retarders in concrete pouring
Uploaded: 2024-11-07T14:48:38.000Z
Duration: 1 min 19 s
Channel: JoVE

En el hormigonado en climas cálidos, cuando el tiempo de fraguado normal se acorta por la temperatura más alta, puede provocar la formación de juntas frías entre lotes sucesivos.
Cuando se utilizan retardadores en el hormigón, el hormigón vertido inicialmente permanece plástico durante más tiempo para garantizar la cohesión con el siguiente lote de capa de hormigón recién vertido.
La cohesión entre las capas puede ser ventajosa para lograr un acabado arquitectónico deseado con agregado visto.
Los retardantes son aditivos que prolongan el tiempo de fraguado del hormigón; este retraso se puede cuantificar mediante la prueba de penetración.
El retraso del fraguado del hormigón, o retardo, se puede lograr mediante la incorporación de sustancias como azúcar, derivados de carbohidratos, sales solubles de zinc y boratos solubles, entre otros.
Agregar alrededor de 0.05 por ciento de azúcar en relación con la masa del cemento puede extender el tiempo de fraguado en aproximadamente cuatro horas.
Se cree que los retardadores alteran el crecimiento de cristales en el concreto, creando un obstáculo más efectivo para la hidratación continua.
Posteriormente, el retardador pasa a formar parte de la estructura sin alterar los productos finales de hidratación.

retardadores

Retarders

Los retardadores son aditivos químicos diseñados para extender el tiempo de fraguado, lo que resulta especialmente útil cuando hay un retraso en los vertidos secuenciales de hormigón para evitar juntas frías y lograr una estructura cohesiva. Los retardadores, cuando se utilizan en cantidades adecuadas, también pueden mejorar el aspecto arquitectónico de los acabados con áridos expuestos.

La función de los retardadores es retrasar el fraguado del hormigón, y este efecto se puede medir mediante una prueba de penetración. El proceso de retardación implica añadir sustancias como azúcar, derivados de carbohidratos, sales solubles de zinc y boratos a la mezcla de hormigón. Una pequeña proporción, como 0,05 por ciento de azúcar por masa de hormigón, puede prolongar el tiempo de fraguado aproximadamente cuatro horas. Se plantea la hipótesis de que los retardadores interfieren con el crecimiento de cristales dentro del hormigón, creando así una barrera más formidable para el proceso de hidratación. Aunque alteran la velocidad inicial de desarrollo de la resistencia, los retardadores no cambian la composición final ni la identidad de los productos de hidratación. La integración de retardadores puede dar como resultado una resistencia inicial menor, pero no afecta a la resistencia máxima alcanzada, que puede ser mayor que en el hormigón sin retardadores. Además, se ha observado que los retardadores aumentan la contracción plástica debido a la etapa plástica prolongada, pero no afectan a la contracción por secado.

Retardadores

En el hormigonado en climas cálidos, cuando el tiempo normal de fraguado se acorta por la temperatura más alta, puede provocar la formación de juntas ...

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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, carbohydrate derivatives, soluble zinc salts, and borates.

Even a small amount can make a difference. For example, sugar at 0.05 percent by mass of cement can extend setting by about four hours. Retarders are thought to work by interfering with crystal growth in the concrete, which creates a stronger barrier to hydration.

Retarders change the early rate of strength development, but they do not change the final composition or identity of the hydration products. Concrete may have lower strength at first, yet its ultimate strength is not affected and may even be higher than in concrete without retarders. They can also increase plastic shrinkage because the plastic stage lasts longer, but they do not affect drying shrinkage.

Retarders in Concrete Pouring

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retarders

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,...

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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

Retarders in Concrete Pouring

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