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

Na concretagem em clima quente, quando o tempo normal de presa é reduzido pela temperatura mais alta, pode levar à formação de juntas frias entre lotes sucessivos.
Quando retardadores são usados em concreto, o concreto inicialmente derramado permanece plástico por mais tempo para garantir a coesão com o próximo lote de camada de concreto recém-derramado.
A coesão entre as camadas pode ser vantajosa para obter um acabamento arquitetônico desejado com agregado aparente.
Os retardadores são aditivos que prolongam o tempo de pega do concreto; esse atraso pode ser quantificado usando o teste de penetração.
O retardo da pega do concreto pode ser obtido pela incorporação de substâncias como açúcar, derivados de carboidratos, sais de zinco solúveis e boratos solúveis, entre outros.
Adicionar cerca de 0,05% de açúcar em relação à massa do cimento pode estender o tempo de pega em cerca de quatro horas.
Acredita-se que os retardadores alterem o crescimento de cristais no concreto, criando um obstáculo mais eficaz para a hidratação contínua.
Posteriormente, o retardador passa a fazer parte da estrutura sem alterar os produtos finais de hidratação.

retardadores

Retarders

Retardadores são aditivos químicos projetados para estender o tempo de pega, o que é especialmente útil quando há um atraso em vazamentos sequenciais de concreto para evitar juntas frias e obter uma estrutura coesa. Retardadores, quando usados ​​em quantidades adequadas, também podem melhorar a aparência arquitetônica de acabamentos de agregados expostos.

A função dos retardadores é atrasar a pega do concreto, e esse efeito pode ser medido usando um teste de penetração. O processo de retardamento envolve a adição de substâncias como açúcar, derivados de carboidratos, sais de zinco solúveis e boratos à mistura de concreto. Uma pequena proporção, como 0,05 por cento de açúcar por massa de cimento, pode prolongar o tempo de pega em aproximadamente quatro horas. Há a hipótese de que os retardadores interfiram no crescimento de cristais dentro do concreto, criando assim uma barreira mais formidável ao processo de hidratação. Embora alterem a taxa inicial de desenvolvimento de resistência, os retardadores não alteram a composição final ou a identidade dos produtos de hidratação. A integração de retardadores pode resultar em menor resistência inicial, mas não afeta a resistência final alcançada, que pode ser maior do que em concreto não retardado. Além disso, observou-se que retardadores aumentam a retração plástica devido ao estágio plástico estendido, mas não afetam a retração de secagem.

Retardadores

Na concretagem em clima quente, quando o tempo normal de presa é reduzido pela temperatura mais alta, pode levar à formação de juntas frias entre ...

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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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key terms and concepts

Learn how concrete retarders delay setting, help prevent cold joints, and affect strength, shrinkage, and exposed aggregate finishes in construction.

Retarders in Concrete Pouring | 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

Retarders in Concrete Pouring

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