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

Considere a concretagem em locais de difícil acesso em um molde. Os plastificantes ajudam o concreto a se compactar por conta própria, aumentando a trabalhabilidade com menos água ou cimento.
Os plastificantes comuns incluem ácidos lignosulfônicos e ácidos carboxílicos hidroxilados, funcionando como aditivos redutores de água que podem reduzir o uso de água em 5 a 15% no concreto.
Os agentes tensoativos nos plastificantes alteram as forças interfaciais entre as fases de não mistura e aderem às partículas de cimento, transmitindo uma carga negativa, promovendo a repulsão e estabilizando sua dispersão enquanto repelem bolhas de ar.
A carga negativa induz uma camada de moléculas de água alinhadas ao redor de cada partícula, distanciando-as efetivamente.
Por fim, o movimento das partículas é aprimorado e a água é liberada do sistema agrupado, tornando-a disponível para facilitar a mistura e melhorar a trabalhabilidade.
Os plastificantes aumentam a dispersão das partículas de cimento, aumentando a área de superfície para hidratação. Essa dispersão aumenta a resistência da idade precoce em relação a misturas sem misturas.
O impacto desses aditivos na resistência é mais pronunciado em cimentos com baixo teor de aluminato tricálcico ou baixos níveis de álcalis.
Antes de usar plastificantes na construção, o teste é essencial para identificar problemas como segregação, sangramento ou redução da trabalhabilidade.

plastificantes

Redutores de água, ou plastificantes, são aditivos químicos usados ​​no concreto para melhorar a resistência e a trabalhabilidade. Esses aditivos reduzem a relação água-cimento sem comprometer a trabalhabilidade, diminuem o teor de cimento mantendo a mesma trabalhabilidade ou aumentam a trabalhabilidade para auxiliar na colocação do concreto em áreas inacessíveis.

Os plastificantes funcionam usando agentes tensoativos para criar forças eletrostáticas repulsivas entre as partículas de cimento. Essa dispersão melhora a trabalhabilidade do concreto e reduz a necessidade de misturar água em 5 a 15 por cento. Apesar do retardo do tempo de pega com certos plastificantes, a perda de trabalhabilidade ao longo do tempo não é necessariamente diminuída. É importante ter misturas de teste para garantir a compatibilidade com agentes incorporadores de ar, que podem introduzir bolsas de ar que afetam as propriedades finais do concreto.

Essas misturas aumentam a resistência do concreto, principalmente nos estágios iniciais, devido à hidratação mais uniforme do cimento. Eles são geralmente eficazes em todos os tipos de cimento, com um aumento de resistência mais pronunciado em cimento com baixo teor de aluminato tricálcico ou álcali. O uso correto de redutores de água também pode melhorar a durabilidade do concreto. No entanto, antes da implementação, é essencial testar possíveis efeitos negativos, como segregação ou sangramento, para garantir a viabilidade a longo prazo da estrutura de concreto.

Plastificantes

Considere a concretagem em locais de difícil acesso em um molde. Os plastificantes ajudam o concreto a compactar por conta própria, aumentando a trabalhabilidade com menos ...

Education

JoVE Core

Civil Engineering

Engenharia Civil

Unit 1

Unidade 1

Admixtures

Aditivos

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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

accelerators

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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