Name: how concrete mixes separate during placement
Uploaded: 2024-11-07T14:48:28.000Z
Duration: 1 min 16 s
Channel: JoVE

O movimento horizontal excessivo do concreto dentro das formas, ou deixá-lo cair de uma altura considerável ou através de espaços estreitos com mudanças direcionais, pode levar à segregação de seus componentes.
A segregação é um fenômeno em que as partículas agregadas mais pesadas tendem a se depositar na parte inferior da forma. Ao mesmo tempo, os componentes mais leves e finos migram para cima, levando a uma distribuição desigual dentro da mistura de concreto.
Outro tipo de segregação ocorre quando a argamassa, composta por cimento e água, tende a se separar do resto da mistura de concreto.
O concreto deve ser preparado o mais próximo possível de sua localização final, reduzindo a distância de transporte para evitar a segregação.
Se muito trabalho for realizado no concreto, como usar um vibrador por um longo tempo para distribuir um monte de concreto por uma vasta área, ele pode segregar os ingredientes do concreto.
Para observar a provável segregação devido à vibração excessiva, o concreto em um cubo pode ser vibrado por aproximadamente 10 minutos. A remoção do molde permitirá a inspeção da distribuição do agregado graúdo.

segregação em concreto fresco

A segregação em concreto fresco é um fenômeno em que os componentes da mistura de concreto se separam, levando à distribuição irregular e à integridade estrutural comprometida. Essa separação geralmente ocorre quando o concreto é submetido a movimento horizontal excessivo dentro das fôrmas, ou quando é derrubado de alturas consideráveis ​​ou forçado por caminhos estreitos e sinuosos. Como resultado, partículas de agregados grossos mais pesados ​​se depositam no fundo, enquanto materiais mais leves e finos, como cimento e água, sobem para o topo.

Outra forma de segregação se manifesta quando a argamassa (composta de cimento e água) se desprende da mistura. Essa separação não afeta apenas a aparência do concreto, mas também enfraquece suas capacidades estruturais. Para minimizar o risco de segregação, o concreto deve ser preparado o mais próximo possível de seu local de colocação final, reduzindo assim a necessidade de transporte extensivo que pode interromper a mistura.

Além disso, o excesso de trabalho no concreto, como o uso prolongado de vibradores para espalhar o concreto sobre uma grande área, pode levar à segregação. Um método prático para testar a segregação potencial envolve vibrar uma amostra de concreto em um molde de cubo por cerca de 10 minutos. Ao remover o molde, a distribuição do agregado grosso pode ser inspecionada para avaliar o grau de segregação. Essas medidas preventivas e testes são cruciais para garantir a uniformidade e a resistência da estrutura de concreto.

Segregação em concreto fresco

O movimento horizontal excessivo do concreto dentro das formas, ou deixá-lo cair de uma altura considerável ou através de espaços estreitos com mudanças direcionais, pode ...

Education

JoVE Core

Civil Engineering

Engenharia Civil

Unit 1

Unidade 1

Fresh Concrete

Concreto Fresco

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

Segregation in Fresh Concrete

how concrete mixes separate during placement

Fresh concrete can separate during placement, which changes how the mix is spread and can weaken the finished structure. This separation is called segregation. It happens when the parts of the mix no longer stay evenly blended.

Segregation often occurs when concrete moves too much inside a form. It can also happen when the mix is dropped from a great height or pushed through narrow paths with sharp turns. In these cases, the heavier coarse aggregate settles at the bottom, while lighter materials such as cement and water move upward.

Another form of segregation happens when the grout pulls away from the rest of the mix. Grout is the cement and water portion of concrete. When this separation occurs, the concrete may look uneven and lose strength.

To reduce segregation, concrete should be placed as close as possible to its final location. This lowers the need for transport that can disturb the mix. Overworking the concrete can also cause problems. For example, using vibrators for too long to spread concrete over a large area may lead to segregation.

A simple test can show whether segregation may occur. A sample of concrete is vibrated in a cube mold for about 10 minutes. After the mold is removed, the coarse aggregate is checked to see how evenly it is distributed. This helps judge the level of segregation and supports stronger, more uniform concrete.

How Concrete Mixes Separate During Placement

how-concrete-mixes-separate-during-placement

workability of concrete

Concrete Flow and Compaction Factors

Concrete workability is the ease with which fresh concrete can be mixed, placed, compacted, and finished. It is an important property during construction because it affects how well the material moves into position and how easily it can be shaped. Workability depends on the internal friction within the mix and the resistance it meets from molds and reinforcements. When the ingredients resist one another, concrete moves less easily. The same is true when it has to pass around barriers in the...

factors affecting workability

Concrete Workability and Mix Design Factors

Concrete workability depends on mix design factors that change how easily the material can be mixed, handled, and finished. The mix needs enough flow so it can move and be placed without losing quality. Water is a key part of this because it acts as a lubricant between the ingredients. The amount of water needed can change with the aggregates, or the solid particles in the mix. Finer particles and angular, rough-textured aggregates need more water than smooth, rounded ones because they have...

segregation in fresh concrete

Fresh concrete can separate during placement, which changes how the mix is spread and can weaken the finished structure. This separation is called segregation. It happens when the parts of the mix no longer stay evenly blended. Segregation often occurs when concrete moves too much inside a form. It can also happen when the mix is dropped from a great height or pushed through narrow paths with sharp turns. In these cases, the heavier coarse aggregate settles at the bottom, while lighter...

bleeding in fresh concrete

Bleeding Water and Laitance in Fresh Concrete

Bleeding in fresh concrete happens when water from the mix rises to the surface after placement. The solid parts of the mix do not hold all the water as they settle, so separation occurs and water collects on top. Engineers can measure the severity of bleeding by checking total settlement or by noting how much the concrete height drops per unit height. Bleeding can create weak spots inside the concrete. Rising water may get trapped under large aggregate particles or reinforcement bars, which...

slump test

Concrete Workability Check with Slump

The slump test checks the workability of fresh concrete. Workability means how easy the mix is to place and handle. The test uses a 12-inch-high truncated cone mold that narrows from eight inches at the base to four inches at the top. Before testing, the mold is fixed to a flat base and dampened. Concrete is added in three layers. Each layer is compacted 25 times with a steel tamping rod that is five-eighths of an inch in diameter and has a rounded end. This helps spread the concrete evenly...

compacting factor test

Concrete Workability by Compacting Factor

The compacting factor test measures the workability of concrete. Workability describes how easily concrete can move and fill a mold or form during construction. This test is especially suitable for concrete mixes with aggregates up to one and a half inches in size. The setup uses specialized equipment with two truncated cone-shaped hoppers and a cylinder. All of the inside surfaces are polished to reduce friction. Concrete is first placed into the upper hopper without any compaction. Then the...

vebe test

Concrete Workability with the Vebe Test

The Vebe test measures the workability of concrete, especially for dry mixes. Workability means how easy concrete is to handle and compact. The test uses a cylindrical chamber, a standard slump cone, and a transparent disc-shaped rider mounted on a vibrating table. The cylindrical chamber measures nine and a half inches in diameter and eight inches in height. Concrete is placed into the slump cone in layers and compacted in the standard way. After the cone is removed, the concrete stays in the...

flow table test

Concrete Spread Measured by Flow Table

The flow table test measures how far fresh concrete spreads, which helps assess workability. Workability means how easily concrete can flow and settle under its own weight. The method is useful for highly flowable concrete mixes. The test uses a flow table made from a wooden board with a steel plate on top. Together, the parts weigh 35 pounds. The board is hinged to a base and measures 27.6 inches on each side. A truncated cone mold is also used. It is 8 inches high, with an 8-inch base...

key terms and concepts

Learn how fresh concrete can segregate during placement, why aggregate and grout separate, and how a cube mold test helps check mix uniformity.

How Concrete Mixes Separate During Placement | 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

How Concrete Mixes Separate During Placement

Description

Transcript

Tags