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

형태 내에서 콘크리트의 과도한 수평 이동이나 상당한 높이에서 떨어뜨리거나 방향 변경이 있는 좁은 공간을 통해 콘크리트를 떨어뜨리면 구성 요소가 분리될 수 있습니다.
분리(Segregation)는 더 무거운 굵은 응집체 입자가 형태의 바닥에 침전되는 경향이 있는 현상입니다. 동시에 더 가볍고 미세한 구성 요소가 위쪽으로 이동하여 콘크리트 혼합물 내에서 고르지 않은 분포를 초래합니다.
또 다른 유형의 분리는 시멘트와 물로 구성된 그라우트가 나머지 콘크리트 혼합물과 분리되는 경향이 있을 때 발생합니다.
콘크리트는 가능한 한 최종 위치에 가깝게 준비해야 하며, 분리를 방지하기 위해 운송 거리를 줄여야 합니다.
광대한 지역에 콘크리트 더미를 분산시키기 위해 바이브레이터를 장시간 사용하는 것과 같이 콘크리트에 너무 많은 작업을 수행하면 콘크리트 재료가 분리될 수 있습니다.
과도한 진동으로 인한 가능한 분리를 관찰하기 위해 큐브의 콘크리트를 약 10분 동안 진동시킬 수 있습니다. 곰팡이를 제거하면 굵은 응집체 분포를 검사할 수 있습니다.

신선한 콘크리트의 분리

신선한 콘크리트의 분리는 콘크리트 혼합물의 구성 요소가 분리되어 불균일한 분포와 손상된 구조적 무결성으로 이어지는 현상입니다. 이러한 분리는 일반적으로 콘크리트가 거푸집 내에서 과도한 수평 이동을 받거나 상당한 높이에서 떨어뜨리거나 좁고 구불구불한 경로를 통해 강제로 통과할 때 발생합니다. 결과적으로 더 무거운 굵은 골재 입자는 바닥에 가라앉고 시멘트와 물과 같은 더 가볍고 미세한 재료는 위로 올라갑니다.


 분리의 또 다른 형태는 그라우트(시멘트와 물로 구성됨)가 혼합물에서 분리되는 것으로 나타납니다. 이러한 분리는 콘크리트의 외관에 영향을 미칠 뿐만 아니라 구조적 성능도 약화시킵니다. 분리 위험을 최소화하기 위해 콘크리트는 최종 배치 위치에 최대한 가깝게 준비해야 하며, 따라서 혼합물을 방해할 수 있는 광범위한 운송의 필요성을 줄여야 합니다.


 또한 콘크리트를 과도하게 사용하는 경우(예: 진동기를 장기간 사용하여 넓은 면적에 콘크리트를 펴는 경우) 분리가 발생할 수 있습니다. 분리 가능성을 테스트하는 실용적인 방법은 콘크리트 샘플을 큐브 몰드에서 약 10분 동안 진동시키는 것입니다. 몰드를 제거하면 굵은 골재의 분포를 검사하여 분리 정도를 평가할 수 있습니다. 이러한 예방 조치와 테스트는 콘크리트 구조의 균일성과 강도를 보장하는 데 필수적입니다.

형태 내에서 콘크리트의 과도한 수평 이동 또는 상당한 높이에서 또는 방향 변경이 있는 좁은 공간을 통해 콘크리트를 떨어뜨리는 것은 ...

Education

교육

JoVE Core

Civil Engineering

토목공학

Unit 1

제1단원

Fresh Concrete

굳지 않은 콘크리트

KEY TERMS AND CONCEPTS

핵심 용어 및 개념

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 offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

How Concrete Mixes Separate During Placement

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