Name: concrete flow and compaction factors
Uploaded: 2024-11-07T14:48:28.000Z
Duration: 1 min 25 s
Channel: JoVE

コンクリート成分が互いに大きな抵抗を提供する場合、コンクリートの動きが妨げられ、配置と取り扱いが困難になります。
この抵抗は、コンクリートの動きに対する型枠や補強材によっても提供され、これらの取り扱いの問題は、コンクリートの施工性を維持することで制御できます。
コンクリートの打設・締固め・仕上げなど、コンクリートの取り扱いの初期段階では、その作業性、つまり全工程でいかに簡単に移動・作業できるかが大きな影響を受けます。
施工性とは、コンクリートの徹底的な締固めを実現するために、さまざまな抵抗を克服するために必要な内部エネルギーを指します。
コンクリートを徹底的に圧縮することで、密度が向上し、ひいては強度が向上します。
コンクリートの空隙含有量が5%の場合、その圧縮強度は最大30%低下する可能性があります。
良好で作業可能なコンクリートは、その質量から最大のボイドを確実に排出します。
コンクリートが流れやすいことを一貫性と呼びます。
特定の制限内で水分含有量が高いコンクリートは、一般的に乾燥した混合物よりも作業性が高くなります。
ただし、同じ一貫性を持つコンクリートは、作業性に違いを示す可能性があります。

コンクリートの作業性

コンクリートの作業性は、建設中の取り扱い、配置、仕上げに影響を与える重要な特性です。作業性とは、コンクリートの混合、配置、圧縮、仕上げのしやすさを表します。作業性は主に、コンクリートが施工過程で型枠や鉄筋などの外部抵抗に対してどれだけ動きやすく、内部摩擦に抵抗できるかに関わります。


 コンクリートの作業性は、材料同士の相互作用によって発生する内部力や、型枠や鉄筋などの外部障害に遭遇したときの抵抗によって決まります。コンクリートの効果的な圧縮は、作業性に大きく影響し、材料の密度と強度が向上します。コンクリートの空隙率が 5 ％でも、強度が最大 30 ％低下する可能性があることが指摘されています。つまり、作業性の高いコンクリートは、空隙の排除を容易にし、完成品の構造的完全性を高めるため、有利です。


 コンクリートの粘稠度は、その流れ易さを意味し、水分含有量に直接関係しています。水分含有量の高いコンクリート混合物は、一般的に、乾燥した混合物よりも作業性が高くなります。ただし、同じ粘稠度のコンクリートでも、その組成や使用条件によって作業性のレベルが異なる場合があることを認識することが重要です。作業性の管理は、最適な強度と耐久性を備えた高品質のコンクリート構造物を実現するために不可欠です。

コンクリート成分が互いに大きな抵抗を提供する場合、コンクリートの動きが妨げられ、配置と取り扱いが...

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Fresh Concrete

生コンクリート

KEY TERMS AND CONCEPTS

主要用語および概念

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 formwork or around steel reinforcement.

Good workability also supports effective compaction, which helps concrete become denser and stronger. Even a void content of 5 percent can reduce concrete strength by up to 30 percent. High workability helps air and other voids escape, which improves the strength and durability of the finished structure.

Consistency is closely related to workability. Consistency describes how easily concrete flows, and it is linked to moisture content. Mixes with more moisture are usually more workable than drier mixes, but concrete with the same consistency can still have different workability depending on its composition and the conditions in which it is used. Managing workability is essential for producing quality concrete.

Concrete Flow and Compaction Factors

workability of concrete

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

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...

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 concrete flow, internal friction, moisture, and compaction affect workability, strength, and durability in construction.

Concrete Flow and Compaction Factors | 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 Flow and Compaction Factors

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