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

型枠内でアクセスしにくい場所にコンクリートを打設することを検討してください。可塑剤はコンクリートを自然に圧縮し、水やセメントを抑えて作業性を向上させます。
一般的な可塑剤には、リグノスルホン酸とヒドロキシル化カルボン酸が含まれ、コンクリートの水使用量を5〜15%削減できる減水混合物として機能します。
可塑剤中の界面活性剤は、非混合相間の界面力を変化させてセメント粒子に付着することで、負の電荷を付与し、反発を促進し、気泡をはじきながら分散を安定させます。
負の電荷は、各粒子の周囲に整列した水分子の層を誘導し、それらを効果的に遠ざけます。
最後に、粒子の移動が促進され、クラスター化されたシステムから水が解放されるため、混合が容易になり、作業性が向上します。
可塑剤はセメント粒子の分散を促進し、水和のための表面積を増加させます。この分散は、混和剤を含まない混合物と比較して、初期の強度を高めます。
これらの混和剤の強度への影響は、アルミン酸三カルシウムが低いセメントやアルカリレベルが低いセメントでより顕著になります。
建設現場で可塑剤を使用する前に、偏析、にじみ、作業性の低下などの問題を特定するためのテストが不可欠です。

可塑剤

減水剤、または可塑剤は、コンクリートの強度と作業性を向上させるために使用する化学混和剤です。これらの添加剤は、作業性を損なうことなく水セメント比を下げたり、作業性を維持しながらセメント含有量を減らしたり、作業性を高めてアクセスできない場所でのコンクリートの配置を容易にしたりします。


 可塑剤は、界面活性剤を使用してセメント粒子間に反発する静電気力を発生させることで機能します。この分散によりコンクリートの作業性が向上し、混合水の必要性が 5 ～ 15 ％減少します。特定の可塑剤では硬化時間が遅くなることがありますが、伸びた時間とともに作業性が失われるとは限りません。空気連行剤との適合性を確認するために、試験混合を行うことが重要です。空気連行剤は、コンクリートの最終的な特性に影響を与える空気ポケットを発生させる可能性があります。


 これらの混和剤は、セメントの水和がより均一になるため、特に初期段階でコンクリートの強度を高めます。これらは一般にすべてのセメントの種類に効果があり、三カルシウムアルミネートまたはアルカリ含有量の低いセメントでは強度がさらに顕著に増加します。減水剤を正しく使用すると、コンクリートの耐久性も向上します。ただし、コンクリート構造物の長期的な存続可能性を確保するために、実装前に分離やブリーディングなどの悪影響の可能性をテストすることが重要です。

型枠内でアクセスしにくい場所にコンクリートを打設することを検討してください。可塑剤は、コンクリートがそれ自体で圧縮されるのを助け、より少ない労力で作業性を向上させます...

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Admixtures

混和剤

KEY TERMS AND CONCEPTS

主要用語と概念

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

Description

Transcript

Tags