Name: retarders in concrete pouring
Uploaded: 2024-11-07T14:48:38.000Z
Duration: 1 min 19 s
Channel: JoVE

暑い気候のコンクリートでは、温度が高くなると通常の硬化時間が短くなると、連続するバッチ間にコールドジョイントが形成される可能性があります。
リターダーをコンクリートに使用すると、最初に注がれたコンクリートは、次に注がれたばかりのコンクリート層との凝集性を確保するために、より長くプラスチックのままになります。
層間の凝集性は、骨材を露出させて所望の建築仕上げを達成するために有利です。
リターダーは、コンクリートの硬化時間を延長する混和剤であり、この遅延は貫入試験を使用して定量化できます。
コンクリート硬化の遅延、または遅延は、砂糖、炭水化物誘導体、可溶性亜鉛塩、可溶性ホウ酸塩などの物質を組み込むことで達成できます。
セメントの質量に対して約0.05%の砂糖を追加すると、硬化時間を約4時間延長できます。
リターダーは、コンクリートの結晶成長を変化させ、継続的な水分補給に対するより効果的な障害を作り出すと考えられています。
その後、リターダーは最終的な水和生成物を変更することなく構造の一部になります。

遅延剤

Retarders

遅延剤は、凝結時間を延長するように設計された化学混和剤で、連続したコンクリートの注入が遅れる場合のコールドジョイントを防ぎ、均一な構造を実現するために特に役立ちます。遅延剤を適切な量使用すると、露出骨材仕上げの建築的な外観を向上させることもできます。


 遅延剤の機能はコンクリートの凝結を遅らせることであり、この効果は貫入試験を用いて測定できます。遅延プロセスでは、砂糖、炭水化物誘導体、可溶性亜鉛塩、ホウ酸塩などの物質をコンクリート混合物に加えます。セメントの質量に対して 0.05 ％の砂糖などの少量の砂糖で、凝結時間を約 4 時間延長できます。遅延剤はコンクリート内の結晶成長を妨げるため、水和プロセスに対するより強力な障壁を作り出すと仮定されています。遅延剤は強度発現の初期速度を変えますが、水和生成物の最終的な構成や性質は変更しません。遅延剤を組み込むと、初期の強度が低下する可能性がありますが、達成される最終強度には影響しません。最終強度は、遅延剤を含まないコンクリートよりも高くなる可能性があります。さらに、遅延剤は塑性段階の延長により塑性収縮を増加させることが観察されていますが、乾燥収縮には影響しません。

暑い気候のコンクリートでは、温度が高くなると通常の硬化時間が短くなると、...

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

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, carbohydrate derivatives, soluble zinc salts, and borates.

Even a small amount can make a difference. For example, sugar at 0.05 percent by mass of cement can extend setting by about four hours. Retarders are thought to work by interfering with crystal growth in the concrete, which creates a stronger barrier to hydration.

Retarders change the early rate of strength development, but they do not change the final composition or identity of the hydration products. Concrete may have lower strength at first, yet its ultimate strength is not affected and may even be higher than in concrete without retarders. They can also increase plastic shrinkage because the plastic stage lasts longer, but they do not affect drying shrinkage.

Retarders in Concrete Pouring

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 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 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. <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 concrete retarders delay setting, help prevent cold joints, and affect strength, shrinkage, and exposed aggregate finishes in construction.

Retarders in Concrete Pouring | 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

Retarders in Concrete Pouring

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