Name: how curing improves concrete strength
Uploaded: 2024-11-07T14:48:35.000Z
Duration: 1 min 20 s
Channel: JoVE

セメントの水和は、セメントペーストの水で満たされた毛細管孔で発生します。
気温、湿度、風などの環境要因により、蒸発が発生し、新しく設置されたコンクリートの表面から水分が除去される可能性があります。
あるいは、コンクリートが密封され、その水とセメントの比率が0.5未満の場合、内部乾燥により自由水が失われます。
硬化は、コンクリートを飽和させて水分補給プロセスを継続するために必要な適切なレベルの水分と温度を維持することにより、コンクリートからの水分損失を防ぎます。 
セメントが最終セットに達した後、硬化が開始され、水和物で満たされるために水和セメントペーストの毛細管が分節化され、コンクリートが不浸透性で耐久性を持つようになるまで続きます。
コンクリートを硬化させずに空気中で乾燥させると、コンクリートが収縮しやすくなり、表面のひび割れが発生します。さらに、連続的に湿潤硬化したコンクリートの約50%の圧縮強度しか達成しません。
最後に、硬化時間が長いほど、コンクリートの圧縮強度は高くなります。

コンクリートの養生

セメントの水和は、水で満たされた毛細管細孔内で起こります。しかし、環境要因によってコンクリート表面から水が蒸発し、このプロセスが妨げられることがあります。水セメント比が 0.5 未満の密閉コンクリートは自己乾燥で水分が失われます。コンクリートの水分損失は養生によって軽減されます。この技術では、コンクリートを飽和状態に保ち、必要な温度と湿度条件を維持して、最初に水で占められていたセメントペーストの空間を水和生成物で最適に満たします。養生は、セメントの最終硬化後に開始します。養生せずに乾燥させたコンクリートは収縮してひび割れる可能性があり、28 日間続けて養生されたコンクリートの半分の強度しか達成できない可能性があります。養生の期間はコンクリートの最終的な圧縮強度と引張強度に直接相関しており、この方法は強度だけでなく、耐久性、防水性、耐摩耗性、凍結融解などの他の望ましい特性を確保するためにも重要であることがわかります。この効果は、薄い構造要素やセメント含有量の多い混合物でより顕著になりますが、軽量骨材コンクリートでは影響は小さくなります。さらに、空気連行コンクリートは、非空気連行コンクリートよりも養生条件による影響が少なくなります。

セメントの水和は、セメントペーストの水で満たされた毛細管孔で発生します。
気温、湿度、風などの環境要因が原因となることがあります...

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Mixing, Placing and Curing Concrete 

コンクリートの練混ぜ、打設および養生

KEY TERMS AND CONCEPTS

主要用語および概念

Curing of Concrete

how curing improves concrete strength

Curing helps concrete gain strength after it has set. It keeps the concrete moist and at the right temperature so cement hydration can continue. Hydration is the process where cement reacts with water in the water-filled capillary pores and forms the products that fill spaces in the paste.

Dry air can interrupt this process by pulling water from the concrete surface. Concrete with a water-cement ratio below 0.5 can also lose water through self-desiccation, which means internal water is used up as hydration continues. Curing reduces this water loss by keeping the surface saturated.

Curing begins after the cement reaches final set. If concrete is allowed to dry without curing, it may shrink and crack. It may also reach only about half the strength of concrete that is continuously cured for 28 days.

The length of curing affects the final compressive strength and tensile strength of concrete. It also helps improve durability, water tightness, abrasion resistance, and freeze-thaw resistance. The effect is stronger in thin structural elements and in mixes with a high cement content. Lightweight aggregate concrete is less affected, and air-entrained concrete is less influenced by curing conditions than non-air-entrained concrete.

How Curing Improves Concrete Strength

mixing concrete

Concrete Mixer Types and Capacity

Concrete mixing creates a uniform blend of cement, aggregates, and paste. The goal is to coat the aggregates evenly with cement paste. Mixers used for this job are usually grouped into two main types: batch mixers and continuous mixers. Batch mixers handle one load at a time. They mix the materials thoroughly, discharge the batch, and then receive the next one. Continuous mixers work differently. They take in a steady flow of ingredients, mix them at a constant rate, and discharge the concrete...

mixing time

Concrete Mixer Charging and Timing

Concrete mixer charging and timing are key to making a uniform concrete mix with the needed strength. Mixing begins only after all ingredients are inside the mixer. The usual charging order starts with 10% of the water, then the solid materials are added steadily, followed by 80% of the water. The last portion of water is added later, within the first quarter of the total mixing period. The minimum mixing time depends on mixer capacity. Mixers with up to 1 cubic yard of capacity need at least...

ready mixed concrete

How Ready-Mixed Concrete Is Delivered

Ready-mixed concrete is prepared at a centralized plant and then delivered by truck to a construction site. It arrives ready for placement, which makes it different from concrete mixed entirely on site. Ready-mixed concrete includes three main forms: central-mixed, truck-mixed, and shrink-mixed. Central-mixed concrete is fully mixed at the plant and carried to the site in agitator trucks. These trucks rotate at 2 to 6 rpm, which helps keep the concrete in motion during transport. Truck-mixed...

pumped concrete

Concrete Pumping for Hard-to-Reach Sites

Concrete pumping moves large amounts of concrete through pipes to places that are hard to reach. It is used for sites such as deep foundation pits and other inaccessible locations. The system includes a hopper, a pump, and pipelines that carry the concrete to the placement point. Direct-acting pumps use a piston to move the concrete. Concrete enters the pump through the inlet valve by gravity and by suction created as the piston moves. The forward movement of the piston then pushes the...

placing concrete

Concrete Placement Methods and Compaction

Concrete placement methods focus on keeping the mix in a uniform shape and position. The concrete is placed as close as possible to its final location to reduce segregation, which is the separation of ingredients. It is then fully compacted to remove trapped air. The next layer is added while the layer below is still plastic, or soft enough to shape. The rate of placing and compacting concrete is kept equal. Concrete is laid in uniform layers, and hand shoveling is avoided. Moving concrete...

vibrating concrete

Concrete Compaction with Vibrators

Concrete compaction with vibrators helps newly poured concrete settle inside formwork and around reinforcement bars. The goal is to remove trapped air pockets and create a dense concrete mass. Mechanical vibration is a key part of that process. One common method uses an internal vibrator, also called a poker vibrator or immersion vibrator. It is quickly inserted through the full depth of the fresh concrete and slightly into the layer below, which is still in a plastic state. The vibrator is...

shotcrete

Shotcrete for Vertical and Overhead Surfaces

Shotcrete is a concrete spraying method used on vertical and overhead surfaces. It uses mortar or small aggregate concrete with a high cement content. The material is sprayed at high velocity, and the impact helps compact it so it can cling without sagging. Builders place shotcrete in layers until it reaches about 4 inches thick. The quality depends strongly on the operator’s skill in managing the nozzle. Careful nozzle control helps the material land evenly and build up properly. Shotcrete...

preplaced aggregate concrete

Concrete Placement for Tight Spaces

Preplaced aggregate concrete is used when a construction site is hard to reach. The process starts by wetting gap-graded coarse aggregates. This helps remove dirt from the stones. The aggregates are then placed in the form and compacted. Next, a mortar mix is pumped under pressure through slotted pipes to fill the spaces between the aggregates. The mortar usually contains Portland cement, pozzolan, fine aggregates, water, and a fluidizing aid. The pozzolan reduces bleeding and segregation and...

finishing concrete

Concrete Surface Finishing Steps

Concrete surface finishing begins right after the concrete has been placed and consolidated. The first step is screeding, which levels the surface by removing extra material until it is even with the top of the formwork. A screed is a straight edge used for this leveling step. After screeding, a bull float or darby is used to smooth the surface further. These tools help lower high spots, fill low areas, and push larger aggregate particles deeper into the concrete. This preparation should...

curing of concrete

Curing helps concrete gain strength after it has set. It keeps the concrete moist and at the right temperature so cement hydration can continue. Hydration is the process where cement reacts with water in the water-filled capillary pores and forms the products that fill spaces in the paste. Dry air can interrupt this process by pulling water from the concrete surface. Concrete with a water-cement ratio below 0.5 can also lose water through self-desiccation, which means internal water is used up...

curing methods

Concrete Curing for Moisture Retention

Concrete curing for moisture retention helps fresh concrete keep the water it needs as it hardens. For members with a small surface-to-volume ratio, the forms are often oiled and moistened before the concrete is placed. These forms may stay in place for a long time to reduce moisture loss. If the form material can be wetted, it can also be kept damp. When forms are removed early, the concrete member is moistened and then covered with polythene sheets. Large horizontal concrete surfaces in dry...

accelerated curing of concrete

How Concrete Gains Strength Faster

Concrete can gain strength faster when heat and extra moisture speed up cement hydration. This faster hydration helps the concrete build early strength sooner than normal curing. The process is used when quicker hardening is needed after casting. One common method is steam curing. Concrete products may move through a chamber on a conveyor belt, or they may be encased in plastic so steam at atmospheric pressure can circulate around them. Steam curing starts with moist curing for about 3 to 5...

key terms and concepts

Learn how curing keeps concrete moist after final set, supports hydration, and improves strength, durability, water tightness, and crack resistance.

How Curing Improves Concrete Strength | 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 Curing Improves Concrete Strength

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