Name: concrete placement for tight spaces
Uploaded: 2024-11-07T14:48:35.000Z
Duration: 1 min 29 s
Channel: JoVE

交換骨材コンクリートは、最初に型枠内に十分に濡れたギャップグレードの粗骨材を配置し、それを圧縮することによって製造されます。
総体積の約3分の1を占める残りの空隙は、ポルトランドセメント、ポッツォラン、細骨材、水、および流動化助剤からなるモルタルで満たされます。
あるいは、セメントと細かい砂のモルタルを高速コロイドミキサーでブレンドして使用することもできます。
モルタルは、一定の間隔で間隔を空けて直径約1.5インチのスロット付きパイプを介して圧力下で導入されます。その後、迫撃砲のレベルが上がるにつれて、パイプは徐々に取り除かれます。
モルタルの最上部での外部振動は、露出面の仕上げを改善することができます。
交換された骨材コンクリートは、分離が減少して均一性を示し、核シールドや水中プロジェクトの建設に使用されます。
保水構造、大型モノリシックブロック、補修工事でも、収縮率が低く浸透性が低いため、交換骨材コンクリートが使用されています。
大規模な建設プロジェクトでは、モルタルを塗る前に、骨材の周りに冷水を循環させることで水和熱を制御し、寒い条件下では循環する蒸気が骨材を暖めます。

事前配置骨材コンクリート

Preplaced Aggregate Concrete

事前配置骨材コンクリートは、アクセスが容易でない建設環境に最適です。このプロセスは、まず、隙間を均等に分けた粗骨材を適切に湿らせて汚れを取り除き、型枠に入れて固めます。隙間はスロット付きのパイプを通して圧力をかけながらポンプで送られるモルタル混合物で埋められます。このモルタルは通常、ポルトランドセメント、ポゾラン、細骨材、水、流動化助剤で構成されています。ポゾランは、モルタルの流動性を向上させながら、ブリーディングと分離を減らすのに役立ちます。一方、流動化助剤は、モルタルの硬化を遅らせます。セメント細砂モルタルも使用されますが、これは、モルタルが送り込まれるまでセメントを浮遊状態に保つために、高速コロイドミキサーで準備されます。モルタルが上昇するにつれて、パイプが徐々に引き抜かれます。モルタルの最上層に外部振動を加えると、露出面の仕上がりを向上させることができます。


 事前配置骨材コンクリートは、均一性と分離リスクの低減という点で好まれており、核シールドの構築や水中プロジェクトに不可欠です。事前配置コンクリートは収縮率と浸透性が低いため、保水構造物、大型モノリシックブロック、および修理作業に使用されます。大規模な建設では、モルタルを追加する前に骨材の周囲に冷却水を循環させて、セメントの水和熱を制御します。対照的に、寒冷条件での凍結損傷を防ぐために蒸気を循環させます。

交換骨材コンクリートは、最初に型枠内に十分に濡れたギャップグレードの粗骨材を配置し、それを圧縮することによって製造されます。
...

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

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 also improves mortar flow. The fluidizing aid delays the setting of the mortar.

A cement and fine sand mortar can also be used. It is mixed in a high-speed colloid mixer so the cement stays suspended until pumping. As the mortar rises to the top, the pipe is slowly withdrawn. External vibration can be applied to the top layer to improve the finish of the exposed surface.

This method is valued for its uniformity and its lower risk of segregation. That makes it useful for nuclear shields and underwater projects. Its low shrinkage and low permeability also support water-retaining structures, large monolithic blocks, and repair work. In large-scale construction, refrigerated water may be circulated around the aggregates to limit heat from cement hydration. In cold conditions, steam may be circulated to help prevent frost damage.

Concrete Placement for Tight Spaces

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

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

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...

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 preplaced aggregate concrete fills hard-to-reach forms with pumped mortar, low segregation, and uses in underwater, repair, and water-retaining projects.

Concrete Placement for Tight Spaces | 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 Placement for Tight Spaces

Description

Transcript