Name: concrete placement methods and compaction
Uploaded: 2024-11-07T14:48:34.000Z
Duration: 1 min 17 s
Channel: JoVE

Le béton doit être placé près de sa position finale en couches horizontales uniformes.
Après la pose, la couche de béton est entièrement compactée pour expulser l’air emprisonné, et la couche suivante est posée au-dessus d’elle alors qu’elle est encore à l’état plastique pour former une structure monolithique.
Pour les surfaces horizontales ou en pente, le béton est placé verticalement contre la couche existante. Les formulaires sont remplis à un taux minimum de 6 pieds par heure pour une finition uniforme sur les surfaces verticales.
Traditionnellement, le béton est placé à l’aide d’une goulotte, d’un buggy, d’un tuyau ou d’un tapis roulant.
Des méthodes spécialisées, telles que le bétonnage à trémie, utilisent un tuyau lisse et vertical avec des joints étanches pour placer du béton hautement ouvrable dans des coffrages profonds ou sous l’eau.
Le béton à l’intérieur du tuyau s’écoule sous l’effet de la gravité au fur et à mesure qu’il est soulevé, ce qui garantit que son extrémité reste immergée dans le béton, empêchant ainsi l’intrusion d’eau.
Une autre méthode spécialisée pour la mise en place et le compactage en continu du béton peu usinable est la technique de coffrage par glissement, qui utilise des coffrages qui peuvent être avancés horizontalement ou verticalement à un rythme régulier une fois que le béton coulé a été pris.

mise en place du béton

Le béton est placé le plus près possible de sa position finale pour éviter la ségrégation. Le béton placé est ensuite entièrement compacté pour évacuer l'air emprisonné, et la couche de béton suivante est posée pendant que la couche sous-jacente est encore à l'état plastique. La vitesse à laquelle le béton est placé et compacté est maintenue égale.


 Lors de la mise en place du béton, il faut veiller à ce que le béton soit posé en couches uniformes et éviter de pelleter à la main et de déplacer le béton à l'aide de vibrateurs. De plus, les retards considérables dans le remplissage du béton dans les coffrages des structures verticales entraînent la formation de joints froids. Lors de la mise en place du béton dans des sections profondes, il faut éviter toute collision avec le coffrage ou l'armature et, pour les surfaces inclinées, le béton est placé dans des plans verticaux contre la couche précédente.


 Des méthodes telles que des goulottes, des chariots, des bandes transporteuses et le pompage du béton à l'aide de tuyaux sont couramment utilisées pour la mise en place du béton. Cependant, des situations spécifiques peuvent nécessiter des techniques avancées. Le bétonnage par trémie, adapté aux mises en place profondes et sous l'eau, implique un tuyau vertical avec des joints étanches qui permettent au béton de s'écouler par gravité. Au fur et à mesure que le béton est mis en place, le tuyau est soulevé tandis que son extrémité reste immergée dans le béton, empêchant toute intrusion d'eau. En revanche, la technique du coffrage glissant est utilisée pour la mise en place et le compactage continus du béton dans les structures verticales. Les coffrages se déplacent régulièrement vers le haut au fur et à mesure que le béton durcit, ce qui permet une construction rapide.


 La technique de coffrage glissant permet la mise en place et le compactage continus du béton en déplaçant les coffrages de manière constante au fur et à mesure que le béton durcit.

Mise en place du béton

Le béton doit être placé près de sa position finale en couches horizontales uniformes.
Après la pose, la couche de béton est entièrement compactée pour expulser le ...

Education

Enseignement

JoVE Core

Civil Engineering

Génie civil

Unit 1

Unité 1

Mixing, Placing and Curing Concrete 

Mélange, mise en œuvre et cure du béton

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 with poker vibrators is also avoided. In vertical forms, long delays can cause cold joints, which are weak lines where fresh concrete does not bond well with older concrete.

Placement also changes with the shape of the structure. In deep sections, concrete should not strike the formwork or reinforcement. On inclined surfaces, concrete is placed in vertical planes against the previous layer. Common placement methods include chutes, buggies, conveyor belts, and pumping concrete through pipes.

Some conditions need special techniques. Tremie concreting is used for deep and underwater placement. It uses a vertical pipe with water-tight seals so concrete flows by gravity. As concrete is placed, the pipe is lifted, but its end stays buried in the concrete to keep water out. Slip-forming is used for continuous placement and compaction in vertical structures. The forms move steadily upward as the concrete sets, which allows rapid construction.

Concrete Placement Methods and Compaction

concrete-placement-methods-and-compaction

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 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

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 concrete is placed, compacted, and moved into forms using layers, pumps, tremie concreting, and slip-forming for vertical structures.

Concrete Placement Methods and Compaction | 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 Methods and Compaction

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