Name: shotcrete for vertical and overhead surfaces
Uploaded: 2024-11-07T14:48:35.000Z
Duration: 1 min 18 s
Channel: JoVE

Le béton projeté consiste à pulvériser du mortier ou du béton en petits agrégats riches en mortier à travers un tuyau à grande vitesse sur une surface généralement renforcée.
L’impact du jet à grande vitesse sur la surface compacte le matériau, facilitant son adhérence sur des surfaces verticales ou aériennes.
Le béton projeté est pulvérisé et stratifié progressivement pour atteindre une épaisseur d’environ 4 pouces. L'habileté de l'opérateur dans la gestion de la buse est cruciale pour garantir la qualité du béton projeté. 
L’application du béton projeté à l’aide de la méthode du mélange sec consiste à mélanger d’abord du ciment et des agrégats humides, puis à introduire le mélange dans un alimentateur et à le propulser à travers un tuyau à l’aide d’un jet d’air comprimé.
Une fois la buse de refoulement atteinte, de l’eau sous pression est injectée dans le mélange sec, le transformant en béton humide prêt à être pulvérisé.
Dans le processus de béton projeté humide, les ingrédients secs et l’eau sont mélangés avant d’être chargés dans l’équipement de livraison.
Ce mélange humide est ensuite transporté pneumatiquement à travers un tuyau, et au niveau de la buse de refoulement, de l’air comprimé est introduit pour augmenter la vitesse à laquelle le mélange est projeté.

béton projeté

Le béton projeté est une technique spécialisée dans laquelle du mortier ou du béton à granulats fins riche en ciment est pulvérisé sur une surface à grande vitesse. La force de l'impact compacte le matériau et lui permet de s'accrocher aux zones verticales ou en hauteur sans s'affaisser. La technique consiste à superposer le béton projeté par étapes jusqu'à ce qu'il atteigne une épaisseur d'environ 10,16 centimètres. La compétence de l'opérateur dans la gestion des buses est essentielle pour déterminer la qualité du béton projeté. Le béton projeté est utilisé dans la construction de revêtements de tunnels, de coques et de toits plats, de réservoirs en béton précontraint, de stabilisation de pentes, de construction de piscines et de restauration de structures en béton détériorées.


 Il existe deux méthodes principales pour appliquer le béton projeté, à savoir le mélange sec et le mélange humide. La méthode du mélange sec commence par combiner du ciment avec des agrégats humides. Ce mélange est ensuite placé dans un alimentateur et propulsé à travers un tuyau par de l'air comprimé. Lorsqu'il arrive à la buse de distribution, de l'eau sous pression est ajoutée au mélange sec, le transformant en béton humide qui est ensuite pulvérisé sur la structure. À l'inverse, le processus de mélange humide consiste à pré-mélanger tous les ingrédients, y compris l'eau, avant de les charger dans le système de distribution. Ce béton humide pré-mélangé est transporté pneumatiquement à travers un tuyau jusqu'à la buse, où de l'air comprimé est injecté pour augmenter la force avec laquelle le béton projeté est appliqué sur la surface.

Béton projeté

Le béton projeté consiste à pulvériser du mortier ou du béton en petits agrégats riches en mortier à travers un tuyau à grande vitesse sur une surface qui est généralement 
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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

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 is used for tunnel linings, shell and flat roofs, pre-stressed concrete tanks, slope stabilization, swimming pools, and repairing damaged concrete structures. These uses show why the method is useful for both new construction and restoration.

There are two main application methods: dry mix and wet mix. In dry mix, cement is first combined with moist aggregate, then sent through a hose by compressed air. Water is added at the nozzle, which turns the mix into wet concrete just before it is sprayed.

In wet mix, all ingredients, including water, are blended before they enter the delivery system. The pre-mixed wet concrete is moved pneumatically through a hose to the nozzle. There, compressed air is injected to increase the force of application onto the surface.

Shotcrete for Vertical and Overhead Surfaces

shotcrete-for-vertical-and-overhead-surfaces

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 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 shotcrete is sprayed onto vertical and overhead surfaces, how dry mix and wet mix methods work, and where this concrete technique is used.

Shotcrete for Vertical and Overhead Surfaces | 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

Shotcrete for Vertical and Overhead Surfaces

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