Name: how ready-mixed concrete is delivered
Uploaded: 2024-11-07T14:48:34.000Z
Duration: 1 min 26 s
Channel: JoVE

Le béton qui est préparé dans une installation centralisée, puis livré sur le chantier dans des camions, prêt à être placé, est connu sous le nom de béton prêt à l’emploi ou prémélangé. Il en existe trois types : béton mélangé central, béton mixte pour camions ou transports en commun et béton mélangé rétractable.
Le béton à mélange central subit un dosage et un mélange complet des ingrédients dans l’usine. Il est ensuite transporté sur le site dans un camion agitateur qui tourne entre 2 et 6 tours/min.
Dans le béton mélangé par camion ou par transit, les ingrédients sont mis en lots à l’usine et mélangés dans le camion, en tournant entre 4 et 16 tr/min, soit pendant le transport, soit juste avant le déchargement du béton sur le site.
Le béton rétractable est partiellement mélangé à l’usine et complètement mélangé dans le camion, en tournant entre 4 et 16 tr/min en route vers le site.
Le béton prêt à l’emploi garantit une qualité uniforme grâce à un dosage contrôlé, utilise des camions agitateurs pour éviter la ségrégation et s’adapte à une utilisation sur des sites encombrés ou lorsque le béton est nécessaire par intermittence.
Selon les directives de l'ASTM, le malaxeur du camion ne doit pas dépasser 300 tours pour éviter la ségrégation, et le béton doit être placé dans les 90 minutes suivant le début du mélange.

béton prêt à l'emploi

Ready Mixed Concrete

Le béton prêt à l'emploi, également appelé béton pré-mélangé, est préparé dans une usine centralisée, puis transporté par camion jusqu'aux chantiers de construction où il est prêt à être mis en place. Ce type de béton est classé en béton mélangé en usine, béton mélangé par camion (ou béton de transit) et béton rétractable. Le béton mélangé en usine est entièrement préparé dans une usine et transporté sur le chantier dans des camions agitateurs qui tournent à une vitesse de 2 à 6 tr/min. Le béton de transit, en revanche, contient les ingrédients dosés à l'usine, mais mélangés dans le camion à une vitesse de 4 à 16 tr/min, soit pendant le transport, soit juste avant le déchargement du béton. Le béton rétractable est préparé en dosant les ingrédients et en les mélangeant partiellement à l'usine, puis en les mélangeant complètement dans le camion tournant à une vitesse de 4 à 16 tr/min pendant le transport vers le chantier.


 Le béton prêt à l'emploi est largement utilisé par rapport au mélange sur place, car il est dicté par ses avantages, tels qu'une uniformité améliorée grâce au dosage contrôlé, la capacité à éviter la ségrégation pendant le transport dans des camions agitateurs, l'adéquation aux sites encombrés et aux projets qui nécessitent de petites coulées de béton intermittentes. Les directives de la norme ASTM C 94-05 stipulent que le béton doit être déchargé avant que le camion malaxeur n'ait effectué 300 tours ou dans les 90 minutes suivant le début du mélange pour garantir la qualité du béton.

Béton prêt à l'emploi

Le béton qui est préparé dans une installation centralisée, puis livré sur le chantier dans des camions, prêt à être placé, est connu sous le nom de béton prêt à l’emploi ou ...

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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

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 concrete is batched at the plant but mixed inside the truck. The mixing can happen during transit or just before the concrete is discharged. In this type, the truck rotates at 4 to 16 rpm.

Shrink-mixed concrete is also batched at the plant, but it is only partly mixed there. The truck finishes the mixing while traveling to the site, and it also rotates at 4 to 16 rpm. Ready-mixed concrete is often chosen instead of on-site mixing because controlled batching improves uniformity, agitator trucks help prevent segregation during transport, and it works well for congested sites and for small, intermittent pours.

ASTM C 94-05 gives a time limit for handling this material. The concrete must be discharged before the truck mixer completes 300 revolutions or within 90 minutes from the start of mixing. These limits help protect concrete quality.

How Ready-Mixed Concrete Is Delivered

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

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

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 ready-mixed concrete is batched, mixed, and transported in trucks, plus the three types and the time limits used to protect quality.

How Ready-Mixed Concrete Is Delivered | 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 Ready-Mixed Concrete Is Delivered

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