Name: concrete workability check with slump
Uploaded: 2024-11-07T14:48:28.000Z
Duration: 1 min 20 s
Channel: JoVE

L’essai d’affaissement mesure la maniabilité du béton et utilise un moule à cône tronqué de 12 pouces de haut, se rétrécissant de huit pouces à la base à quatre pouces au sommet, solidement fixé à une base plate avant que le béton ne soit rempli.
Le béton est ajouté au moule humide en trois couches, chacune compactée 25 fois à l’aide d’une tige de bourrage en acier d’un diamètre de cinq huitièmes de pouce et d’une extrémité arrondie. Enfin, la surface supérieure est barrée.
Après le remplissage, le cône est doucement soulevé et le béton s’affaisse. Cette diminution de sa hauteur, appelée affaissement, est mesurée au quart de pouce le plus proche.
Un affaissement uniforme est appelé un véritable affaissement, tandis que le béton qui glisse dans le moule indique un affaissement par cisaillement, qui nécessite de nouveaux tests. Un affaissement persistant suggère que le mélange manque de cohésion.
Parfois, le béton peut s'effondrer pour les mélanges maigres, ce qui met en évidence le manque de fiabilité du test d'affaissement pour les mélanges maigres.
L’affaissement, qu’il soit trop élevé ou trop faible, sert d’alerte immédiate, incitant à la correction du problème avec le mélange dans le bétonnage en vrac. Les valeurs d’affaissement recommandées pour différentes capacités de travail sont prédéterminées.

test d'affaissement

Le test d'affaissement est une méthode largement utilisée pour mesurer l'ouvrabilité du béton. Il utilise un moule en forme de cône tronqué de 30,48 centimètres de haut qui se rétrécit de 20,32 centimètres à la base à 10,16 centimètres au sommet. Avant le test, le moule est solidement fixé sur une base plate et humidifié.


 Le béton est coulé dans le moule en trois couches pour effectuer le test. Chaque couche est compactée 25 fois avec une tige de bourrage en acier, qui a un diamètre de 1.58 centimètres et une extrémité arrondie, pour assurer une distribution uniforme et éliminer les poches d'air. Après le compactage, la surface supérieure du béton est nivelée.


 Une fois le moule rempli, il est soulevé doucement vers le haut, ce qui permet au béton de s'affaisser sous l'effet de la gravité. La diminution de la hauteur du béton, appelée affaissement, est ensuite mesurée à 0,63 centimètre près. Un affaissement correct, où le béton conserve sa forme conique, est un véritable affaissement. Si le béton s'effondre ou s'étale, indiquant un affaissement par cisaillement, le test peut devoir être répété car cela suggère que le mélange manque de cohésion et pourrait être problématique pour les applications structurelles.


 Des valeurs d'affaissement excessivement élevées ou faibles sont des indicateurs de problèmes potentiels dans le mélange du béton, nécessitant des ajustements. Le test d'affaissement est particulièrement efficace pour identifier le besoin immédiat de corrections dans les opérations de bétonnage en vrac, bien qu'il puisse être moins fiable pour les mélanges maigres où le béton a tendance à s'effondrer. Les valeurs d'affaissement recommandées sont prédéterminées en fonction des exigences spécifiques pour différents types d'ouvrabilité.

Test d'affaissement

L’essai d’affaissement mesure l’ouvrabilité du béton et utilise un moule conique tronqué de 12 pouces de haut, se rétrécissant de huit pouces à la base à quatre pouces ...

Education

Enseignement

JoVE Core

Civil Engineering

Génie civil

Unit 1

Unité 1

Fresh Concrete

Béton frais

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Slump Test

concrete workability check with slump

The slump test checks the workability of fresh concrete. Workability means how easy the mix is to place and handle. The test uses a 12-inch-high truncated cone mold that narrows from eight inches at the base to four inches at the top.

Before testing, the mold is fixed to a flat base and dampened. Concrete is added in three layers. Each layer is compacted 25 times with a steel tamping rod that is five-eighths of an inch in diameter and has a rounded end. This helps spread the concrete evenly and remove air pockets. The top surface is then leveled off.

After the mold is full, it is lifted straight up. The concrete drops under gravity, and the drop in height is called the slump. The slump is measured to the nearest quarter inch. If the concrete keeps its cone shape, it is called a true slump.

If the concrete collapses or spreads out, it is a shear slump. That result can mean the mix lacks cohesion and may not work well for structural use. Very high or very low slump values also point to problems in the mix and may require adjustment. The slump test is especially useful for finding quick fixes in bulk concreting work, but it may be less reliable for lean mixes that tend to collapse. Recommended slump values are set ahead of time for the workability needed in each type of job.

Concrete Workability Check with Slump

workability of concrete

Concrete Flow and Compaction Factors

Concrete workability is the ease with which fresh concrete can be mixed, placed, compacted, and finished. It is an important property during construction because it affects how well the material moves into position and how easily it can be shaped. Workability depends on the internal friction within the mix and the resistance it meets from molds and reinforcements. When the ingredients resist one another, concrete moves less easily. The same is true when it has to pass around barriers in the...

factors affecting workability

Concrete Workability and Mix Design Factors

Concrete workability depends on mix design factors that change how easily the material can be mixed, handled, and finished. The mix needs enough flow so it can move and be placed without losing quality. Water is a key part of this because it acts as a lubricant between the ingredients. The amount of water needed can change with the aggregates, or the solid particles in the mix. Finer particles and angular, rough-textured aggregates need more water than smooth, rounded ones because they have...

segregation in fresh concrete

How Concrete Mixes Separate During Placement

Fresh concrete can separate during placement, which changes how the mix is spread and can weaken the finished structure. This separation is called segregation. It happens when the parts of the mix no longer stay evenly blended. Segregation often occurs when concrete moves too much inside a form. It can also happen when the mix is dropped from a great height or pushed through narrow paths with sharp turns. In these cases, the heavier coarse aggregate settles at the bottom, while lighter...

bleeding in fresh concrete

Bleeding Water and Laitance in Fresh Concrete

Bleeding in fresh concrete happens when water from the mix rises to the surface after placement. The solid parts of the mix do not hold all the water as they settle, so separation occurs and water collects on top. Engineers can measure the severity of bleeding by checking total settlement or by noting how much the concrete height drops per unit height. Bleeding can create weak spots inside the concrete. Rising water may get trapped under large aggregate particles or reinforcement bars, which...

slump test

The slump test checks the workability of fresh concrete. Workability means how easy the mix is to place and handle. The test uses a 12-inch-high truncated cone mold that narrows from eight inches at the base to four inches at the top. Before testing, the mold is fixed to a flat base and dampened. Concrete is added in three layers. Each layer is compacted 25 times with a steel tamping rod that is five-eighths of an inch in diameter and has a rounded end. This helps spread the concrete evenly...

compacting factor test

Concrete Workability by Compacting Factor

The compacting factor test measures the workability of concrete. Workability describes how easily concrete can move and fill a mold or form during construction. This test is especially suitable for concrete mixes with aggregates up to one and a half inches in size. The setup uses specialized equipment with two truncated cone-shaped hoppers and a cylinder. All of the inside surfaces are polished to reduce friction. Concrete is first placed into the upper hopper without any compaction. Then the...

vebe test

Concrete Workability with the Vebe Test

The Vebe test measures the workability of concrete, especially for dry mixes. Workability means how easy concrete is to handle and compact. The test uses a cylindrical chamber, a standard slump cone, and a transparent disc-shaped rider mounted on a vibrating table. The cylindrical chamber measures nine and a half inches in diameter and eight inches in height. Concrete is placed into the slump cone in layers and compacted in the standard way. After the cone is removed, the concrete stays in the...

flow table test

Concrete Spread Measured by Flow Table

The flow table test measures how far fresh concrete spreads, which helps assess workability. Workability means how easily concrete can flow and settle under its own weight. The method is useful for highly flowable concrete mixes. The test uses a flow table made from a wooden board with a steel plate on top. Together, the parts weigh 35 pounds. The board is hinged to a base and measures 27.6 inches on each side. A truncated cone mold is also used. It is 8 inches high, with an 8-inch base...

key terms and concepts

Learn how the slump test measures concrete workability using a cone mold, layered filling, tamping, and slump measurement for fresh concrete.

Concrete Workability Check with Slump | 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 Workability Check with Slump

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