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Essai d’étalement à la table à choc
L’essai d’étalement est une méthode établie utilisée pour évaluer l’ouvrabilité du béton, particulièrement utile pour évaluer les mélanges de béton tr…
L’essai sur table d’écoulement, utilisé pour déterminer la maniabilité du béton et évaluer le béton hautement fluide, implique un appareil composé d’une planche de bois surmontée d’une plaque d’acier, d’un poids total de 35 livres.
Une charnière relie la planche à une base, chaque côté de la planche mesurant 27,6 pouces.
La planche supérieure est conçue pour être soulevée à une hauteur de 1,6 pouce, et la table a des marquages spécifiques qui guident l’endroit où le béton doit être placé.
Un cône tronqué de 8 pouces de haut, avec un diamètre de base de 8 pouces et un diamètre supérieur de 5 pouces, est rempli de béton. Il est doucement compacté, l’excès de béton est éliminé et le moule conique est soigneusement retiré après 30 secondes.
La table est secouée 15 fois, chaque secousse étant donnée à 4 secondes d’intervalle, ce qui provoque l’étalement du béton.
La moyenne de l'étendue de l'étalement parallèle aux deux bords de la table, mesurée après secousses, indique l'usinabilité du béton, avec des valeurs spécifiques correspondant à une usinabilité moyenne ou élevée.
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Q1: What is the flow table test used for in concrete testing?
The flow table test assesses the workability of concrete, particularly for highly flowable mixes. It measures how easily concrete spreads and flows under controlled jolting, providing data on the concrete's ability to settle under its own weight. This information determines suitability for construction applications requiring high fluidity and even distribution.
Q2: What are the key components of a flow table apparatus?
The flow table apparatus consists of a wooden board topped with a steel plate, weighing 35 pounds total. The board measures 27.6 inches on each side and connects to a base via a hinge. The upper board lifts to 1.6 inches height during testing. A truncated cone mold, 8 inches high with an 8-inch base and 5-inch top diameter, holds the concrete sample.
Q3: How is concrete prepared and placed in the flow table test?
Concrete is placed in the truncated cone mold and gently compacted to ensure uniform density. Excess concrete is carefully cleared away from the top of the mold. After 30 seconds, the cone mold is carefully removed, leaving the concrete sample on the steel plate ready for jolting.
Q4: What happens during the jolting phase of the flow table test?
The table is jolted 15 times at 4-second intervals by lifting the upper board to 1.6 inches and releasing it. Each jolt causes the concrete to spread outward from its initial cone shape. The controlled jolting simulates the effects of vibration during concrete placement in construction applications.
Q5: How is concrete workability determined from flow table test results?
After jolting completes, the extent of concrete spread is measured parallel to the two edges of the table. The average of these two measurements indicates the concrete's workability. Specific spread values categorize the concrete as having medium or high workability, reflecting its flow characteristics.
Q6: Why is measuring concrete spread important for construction?
Measuring concrete spread reveals how well the material flows and distributes under its own weight. This data ensures the concrete meets project requirements for fluidity and even placement. Understanding spread behavior helps prevent segregation and ensures proper concrete consolidation in structural elements.
Q7: How does the flow table test differ from other concrete workability assessments?
The flow table test specifically evaluates highly flowable concrete through controlled jolting and spread measurement. Unlike other workability tests, it simulates vibration effects during placement. This method provides precise quantitative data on concrete flow behavior, making it ideal for self-consolidating and high-performance concrete mixes.