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

Il test di crollo misura la lavorabilità del calcestruzzo e utilizza uno stampo troncoconico alto 12 pollici, che si restringe da otto pollici alla base a quattro pollici nella parte superiore, fissato saldamente a una base piatta prima che il calcestruzzo venga riempito.
Il calcestruzzo viene aggiunto allo stampo inumidito in tre strati, ciascuno compattato 25 volte utilizzando un'asta di rincalzatura in acciaio con un diametro di cinque ottavi di pollice e un'estremità arrotondata. Infine, la superficie superiore viene cancellata.
Dopo il riempimento, il cono viene sollevato delicatamente e il calcestruzzo crolla. Questa diminuzione della sua altezza, chiamata crollo, viene misurata con l'approssimazione di un quarto di pollice.
Un crollo uniforme è chiamato vero crollo, mentre il calcestruzzo che scivola lungo lo stampo indica un crollo a taglio, che richiede un nuovo test. Il persistente cedimento suggerisce che la miscela manca di coesione.
A volte, il calcestruzzo può collassare per le miscele magre, il che evidenzia l'inaffidabilità del test di crollo per le miscele magre.
Il crollo, troppo alto o troppo basso, funge da allerta immediata, sollecitando la correzione del problema con la miscela nel calcestruzzo sfuso. I valori di crollo raccomandati per le diverse lavorabilità sono predeterminati.

prova di abbassamento

La prova di abbassamento, conosciuta anche come Slump Test, è un metodo ampiamente utilizzato per misurare la lavorabilità del calcestruzzo. Utilizza uno stampo a tronco di cono alto 30 centimetri che si assottiglia da 20 centimetri alla base fino a 10 centimetri in cima. Prima del test, lo stampo viene fissato saldamente a una base piana e inumidito.


 Per condurre il test, il calcestruzzo viene versato nello stampo in tre strati. Ogni strato viene compattato 25 volte con una barra di pressatura in acciaio, con diametro di 1,58 centimetri e avente un'estremità arrotondata, al fine di garantire una distribuzione uniforme ed eliminare le sacche d'aria. Dopo la compattazione, la superficie superiore del calcestruzzo viene livellata.


 Una volta riempito lo stampo, esso viene sollevato delicatamente verso l'alto, consentendo al calcestruzzo di cedere verso il basso per effetto della gravità. La diminuzione di altezza del calcestruzzo, definita abbassamento, viene quindi misurata con una precisione di mezzo centimetro. Un abbassamento corretto, in cui il calcestruzzo mantiene la sua forma conica, è detto abbassamento “vero”. Se il calcestruzzo crolla o si allarga, indicando un cedimento di taglio, potrebbe essere necessario ripetere il test poiché suggerisce che la miscela manca di coesione e potrebbe essere problematica per le applicazioni strutturali.


 Valori di abbassamento eccessivamente alti o bassi indicano potenziali problemi nella miscela di calcestruzzo, richiedendone l’aggiustamento. Il test di abbassamento è particolarmente efficace per identificare l'esigenza immediata di correzioni nelle operazioni di calcestruzzo in massa, sebbene possa essere meno affidabile per miscele magre in cui il calcestruzzo tende comunque a collassare. I valori di abbassamento consigliati sono predeterminati in base ai requisiti specifici per diversi tipi di lavorabilità.

Prova di abbassamento

Il test di crollo misura la lavorabilità del calcestruzzo e utilizza uno stampo tronco di cono alto 12 pollici, che si restringe da otto pollici alla base a quattro pollici ...

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Fresh Concrete

Calcestruzzo fresco

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

Description

Transcript

Tags