Name: choosing well-graded sand for concrete
Uploaded: 2024-11-07T14:48:54.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Biology

BIO.2

BIO.2.D

Design Example: Aggregate Gradation

Il gestore di un impianto di betonaggio deve scegliere tra due impianti di produzione di sabbia fabbricata, A e B, per acquistare sabbia che soddisfi la gradazione richiesta per l'uso nel calcestruzzo.
I campioni di sabbia prodotta dai nastri trasportatori di entrambi gli impianti vengono raccolti dopo l'arresto dei nastri.
Due sagome sono distanziate e inserite nel flusso di sabbia.
L'intero materiale nello spazio tra la dima viene trasferito in un contenitore.
Questo viene ripetuto in altre due posizioni casuali sul nastro.
I campioni raccolti vengono quindi mescolati per formare un campione rappresentativo, etichettati e conservati in forno ad asciugare.
I campioni essiccati vengono divisi in parti uguali utilizzando un divaricatore di sabbia, che vengono poi sottoposti ad analisi al setaccio passando attraverso una serie di setacci standard.
Viene tracciata la curva di gradazione corrispondente.
Si osserva che la curva di gradazione per la sabbia proveniente dall'impianto A si trova all'interno della regione delimitata dai limiti prescritti secondo il progetto del calcestruzzo conglomerato.
Al contrario, la sabbia dell'impianto B cade al di fuori di questa regione. Di conseguenza, il manager decide di acquistare la sabbia prodotta nello stabilimento A.

esempio di progettazione: gradazione degli aggregati

Il tipo e la qualità giusti di aggregati sono cruciali per il calcestruzzo, poiché influenzano significativamente le sue proprietà, le proporzioni della miscela e la convenienza economica. Se sono disponibili diverse fonti di sabbia, l'aggregato fine comunemente utilizzato nel calcestruzzo, la selezione della sabbia si basa principalmente sulla sua gradazione.


 La granulometria, o distribuzione delle dimensioni delle particelle, della sabbia viene determinata tramite analisi al setaccio, con dimensioni standard che vanno da 150 μm a 10 mm (da setaccio UNI EN 0,150 mm a setaccio da 9,52 millimetri). La sabbia viene campionata per la granulometria da un flusso di aggregati in movimento, nastri trasportatori o cumuli di stoccaggio. Un singolo campione rappresenta in genere circa 45.000-50.000 chilogrammi di sabbia. Infine, le porzioni di prova per l'analisi al setaccio vengono ottenute dal campione prelevato sul campo utilizzando un apposito separatore.


 Il calcestruzzo che utilizza sabbie molto fini può essere antieconomico, mentre le sabbie grossolane possono dare origine a miscele meno lavorabili. In genere, nel calcestruzzo si preferisce la sabbia ben graduata, senza grandi carenze o eccessi di qualsiasi dimensione e che fornisca una curva di granulometria uniforme all'interno della regione delimitata dalla curva di granulometria per sabbia fine e grossolana.

Esempio di progettazione: gradazione degli aggregati

Il gestore di un impianto di betonaggio deve scegliere tra due impianti di produzione di sabbia fabbricata, A e B, per acquistare sabbia che soddisfi i requisiti richiesti ...

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Design Examples

Esempi di progettazione

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

choosing well-graded sand for concrete

Well-graded sand is important in concrete because aggregate choice affects strength, mix proportions, and cost. In concrete, sand is the common fine aggregate. When more than one sand source is available, its gradation often guides the selection.

Gradation means the particle-size distribution of the sand. Engineers measure it with sieve analysis, which uses standard sieve sizes from 150 μm to 10 mm, from ASTM No. 100 to the 3/8 in. sieve. This test shows how much sand stays on each sieve and helps compare one source with another.

Sand for gradation testing can be taken from a flowing aggregate stream, conveyor belts, or stockpiles. A single field sample usually represents about 45 to 50 tons of sand. The test portions for sieve analysis are then taken from that field sample with a sample splitter.

Both very fine and very coarse sands can cause problems in concrete. Very fine sands can make the mix uneconomical. Coarse sands can reduce workability, which makes the concrete harder to place and finish.

For this reason, well-graded sand is preferred. It has no major lack or excess of any size and gives a smooth grading curve between the limits for fine and coarse sand. This balance helps concrete perform better and keeps the mix practical to use.

Choosing Well-Graded Sand for Concrete

design example: dimensioning of concrete masonry construction

design-example-dimensioning-of-concrete-masonry-construction

Sizing a Storeroom with Masonry Blocks

Sizing a storeroom with concrete masonry blocks starts with matching the wall plan to the actual block size and mortar joints. The site has concrete masonry units with a nominal size of 8 by 8 by 16 inches. The storeroom is planned with external dimensions of 12 feet long and 8 feet wide. The wall layout uses nine blocks along the length and six blocks along the width. Each block is actually 7 and 5/8 inches high and wide, and 15 and 5/8 inches long. A 3/8 inch mortar joint is included, so the...

design example: joints in concrete pavements

design-example-joints-in-concrete-pavements

Concrete Pavement Joint Types and Functions

Concrete pavement joints guide where slabs crack and help protect the pavement over time. They support the structural integrity and long life of the concrete by controlling movement and cracking. Contraction joints, also called control joints, are made by sawing a groove into the concrete soon after it hardens. This groove creates a weakened vertical plane. It encourages cracking at a planned location instead of letting cracks form randomly across the slab. Isolation joints are used where the...

design example: aggregate gradation

Well-graded sand is important in concrete because aggregate choice affects strength, mix proportions, and cost. In concrete, sand is the common fine aggregate. When more than one sand source is available, its gradation often guides the selection. Gradation means the particle-size distribution of the sand. Engineers measure it with sieve analysis, which uses standard sieve sizes from 150 μm to 10 mm, from ASTM No. 100 to the 3/8 in. sieve. This test shows how much sand stays on each sieve and...

design example: managing concrete workability

design-example-managing-concrete-workability

Concrete Slump Test in Hot Weather

Concrete slump testing helps track workability during a raft foundation pour in hot weather. Workability means fresh concrete is easy to place, compact, and finish. In this example, the concrete had to be prepared for a large foundation, so keeping it workable was important for quality and durability. The first slump test showed low workability. The mix was losing water quickly, and the high temperature made the coarse aggregates hotter as well. To reduce that effect, the site engineer cooled...

design example: distributing reinforcements in concrete sections

design-example-distributing-reinforcements-in-concrete-sections

Sizing Steel Bars for a Concrete Beam

Sizing steel bars for a concrete beam helps meet a required reinforcement area. In reinforced concrete design, the steel must be arranged so the beam stays strong and uses material efficiently. This example uses a beam that needs a total steel cross-section of 4 square inches. The available bars in the example have a nominal diameter of 1.693 inches. Each bar provides a cross-sectional area of 2.25 square inches. When the engineer divides the required area by the area of one bar, the result is...

design example: sustainability in concrete building

design-example-sustainability-in-concrete-building

Green Features in a Concrete Building

A sustainable concrete building can use several green design features to save energy, water, and materials. Concrete is a flexible material for these choices, so it supports eco-friendly construction in commercial buildings. One strategy is to place a concrete parking area under the building. Open areas can use pervious concrete paver blocks, which let rainwater pass through and collect in an underground cistern. That stored water can then be reused for gardening, which improves water...

key terms and concepts

Learn how sand gradation affects concrete mix quality, workability, and cost. See how sieve analysis helps choose well-graded fine aggregate.

Choosing Well-Graded Sand for Concrete | JoVE K12

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Choosing Well-Graded Sand for Concrete

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