Name: concrete fillers that improve performance
Uploaded: 2024-11-07T14:48:38.000Z
Duration: 1 min 29 s
Channel: JoVE

I riempitivi e gli additivi sono materiali a grana fine con una finezza simile al cemento Portland.
Le pozzolane e le scorie d'altoforno, utilizzate come additivi cementizi, migliorano le qualità del calcestruzzo come la lavorabilità e la densità, riducendo al contempo il sanguinamento e la fessurazione.
I riempitivi possono aumentare il processo di idratazione del cemento Portland fornendo punti di nucleazione che formano carbonato di calcio. Questi siti di nucleazione sono osservati nel calcestruzzo con ceneri volanti e particelle di biossido di titanio.
Il carbonato di calcio si fonde con la fase di silicato di calcio idrato, alterando favorevolmente la struttura della pasta cementizia una volta idratata.
I riempitivi possono anche essere derivati da sostanze inorganiche naturali o lavorate ed esercitano principalmente un effetto fisico, come la calce idrata o la polvere di aggregati.
Tipicamente, questi materiali di riempimento fungono da miglioratori di lavorabilità nelle malte e nelle malte da muratura. Anche i pigmenti colorati sono considerati aggiunte inerti.
Quando lo zinco o l'alluminio in polvere vengono introdotti in presenza di idrossido di calcio, producono idrogeno gassoso. Questi materiali, noti come additivi per la formazione di gas, creano calcestruzzo aerato.
Il perossido di idrogeno, un altro esempio, rilascia bolle di ossigeno trattenute all'interno della miscela sabbia-cemento per produrre calcestruzzo aerato.

additivi e riempitivi nel calcestruzzo

Additivi e riempitivi sono parte integrante del miglioramento delle proprietà del calcestruzzo. Pozzolane e scorie d'altoforno sono additivi per via delle loro reazioni con l'idrossido di calcio rilasciato durante l'idratazione del cemento. I riempitivi, che sono finemente macinati e simili per finezza al cemento Portland, migliorano gli attributi del calcestruzzo come la densità di lavorabilità e riducono la perdita capillare o le crepe. Alcuni riempitivi possiedono proprietà idrauliche o partecipano a reazioni benigne all'interno della pasta di cemento.


 Il ruolo dei riempitivi è quello di promuovere l'idratazione del cemento Portland, fornendo siti di nucleazione, un ruolo spesso svolto da ceneri volanti e biossido di titanio, che contribuiscono alla microstruttura della pasta di cemento risultante. I riempitivi possono essere naturali o lavorati ed aventi proprietà costanti, come in particolare la finezza. Non dovrebbero aumentare la richiesta di acqua o influire negativamente sulla durata e la resistenza del calcestruzzo.


 I riempitivi e gli additivi sono per lo più miscelati fisicamente con il cemento e devono essere compatibili. Ad esempio, alcune particelle di cemento molto fini sono essenziali per la resistenza iniziale. Materiali inerti come calce idrata o aggregati di peso normale vengono aggiunti per migliorare la lavorabilità, non la resistenza. Gli additivi che rilasciano idrogeno in presenza di alcali o idrossido di calcio vengono utilizzati per realizzare calcestruzzo gassoso o calcestruzzo aerato, fornendo isolamento termico. Gli additivi che formano gas come il perossido di idrogeno generano bolle di ossigeno nelle miscele di calcestruzzo aerato.

Additivi e riempitivi nel calcestruzzo

I riempitivi e gli additivi sono materiali a grana fine con una finezza simile al cemento Portland.
Pozzolane e scorie d'altoforno, utilizzate come materiali cementizi ...

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Admixtures

Additivi

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

Additives and Fillers in Concrete

concrete fillers that improve performance

Concrete fillers and additives help change how cement paste performs. Pozzolans and blast-furnace slag act as additives or admixtures because they react with calcium hydroxide released during cement hydration. Fine fillers are close in fineness to Portland cement and can improve workability, density, and resistance to capillary bleeding or cracking.

Some fillers are hydraulic, which means they can react with water, while others take part in harmless reactions inside the cement paste. A key role of many fillers is to support Portland cement hydration by giving the paste nucleation sites, or places where new crystals can start forming. Fly ash and titanium dioxide can play this role and help shape the microstructure of the hardened cement paste.

Fillers may be natural or processed, but they should have steady properties, especially fine particle size. They should not raise the water demand of the mix or reduce durability and strength. In concrete, fillers and additives are usually mixed in physically, so they must be compatible with the cement system.

Very fine cement particles can also matter for early strength. Inert materials such as hydrated lime or normal-weight aggregates may be added to improve workability rather than strength. Some additives release hydrogen in the presence of alkalis or calcium hydroxide and are used to make gas concrete, also called aerated concrete, which provides thermal insulation. Gas-forming admixtures such as hydrogen peroxide can create oxygen bubbles in aerated concrete mixes.

Concrete Fillers That Improve Performance

concrete-fillers-that-improve-performance

accelerators

Calcium Chloride in Concrete Mixes

Calcium chloride is a concrete admixture that speeds up hardening and helps concrete gain early strength faster. It does not always change the setting time itself, but it can reduce the time needed in practice. This makes it useful in cold weather and in rapid repair work where quick heat generation after mixing is helpful. A common amount is 1 to 2 percent of the cement mass. Its effect can be compared with raising the concrete temperature by 11 degrees Fahrenheit. To spread it evenly through...

retarders

Retarders in Concrete Pouring

Retarders are chemical admixtures used in concrete to slow the setting time. They are especially helpful when one pour must follow another after a delay. By keeping the concrete workable for longer, they can help prevent cold joints and support a more cohesive structure. Retarders can also improve the look of exposed aggregate finishes when they are used in the right amount. Their effect on setting time can be checked with a penetration test. Common retarding substances include sugar,...

plasticizers

Concrete Workability with Plasticizers

Concrete plasticizers are water-reducing chemical admixtures that improve workability and strength. They help concrete use less water while keeping the same flow, reduce cement content without losing workability, or make mixes easier to place in hard-to-reach areas. Plasticizers work by using surface-active agents. These agents create repulsive electrostatic forces between cement particles. The particles disperse more evenly, and the concrete needs about 5 to 15 percent less mixing water. <br...

superplasticizers

Superplasticizers for Stronger Concrete Mixes

Superplasticizers are concrete admixtures that make mixes flow better while using less water. They are strong water reducers, so concrete can be easier to place without losing strength. This makes them useful when concrete must reach tight spaces or heavily reinforced areas without mechanical vibration. These admixtures work through sulfonated melamine or naphthalene formaldehyde condensates. These chemicals give cement particles a negative charge. The particles repel each other and spread out...

additives and fillers in concrete

Concrete fillers and additives help change how cement paste performs. Pozzolans and blast-furnace slag act as additives or admixtures because they react with calcium hydroxide released during cement hydration. Fine fillers are close in fineness to Portland cement and can improve workability, density, and resistance to capillary bleeding or cracking. Some fillers are hydraulic, which means they can react with water, while others take part in harmless reactions inside the cement paste. A key...

waterproofing and anti-bacterial admixtures in concrete

waterproofing-and-anti-bacterial-admixtures-in-concrete

Concrete Water Resistance and Biological Protection

Concrete can absorb water because of capillary action in the pores of its hydrated cement paste. That movement pulls water into the material. Waterproofing admixtures are added to reduce this penetration and help concrete resist water. The effect of a waterproofing admixture depends on the water pressure acting on the concrete. Rain, capillary rise, and hydrostatic pressure in structures made to hold water can all affect performance. These admixtures make concrete hydrophobic, which means they...

key terms and concepts

Learn how concrete fillers and additives affect workability, density, early strength, cracking, and aerated concrete through simple, science-based examples.

Concrete Fillers That Improve Performance | 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 Fillers That Improve Performance

Description

Transcript

Tags