Name: concrete materials and reinforcement
Uploaded: 2024-09-12T16:16:35.000Z
Duration: 1 min 20 s
Channel: JoVE

Il calcestruzzo è un materiale strutturale comunemente usato nella costruzione di edifici, ponti, aeroporti, autostrade, dighe e silos.
Il calcestruzzo viene prodotto mescolando proporzioni specifiche di materiali cementizi come il cemento, aggregati fini come la sabbia e aggregati grossolani come la ghiaia con l'acqua. A volte, l'additivo viene anche miscelato per modificare le caratteristiche del calcestruzzo risultante.
In una matrice di calcestruzzo fresco, i vuoti degli aggregati più grandi vengono riempiti da aggregati più piccoli e i vuoti rimanenti vengono riempiti con pasta cemento-acqua, formando un rivestimento sopra gli aggregati.
Questa miscela si indurisce con il tempo fino a diventare una massa rocciosa, forte in compressione e debole in tensione. Di conseguenza, possono essere introdotti rinforzi per rafforzare il calcestruzzo.
La selezione dei materiali, la miscelazione, il trasporto, il posizionamento, la compattazione e l'indurimento determinano le prestazioni del calcestruzzo.
Il calcestruzzo fresco dovrebbe essere lavorabile e, una volta posizionato, gli ingredienti non dovrebbero segregare o spurgare l'acqua.
Generalmente, il calcestruzzo viene prodotto come calcestruzzo preconfezionato, sezioni prefabbricate in calcestruzzo e unità di muratura in calcestruzzo.

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calcestruzzo

Il calcestruzzo è un materiale da costruzione essenziale ampiamente utilizzato in tutto il mondo, apprezzato principalmente per la sua resistenza, durevolezza e versatilità, utili a vari progetti strutturali. Il calcestruzzo generalmente comprende ingredienti come cemento Portland, ghiaia grossolana, sabbia fine e acqua. Il calcestruzzo può essere miscelato con semplici metodi manuali o industrialmente in impianti controllati da computer. La miscela è composta da aggregati e una pasta fatta di acqua e cemento Portland. Questa pasta riveste gli aggregati e, attraverso l'idratazione, una reazione chimica, si indurisce in una massa solida nota come calcestruzzo. Sebbene forte in compressione, il calcestruzzo non ha resistenza alla trazione e necessita di rinforzi in acciaio per una maggiore resistenza a questi sforzi.

La storia del calcestruzzo risale a oltre 2.000 anni fa, quando gli antichi Romani, pionieri nell'uso del calcestruzzo fatto di malta di calce e cenere vulcanica, lo impiegarono in numerose strutture impermeabili. L'era moderna del calcestruzzo iniziò con la riscoperta del suo processo di produzione da parte di Joseph Aspdin nel 1824, che sviluppò quello che oggi è noto come cemento Portland. Nel corso dei secoli, la tecnologia del calcestruzzo si è evoluta, sviluppando vari tipi adatti ad usi specifici, tra cui calcestruzzo preconfezionato per costruzioni comuni, calcestruzzo prefabbricato per qualità e durata controllate e unità di muratura in calcestruzzo per scopi strutturali ed estetici. Oggi, rimane fondamentale per le costruzioni moderne, e viene perfezionato in continuazione attraverso nuovi standard e innovazioni ingegneristiche.

Calcestruzzo

Il calcestruzzo è un materiale strutturale comunemente usato nella costruzione di edifici, ponti, aeroporti, autostrade, dighe e silos.
Il calcestruzzo è prodotto ...

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Introduction to Concrete

Introduzione al calcestruzzo

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

Concrete

concrete materials and reinforcement

Concrete is a major construction material used in buildings, bridges, airfields, highways, dams, and silos. It is valued for strength, durability, and versatility in many structural designs. A concrete mix usually includes Portland cement, coarse gravel, fine sand, and water.

Concrete can be mixed by hand or made at industrial plants with computer control. The mix has aggregates and a paste made from water and Portland cement. This paste coats the aggregates. Through hydration, a chemical reaction, the mix hardens into a solid mass called concrete.

Concrete is strong under compression, which means it resists being squeezed. It is weaker under tension, which means it does not resist pulling forces well. For that reason, steel reinforcement is often added to give concrete extra strength.

Concrete has a long history that goes back more than 2,000 years. The Romans made early concrete from lime mortar and volcanic ash. They used it in many waterproof structures. Modern concrete began in 1824 when Joseph Aspdin rediscovered the process and developed Portland cement.

Over time, concrete technology has expanded to meet different needs. Ready-mix concrete is used for general construction. Pre-cast concrete is made under controlled conditions for quality and durability. Concrete masonry units are also used for structural and aesthetic purposes. Today, concrete remains a basic material in modern construction and continues to be improved through engineering standards and new methods.

Concrete Materials and Reinforcement

concrete

Concrete is a major construction material used in buildings, bridges, airfields, highways, dams, and silos. It is valued for strength, durability, and versatility in many structural designs. A concrete mix usually includes Portland cement, coarse gravel, fine sand, and water. Concrete can be mixed by hand or made at industrial plants with computer control. The mix has aggregates and a paste made from water and Portland cement. This paste coats the aggregates. Through hydration, a chemical...

portland cement

How Portland Cement Is Made

Portland cement is the main binding material in concrete. It is made from finely ground ingredients that include lime, iron, silica, and alumina. These materials give cement the properties it needs to hold concrete together. The raw ingredients come from several common natural sources. Lime is obtained mainly from limestone, marble, marl, seashells, and clays. Those same clays can also supply iron and alumina. Silica is sourced from sand, chalk, and bauxite. Making Portland cement starts by...

hydration of cement

Cement Setting and Strength Formation

Cement setting and strength formation begin when water is added to cement particles. The main reaction is called hydration. During hydration, the anhydrous cement compounds react with water and form new solids that help harden the material. Hydration can happen by two main paths: through-solution and topochemical. In through-solution, anhydrous compounds dissolve into their parts, hydrates form in the liquid, and then they come out of a supersaturated solution. In topochemical hydration,...

strength and heat of hydration

Cement Hydration Heat and Strength Gain

Cement hydration produces heat and builds strength at the same time. Hydration is an exothermic reaction, which means it releases heat as cement reacts with water. That heat of hydration is a key part of how cement develops strength. Most of the heat is released early in the process. About half is given off in the first three days, and about 75% is released in the first week. The rate of heat release also affects how much the temperature rises during hydration. Some cement compounds...

fineness of cement

How Cement Particle Size Changes Behavior

Cement particle size changes how cement behaves in concrete. Finer cement has more surface area, so hydration starts faster at the particle surface. This affects the rate of hardening and also influences workability, gypsum requirement, and long-term behavior. Cement fineness is usually described by its specific surface area. This is the total surface area of cement particles per unit mass, and it is often measured in square meters per kilogram. Several methods can be used to determine it,...

setting time of cement

Cement Initial and Final Set

Cement setting time describes how cement paste changes from a plastic state to a solid state. This change matters in construction because it sets the window for placing, compacting, and finishing concrete. The first stage is called the initial set. At that point, the paste becomes unworkable. The next stage is the final set. By then, the paste has solidified completely, and further handling can no longer change its shape. Cement strength is still very low at this stage because hydration of...

soundness of cement

Cement Expansion Tests for Soundness

Cement soundness is the ability of cement paste to keep its volume after it sets. If cement is unsound, it can expand later and damage a structure. This problem can come from free lime, magnesia, and calcium sulfate in the cement. Free lime hydrates very slowly. As it reacts, it can expand and cause unsoundness. It is also hard to detect because it intercrystallizes with other compounds in the cement structure. Magnesia can also react with water. It forms crystals that may disrupt the cement...

strength of cement

Cement Strength Tests and Standards

Cement strength is measured with standard tests that use mortar, not neat cement paste. Cement paste alone is hard to shape into specimens that give consistent and reliable results. For that reason, the test samples are usually made with cement and sand. For compressive strength, ASTM C 109-05 uses a cement-sand mix ratio of 1:2.75 and a water/cement ratio of 0.485. The mixture is cast into 2-inch cubes and cured in saturated lime water at 23°C until testing. This method measures how well the...

types of cement i

Portland Cement Grades and Uses

Portland cement comes in several grades with different properties and uses. Its chemical composition and hydration behavior help determine how it performs in concrete. These differences matter in general construction, fast repairs, large structures, and places where sulfate exposure is a concern. Type I, or Ordinary Portland Cement, is the common choice for general construction. It is used when special properties are not required. This type has moderate sulfate resistance and moderate heat of...

types of cement ii

Special Portland Cements for Durability

Special Portland cements are made for specific building needs, such as added durability, color, or lower cracking risk. One major example is Portland blast-furnace cement. It is made by blending Portland cement clinker with granulated blast-furnace slag, which makes up about 25 to 65 percent of the cement by weight. Portland blast-furnace cement sets at about the same rate and has about the same fineness as ordinary Portland cement, which is Type I cement. Its early strength is lower, but it...

pozzolans

Pozzolans in Stronger Concrete Mixes

Pozzolans are siliceous or aluminous materials used with Portland cement to improve concrete performance. They react with the calcium hydroxide formed during cement hydration. This reaction helps increase strength and durability. The usefulness of a pozzolan is measured by its pozzolanic activity. One common test is the strength activity index from ASTM C 618-93. It compares the compressive strength of cement mixtures made with and without pozzolan. Fly ash is a common artificial pozzolan. It...

key terms and concepts

Learn how concrete is made, why it is strong in compression, and how steel reinforcement, ready-mix, pre-cast concrete, and CMUs are used in construction.

Concrete Materials and Reinforcement | 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 Materials and Reinforcement

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