Name: special portland cements for durability
Uploaded: 2024-09-12T16:16:36.000Z
Duration: 1 min 22 s
Channel: JoVE

L'intermacinazione del clinker di cemento Portland con le loppe granulate d'altoforno, un sottoprodotto del processo di produzione del ferro, produce cemento di scoria.
Può essere utilizzato per costruire grandi strutture progettate per resistere all'attacco di cloruri e solfati.
Il cemento bianco, composto da gesso e argilla cinese contenente meno quantità di ossidi di ferro e manganese, ha un caratteristico colore bianco e può essere utilizzato per creare facciate con un'estetica eccellente.
L'aggiunta di pigmenti colorati che non sono dannosi per il calcestruzzo con cemento bianco produce cemento colorato.
I cementi espansivi, come i tipi K, M e S, sono prodotti combinando il cemento Portland con un agente espansivo e uno stabilizzante. Ciò impedisce la formazione di fessurazioni da ritiro attraverso l'espansione controllata dovuta alla formazione precoce di ettringite durante l'indurimento.
Il cemento Portland trascinato all'aria utilizza quantità minori di materiali che trascinano l'aria per formare milioni di bolle d'aria microscopiche all'interno della matrice cementizia.
Ciò fornisce spazi in cui l'acqua può espandersi quando si congela, prevenendo le crepe causate dai cicli di gelo-disgelo. 
Il cemento Portland impermeabile incorpora sostanze idrorepellenti, garantendo che le strutture esposte all'umidità siano protette dalle infiltrazioni d'acqua.

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tipi di cemento ii

Types of Cement II

Il cemento Portland d'altoforno è prodotto miscelando clinker di cemento Portland con scorie d'altoforno granulate, con un apporto che va dal 25 al 65 percento del peso del cemento. Nonostante le sue somiglianze con il normale cemento Portland (tipo I) in termini di finezza e tempi di presa, la sua resistenza iniziale è inferiore, sebbene raggiunga una resistenza comparabile in seguito. È particolarmente adatto per strutture in calcestruzzo di massa e ambienti marini grazie al suo calore di idratazione inferiore e alla superiore resistenza ai solfati.

I cementi Portland bianchi e colorati sono utilizzati principalmente dove le considerazioni estetiche sono fondamentali, come pannelli prefabbricati per facciate continue, pannelli di rivestimento, pavimenti in graniglia, stucco, intonaco di finitura e malta per piastrelle. Questi cementi sono più costosi a causa dei severi requisiti di produzione necessari ad evitare impurità e ottenere un colore uniforme.

Il cemento espansivo si espande durante il periodo di indurimento iniziale per compensare il ritiro da essiccazione. Esso è disponibile in tre tipi: K, M e S, che differiscono principalmente nella loro composizione chimica. Il tipo K è progettato per il controllo generale del restringimento, il tipo M è per la resistenza ai solfati e il tipo S è per un'elevata esposizione ai solfati. Ogni tipo è progettato per ridurre al minimo le crepe, contrastando gli effetti del restringimento. Il cemento espansivo è adatto per situazioni che richiedono una variazione minima del volume allo scopo di prevenire le crepe.

Il cemento Portland impermeabile include additivi come stearato di calcio o stearato di alluminio mescolati al clinker di cemento Portland durante la macinazione, migliorando la resistenza del cemento alla penetrazione dell'umidità.

Tipi di cemento II

L'intermacinazione del clinker di cemento Portland con le loppe granulate d'altoforno, un sottoprodotto del processo di produzione del ferro, produce cemento di scoria.
Può essere utilizzato per ...

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Introduction to Concrete

Introduzione al calcestruzzo

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 reaches similar strength later on. It is useful for mass concrete structures and marine environments because it gives off less heat during hydration and resists sulfate better.

White and colored Portland cements are used when appearance matters most. They are common in precast curtain-wall panels, facing panels, terrazzo floors, stucco, finish-coat plaster, and tile grout. These cements cost more because they must be made with careful control to avoid impurities and keep the color uniform.

Expansive cement is made to expand during early hardening so it can offset drying shrinkage. This helps reduce cracking when minimal volume change is important. Three types are available: K, M, and S. Type K is used for general shrinkage control, Type M is made for sulfate resistance, and Type S is for high sulfate exposure.

Waterproof Portland cement is another special type. It includes additives such as calcium stearate or aluminum stearate mixed into the Portland cement clinker during grinding. These additives improve the cement’s resistance to moisture penetration.

Special Portland Cements for Durability

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...

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 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

Explore Portland blast-furnace, white and colored, expansive, and waterproof cements, and see how each type supports strength, appearance, and moisture resistance.

Special Portland Cements for Durability | 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

Special Portland Cements for Durability

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