Name: how cement particle size changes behavior
Uploaded: 2024-09-12T16:16:36.000Z
Duration: 1 min 15 s
Channel: JoVE

La curva di distribuzione dimensionale del cemento indica la sua finezza mostrando la proporzione di particelle di dimensioni variabili. La curva sale ripidamente, indicando una porzione significativa di particelle fini. Circa il 90% delle particelle di cemento sono più piccole di 2,36 mil.
L'idratazione del cemento inizia sulla superficie delle particelle di cemento. Più fine è il cemento, maggiore è la superficie, portando a un'idratazione e a uno sviluppo della forza più rapidi.
La finezza del cemento è la superficie totale delle particelle di cemento per unità di peso del cemento.
Il test di permeabilità all'aria di Blaine è comunemente usato per determinare la superficie specifica del cemento.
Per questo, il cemento viene imballato in una cella a una densità specifica e viene creato un vuoto parziale, provocando l'aspirazione di un volume definito di aria attraverso il letto di cemento. Viene misurato il tempo impiegato per questo e viene calcolata la superficie specifica del cemento.
Inoltre, setacciando a secco una massa definita di cemento attraverso un setaccio da 45 micron e misurando il peso del residuo trattenuto sul setaccio si ottiene la finezza del cemento.

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finezza del cemento

La finezza del cemento influenza direttamente la velocità di idratazione, poiché l'idratazione inizia sulla superficie delle particelle di cemento. Oltre all'idratazione, la finezza del cemento è fondamentale per varie proprietà del calcestruzzo, tra cui lavorabilità, fabbisogno di gesso e comportamento a lungo termine. La finezza del cemento è rappresentata in termini di superficie specifica del cemento, che viene solitamente misurata in metri quadrati per chilogrammo. Esistono diversi metodi per determinare questa grandezza.

La misurazione diretta di una superficie specifica può essere effettuata tramite sedimentazione o elutriazione, utilizzando la legge di Stokes per trovare la velocità terminale delle particelle sferiche in un fluido. Un altro metodo è quello del turbidimetro di Wagner, che stima la concentrazione di particelle in una sospensione e misura l'area superficiale delle particelle tramite trasmissione della luce.

Inoltre, vengono utilizzati metodi di permeabilità all'aria come il metodo Lea e Nurse e il metodo Blaine. Il metodo Lea e Nurse misura la caduta di pressione dell'aria che scorre attraverso un letto di cemento, mettendola in relazione alla permeabilità del letto, che fornisce indirettamente l'area superficiale specifica per unità di massa di cemento. Il metodo Blaine, invece, registra il tempo impiegato da un volume noto di aria per attraversare il letto di cemento a una velocità costante, consentendo così anche il calcolo dell'area superficiale specifica.

Finezza del cemento

La curva di distribuzione dimensionale del cemento indica la sua finezza mostrando la proporzione di particelle di dimensioni variabili. La curva sale ripidamente, indicando ...

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

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, depending on the test setup.

Some methods measure the surface area directly. Sedimentation and elutriation use Stokes' law to calculate the terminal velocity of spherical particles in a fluid. The Wagner turbidimeter is another direct approach. It estimates particle concentration in a suspension and uses light transmission to measure particle surface area.

Other methods use air flow through a cement bed. The Lea and Nurse method measures the pressure drop of air and links it to bed permeability, which gives the specific surface area indirectly. The Blaine method measures how long a known volume of air takes to pass through the cement bed at a constant rate. That time is then used to calculate specific surface area.

How Cement Particle Size Changes Behavior

how-cement-particle-size-changes-behavior

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

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

Explore how cement particle size affects hydration, workability, gypsum requirement, and long-term behavior. Learn the main methods used to measure specific surface area.

How Cement Particle Size Changes Behavior | 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

How Cement Particle Size Changes Behavior

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