Name: cement hydration heat and strength gain
Uploaded: 2024-09-12T16:16:35.000Z
Duration: 1 min 29 s
Channel: JoVE

La reazione del cemento con l'acqua per produrre prodotti di idratazione rilascia calore, noto come calore di idratazione.
Inizialmente, la generazione di calore è rapida a causa dell'idratazione degli alluminati e dei silicati nel cemento. Segue un calo improvviso quando i prodotti di idratazione rivestono i silicati, quindi un aumento graduale quando i silicati rimanenti reagiscono dopo la dissoluzione del rivestimento, seguito da una diminuzione e un'eventuale stabilizzazione quando l'idratazione rallenta.
I composti del cemento contribuiscono al suo calore di idratazione; Il C3A contribuisce maggiormente e il C2S il minore.
Per il cemento Portland, circa il cinquanta per cento del calore totale viene liberato tra uno e tre giorni, circa il settantacinque per cento in sette giorni e quasi il novanta per cento in sei mesi.
Il C-S-H formatosi durante l'idratazione dei silicati nel cemento contribuisce alla sua resistenza.
Considerando la variazione della resistenza del cemento idrato nel tempo, l'idratazione del C3S contribuisce maggiormente allo sviluppo della forza durante le prime quattro settimane, mentre l'idratazione del C2S contribuisce alla forza acquisita successivamente.
Tuttavia, entro circa un anno, l'idratazione sia del C3S che del C2S contribuisce ugualmente all'aumento della forza.
Al contrario, l'idratazione di C3A e C4AF contribuisce poco alla forza.

Nessun conflitto di interessi dichiarato.

resistenza e calore di idratazione

Strength and Heat of Hydration

L'idratazione del cemento è una reazione esotermica in cui il calore viene generato quando il cemento si idrata. Questo calore di idratazione è fondamentale per lo sviluppo della resistenza del cemento. La velocità con cui questo calore viene generato influisce sull'aumento della temperatura, con la maggior parte del calore rilasciato all'inizio del processo di idratazione, metà entro i primi tre giorni e circa il 75% entro la prima settimana.

Il calore di idratazione per ogni composto di cemento è significativo; ad esempio, l'alluminato tricalcico (C_3A) e il silicato tricalcico (C_3S) contribuiscono maggiormente a questo processo. La Tabella 1 riassume il calore di idratazione per composti di cemento come C_3S, C_2S, C_2A e C_4A. Regolando le proporzioni di questi composti è possibile gestire la velocità e la quantità totale di calore rilasciato durante l'idratazione del cemento.

Tabella 1. Calore di idratazione per composti di cemento

<div style="text-align: center; display: flex; align-items: center; justify-content: center;">
<table style="text-align: center;" border="1">
	<tbody>
		<tr>
			<td>Composto</td>
			<td>Calore di idratazione (J/kg)</td>
		</tr>
		<tr>
			<td>C_3A</td>
			<td>867</td>
		</tr>
		<tr>
			<td>C_3S</td>
			<td>502</td>
		</tr>
		<tr>
			<td>C_4AF</td>
			<td>419</td>
		</tr>
		<tr>
			<td>C_2S</td>
			<td>260</td>
		</tr>
	</tbody>
</table>
</div>

Lo sviluppo della resistenza del cemento idratato è influenzato principalmente dai composti silicato tricalcico (C_3S) e silicato bicalcico (C_3S). C_3S contribuisce in modo significativo alla resistenza durante le prime quattro settimane dopo l'idratazione, mentre C_2S svolge un ruolo più cruciale nei guadagni di resistenza a lungo termine, specialmente dopo il primo anno. Dopo un anno, entrambi i composti, se considerati su base massa per massa, contribuiscono in egual modo alla resistenza complessiva del cemento.

Resistenza e calore di idratazione

La reazione del cemento con l'acqua per produrre prodotti di idratazione rilascia calore, noto come calore di idratazione.
Inizialmente, la generazione di calore è rapida a causa ...

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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 contribute more heat than others. Tricalcium aluminate, or C3A, and tricalcium silicate, or C3S, are the main contributors. Table 1 shows the heat of hydration for C3A, C3S, C4AF, and C2S. Their values are 867 J/kg, 502 J/kg, 419 J/kg, and 260 J/kg, respectively. By changing the amounts of these compounds, it is possible to control both the rate and the total heat released.

Strength development depends mostly on tricalcium silicate, C3S, and dicalcium silicate, C2S. C3S is important for early strength during the first four weeks after hydration. C2S becomes more important for long-term strength gain, especially after the first year. After one year, both compounds contribute equally to cement strength on a mass-for-mass basis.

Cement Hydration Heat and Strength Gain

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 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 cement hydration releases heat, raises temperature, and drives strength gain. See how C3A, C3S, and C2S affect early and long-term strength.

Cement Hydration Heat and Strength Gain | 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.

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Cement Hydration Heat and Strength Gain

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