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

Bei der Reaktion von Zement und Wasser zur Herstellung von Hydratationsprodukten wird Wärme freigesetzt, die als Hydratationswärme bezeichnet wird.
Anfangs erfolgt die Wärmeerzeugung aufgrund der Hydratation von Aluminaten und Silikaten im Zement schnell. Es folgt ein plötzlicher Abfall, wenn Hydratationsprodukte die Silikate überziehen, dann ein allmählicher Anstieg, wenn verbleibende Silikate nach dem Auflösen der Beschichtung reagieren, gefolgt von einer Abnahme und schließlich einer Stabilisierung, wenn sich die Hydratation verlangsamt.
Die Verbindungen im Zement tragen zu seiner Hydratationswärme bei; C3A trägt am meisten bei, und C2S trägt am wenigsten bei.
Bei Portlandzement werden etwa fünfzig Prozent der gesamten Wärme zwischen einem und drei Tagen freigesetzt, etwa fünfundsiebzig Prozent in sieben Tagen und fast neunzig Prozent in sechs Monaten.
Das C-S-H, das bei der Hydratation von Silikaten im Zement gebildet wird, trägt zu seiner Festigkeit bei.
In Anbetracht der Variation der Festigkeit von hydratisiertem Zement im Laufe der Zeit trägt die Hydratation von C3S mehr zur Festigkeitsentwicklung in den ersten vier Wochen bei, während die Hydratation von C2S zu der danach gewonnenen Festigkeit beiträgt.
Nach etwa einem Jahr trägt die Hydratation von C3S und C2S jedoch gleichermaßen zum Kraftzuwachs bei.
Im Gegensatz dazu trägt die Hydratation von C3A und C4AF wenig zur Stärke bei.

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festigkeit und hydratationswärme

Strength and Heat of Hydration

Die Hydratation von Zement ist eine exotherme Reaktion, bei der Wärme freigesetzt wird, wenn Zement hydratisiert. Diese Hydratationswärme ist entscheidend für die Festigkeitsentwicklung von Zement. Die Geschwindigkeit, mit der diese Wärme freigesetzt wird, beeinflusst den Temperaturanstieg, wobei ein Großteil der Wärme früh im Hydratationsprozess freigesetzt wird, die Hälfte innerhalb der ersten drei Tage und etwa 75 % innerhalb der ersten Woche.

Die Hydratationswärme ist für jede Zementverbindung von Bedeutung; beispielsweise tragen Tricalciumaluminat (C_3A) und Tricalciumsilikat (C_3S) am meisten zu diesem Prozess bei. Tabelle 1 fasst die Hydratationswärme für Zementverbindungen wie C_3S, C_2S, C_2A und C_4A zusammen. Durch Anpassen der Anteile dieser Verbindungen können die Geschwindigkeit und die Gesamtmenge der während der Zementhydratation freigesetzten Wärme gesteuert werden.

Tabelle 1. Hydratationswärme für Zementverbindungen

<table border="1">
	<tbody>
		<tr>
			<td>Verbindung</td>
			<td>Hydratationswärme (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>

Die Festigkeitsentwicklung von hydratisiertem Zement wird hauptsächlich von den Verbindungen Tricalciumsilikat (C_3S) und Dicalciumsilikat (C_3S) beeinflusst. C_3S trägt in den ersten vier Wochen nach der Hydratation erheblich zur Festigkeit bei, während C_2S eine wichtigere Rolle bei den langfristigen Festigkeitszuwächsen spielt, insbesondere nach dem ersten Jahr. Nach einem Jahr tragen beide Verbindungen, wenn man sie auf Masse-für-Masse-Basis betrachtet, gleichermaßen zur Gesamtfestigkeit des Zements bei.

Festigkeit und Hydratationswärme

Bei der Reaktion von Zement und Wasser zur Herstellung von Hydratationsprodukten wird Wärme freigesetzt, die als Hydratationswärme bezeichnet wird.
Anfangs ist die Wärmeerzeugung aufgrund der ...

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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

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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...

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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...

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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,...

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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...

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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...

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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...

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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...

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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...

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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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