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

セメントと水が反応して水和生成物が生成されると、水和熱として知られる熱が放出されます。
当初、セメント中のアルミン酸塩とケイ酸塩の水和により、発熱が急速です。水和生成物がケイ酸塩をコーティングすると突然の低下が続き、コーティングの溶解後に残りのケイ酸塩が反応すると徐々に増加し、水和が遅くなると減少して最終的に安定します。
セメント中の化合物は、その水和熱に寄与します。C3Aが最も貢献し、C2Sが最も貢献していません。
ポルトランドセメントの場合、総熱の約50%が1〜3日で、約75%が7日で、約90%が6か月で放出されます。
セメント中のケイ酸塩の水和中に形成されるCSHは、その強度に寄与します。
水和セメントの強度の経時的な変化を考慮すると、C3Sの水和は最初の4週間の強度発現に大きく寄与し、C2Sの水和はその後の強度向上に寄与します。
しかし、約1年で、C3SとC2Sの両方の水分補給が等しく筋力の向上に貢献します。
対照的に、C3AとC4AFの水分補給は強度にほとんど寄与しません。

利益相反は宣言されていません。

強度と水和熱

Strength and Heat of Hydration

セメントの水和は発熱反応であり、セメントが水和すると熱が発生します。この水和熱はセメントの強度発現に不可欠です。この熱の発生速度は温度上昇に影響し、熱の大部分は水和プロセスの初期に放出され、最初の3日以内に半分、最初の1週間以内に約75%が放出されます。

各セメント化合物の水和熱は重要です。たとえば、アルミン酸三カルシウム(C_3A)とケイ酸三カルシウム(C_3S)がこのプロセスに最も寄与します。表1は、C_3S、C_2S、C_2A、C_4Aなどのセメント化合物の水和熱をまとめたものです。これらの化合物の割合を調整することで、セメントの水和中に放出される熱の速度と総量を管理できます。

表1. セメント化合物の水和熱


<table border="1">
 <tbody>
 <tr>
 <td>化合物</td>
 <td>水和熱（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>

水和セメントの強度発現は、主にケイ酸三カルシウム(C_3S)とケイ酸二カルシウム(C_3S)の化合物によって左右されます。C_3Sは水和後の最初の4週間は強度に大きく寄与しますが、C_2Sは特に1年目以降の長期的な強度増加に重要な役割を果たします。1年後、質量比で考えると、両方の化合物は、セメント全体の強度に等しく寄与します。

セメントと水が反応して水和生成物が生成されると、水和熱として知られる熱が放出されます。
当初、発熱が速いのは...

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Introduction to Concrete

コンクリート入門

KEY TERMS AND CONCEPTS

主要用語と概念

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.

civil engineering

Cement Hydration Heat and Strength Gain

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