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

水泥与水反应生成水化产物时会释放热量，这种热量称为水化热。
最初，由于水泥中铝酸盐和硅酸盐的水化反应，热量迅速产生。随后，水化产物包覆在硅酸盐表面，导致反应骤降；之后随着包覆层溶解，残余硅酸盐继续反应，热量逐渐上升；最终水化反应减缓，热量下降并趋于稳定。
水泥中的化合物促使其水化热产生；其中C3A贡献最大，C2S贡献最小。
对于波特兰水泥，大约50%的总热量在1至3天内释放，约75%在7天内释放，近90%在六个月内释放。
水泥中硅酸盐水化过程中形成的水化硅酸钙（C-S-H）有助于其强度的提升。
考虑到水泥水化强度随时间的变化，C3S 的水化在前四周对强度发展贡献较大，而 C2S 的水化则对之后获得的强度起主要作用。
然而，大约一年后，C3S 和 C2S 的水化对强度增长的贡献相当。
相比之下，C3A 和 C4AF 的水化对强度贡献很小。

强度和水化热

Strength and Heat of Hydration

水泥的水化是一种放热反应，在水泥水化过程中会产生热量。水化热对水泥强度的发展至关重要。产生热量的速度会影响温度升高，大部分热量在水化过程的早期释放，一半在前三天释放，约 75% 在第一周释放。

每种水泥化合物的水化热都很大；例如，铝酸三钙 (C_3A) 和硅酸三钙 (C_3S) 对此过程贡献最大。表 1 总结了 C_3S、C_2S、C_2A 和 C_4A 等水泥化合物的水化热。调整这些化合物的比例可以控制水泥水化过程中热量释放的速度和总热量。

表 1. 水泥化合物的水化热

<table border="1">
	<tbody>
		<tr>
			<td>化合物</td>
			<td>水化热（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>

水化水泥的强度发展主要受化合物三钙硅酸盐 (C_3S) 和二钙硅酸盐 (C_3S) 的影响。C_3S 在水化后的最初四周内对强度有显著贡献，而 C_2S 在长期强度增长中起着更重要的作用，尤其是在第一年之后。一年后，从质量角度考虑，这两种化合物对水泥整体强度的贡献相同。

水泥与水反应生成水化产物时会释放热量，这种热量称为水化热。  
最初，由于……，热量的产生速度较快。

Education

教育

JoVE Core

Civil Engineering

土木工程

Unit 1

第一单元

Introduction to Concrete

混凝土简介

KEY TERMS AND CONCEPTS

关键术语与概念

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

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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...

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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...

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...

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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...

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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