Name: cement expansion tests for soundness
Uploaded: 2024-09-12T16:16:36.000Z
Duration: 1 min 17 s
Channel: JoVE

時折、セメントペーストが固まった後、遊離石灰、マグネシア、および硫酸カルシウムが水和し、硬化したセメントに破壊的な膨張を引き起こすことがあります。
健全性は、セメントペーストが硬化後の大幅な膨張に耐える能力です。
ルシャトリエとオートクレーブ加速試験は、セメントの健全性を判断するために使用されます。
ル・シャトリエの試験では、セメントペーストを型に充填し、一定時間水中で保管します。
その後、インジケーター間の距離が測定されます。次に、型を水に浸し、セメントの水和を促進するために指定時間煮沸します。
次に、セットアップを冷却し、インジケーター間の距離を再度測定して、遊離石灰による試験片の膨張を決定します。 
あるいは、オートクレーブ試験では、セメントペースト試験片を調製し、湿った空気中で硬化させます。
試料の長さを測定してから、高圧蒸気加熱用のオートクレーブ内に入れます。
加熱後、試料を冷却し、その長さを測定して、遊離石灰とマグネシアによる膨張を決定します。

利益相反は宣言されていません。

セメントの健全性

Soundness of Cement

セメントの健全性とは、セメントペーストが硬化後に体積を保持する能力を指します。セメントが健全でない場合、遊離石灰、マグネシア、硫酸カルシウムの存在により膨張や構造損傷を引き起こす可能性があります。遊離石灰は水和が非常に遅く、膨張して不健全性を引き起こしますが、他の化合物と結晶化するため検出が困難です。マグネシアも水と反応して結晶を形成し、セメントの構造を乱す可能性があります。硫酸カルシウムはエトリンガイトを生成する可能性があり、硬化プロセス中に十分に消費されないと膨張に繋がります。

一般的なセメントの健全性試験は、ルシャトリエ試験とオートクレーブ試験です。ルシャトリエ試験は主に遊離石灰による不健全性を検出し、オートクレーブ試験は遊離石灰とマグネシアによる不健全性を測定します。オートクレーブ処理後の膨張が元の長さの0.8%を超える場合、セメントは健全でないとみなされます。遊離石灰による不健全性は稀であり、米国産セメントでは、使用される原材料のせいでマグネシウム関連の問題がより多く発生しています。

時折、セメントペーストが固まった後、遊離石灰、マグネシア、および硫酸カルシウムが水和し、硬化した石灰に破壊的な膨張を引き起こす可能性があります...

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 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 structure. Calcium sulfate can form ettringite, which can also lead to expansion if it is not fully consumed during setting.

Two standard tests are used to check cement soundness. Le Chatelier’s test mainly detects unsoundness from free lime. The autoclave test measures unsoundness from free lime and magnesia. If the expansion is more than 0.8% of the original length after autoclaving, the cement may be considered unsound.

Unsoundness from free lime is rare. In the United States, magnesium-related problems are more common in cement because of the raw materials used.

Cement Expansion Tests for Soundness

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

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 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 free lime, magnesia, and calcium sulfate can cause cement expansion, and how Le Chatelier’s and autoclave tests check cement soundness.

Cement Expansion Tests for Soundness | 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 Expansion Tests for Soundness

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