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

때때로 시멘트 페이스트가 굳은 후 유리 석회, 마그네시아 및 황산칼슘이 수화되어 경화된 시멘트에 파괴적인 팽창을 일으킬 수 있습니다.
건전성은 경화 후 상당한 팽창에 저항하는 시멘트 페이스트의 능력입니다.
Le Chatelier 및 오토클레이브 가속 테스트는 시멘트의 건전성을 결정하는 데 사용됩니다.
르 샤틀리에(Le Chatelier) 테스트에서는 시멘트 페이스트를 주형에 채워 특정 시간 동안 수중에 보관합니다.
그 후 표시기 사이의 거리가 측정됩니다. 다음으로, 곰팡이를 물에 담그고 시멘트 수화를 가속화하기 위해 지정된 시간 동안 끓입니다.
그런 다음 설정을 냉각하고 표시기 사이의 거리를 다시 측정하여 유리 석회로 인한 시편의 팽창을 결정합니다. 
또는 오토클레이브 시험에서는 시멘트 페이스트 시편을 습한 공기에서 준비하고 경화합니다.
시편의 길이는 고압 증기 가열을 위해 오토클레이브 내부에 넣기 전에 측정됩니다.
가열 후, 시편을 냉각시키고 길이를 측정하여 유리 석회와 마그네시아로 인한 팽창을 측정합니다.

시멘트 안정도

Soundness of Cement

시멘트의 안정도는 시멘트 페이스트가 응결 후 부피를 유지하는 능력을 말합니다. 안정성이 불량한 시멘트는 유리 석회, 마그네시아, 황산 칼슘의 존재로 팽창 및 구조적 손상으로 이어질 수 있습니다. 유리 석회는 매우 느리게 수화되어 팽창하고 안정하지 못한 상태를 유발하는데, 이는 다른 화합물과 결정화되기 때문에 감지하기 어렵습니다. 마그네시아는 물과 반응하여 시멘트 구조에 지장을 줄 수 있는 결정을 형성합니다. 황산 칼슘은 에트링가이트를 생성할 수 있으며, 경화 과정에서 적절하게 소모되지 않으면 팽창으로 이어집니다.

시멘트 안정도에 대한 표준 검사는 르 샤틀리에 검사와 오토클레이브 검사가 있습니다. 르 샤틀리에 검사는 주로 유리 석회의 안정도 문제를 감지하며, 오토클레이브 검사는 유리 석회와 마그네시아의 안정도을 측정합니다. 오토클레이브 검사 후 팽창이 원래 길이의 0.8%를 초과하면 시멘트의 안정성이 불량한 것으로 간주될 수 있습니다. 유리석회에 의한 안전성 문제는 드물지만, 미국산 시멘트의 경우 원료로 인해 마그네슘 관련 문제가 더 흔하게 나타납니다.

때때로, 시멘트 페이스트가 굳은 후, 유리 석회, 마그네시아 및 황산 칼슘이 수화되어 경화 된 섬유에 파괴적인 팽창을 일으킬 수 있습니다 ...

Education

교육

JoVE Core

Civil Engineering

토목공학

Unit 1

제1단원

Introduction to Concrete

콘크리트 입문

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

Cement Expansion Tests for Soundness

Description

Transcript