Name: cement initial and final set
Uploaded: 2024-09-12T16:16:36.000Z
Duration: 1 min 12 s
Channel: JoVE

시멘트의 응결 시간은 시멘트 페이스트가 플라스틱 상태에서 강성 상태로 변하는 데 걸리는 시간이며, Vicat 장치를 사용하여 결정합니다.
처음에는 시멘트에 물을 넣고 필요한 농도의 페이스트를 준비한 다음 주형에 채웁니다.
그런 다음 직경이 0.04인치인 바늘을 금형 바닥에서 지정된 거리를 관통할 때까지 일정한 시간 간격으로 시멘트 페이스트 속으로 내립니다. 이 인스턴스에 물을 추가하는 데 걸리는 시간은 시멘트의 초기 경화 시간을 제공합니다. 
그 후, 환형 부착물이 있는 바늘은 부착물이 페이스트 표면에 자국을 남기지 않을 때까지 특정 시간 간격으로 시멘트 페이스트 안으로 내려갑니다. 이 인스턴스에 물을 추가한 후 경과된 시간은 시멘트의 최종 응결 시간을 제공합니다.
마지막으로, 미국 표준에 따르면 포틀랜드 시멘트의 초기 경화 시간은 60분 이상이어야 하며 최종 경화 시간은 10시간을 초과해서는 안 됩니다.

시멘트의 응결 시간

시멘트의 응결 시간은 시멘트 페이스트가 플라스틱 상태에서 고체 상태로 전이하는 과정을 말합니다. 이 과정은 콘크리트를 배치하고 압축하며 마감하는 데 필요한 시간을 결정하기 때문에 건설에서 매우 중요합니다. 응결이 처음 시작하는 시기를 초결라고 하며, 페이스트 작업이 불가능해집니다. 종결 시점은 페이스트가 완전히 응고되여 더 이상 취급이나 조작으로 모양에 영향을 미칠 수 없는 시점입니다. 이 단계에서는 삼칼슘 규산염의 수화가 막 시작되기 때문에 시멘트 강도는 아직 미미합니다.

초결 및 종결 시점은 일반적으로 비카트 시험장치를 사용하여 측정합니다. 이 기구는 표준화된 시멘트 페이스트의 바늘이 침투하는 저항성을 평가합니다.

시멘트를 습한 조건에 보관하면 위응결이 발생할 수 있습니다. 혼합 후 몇 분 이내에 시멘트가 빠르게 굳어져 상당한 열을 발생시키지 않는 상황입니다. 마찬가지로, 분쇄된 포틀랜드 시멘트 클링커에 충분한 양의 석고를 첨가하지 않으면 물을 첨가하자마자 삼칼슘의 수화가 빠르게 일어나 열이 급하게 발생하여 즉각적인 응결, 순결이 발생합니다.

시멘트의 응결 시간은 시멘트 페이스트가 플라스틱 상태에서 강성 상태로 변하는 데 걸리는 시간이며, Vicat을 사용하여 결정됩니다.

Education

교육

JoVE Core

Civil Engineering

토목공학

Unit 1

제1단원

Introduction to Concrete

콘크리트 입문

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 tricalcium silicate has only just begun.

Initial and final setting times are usually measured with the Vicat apparatus. This device checks how much resistance a standardized cement paste gives to a needle. Cement can also show false set if it is stored in humid conditions. In this case, it stiffens within minutes after mixing but does not give off much heat.

A different problem is flash set. This can happen when not enough gypsum is added to ground Portland cement clinker. Then tricalcium hydration happens very quickly after water is added. The cement sets almost at once and releases heat rapidly.

Cement Initial and Final Set

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 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 paste changes from plastic to solid, what initial and final set mean, and how the Vicat apparatus measures setting time.

Cement Initial and Final Set | 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 Initial and Final Set

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