Cement Setting Time and Factors
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Questions and Answers

What is the main purpose of understanding the physical properties of Portland cement for a materials specialist?

  • To understand the chemical composition of Portland cement
  • To control the quality of civil engineering projects (correct)
  • To ensure the proper production of Portland cement
  • To determine the appropriate mix design for concrete
  • Which of the following is NOT a raw ingredient used in the production of Portland cement?

  • Limestone
  • Sand (correct)
  • Oyster shells
  • Chalk
  • What is the primary purpose of adding admixtures to Portland cement concrete?

  • To improve the setting time (correct)
  • To increase the compressive strength
  • To enhance the aesthetic appearance
  • To reduce the cost of production
  • Which of the following is a characteristic of the mixing water used in Portland cement concrete?

    <p>It should be free from impurities</p> Signup and view all the answers

    How does the addition of admixtures influence the setting time of Portland cement concrete?

    <p>Admixtures can either increase or decrease the setting time, depending on the type of admixture</p> Signup and view all the answers

    What is the primary purpose of understanding the chemical composition of Portland cement for a materials specialist?

    <p>To understand the hydration rates of Portland cement</p> Signup and view all the answers

    What is the purpose of adding gypsum during cement manufacturing?

    <p>To regulate the setting time of the cement</p> Signup and view all the answers

    What is a false set in cement?

    <p>When the cement stiffens within a few minutes of being mixed, without much heat evolution</p> Signup and view all the answers

    How can a false set in cement be resolved?

    <p>By vigorously remixing the cement paste without adding water</p> Signup and view all the answers

    What does the soundness of cement paste refer to?

    <p>The ability of the cement paste to retain its volume after setting</p> Signup and view all the answers

    Which test is used to check the soundness of cement paste?

    <p>The autoclave expansion test</p> Signup and view all the answers

    What factors affect the setting time of cement, apart from the addition of gypsum?

    <p>The fineness of the cement, the water-cement ratio, and the use of admixtures</p> Signup and view all the answers

    What is the purpose of determining the initial and final set times for cement paste?

    <p>To assess the workability and handling characteristics of the concrete mix</p> Signup and view all the answers

    Which test method is described for determining the initial set time of cement paste?

    <p>The Vicat needle test</p> Signup and view all the answers

    How does the Gillmore needle test differ from the Vicat needle test in determining the initial set time?

    <p>The Gillmore test uses a lighter needle and measures the indentation depth</p> Signup and view all the answers

    What is the criterion for determining the final set time using the Vicat needle test?

    <p>When the needle does not penetrate visibly into the paste</p> Signup and view all the answers

    What is the significance of the initial set time in concrete construction?

    <p>It determines the optimal time for concrete placement and finishing</p> Signup and view all the answers

    Which factor can influence the setting times of cement paste?

    <p>All of the above</p> Signup and view all the answers

    Study Notes

    Portland Cement Concrete

    • Portland cement concrete is the most widely used manufactured construction material in the world.
    • It is used in structures such as buildings, bridges, tunnels, dams, factories, pavements, and playgrounds.
    • Portland cement concrete consists of Portland cement, aggregates, water, air voids, and in many cases, admixtures.

    History of Portland Cement

    • Portland cement was patented by Joseph Aspdin in 1824.
    • It was named after the limestone cliffs on the Isle of Portland in England.

    Importance of Understanding Portland Cement

    • Materials specialists should understand the production, chemical composition, hydration rates, and physical properties of Portland cement.

    Portland Cement Production

    • Production of Portland Cement starts with two basic raw ingredients: a calcareous material and an argillaceous material.
    • The calcareous material is a calcium oxide, such as limestone, chalk, or oyster shells.

    Setting of Portland Cement

    • The maximum final set time is specified and measured to ensure normal hydration.
    • Factors that affect the set time include the fineness of the cement, the water-cement ratio, and the use of admixtures.
    • A false set can occur if the cement is exposed to humidity during storage, but it can be remedied by remixing.

    Soundness of Portland Cement

    • Soundness refers to the ability of the cement paste to retain its volume after setting.
    • The autoclave expansion test is used to check the soundness of the cement paste.
    • Expansion after setting can result from delayed or slow hydration or other reactions if the cement is unsound.

    Setting Tests

    • The Vicat test and the Gillmore test are used to determine the initial and final set times of the cement paste.
    • The Vicat test involves measuring the penetration of a needle into the cement paste.
    • The Gillmore test involves applying a needle to the surface of a molded cement paste pat.
    • The initial set time must allow for handling and placing the concrete before stiffening.

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    Description

    Learn about the factors affecting the setting time of cement, including the addition of gypsum, water-cement ratio, fineness of the cement, and use of admixtures. Understand how exposure to humidity can lead to a false set in cement during storage and how to resolve this issue.

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