Cement Properties and Testing Methods
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Cement Properties and Testing Methods

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Questions and Answers

What causes unsoundness in cement?

  • Excessive application of water during mixing
  • Low temperature during setting
  • Reactions of gypsum with C3A (correct)
  • Rapid hydration of free lime or magnesia

    • What is the limit for autoclave expansion according to ASTM C150?

  • 1.5%
  • 1.0%
  • 0.5%
  • 0.8% (correct)

    • Which of the following tests determines both initial and final setting times of cement?

  • The Vicat Test (correct)
  • The Compressive Strength Test
  • The Slump Test
  • The Shear Test

    • What characterizes the ‘initial set’ of cement?

    <p>The paste is beginning to stiffen considerably</p> Signup and view all the answers

    What is the minimum initial setting time according to the Gillmore needle test?

    <p>60 minutes</p> Signup and view all the answers

    What is defined as the mass of a unit volume of the solids or particles in cement?

    <p>Density</p> Signup and view all the answers

    What is the specific gravity range for cement?

    <p>3.10 to 3.25</p> Signup and view all the answers

    Which test is mostly used to measure the fineness of cement?

    <p>Blaine Air Permeability test</p> Signup and view all the answers

    Which of the following statements accurately describes the relation between fineness of cement and hydration?

    <p>Higher fineness increases the rate of strength development.</p> Signup and view all the answers

    What property measures the ability of a hardened cement paste to retain its volume after setting?

    <p>Soundness</p> Signup and view all the answers

    What is one consequence of using high fineness in cement?

    <p>Increased water required for workability</p> Signup and view all the answers

    How is fineness of cement expressed?

    <p>Specific surface area per unit mass</p> Signup and view all the answers

    What is the typical weight of a commercial bag of cement in Saudi Arabia?

    <p>50 kg</p> Signup and view all the answers

    What is the primary use of Portland cement?

    <p>To produce Portland cement concrete</p> Signup and view all the answers

    Which of the following is not a physical property assessed for Portland cement?

    <p>Compressive strength</p> Signup and view all the answers

    How does the bulk density of cement change?

    <p>It varies based on handling and storage</p> Signup and view all the answers

    What does a higher bulk density of cement typically indicate?

    <p>Lower voids between particles</p> Signup and view all the answers

    What is the significance of measuring cement by mass rather than volume during batching?

    <p>It accounts for variations in bulk density</p> Signup and view all the answers

    Which of the following properties can affect the time of setting of cement?

    <p>Fineness of cement</p> Signup and view all the answers

    What range of values can the bulk density of cement vary between?

    <p>830 to 1650 kg/m3</p> Signup and view all the answers

    Which testing method is used to assess the physical properties of cement as per ASTM standards?

    <p>Laboratory tests</p> Signup and view all the answers

    What is the primary characteristic of false set in concrete?

    <p>Loss of plasticity without much heat evolution</p> Signup and view all the answers

    Which of the following accurately describes flash (quick) set?

    <p>Is accompanied by considerable heat evolution</p> Signup and view all the answers

    What effect does low gypsum content in cement have?

    <p>Causes flash (quick) set</p> Signup and view all the answers

    Which factor does NOT affect the heat of hydration?

    <p>Type of hydraulic cement used</p> Signup and view all the answers

    What is the usual method to measure the consistency of cement paste?

    <p>Flow table (ASTM C230)</p> Signup and view all the answers

    What will happen if gypsum content in cement is too high?

    <p>Potential for false set</p> Signup and view all the answers

    At what stages are hydration heat measurements typically taken?

    <p>7 and 28 days</p> Signup and view all the answers

    What characteristic does the heat of hydration depend on?

    <p>Temperature at which hydration occurs</p> Signup and view all the answers

    What is the diameter of the needle used in the Vicat test for initial setting time?

    <p>1 mm</p> Signup and view all the answers

    According to ASTM C 150, what is the minimum initial setting time for Portland cements?

    <p>60 minutes</p> Signup and view all the answers

    What indicates the final setting time in the Vicat test?

    <p>The needle does not sink visibly into the cement paste</p> Signup and view all the answers

    Which apparatus is less commonly used than the Vicat apparatus?

    <p>Gillmore apparatus</p> Signup and view all the answers

    In the Gillmore test, what signifies the initial setting of cement?

    <p>The left needle fails to penetrate the paste</p> Signup and view all the answers

    What is considered the maximum final setting time for Portland cement according to ASTM C 150?

    <p>10 hours</p> Signup and view all the answers

    What does early stiffening of cement paste refer to?

    <p>Early development of stiffness</p> Signup and view all the answers

    What is the significance of the difference in results between the Vicat and Gillmore tests?

    <p>They assess different stages of setting</p> Signup and view all the answers

    Study Notes

    Cement Properties

    • Portland cement is a fine powder that, when mixed with water, acts as a binder for aggregates in concrete.
    • The quality of Portland cement is assessed based on its physical properties.
    • Bulk density measures the mass of the cement particles and air voids per unit volume.
    • The bulk density of cement varies depending on handling and storage.
    • Cement should be measured by weight for concrete batching due to varying density.
    • Density refers to the mass of a unit volume of cement solids, excluding air.
    • Specific gravity is the ratio of cement density to water density, ranging from 3.10 to 3.25.
    • Fineness refers to the particle size distribution, and it significantly impacts the hydration rate and properties of the cement.
    • Finer cement particles lead to faster strength development, higher heat evolution, and increased water demand for workability.
    • Cement fineness is expressed as the specific surface area, typically in m2/kg.

    Testing Methods for Cement Properties

    • Bulk density: Not a standardized test, but measured using a specific volume container.
    • Density and specific gravity: Determined using a Le Chatelier flask and kerosene or a helium pycnometer.
    • Fineness: Measured using the Wagner Turbidimeter test, Blaine Air Permeability test (most widely used), or by determining the percentage passing through a 0.045mm sieve.
    • Soundness: Evaluated using the ASTM C150 standard test for Autoclave Expansion of Portland Cement, which measures the expansion after autoclaving to detect unsoundness due to excess free CaO or MgO.
    • Time of setting: Determined using the Gillmore needle test or the Vicat test.
    • Consistency: Measured using the Vicat apparatus or the flow table test.
    • Heat of hydration: Measured using ASTM C 186 or conduction calorimetry, and reported in cal/g or kJ/kg.

    Time of Setting and Hardening

    • Initial setting time: The time when the cement paste begins to stiffen and can no longer be molded.
    • Final setting time: The time when the cement paste has hardened enough to sustain a load.
    • Stiffening: The gradual loss of consistency as the cement hydrates.
    • False set: A temporary loss of plasticity due to rapid early stiffening, which can be reversed by further mixing.
    • Flash (quick) set: A sudden and irreversible loss of workability due to rapid and excessive hydration, often caused by insufficient gypsum content.
    • Gypsum's role: Regulates the setting time of cement by slowing down the hydration process.

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    Description

    This quiz covers essential properties of Portland cement and various testing methods used to assess its quality. Topics include bulk density, specific gravity, fineness, and their effects on cement performance. Test your knowledge on how these properties influence concrete batching and hydration rates.

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