Concrete Technology-I Chapter 2: Cement
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Questions and Answers

What is the primary property of hydraulic cements?

  • Setting and hardening under water (correct)
  • Absorbing water
  • Conducting electricity
  • Resisting water

    • What was the main material used by early Egyptians for cementing?

  • Limestone
  • Gypsum (correct)
  • Shale
  • Chalk

    • Who is credited with the invention of Portland cement?

  • Joseph Aspdin's father
  • Joseph Aspdin (correct)
  • A Roman engineer
  • An Indian architect

    • What was the name 'Portland' attributed to?

    <p>The resemblance of the hardened cement to natural stone</p> Signup and view all the answers

    What was the process used by Joseph Aspdin to create Portland cement?

    <p>Both A and B</p> Signup and view all the answers

    What type of materials does the definition of cement embrace?

    <p>A large variety of cementing materials</p> Signup and view all the answers

    When did Joseph Aspdin take the patent of Portland cement?

    <p>21st October 1824</p> Signup and view all the answers

    What are the two main components of Portland cement?

    <p>Limestone and clay</p> Signup and view all the answers

    What is the general description of cement?

    <p>A material with adhesive and cohesive properties</p> Signup and view all the answers

    What percentage of the dry material becomes liquid in the hottest part of the kiln?

    <p>20 to 30 percent</p> Signup and view all the answers

    What is the resulting product after the dry material undergoes a series of chemical reactions?

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

    What is added to the clinker to prevent flash-setting of the cement?

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

    What is the main difference between the wet and dry processes of cement manufacture?

    <p>The amount of water used</p> Signup and view all the answers

    Which process is more economic due to lower fuel consumption?

    <p>Dry process</p> Signup and view all the answers

    What is the advantage of the wet process in terms of mixing raw materials?

    <p>It is more possible to get a homogeneous mix</p> Signup and view all the answers

    What is the main component of the raw materials used for the manufacture of cement?

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

    What is the reason for the difference in equipment size between the wet and dry processes?

    <p>The friction forces between particles and kiln</p> Signup and view all the answers

    What is the main advantage of the dry process in terms of maintenance?

    <p>It requires less maintenance</p> Signup and view all the answers

    What is the recommended maximum size of particles in a sample of cement?

    <p>100 microns</p> Signup and view all the answers

    What is the average size of cement particles?

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

    What percentage of particles in commercial cement should be less than 7 microns in size?

    <p>25-30%</p> Signup and view all the answers

    What is the main reason for unsoundness in cement?

    <p>Excess of lime (CaO)</p> Signup and view all the answers

    Why are strength tests not made on a neat cement paste?

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

    What is the most commonly used test for determining the strength of cement?

    <p>Compressive strength of sand-cement mortar</p> Signup and view all the answers

    What is the purpose of field testing in cement?

    <p>To check the quality of cement for minor works</p> Signup and view all the answers

    What should be the color of good quality cement?

    <p>Greenish grey</p> Signup and view all the answers

    What should be the texture of cement when felt between the fingers?

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

    What is the minimum time required for complete hydration of cement?

    <p>1 year or more</p> Signup and view all the answers

    What is the approximate depth of hydration of cement grains after 28 days?

    <p>4μ</p> Signup and view all the answers

    What is the maximum size of cement particles that can undergo complete hydration under normal conditions?

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

    What is the product of the reaction of C3S and C2S with water that determines the good properties of concrete?

    <p>Calcium Silicate Hydrates</p> Signup and view all the answers

    What percentage of the volume of solids in a completely hydrated cement paste is made up of Calcium Silicate Hydrates?

    <p>50-60%</p> Signup and view all the answers

    What is the undesirable product of the hydration of C3S and C2S?

    <p>Calcium Hydroxide</p> Signup and view all the answers

    Why is C3S preferred in cold weather concreting?

    <p>It produces more heat of hydration</p> Signup and view all the answers

    What is responsible for the later strength of concrete?

    <p>C2S</p> Signup and view all the answers

    What is the reason for the lack of durability of concrete?

    <p>Presence of Calcium Hydroxide</p> Signup and view all the answers

    What is the characteristic of rapid-hardening Portland cement?

    <p>It has a higher rate of heat development</p> Signup and view all the answers

    What is the difference between rapid-hardening and ordinary cement in terms of setting times?

    <p>Both have similar setting times</p> Signup and view all the answers

    What is the recommended use of rapid-hardening Portland cement?

    <p>In pre-fabricated concrete construction or road repair works</p> Signup and view all the answers

    What is the reason for the increased rate of gain of strength of rapid-hardening Portland cement?

    <p>A higher C3S content and lower C2S content</p> Signup and view all the answers

    What is the characteristic of Type III cements in terms of fineness?

    <p>They have a higher fineness than Type I cement</p> Signup and view all the answers

    What is the purpose of using low heat Portland cement (Type IV)?

    <p>To limit the rate of heat evolution of the cement used in large concrete structures</p> Signup and view all the answers

    In which type of construction is rapid-hardening cement not suitable?

    <p>Mass concrete construction or large structural sections</p> Signup and view all the answers

    What is the benefit of using rapid-hardening Portland cement in cold weather concrete?

    <p>It reduces the vulnerability of concrete to frost damage</p> Signup and view all the answers

    What is the specific use of low heat Portland cement (Type IV)?

    <p>In mass concrete construction, such as dams</p> Signup and view all the answers

    Study Notes

    What is Cement

    • Cement is a material with adhesive and cohesive properties that bonds mineral fragments into a compact whole.
    • Portland cement is a type of cement made from calcareous materials, alumina, and silica found as clay or shale.

    Historical Background

    • The history of cementing materials dates back to ancient Egyptian, Roman, and Indian constructions.
    • Egyptians used cementing materials obtained by burning gypsum.
    • Joseph Aspdin, a Leeds builder and bricklayer, invented Portland cement in 1824.
    • Aspdin's process involved mixing and grinding hard limestone and clay, then calcining it in a furnace, resulting in clinker.

    Manufacturing Process of Cement

    • There are two processes of manufacturing cement: wet process and dry process.
    • Wet process:
      • Slurry contains 35-50% water.
      • More fuel is required due to higher heat.
      • Kiln and equipment are larger.
      • Less maintenance due to low friction forces.
      • Less economic due to high fuel consumption.
    • Dry process:
      • Quantity of water is about 12%.
      • Less fuel is required due to lower heat.
      • Equipment used is smaller.
      • More maintenance required.
      • More economic due to lower fuel consumption.

    Chemical Composition of Portland Cement

    • Raw materials consist mainly of lime, silica, alumina, and iron oxide.
    • Complete hydration cannot be obtained within a year or more.
    • Cement particles should be smaller than 50μ for complete hydration.

    Calcium Silicate Hydrates (C-S-H)

    • Formed during the reaction of C3S and C2S with water.
    • C-S-H is the most important product, making up 50-60% of the volume of solids in a completely hydrated cement paste.
    • C3S produces less C-S-H and more Ca(OH)2 than C2S.
    • C2S hydrates slowly, responsible for later strength, and produces less heat of hydration.

    Calcium Hydroxide (Ca(OH)2)

    • Constitutes 20-25% of the volume of solids in the hydrated paste.
    • Presence of Ca(OH)2 leads to lack of durability in concrete.
    • Maximum particle size should be less than 100 microns, with an average size of about 10 microns.

    Soundness of Cement

    • Cement should not undergo significant volume changes after setting.
    • Unsatisfactory soundness is caused by excess lime (CaO), magnesia (MgO), or excessive proportion of sulphates (CaSo4).

    Strength of Cement

    • Strength tests are usually conducted on cement-sand mortars due to difficulties in testing neat cement paste.
    • Compressive strength is considered crucial, and sand-cement mortar tests are the most appropriate.

    Testing of Cement

    • Field testing includes:
      • Visual inspection for lumps.
      • Checking color (greenish grey).
      • Feeling for temperature (cool).
      • Feeling for smoothness (not gritty).
    • Laboratory testing includes compressive strength tests.

    Types of Portland Cement

    • Rapid-hardening Portland cement (Type III):
      • Develops strength more rapidly.
      • High early strength cement.
      • Not suitable for mass concrete construction or large structural sections due to higher rate of heat development.
    • Low heat Portland cement (Type IV):
      • Developed for use in mass concrete construction, such as dams.
      • Limits rate of heat evolution to prevent cracking.

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    Description

    This quiz covers the basics of cement, its properties, and uses in construction. It's a part of the Concrete Technology-I course for 2nd-year Civil Engineering students.

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