Chemistry K0002B 2024 Quiz
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Questions and Answers

Which secondary cementitious material is most recommended for lowering the hydration heat in concrete used for casting in hot weather?

  • Natural clay
  • Silica fume
  • Industrial by-product with high alumina content
  • Ground Granulated Blast furnace slag (correct)

    • What is the primary characteristic of silica fume in concrete?

  • It significantly increases the hydration temperature.
  • It reduces the compressive strength of concrete.
  • It provides strong pozzolanic reactivity. (correct)
  • It is used primarily for lightweight concrete.

    • What type of cement is classified as white cement?

  • Cement specifically made for high-temperature environments.
  • Alkali-activated binder with no alumina.
  • Portland cement that appears white after production. (correct)
  • Portland cement with a gray color.

    • During the hydration of cement, which phases are primarily formed?

    <p>Portlandite and AFm phases</p> Signup and view all the answers

    What is ettringite's role in cement hydration?

    <p>It is the main hydration product under high curing temperatures.</p> Signup and view all the answers

    Which statement accurately describes cement hydration?

    <p>It is a chemical reaction involving the addition of water to Portland cement.</p> Signup and view all the answers

    What is a defining property of natural clay as a cementitious material?

    <p>It generates less heat due to slower reaction rates.</p> Signup and view all the answers

    Which of the following correctly describes the use of silica fume in concrete?

    <p>It can raise the temperature during hydration.</p> Signup and view all the answers

    What should be done if there is snow accumulation and ice formation on reinforcement before casting concrete?

    <p>Casting can be performed but steam must be used to remove all snow and ice</p> Signup and view all the answers

    What happens when CO2 reacts with Portlandite in concrete?

    <p>It forms Calcium Carbonate and lowers the pH.</p> Signup and view all the answers

    What is the recommended action shortly after casting concrete to prevent cracking?

    <p>The surface should be covered with plastic foil or sprayed membranes</p> Signup and view all the answers

    Delayed ettringite formation can occur under which condition?

    <p>The concrete temperature during hydration reached 70°C, and water with sulfates penetrated</p> Signup and view all the answers

    In what area does the corrosion of steel predominantly occur?

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

    What is a result of alkali aggregate reaction?

    <p>Formation of silica-rich gel around reactive aggregates</p> Signup and view all the answers

    What is the primary advantage of a cathodic protection system in concrete structures?

    <p>It prevents and stops corrosion.</p> Signup and view all the answers

    Which zone imposes the biggest threat to concrete durability compared to seawater?

    <p>The permanently immersed zone</p> Signup and view all the answers

    What contributes to frost damage in concrete?

    <p>Both expansion of water during freezing and internal tension from water movement.</p> Signup and view all the answers

    How does CO2 affect the corrosion of reinforcement steel in concrete?

    <p>It makes the steel more susceptible to corrosion.</p> Signup and view all the answers

    What characterizes carbonation of concrete?

    <p>Reaction with atmospheric carbon dioxide leading to pH changes</p> Signup and view all the answers

    What is a potential consequence of the concrete being partially frozen during hydration?

    <p>Delayed setting time and potential for cracking</p> Signup and view all the answers

    Which condition increases the likelihood of cracks in concrete due to the alkali-silica reaction?

    <p>Use of reactive aggregates within the mix</p> Signup and view all the answers

    What is an atom?

    <p>The smallest particle of an element</p> Signup and view all the answers

    Most atoms are classified as which type?

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

    What does the electron octet refer to?

    <p>The tendency of atoms to contain eight electrons in the valence shell</p> Signup and view all the answers

    What role does Portlandite play in the hydration process of cement?

    <p>It stabilizes early hydration products of cement.</p> Signup and view all the answers

    Ionic bonds are formed between which types of ions?

    <p>Two ions with opposite charges</p> Signup and view all the answers

    What type of bonding is primarily found in concrete and other brittle materials?

    <p>Ionic bonds</p> Signup and view all the answers

    What describes a pozzolanic reaction?

    <p>The reaction between pozzolanic material and Portlandite forming CSH.</p> Signup and view all the answers

    Which of the following is a pozzolanic material?

    <p>Fly ash.</p> Signup and view all the answers

    The concept of the 'sea of electrons' is associated with which type of bonding?

    <p>Metallic bonding</p> Signup and view all the answers

    What is the primary function of an air-entraining agent in concrete?

    <p>To create small air voids that improve frost durability.</p> Signup and view all the answers

    In solids, the molecules primarily exhibit which type of movement?

    <p>Vibrate but cannot move</p> Signup and view all the answers

    How does a plasticizer affect the properties of concrete?

    <p>It allows reduction of water while maintaining workability.</p> Signup and view all the answers

    What does elastic deformation refer to?

    <p>Shape change is reversible upon load removal</p> Signup and view all the answers

    What is the minimum temperature considered safe to prevent permanent damage to concrete in winter conditions?

    <p>0 °C.</p> Signup and view all the answers

    Under winter conditions, what is the maximum compressive strength of concrete that can develop due to the presence of ice?

    <p>80 MPa.</p> Signup and view all the answers

    What should be a primary consideration when planning concrete casting during the winter?

    <p>Casting should begin when temperatures are consistently above freezing.</p> Signup and view all the answers

    Study Notes

    Atomic Structure and Bonding

    • An atom is the smallest particle of an element.
    • Most atoms are metals.
    • Electron octet refers to the tendency of atoms to have eight electrons in the valence shell.
    • Ionic bonds form between ions with opposite charges, critical for the stability of various compounds.

    Materials and Their Properties

    • Concrete and other brittle materials mainly consist of ionic bonds.
    • The “sea of electrons” concept applies to metallic bonding, which allows for conductivity and malleability.
    • In solids, molecules can vibrate but cannot move freely.

    Deformation and Structural Integrity

    • Elastic deformation is reversible, allowing materials to return to their original shape once the load is removed.
    • Pure compression can cause failure when atomic bonds are fractured, rather than just increasing repulsion forces.
    • Hooke's law states that deformation is proportional to the applied load within elastic limits.

    Cement and Concrete Chemistry

    • If gypsum isn't added, the cement phase can cause flash set after mixing with water.
    • Silica fume enhances concrete durability and strength, particularly in ultra-high strength applications but might increase temperature during hydration.
    • White cement is a specially produced Portland cement that hardens to a white color and is alkali-activated.

    Hydration and Reaction Products

    • Cement hydration creates various phases, including Portlandite and CSH.
    • Ettringite forms from the reaction of gypsum with tricalcium aluminate, controlling setting times in cement.
    • Pozzolanic reactions involve the interaction of pozzolanic materials with Portlandite, producing CSH.

    Additives and Their Functions

    • Air entraining agents create small air voids in concrete, improving frost resistance and durability.
    • Plasticizers reduce water requirements without compromising the workability or strength of the concrete.

    Temperature Concerns in Concrete Casting

    • A safe minimum temperature for concrete in winter is typically around 0 °C.
    • Post-casting actions include covering the surface to prevent water evaporation and cracking.
    • Delayed ettringite formation can happen if conditions such as high temperature and sulfate presence allow water penetration into concrete.

    Environmental Effects and Durability

    • Alkali aggregate reactions can create expansive gels, threatening structural integrity.
    • The splash zone in seawater poses the greatest threat to concrete durability due to constant exposure.
    • Carbonation lowers pH levels in concrete, resulting in increased susceptibility to corrosion.

    Corrosion Mechanism and Protection

    • Corrosion of steel occurs mainly at anodic areas, with cathodic areas not being directly affected.
    • Cathodic protection systems can prevent and halt corrosion, altering the electrochemical reactions within concrete structures.
    • Frost damage is caused by the expansion of freezing water and the internal stress generated by moisture movement during freeze-thaw cycles.

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    Description

    Test your knowledge of basic chemistry concepts with this quiz designed for K0002B 2024. Questions cover fundamental topics such as atomic structure and the electron octet rule. Ideal for students preparing for their assessments.

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