ARCH 111 Strength of Materials I: Concrete
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Questions and Answers

What type of cement is preferred for constructions that do not require high early strength?

  • Coloured Cement
  • Sulphate Resisting Cement
  • White Cement
  • Portland Pozzolana Cement (PPC) (correct)

    • What determines the strength of a concrete?

  • Quantity of water
  • Quality of cement
  • Quality of aggregates (correct)
  • Type of construction

    • Who is credited with the invention of concrete?

  • The Egyptians
  • The Chinese
  • The Greeks
  • The Romans (correct)

    • What is the primary use of White Cement?

    <p>Decorative works and prestige construction</p> Signup and view all the answers

    What happens to concrete during the hardening process?

    <p>It shrinks slightly</p> Signup and view all the answers

    What is the percentage of ground pigments added to white cement to produce coloured cement?

    <p>18%</p> Signup and view all the answers

    What is the primary binding mechanism in concrete?

    <p>Chemical reactions</p> Signup and view all the answers

    What is a characteristic of good quality aggregates?

    <p>Clean and strong</p> Signup and view all the answers

    What is the consequence of using aggregates with inert particles?

    <p>Contamination of the cement paste with inert particles</p> Signup and view all the answers

    What is the primary advantage of concrete in construction?

    <p>High compressive strength</p> Signup and view all the answers

    What is the size limit for fine aggregate particles?

    <p>5 mm</p> Signup and view all the answers

    What is the purpose of curing in concrete?

    <p>To keep the concrete moist at a preferred temperature</p> Signup and view all the answers

    What type of cement is used where the concrete will be in contact with water having a high concentration of sulphates?

    <p>Sulphate Resisting Cement</p> Signup and view all the answers

    What is a major disadvantage of concrete?

    <p>Members once cast cannot be easily dismantled</p> Signup and view all the answers

    Why are different types of cement used for specific structures?

    <p>Because they have different properties, such as resistance to corrosion</p> Signup and view all the answers

    What is a characteristic of concrete?

    <p>It has no form of its own</p> Signup and view all the answers

    What should reinforcement be free from?

    <p>Rust and coats of paints, oil, muds or other coating</p> Signup and view all the answers

    What is the diameter range of steel bars used as reinforcement?

    <p>5 to 50 mm</p> Signup and view all the answers

    What is the main requirement of a reinforcing material?

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

    Why does bamboo have high resistance against wind forces?

    <p>Due to its hollow tubular structure</p> Signup and view all the answers

    What should be done to bamboo before using it as reinforcement?

    <p>Test bamboo for the basic strength values as a quality check</p> Signup and view all the answers

    Why is it essential to know the characteristics of different bamboo species?

    <p>To know which species is best for reinforcing and which is not</p> Signup and view all the answers

    What influences the quality of hardened concrete?

    <p>Properties of fresh concrete</p> Signup and view all the answers

    What is the purpose of testing the basic strength values of a reinforcing material?

    <p>To ensure the material meets the quality standards</p> Signup and view all the answers

    What would happen if the two materials, steel and concrete, were chemically incompatible?

    <p>The steel would corrode or the concrete would be degraded</p> Signup and view all the answers

    Why does steel not corrode when in contact with concrete?

    <p>Because the alkaline chemistry of concrete protects the steel</p> Signup and view all the answers

    What is the primary reason for using steel reinforcement in concrete structures?

    <p>To adapt brittle concrete to structural elements that must resist tension, shear, and bending</p> Signup and view all the answers

    What type of forces does the steel reinforcing resist in a structural member?

    <p>Tensile, shear, and bending forces</p> Signup and view all the answers

    What is the shape of the cross-section of a typical steel reinforcing bar?

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

    What is the purpose of the surface ribs on a steel reinforcing bar?

    <p>To improve the bonding to concrete</p> Signup and view all the answers

    What is an alternative material to steel for reinforcing concrete?

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

    What is the primary reason for using bamboo reinforcement?

    <p>Because it is more sustainable than steel</p> Signup and view all the answers

    What is the minimum temperature of fresh concrete in cold weather conditions?

    <p>5 °C</p> Signup and view all the answers

    What is the purpose of air entrainment in concrete?

    <p>To introduce evenly distributed, microscopic air bubbles</p> Signup and view all the answers

    What is the effect of too much air in concrete?

    <p>It reduces the strength of concrete</p> Signup and view all the answers

    What is the approximate air content by volume of fresh concrete for cold weather conditions?

    <p>5.5%</p> Signup and view all the answers

    What is the primary determinant of the use of concrete?

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

    How is the compressive strength of concrete determined?

    <p>By using a hydraulic press</p> Signup and view all the answers

    What is the primary factor affecting the choice of mix design and grade of concrete?

    <p>Exposure conditions and durability</p> Signup and view all the answers

    What type of structure would require a denser and higher grade of concrete?

    <p>A structure subjected to corrosive conditions</p> Signup and view all the answers

    Study Notes

    Concrete

    • Invented by the Romans, concrete is the universal material of construction and the most widely used material on earth, aside from water.
    • Concrete is a rock-like material produced by mixing coarse and fine aggregates, cementing material, water, and other materials (additives and admixtures), and allowing the mixture to harden.
    • The properties of concrete are dependent on several factors, including the amount of cementing material, fine and coarse aggregates, water/cement ratio, temperature, and time of mixing.
    • Concrete is strong in compression and weak in tension, and is also brittle.
    • Concrete shrinks slightly during the hardening process due to excess water evaporation.

    Characteristics of Concrete

    • Only major structural material commonly manufactured on site.
    • Does not burn.
    • Does not rot.
    • Has no form of its own.
    • Has no useful tensile strength.
    • One main disadvantage is that members once cast cannot be easily dismantled.

    Cement

    • Different types of cement are required for specific structures.
    • Some cement types have high resistance to corrosion, while others harden faster than others.
    • Common types of cement used for construction include:
      • PPC (preferred for mass concreting works that do not require high early strength)
      • White Cement (used for decorative works, flooring, and ornamental concrete products)
      • Coloured Cement (produced by adding ground pigments to white cement or OPC, used for designing coloured floors)
      • Sulphate Resisting Cement (used for structures that will be in contact with water with high sulphate concentrations)

    Aggregates

    • Aggregates make up roughly three-quarters of the volume of concrete.
    • The strength of a concrete is heavily dependent on the quality of the aggregates.
    • Aggregates must be:
      • Clean
      • Strong
      • Resistant to freeze-thaw deterioration
      • Chemically stable
      • Properly graded for size distribution
    • Size distribution of aggregate particles is important for achieving close packing of the particles.

    Fine Aggregates

    • Fine aggregates are basically sand or crushed stones.
    • The size of fine particles is not bigger than 5 mm.

    Reinforcing Materials

    • Reinforcement can be:
      • Mild steel bars
      • High yield steel
      • Steel fibres
      • Bamboo reinforcement
    • Steel is generally used because of its easy availability, high strength, and good bond with concrete.
    • Steel reinforcing bars (rebar) are round in cross-section and deformed with surface ribs for better bonding to concrete.

    Steel Reinforcement

    • Different types of steel bars are available, including hot rolled bars, cold twisted bars, and hard drawn steel wire fabrics.
    • Steel reinforcing bars typically have diameters varying from 5 to 50 mm.

    Bamboo Reinforcement

    • Bamboo reinforced concrete construction follows the same design, mix proportions, and construction techniques as used for steel reinforced concrete.
    • Bamboo has high tensile strength, making it a suitable reinforcing material.
    • The structure of bamboo from its origin gives it high resistance against wind forces.

    Properties of Fresh and Hardened Concrete

    • Fresh Concrete:
      • Properties are important because they influence the quality of the hardened concrete.
      • Temperature of fresh concrete should not be less than 5°C in cold weather conditions or exceed 30°C in hot weather conditions.
      • Air content is typically around 1-2% of the volume of fresh concrete.
    • Hardened Concrete:
      • Compressive strength is a major determinant in deciding the particular use of concrete.
      • Compressive strength is typically measured after 28 days.
      • Exposure conditions and durability affect the choice of mix design and the grade of concrete.

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    Description

    This quiz covers the properties and composition of concrete, a widely used construction material invented by the Romans. Learn about the mixture of aggregates, cementing materials, and additives that create this rocklike substance.

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