Concrete Stages: Hydration and Hardening
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Questions and Answers

What is the primary purpose of using supplementary cementitious materials in concrete?

  • To increase the density of concrete
  • To change the color of concrete
  • To reduce the carbon footprint of concrete by reducing portland cement consumption (correct)
  • To increase the strength of concrete

    • What type of materials react chemically with calcium hydroxide to form calcium silicate hydrates?

  • Fly ash
  • Pozzolans (correct)
  • Ground granulated blast furnace slag
  • Supplementary cementitious materials

    • What is the typical size range of fly ash particles?

  • 5 to 500 µm
  • 0.1 to 10 µm
  • 0.5 to 100 µm (correct)
  • 1 to 1000 µm

    • What is the fineness range of fly ash in m²/kg?

    <p>250 to 600 m²/kg</p> Signup and view all the answers

    What is the byproduct of coal-fired thermal power plants used as a supplementary cementitious material?

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

    What is the chemical reaction between pozzolans and calcium hydroxide that contributes to the strength development in concrete?

    <p>Pozzolan + calcium hydroxide → calcium silicate hydrates</p> Signup and view all the answers

    What is the primary reason why sand is usually well graded in a concrete mix?

    <p>To ensure good workability and packing of materials</p> Signup and view all the answers

    What is the primary reason for the higher rate of hydration in cement with higher fineness?

    <p>Larger surface area</p> Signup and view all the answers

    What is the effect of a larger maximum size of aggregate on the concrete mix?

    <p>It reduces the water content required for the concrete</p> Signup and view all the answers

    What is the typical specific surface area range of Rapid Hardening Portland Cement (ASTM Type III)?

    <p>450 to 600 m 2 /kg</p> Signup and view all the answers

    What is the primary purpose of Stage II in the hydration process of concrete?

    <p>To allow for proper mixing, transporting, and placement of concrete</p> Signup and view all the answers

    What is the primary reason why elongated and flaky aggregates are not desirable in concrete?

    <p>They adversely affect the durability and strength of the concrete</p> Signup and view all the answers

    What is the primary cause of the initial set of cement paste?

    <p>Hydration of C 3 A and C 3 S</p> Signup and view all the answers

    What is the main factor that determines the increase in temperature of concrete due to hydration?

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

    What is the primary difference between coarse aggregate and sand in terms of grading?

    <p>Coarse aggregate can be graded or single-sized, while sand is always well-graded</p> Signup and view all the answers

    What is the relationship between the carbon content and the elongation of carbon steel?

    <p>Increasing carbon content results in decreased elongation</p> Signup and view all the answers

    What is the primary purpose of the Vicat needle test (ASTM C191, 2008)?

    <p>To determine the consistency and setting time of cement paste</p> Signup and view all the answers

    What is the characteristic of round aggregates that makes them beneficial in concrete?

    <p>They have a lower water demand</p> Signup and view all the answers

    What is the characteristic of the hydration reaction during Stage III?

    <p>It is rapid and generates significant heat</p> Signup and view all the answers

    What is the purpose of controlling the grading of aggregates in a concrete mix?

    <p>To enhance the workability of the concrete mix</p> Signup and view all the answers

    What is the primary advantage of using angular aggregates in concrete?

    <p>They bond well with the cement paste</p> Signup and view all the answers

    What is the primary consequence of high heat of hydration in massive concrete constructions?

    <p>Thermal cracking</p> Signup and view all the answers

    What happens to the electrical conductivity of the cement paste after the final set?

    <p>It decreases significantly</p> Signup and view all the answers

    What is the classification of coarse aggregates with a density of 3000-5000 kg/m³?

    <p>Heavy weight</p> Signup and view all the answers

    What is the characteristic of a cement with normal consistency?

    <p>A 10 mm diameter plunger penetrates to 4-6 mm from the bottom of the mold</p> Signup and view all the answers

    What is the stage during which the concrete densifies over time?

    <p>Stage V</p> Signup and view all the answers

    What is the primary reason for the decrease in hydration of cement during Stage IV?

    <p>The formation of layers of hydration product covering cement particles</p> Signup and view all the answers

    What is the effect of coarse surface texture on the workability of concrete?

    <p>It reduces the workability</p> Signup and view all the answers

    What is the primary reason why aggregates with a coarse surface texture bond well with the cement paste?

    <p>They have a larger surface area</p> Signup and view all the answers

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