Chapter 10: Concrete Construction
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Questions and Answers

What is the purpose of adding admixtures to concrete?

  • To tailor concrete for specific functions (correct)
  • To reduce the compressive strength
  • To decrease the density
  • To increase the tensile strength

    • Which type of concrete has good insulating properties and is fundamentally noncombustible?

  • Gypsum concrete (correct)
  • High early-strength concrete
  • Water-permeable concrete
  • Ordinary stone concrete

    • What is the role of reinforcing steel in concrete?

  • To weaken the concrete structure
  • To increase the permeability of concrete
  • To reduce the density of concrete
  • To add compressive strength (correct)

    • Which method of prestressing concrete uses steel strands stretched between anchors?

    <p>Pretensioning (C)</p> Signup and view all the answers

    What is the ultimate compressive strength range of concrete in psi mentioned in the text?

    <p>$2500$ to $6000$ psi (D)</p> Signup and view all the answers

    What is the significance of the depth of concrete cover around reinforcing bars?

    <p>It protects the bars from corrosion (A)</p> Signup and view all the answers

    When prestressing concrete, what do the initial forces applied aim to achieve?

    <p>To place the concrete in compression (C)</p> Signup and view all the answers

    In post-tensioned concrete, what danger is associated with cutting through reinforcing steel?

    <p>It weakens the post-tensioned element (A)</p> Signup and view all the answers

    What does a superplasticizer do when used with concrete mix?

    <p>+Improves workability and pliability using less water (C)</p> Signup and view all the answers

    Which property does concrete excel in?

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

    What is the main difference between pretensioned and post-tensioned reinforcement?

    <p>Pretensioned reinforcement involves steel strands that are tensioned before the concrete hardens. (C)</p> Signup and view all the answers

    What is the purpose of covering reinforcing strands with grease or plastic tubing in post-tensioning?

    <p>To avoid binding of the strands with the concrete (D)</p> Signup and view all the answers

    Why is precast concrete set in a controlled environment before being shipped to a construction site?

    <p>To ensure that it reaches its design strength before use (D)</p> Signup and view all the answers

    What makes prestressed concrete systems more vulnerable to failure compared to ordinary reinforced concrete?

    <p>They may fail sooner due to the materials used and their design (B)</p> Signup and view all the answers

    How can excessive vibration of concrete affect its quality?

    <p>It may cause water and cement to separate in the mix (D)</p> Signup and view all the answers

    Why is the water-to-cement ratio considered the most important factor in determining concrete strength?

    <p>It influences the ultimate strength of the concrete (A)</p> Signup and view all the answers

    What effect can using sand from an ocean beach have on concrete quality?

    <p>Introduces salt that can corrode reinforcing steel over time (A)</p> Signup and view all the answers

    Why is good quality control important for concrete construction?

    <p>To ensure good strength and durability of structures (D)</p> Signup and view all the answers

    What is done to reinforcing cables after they are anchored at one end during post-tensioning?

    <p>The cables are stretched using a jack at one end. (D)</p> Signup and view all the answers

    What happens to precast concrete members after pouring and setting them according to specifications?

    <p>They are shipped to a construction site for immediate use. (A)</p> Signup and view all the answers

    What is the primary cause of spalling in concrete?

    <p>The expansion of moisture within the concrete (A)</p> Signup and view all the answers

    Which temperature range is ideal for the curing of concrete?

    <p>50F - 70F (10C - 21C) (B)</p> Signup and view all the answers

    How does concrete act as insulation during a fire?

    <p>By retaining and releasing heat slowly (B)</p> Signup and view all the answers

    What is a common form of construction used with precast concrete?

    <p>Tilt-up construction (A)</p> Signup and view all the answers

    What strategy is recommended to minimize complications in the hardening of concrete?

    <p>Pouring concrete in batches (B)</p> Signup and view all the answers

    Which factor affects the fire resistance of a concrete assembly?

    <p>Depth of concrete cover over reinforcing bars (A)</p> Signup and view all the answers

    What is the purpose of compression testing in concrete quality assessment?

    <p>To assess the compression strength of a batch (D)</p> Signup and view all the answers

    What role does proper moisture play in the hardening of concrete?

    <p>Affects the final strength of the concrete (C)</p> Signup and view all the answers

    What is the purpose of proper curing in concrete?

    <p>To keep the concrete moist until it reaches desired strength (B)</p> Signup and view all the answers

    What is the function of a superplasticizer when added to concrete mix?

    <p>Make the concrete more workable with less water (D)</p> Signup and view all the answers

    Which type of concrete reinforcement involves embedding steel reinforcement bars or mesh within the concrete?

    <p>Reinforced concrete (A)</p> Signup and view all the answers

    How does concrete act as insulation during a fire?

    <p>It retains heat and releases it slowly (B)</p> Signup and view all the answers

    What is the primary effect of spalling on concrete?

    <p>Weakens the structure and exposes reinforcing steel (D)</p> Signup and view all the answers

    In prestressing concrete, what does the process aim to achieve by tightening the reinforcing steel?

    <p>Add compressive stresses to the surrounding concrete (B)</p> Signup and view all the answers

    Which type of concrete frame system does not rely on beams for support?

    <p>Flat plate (A)</p> Signup and view all the answers

    Which reinforcement method involves using steel strands stretched between anchors and then placing concrete around them?

    <p>Prestressed reinforcement (A)</p> Signup and view all the answers

    What factor affects the fire resistance of a concrete assembly?

    <p>The density and thickness of the concrete (C)</p> Signup and view all the answers

    What is the main disadvantage of cutting through reinforcing steel during fire fighting operations in reinforced concrete structures?

    <p>Decreases structural stability (B)</p> Signup and view all the answers

    In precast concrete construction, what is a disadvantage of transportation?

    <p>Increased cost due to transportation (D)</p> Signup and view all the answers

    Why is it essential for the design engineer to specify the number, size, and depth of concrete cover around reinforcing bars?

    <p>To ensure adequate strength and durability (C)</p> Signup and view all the answers

    What distinguishes a flat-slab concrete frame from a flat plate system?

    <p>Absence of beams for support (D)</p> Signup and view all the answers

    Which property of concrete makes it vulnerable to failure when exposed to tensile forces?

    <p>Inadequate reinforcing elements (A)</p> Signup and view all the answers

    What role do compression tests play in assessing concrete quality?

    <p>To check compression strength (A)</p> Signup and view all the answers

    What role do aggregates play in the properties of concrete?

    <p>Aggregates provide volume and stability (B)</p> Signup and view all the answers

    What does proper temperature maintenance aim to achieve during concrete curing?

    <p>Avoid excessive heat generation during hydration (A)</p> Signup and view all the answers

    Why is it crucial to avoid cutting through reinforcing steel during firefighting operations in post-tensioned concrete structures?

    <p>It maintains structural integrity under fire conditions (B)</p> Signup and view all the answers

    What is the critical aspect of connecting precast structural components in a building?

    <p>Resisting horizontal forces by lateral tying (A)</p> Signup and view all the answers

    Why is post-tensioned reinforcement preferred over pretensioned reinforcement in terms of assembly life?

    <p>Post-tensioning reduces the risk of concrete corrosion over time. (A)</p> Signup and view all the answers

    What is the primary reason for covering reinforcing strands with grease or plastic tubing in post-tensioning?

    <p>To prevent the strands from bonding with the concrete (D)</p> Signup and view all the answers

    How does improper curing affect the finished surface of concrete?

    <p>It leads to a rough and porous finish. (B)</p> Signup and view all the answers

    What can happen if basic materials such as aggregates used in concrete have a wide range of quality and features?

    <p>The quality of the concrete may vary, impacting its strength and durability. (B)</p> Signup and view all the answers

    In what scenario would poor-quality concrete most likely be used?

    <p>Non-load-bearing applications such as decorative items (B)</p> Signup and view all the answers

    What role does water play in concrete that has an excessive water-to-cement ratio?

    <p>Negatively impacts ultimate strength (A)</p> Signup and view all the answers

    Why are precast and cast-in-place concrete differentiated in terms of design strength development?

    <p>Precast concrete achieves its design strength before placement. (A)</p> Signup and view all the answers

    How does excessive vibration affect concrete quality?

    <p>Causes segregation of materials (A)</p> Signup and view all the answers

    What is a potential consequence of using sand from an ocean beach in concrete production?

    <p>Increased risk of corroding reinforcing steel over time (C)</p> Signup and view all the answers

    Why is it vital to exercise great care in mixing, placing, and curing concrete?

    <p>To guarantee good quality and durability of the final product (A)</p> Signup and view all the answers

    Why can prestressed concrete systems be more vulnerable to failure compared to ordinary reinforced concrete?

    <p>The steel used can yield at lower temperatures (A)</p> Signup and view all the answers

    What is the primary reason for covering reinforcing strands with grease or plastic tubing during post-tensioning?

    <p>To prevent corrosion of the strands (B)</p> Signup and view all the answers

    How does excessive vibration during concrete pouring affect its quality?

    <p>Makes heavy aggregates settle at the bottom (B)</p> Signup and view all the answers

    What is the primary effect of spalling on concrete structures?

    <p>Reduces the durability of the structure (C)</p> Signup and view all the answers

    What role does water-to-cement ratio play in determining concrete strength?

    <p>The single most important factor in determining ultimate strength (B)</p> Signup and view all the answers

    Why is using sand from an ocean beach discouraged in concrete production?

    <p>Introduces salt into the mix, which can corrode steel reinforcement (B)</p> Signup and view all the answers

    What reaction occurs when water is added to cement in concrete mixes?

    <p>Hydration (A)</p> Signup and view all the answers

    What happens if aggregates used in concrete have a wide range of quality and features?

    <p>The quality and durability of the concrete can be compromised (C)</p> Signup and view all the answers

    What is the primary purpose of adding admixtures to concrete?

    <p>Enhancing the workability of the concrete mix (B)</p> Signup and view all the answers

    In what situation is reinforced concrete particularly vulnerable due to its material properties?

    <p>Under tensile forces (A)</p> Signup and view all the answers

    What distinguishes prestressing from ordinary reinforcing in concrete construction?

    <p>Prestressing involves stretching steel strands to preload the concrete while ordinary reinforcing does not (C)</p> Signup and view all the answers

    Why is it essential to avoid cutting through reinforcing steel during firefighting in post-tensioned concrete structures?

    <p>To avoid releasing the post-tensioned element and risking structural failure (B)</p> Signup and view all the answers

    Which process aims to place concrete in compression before applying loads to it?

    <p>Pretensioning (B)</p> Signup and view all the answers

    What is the main purpose of ordinary reinforcing bars (rebar) in concrete construction?

    <p>To resist tensile forces in the structure (D)</p> Signup and view all the answers

    Which type of concrete has a significant advantage due to its good insulating properties and noncombustible nature?

    <p>Gypsum concrete (A)</p> Signup and view all the answers

    What is the purpose of vertical reinforcing bars (stirrups) in concrete construction?

    <p>To provide stability against diagonal tension (D)</p> Signup and view all the answers

    Why is prestressing considered a more efficient use of concrete compared to ordinary reinforcing?

    <p>It places concrete in compression before loads are applied (A)</p> Signup and view all the answers

    What is the purpose of keeping concrete moist during the curing process?

    <p>To help the concrete achieve its desired strength (B)</p> Signup and view all the answers

    What strategy can be used to minimize complications related to heat of hydration in concrete?

    <p>Pour concrete in batches and allow each to cure before adding more (A)</p> Signup and view all the answers

    In fire resistance testing, which type of concrete is considered a better insulator against heat than ordinary concrete?

    <p>Structural lightweight concrete (D)</p> Signup and view all the answers

    What is the primary cause of spalling in concrete when exposed to extreme temperatures?

    <p>Expansion of moisture within the concrete (D)</p> Signup and view all the answers

    Which type of construction involves casting concrete panels on-site and then tilting them into position?

    <p>Tilt-up construction (D)</p> Signup and view all the answers

    What type of structural system consists of a concrete slab supported by closely spaced concrete beams?

    <p>One-way reinforced slab (C)</p> Signup and view all the answers

    In precast concrete construction, what is a significant disadvantage related to transportation?

    <p>It limits the dimensions of precast shapes that can be transported (B)</p> Signup and view all the answers

    What role does heat play in causing structural weaknesses in concrete during a fire?

    <p>Heat generates internal steam pressure (A)</p> Signup and view all the answers

    Which factor contributes to fire-resistance ratings in concrete structural systems?

    <p>Concrete density (B)</p> Signup and view all the answers

    What is the primary reason for using drop panels or mushroom capitals in flat-slab concrete frame construction?

    <p>To prevent shear stresses in the slab (B)</p> Signup and view all the answers

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