Concrete Strength and Maturity
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Questions and Answers

What is the percentage of f c represented by point C in Fig. 3-12a?

  • 110 percent
  • 105 percent
  • 107 percent (correct)
  • 112 percent
  • What type of stress state exists in the webs of beams?

  • Uniaxial tension
  • Biaxial tension–compression (correct)
  • Uniaxial compression
  • Triaxial compression
  • Why is the splitting tensile strength less than the flexural tensile strength?

  • Due to the difference in loading conditions
  • Due to the difference in specimen geometry
  • Due to the difference in material properties
  • Due to the difference in biaxial stress state (correct)
  • What happens to the strength and stiffness of concrete under compression parallel to the cracks in cracked reinforced concrete?

    <p>They decrease</p> Signup and view all the answers

    What is the primary reason why cracking does not represent failure of a reinforced concrete member?

    <p>The reinforcement resists the tensile forces after cracking</p> Signup and view all the answers

    What is the primary cause of failure in zones 1 and 2 in Fig. 3-12?

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

    What is the primary purpose of the relationship shown in Figure 3-8?

    <p>To provide guidance on when forms can be removed</p> Signup and view all the answers

    What is the effect of a very slow rate of loading on the axial compressive strength?

    <p>It reduces the strength to about 75% of the standard test strength</p> Signup and view all the answers

    What is the approximate strain rate experienced during the standard cylinder test?

    <p>10 microstrain/sec</p> Signup and view all the answers

    What is the purpose of capping and testing cores drilled from a structure?

    <p>To determine the compressive strength of concrete</p> Signup and view all the answers

    What is the approximate percentage of the standard test strength reached at a rate of 30,000 psi/sec?

    <p>115%</p> Signup and view all the answers

    What is the primary advantage of using Figure 3-8 for determining when forms can be removed?

    <p>It provides general guidance, but is not a sole determinant of adequate strength</p> Signup and view all the answers

    What type of stress distribution occurs across the vertical diameter of a concrete specimen?

    <p>High transverse compression at the top and bottom, with nearly uniform tension elsewhere</p> Signup and view all the answers

    What is the relationship between the modulus-of-rupture strength and the splitting tensile strength of concrete?

    <p>The modulus-of-rupture strength is 1.5 times the splitting tensile strength</p> Signup and view all the answers

    What is the approximate relationship between the tensile strength and compressive strength of concrete?

    <p>The tensile strength is proportional to the square root of the compressive strength</p> Signup and view all the answers

    What is the typical decrease in strength observed when the volume of concrete under high tension is increased?

    <p>A general decrease in strength, but the exact percentage varies</p> Signup and view all the answers

    What is the equation used to compute the splitting tensile strength of concrete from a split-cylinder test?

    <p>fct = 2P / d</p> Signup and view all the answers

    What is the average ratio of the direct tensile strength to the splitting tensile strength of concrete?

    <p>0.86</p> Signup and view all the answers

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