Massachusetts Unrestricted Construction Supervisor License Practice Test

What is the compressive strength of concrete tested in a standard test cylinder of 6 inch diameter, which fails under a load of 84,700 lbs?

1. 479 psi

2. 749 psi

3. 2,247 psi

4. 2,997 psi

The correct answer is: 2,997 psi

To determine the compressive strength of concrete tested in a standard test cylinder, you can use the formula that relates load, area, and stress: Compressive Strength (psi) = Load (lbs) / Area (in²) For a standard concrete cylinder with a diameter of 6 inches, the area can be calculated using the formula for the area of a circle: Area = π × (radius)² Since the diameter is 6 inches, the radius is 3 inches. Thus, Area = π × (3 in)² Area = π × 9 in² Area ≈ 28.27 in² (using π ≈ 3.14) Now, plugging the numbers into the compressive strength formula gives: Compressive Strength = 84,700 lbs / 28.27 in² Compressive Strength ≈ 2,997 psi This calculation shows that the compressive strength of the concrete cylinder that failed under a load of 84,700 lbs is approximately 2,997 psi. This value corresponds to the correct answer and illustrates how the compressive strength reflects the material's ability to withstand axial loads without failing.