Massachusetts Unrestricted Construction Supervisor License Practice Test

In a standard concrete cylinder, what is the compressive strength of concrete that fails under a loading of 50,000 lbs.?

1. A. 2,000 psi

2. B. 442 psi

3. C. 1,769 psi

4. D. 2,500 psi

The correct answer is: C. 1,769 psi

To find the compressive strength of concrete in a standard concrete cylinder, one must consider the load applied and the cross-sectional area of the cylinder. The compressive strength is calculated with the formula: \[ \text{Compressive Strength (psi)} = \frac{\text{Load (lbs)}}{\text{Area (in}^2)} \] In most instances, a concrete cylinder has a standard diameter of 6 inches, which results in a cross-sectional area of approximately 28.27 square inches (using the formula for the area of a circle: \( \pi r^2 \), where the radius is 3 inches). Here’s the calculation: 1. Calculate the area of the cylinder: - \( \text{Area} = \pi (3)^2 \approx 28.27 \text{ in}^2 \) 2. Use the load provided in the question: - Load = 50,000 lbs 3. Calculate the compressive strength using the formula: - \( \text{Compressive Strength} = \frac{50,000 \text{ lbs}}{28.27 \text{ in}^2} \approx 1,769 \text{ psi} \