Massachusetts Construction Supervisor License (CSL) Practice Test

If a concrete cylinder fails under a loading of 50,000 lbs., what is its compressive strength if it's 6 inches in diameter?

1. 2,000 psi

2. 442 psi

3. 1,769 psi

4. 2,500 psi

The correct answer is: 1,769 psi

To find the compressive strength of the concrete cylinder, you need to calculate the area of the cylinder's cross-section and then divide the load by that area. The compressive strength in psi (pounds per square inch) is determined using the formula: \[ \text{Compressive Strength} = \frac{\text{Load}}{\text{Area}} \] First, calculate the area of the circular cross-section of the cylinder. The formula for the area \(A\) of a circle is: \[ A = \pi r^2 \] Given that the diameter of the cylinder is 6 inches, the radius \(r\) is half of the diameter: \[ r = \frac{6}{2} = 3 \text{ inches} \] Now, substitute the radius into the area formula: \[ A = \pi (3^2) = 9\pi \text{ square inches} \] Using the value of \(\pi \approx 3.14\): \[ A \approx 9 \times 3.14 = 28.26 \text{ square inches} \] Next, substitute the load and area into the compressive strength formula: \