Massachusetts Construction Supervisor License (CSL) 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. A. 479 psi

2. B. 2,247 psi

3. C. 749 psi

4. D. 2,997 psi

The correct answer is: D. 2,997 psi

To determine the compressive strength of concrete, you first need to calculate the area of the test cylinder and then use the load at which the cylinder fails to find the strength. The compressive strength (psi) is calculated using the formula: \[ \text{Compressive Strength} = \frac{\text{Load}}{\text{Area}} \] 1. **Calculate the area of the cylinder**: The standard test cylinder has a diameter of 6 inches. The radius is half of the diameter, which is 3 inches. The area \(A\) can be calculated using the formula for the area of a circle, \(A = \pi r^2\). \[ A = \pi (3 \text{ inches})^2 = \pi (9 \text{ square inches}) \approx 28.27 \text{ square inches} \] 2. **Calculate compressive strength**: The load at failure is given as 84,700 lbs. Using the area calculated above, the compressive strength can be found as: \[ \text{Compressive Strength} = \frac{84,700 \text{ lbs}}{28.27 \text{ square inches}}