How is compressive strength of concrete tested on the job?

How is compressive strength of concrete tested on the job?

• A. Test samples
• B. Slump test
• C. Core sampling
• D. Rebound number

Answer: (A)

The key idea is that the official measure of concrete’s compressive strength comes from testing specimens molded from the same batch of concrete and then cured under standard conditions. In practice, you cast standard test cylinders (or cubes) from the fresh concrete, keep them moist and curved to the prescribed age, and then place them in a compression testing machine to failure. The result at a specified age (commonly 28 days) represents the concrete’s strength for that batch. Slump testing, while important for workability and placement, does not measure strength. Core sampling is used when you want to estimate the strength of hardened concrete in place, but it’s not the standard method for determining the strength of the mix itself—the strength of those cores is tested, but only after they’re extracted and cured, and it’s used mainly for in-situ verification rather than the designed strength of the freshly mixed concrete. Rebound numbers from a Schmidt hammer are a quick, rough estimate and are not accepted as a substitute for the standard test specimens. So, the best answer is that compressive strength is determined by testing test samples—standard molded specimens cast from the batch and tested in compression after curing.

The key idea is that the official measure of concrete’s compressive strength comes from testing specimens molded from the same batch of concrete and then cured under standard conditions. In practice, you cast standard test cylinders (or cubes) from the fresh concrete, keep them moist and curved to the prescribed age, and then place them in a compression testing machine to failure. The result at a specified age (commonly 28 days) represents the concrete’s strength for that batch.

Slump testing, while important for workability and placement, does not measure strength. Core sampling is used when you want to estimate the strength of hardened concrete in place, but it’s not the standard method for determining the strength of the mix itself—the strength of those cores is tested, but only after they’re extracted and cured, and it’s used mainly for in-situ verification rather than the designed strength of the freshly mixed concrete. Rebound numbers from a Schmidt hammer are a quick, rough estimate and are not accepted as a substitute for the standard test specimens.

So, the best answer is that compressive strength is determined by testing test samples—standard molded specimens cast from the batch and tested in compression after curing.