At what age are compressive strength tests commonly performed for cured concrete cylinders?

• A. 7 days
• B. 28 days
• C. 14 days
• D. 56 days

Answer: (B)

Concrete strength is most reliably assessed after about 28 days of curing, which is why compressive strength tests on cured cylinders are commonly performed at this age. By 28 days, the cement hydration process has progressed enough that the strength measurement reflects the long-term performance the mix is designed to achieve, and it provides a standardized, repeatable basis for acceptance tests across projects and codes. Early-age tests, like at 7 or 14 days, can show how quickly strength develops and are useful for early decisions or early strength estimates, but they aren’t the standard for acceptance because strength continues to grow and may vary more after 28 days. Testing at 56 days is not typical for routine acceptance because 28 days already gives a stable, widely accepted benchmark.