In a lab, how are concrete cylinders tested?

• A. Cylinders are cured under specified conditions and tested at designated ages (commonly 28 days) for compressive strength
• B. Cylinders are tested fresh for workability
• C. Cylinders are discarded after casting
• D. Cylinders are tested after 6 hours

Answer: (A)

Concrete cylinder strength is determined by curing specimens under controlled conditions and testing them at a specific age, typically 28 days. After casting, cylinders are kept moist and at a steady temperature so hydration proceeds evenly. When the designated age is reached, each cylinder is placed in a compression testing machine and loaded until failure. The maximum load, divided by the cylinder’s cross-sectional area, gives the compressive strength. This standardized approach provides a repeatable, comparable measure of the batch’s strength and is used to verify the mix meets the required design strength. Fresh tests of workability measure different properties and don’t reflect cured strength, while testing too soon (like after a few hours) won’t show meaningful strength development. Casting and discarding cylinders immediately without curing would likewise fail to provide a valid strength result.