What standard test is used to measure the compressive strength of concrete cylinders?

• A. ASTM C39
• B. ASTM C150
• C. ASTM C1311
• D. ASTM C33

Answer: (A)

ASTM C39 is the standard test method used to determine the compressive strength of cylindrical concrete specimens. In practice, concrete is molded into cylinders (commonly 6 inches in diameter and 12 inches tall), cured under standard conditions (often about 28 days), and then loaded in a hydraulic compression machine along its axis until it fails. The maximum load at failure divided by the cylinder’s cross-sectional area gives the compressive strength, typically reported as psi or MPa (f'c). This standard also specifies how the specimen should be prepared, cured, and loaded, ensuring consistent results that are comparable across tests and laboratories. The other standards listed pertain to different materials or testing aspects (for example, cement specifications or other non-cylinder compression tests), so they do not apply to measuring the compressive strength of concrete cylinders.