Which standard is primarily referenced for compression testing of concrete cylinders?

The correct choice highlights the standards that are specifically relevant for the compression testing of concrete cylinders. ASTM C39 is the standard test method for compressive strength of cylindrical concrete specimens, such as cylinders, which are the most common form used for strength testing in concrete construction. This standard provides detailed procedures on how to prepare the specimens, how to conduct the test, and how to report the results.

ACI 318, on the other hand, is a comprehensive code for structural concrete design and construction, which references ASTM C39 but does not provide the specific testing procedures itself. Its relevance lies more in the structural aspects and design requirements rather than the actual testing methodology.

Together, ACI 318 and ASTM C39 form a crucial framework for both the design and quality assurance processes in concrete construction, underscoring the importance of accurate strength testing through ASTM C39 when evaluating concrete cylinders.