The sample of concrete used in this test method must be obtained in accordance with which ASTM Standard?

The correct option, ASTM C172, pertains to the standard practices for sampling fresh concrete. This standard provides detailed procedures and guidelines for obtaining samples of fresh concrete during the mixing and placement operations to ensure that the samples collected are representative of the batch being tested. Proper sampling is crucial for accurate testing results and quality control in concrete production, making compliance with ASTM C172 essential when conducting various tests on concrete.

The other standards do not focus specifically on the sampling of fresh concrete. ASTM C160 is related to the determination of the consistency of concrete. ASTM C231 addresses the determination of air content in concrete using the pressure method, while ASTM C1231 is for the use of unbonded caps in compressive strength testing of cylindrical concrete specimens. Understanding the purpose of each standard helps to clarify why ASTM C172 is the appropriate choice for sampling fresh concrete.