Answer :
Final answer:
The correct ASTM standard for obtaining a sample of concrete for testing is C172, which outlines the procedures for sampling freshly mixed concrete.
Explanation:
The sample of concrete used for this test is to be obtained in accordance with ASTM Standard C172. This standard specifies the procedure for sampling freshly mixed concrete and includes provisions for ensuring that the sample is representative of the batch. The proper collection and handling of the concrete sample are vital for accurate test results, such as those that might be done for slump tests, air content measurement, and strength testing. Other ASTM standards, like C31, D75, and C143, pertain to different aspects of concrete testing and handling, such as making and curing concrete specimens in the field (C31), sample aggregate (D75), and the slump test for consistency (C143).