The sample of concrete used for this test is to be obtained in accordance with which ASTM Standard?

The correct choice is ASTM C172, which outlines the procedures for sampling fresh concrete. This standard is critical for ensuring that concrete samples are collected in a manner that accurately represents the entire batch being tested. It specifies guidelines for obtaining samples, including where to sample from, how to transport the samples, and the quantity needed for testing.

The relevance of this standard is significant because improper sampling methods can lead to results that do not truly reflect the concrete’s properties, which could affect the integrity and performance assessments of concrete when it is placed in a construction environment.

The other standards listed do not pertain specifically to the sampling process for fresh concrete. ASTM C150 deals with the specification for Portland cement, ASTM C31 outlines procedures for making and curing concrete test specimens in the field, and ASTM C39 pertains to the testing of concrete compressive strength. While all of these standards are vital in their respective areas, ASTM C172 is uniquely focused on the critical step of correctly obtaining concrete samples for subsequent testing.