In accordance with what ASTM Standard must a concrete sample be obtained for molding test specimens?

The ASTM Standard that outlines the procedures for obtaining concrete samples for molding test specimens is C172, titled "Standard Practice for Sampling Freshly Mixed Concrete." This standard provides guidance on how to properly collect samples of freshly mixed concrete to ensure representative and accurate testing, enabling consistent results in evaluating the material's properties.

The focus of C172 is on techniques for obtaining the sample from various locations and ensuring that it reflects the entirety of the batch being tested. This is crucial because the characteristics of the concrete can vary from batch to batch, and any discrepancies in sampling can lead to misleading test results.

Other options, while relevant to concrete testing, do not specifically focus on the sampling process for molding test specimens. For instance, C31 deals with the making of test specimens and does not address how to sample concrete for these tests, while C1202 focuses on determining the rapid chloride permeability of concrete. C143 provides a method for determining the slump of fresh concrete, which again does not pertain to the sampling process itself. Thus, C172 is the correct standard for obtaining concrete samples for molding test specimens.