When sampling concrete with a bean mold measuring 6" x 6" x 20", how many blows per layer must be applied?

To determine the number of blows per layer that must be applied when sampling concrete with a beam mold measuring 6" x 6" x 20", one must understand the standard practices established by organizations such as ASTM (American Society for Testing and Materials). In accordance with these standards, the compaction of concrete in a mold is essential for achieving a proper density and ensuring that the sample is representative of the material being evaluated.

For a mold of this specific size, the standard methodology dictates that for each layer of concrete placed into the mold, a specified number of blows must be applied using a suitable tamping rod or similar tool. This is necessary to eliminate air pockets and ensure that the concrete is adequately compacted. The widely accepted practice is to apply 60 blows for each layer, which effectively densifies the mix without over-compaction that could lead to segregation or alteration of the material's characteristics.

This number of blows is not arbitrary; it is based on empirical studies that have determined it to be effective in achieving optimal compaction in similar molds. Thus, for the beam mold specified in the question, applying 60 blows per layer is both the correct and standardized approach for sampling concrete.