Answer :
Final answer:
According to ASTM C138, when using a tamping rod, concrete should be placed in three layers for proper compaction around re-bar, which is critical for the tensile strength and integrity of the structure.
Explanation:
When preparing reinforced concrete, which involves concrete poured around a grid of steel rods known as re-bar, the ASTM C138 standard specifies how the concrete should be placed and worked. The standard recommends that the concrete be placed in three layers if you are going to rod the concrete. Each layer should be rodded with a tamping rod to compact the concrete and ensure that it fully encases the re-bar and fills all corners of the formwork. This practice is crucial to achieving the desired tensile strength and structural integrity for foundations, columns, and vertical slabs.