What is the specified number of strokes required after each layer of concrete?

The correct answer is 25 times, which is a standard practice in the field of concrete placement and compaction. This number aligns with industry guidelines to ensure proper consolidation of each layer of concrete.

The requirement for stroking, or using a tamping rod, is critical for achieving good compaction and eliminating air pockets that can compromise the integrity and strength of the concrete. The specified 25 strokes allows adequate vibration and movement of the concrete to fill all voids and ensure a dense, uniform structure. Following such a standard helps in achieving the desired strength and stability of the concrete once it cures.

While other numbers of strokes, such as 10, 20, or 30, might seem plausible, they do not correspond with the commonly accepted practices and specifications outlined in concrete placement standards. Such standards are informed by extensive research and practical applications in construction, emphasizing effective compaction techniques to meet structural requirements.