How many times should the tamping rod be used to rod each layer uniformly?

In the context of concrete testing, particularly when conducting a test like the slump test, the use of the tamping rod to compact each layer of concrete is critical for achieving a uniform density and consistency. The correct number of times to use the tamping rod is twenty-five. This figure is based on standardized procedures that ensure adequate compaction of the concrete within the mold, leading to consistent test results.

Using twenty-five strokes helps to displace air pockets and eliminates voids that might affect the integrity of the sample, ensuring that the concrete is well-mixed and properly aerated before the test is conducted. This precise number is part of established guidelines that have been honed over time for optimal performance in concrete testing.

Other options, such as ten, twenty, or thirty strokes, either under-compact or over-compact the concrete, which could lead to variability in test results and potentially compromise the quality of the concrete mix being tested. Therefore, sticking to the recommended twenty-five strokes is essential for reliable and accurate results in concrete testing practices.