What is the required shape of the tamping end of the rod in the slump test?

The correct shape of the tamping end of the rod in the slump test is a hemispherical tip. This design is essential for several reasons related to the effectiveness and consistency of the test.

The hemispherical tip allows for uniform pressure to be applied to the concrete mix when tamping, ensuring that the material is adequately compacted without introducing air pockets or unevenness. This uniformity is crucial as it helps achieve accurate and repeatable results, which is essential when measuring the workability of concrete. A flat end might not distribute force evenly, while a pointed tip could lead to localized compaction that does not reflect the true consistency of the concrete mixture. A cylindrical tip could also create similar issues as a flat end regarding uniform compaction.

By using a hemispherical tip, technicians can ensure a balanced application of pressure, which leads to more reliable measurements of slump and ultimately aids in assessing the quality and workability of the concrete.