When using a 4"x 8" cylinder, what is the specification for the rod?

When preparing concrete test specimens using a 4"x 8" cylinder, the specification for the rod is to use straight steel with a hemispherical tip that is 3/8" in diameter. This design helps to effectively consolidate the concrete within the mold without causing damage. The hemispherical tip allows for better penetration and mixing of the concrete as it is inserted and vibrated, ensuring that air pockets are minimized and the specimen is uniformly compacted.

This method aids in achieving the desired density and consistency for the concrete sample, which is crucial for obtaining accurate test results regarding its compressive strength and other properties. Using a rod with a flat or conical tip would not achieve the same consolidation effect, leading to improperly prepared specimens. Similarly, a curved rod would not provide the necessary straight up-and-down motion for effective compaction. Therefore, the specification of a straight steel rod with a hemispherical tip is essential for proper cylindrical concrete sample preparation.