A capping set (vertical) is used to ensure that the ends of concrete cylinder specimens are flat and parallel for compressive strength testing. This is critical because uneven or non-parallel surfaces can lead to inaccurate test results, as the load applied during the test may not be uniformly distributed.

The capping process typically involves applying a thin layer of capping material (such as sulfur-based compounds or high-strength gypsum) to the ends of the cylinder using a capping set. The vertical capping set ensures precise alignment and a smooth, level surface. This preparation allows for reliable and repeatable compressive strength test results, which are vital for assessing the quality and performance of concrete in construction projects.